text stringlengths 11 320k | source stringlengths 26 161 |
|---|---|
The Southeastern Anatolia Project ( Turkish : G üneydoğu A nadolu P rojesi , GAP ) is a multi-sector integrated regional development project based on the concept of sustainable development for the 9 million people (2023) living in the Southeastern Anatolia region of Turkey . According to the Southeastern Anatolia Project Regional Development Administration, the aim of the GAP is to eliminate regional development disparities by raising incomes and living standards and to contribute to the national development targets of social stability and economic growth by enhancing the productive and employment generating capacity of the rural sector.The Southeastern Anatolia Region extending over wide plains in the Euphrates-Tigris Basin encompass the administrative provinces of ( Adıyaman , Batman , Diyarbakır , Gaziantep , Kilis , Siirt , Şanlıurfa , Şırnak and Mardin )which are located in the basins of the Euphrates and Tigris and in Upper Mesopotamia . The surface area of the region bordering with Syria to the south and with Iraq to the southeast is 75,193 square kilometres which corresponds to 9.7% of Turkey’s total surface area. [ 1 ] Turkey has in total 8.5 million hectares of irrigable land and GAP’s share in this total is 20 per cent.The total cost of the project is over 190 billion Turkish lira (TL) (2020 adjusted price). [ 2 ]
Current activities under GAP include sectors like agriculture and irrigation, hydroelectric power production, urban and rural infrastructure, forestry, education and health. Water resources development envisaged the construction of 22 dams and 19 power plants. [ 3 ]
The initial idea and decision to utilize the waters of the Euphrates and Tigris rivers came from Atatürk , the founder of the Republic. During the one party era , the need for electrical energy was a priority issue. The Electricity Studies Administration was founded in 1936 to investigate how rivers in the country could be utilized for energy production. The Administration began its detailed studies with the " Keban Dam Project" and established observation stations to assess the flow and other characteristics of the Euphrates. The GAP as it is structured today, was planned in the 1970s consisting of projects for irrigation and hydraulic energy production on the Euphrates and Tigris, but transformed into a multi-sector social and economic development program for the region in the early 80s. The development program encompassed such sectors as irrigation, hydraulic energy, agriculture , rural and urban infrastructure, forestry , education and health . With the development of new GAP Administrative structure in 1988–1989, its basic objectives included the improvement of living standards and income levels of people so as to eliminate regional development disparities ( economic inequality ) and contributing to national goals such as social stability and economic growth by enhancing productivity and employment opportunities in the rural sector. [ 4 ]
Tensions between Turkey , Syria and Iraq were raised from time to time due to GAP. Syria and Iraq demanded more water to be released, while Turkey declined so as to form the dam reservoirs . Because of this GAP is one of the world's most well protected dam projects, especially against aircraft. GAP also almost came to a complete halt in the early 1990s due to the high level of Kurdish ( PKK ) activities in the region. The PKK is not only blamed for a number of funding cuts as funds were diverted to support the counter-terrorism effort, but is also blamed for damaging several dams and canals, as well as killing engineers working at the dams. A number of economic crises also played a very important part in the delays of GAP.
The UN embargo on Iraq (which was lifted after the Second Gulf War ) had negative effects on development efforts and region's trade with Middle Eastern countries, which are its natural economic partners. Furthermore, imbalances in public financing delayed the financing needs of the project. Finally, a number of judicial questions needed clearing over the flooding of several historical sites as well as local residences as described in the " Social effect " section.
Historically, Southeastern Anatolia was located on the trading route between East and West. The region had been an important source of cultural diversity. However the changes in the trading routes and the agricultural methods ended the old importance of the region.
The 1989 Master Plan had aimed to initiate the revitalization of the economic, social and cultural life in the region through an "integrated regional development project". The rise in the income of the region was directly transferred to restoration and revitalization of the cultural activities in the region, instead of moving into the national budget. This master plan did not reach its goals because of the issues stated under the introduction section. However, for this negative perspective, with the international community involvement, project added new dimensions and concepts to the definitions.
The concerns and concepts of the environment , sustainability and participation , which were either overlooked or totally absent in the original plan has been added with the UNDP support. The revised "GAP Regional Development Plan" with a new understanding is currently in place. The macro frame of the GAP Regional Development Plan (GAP-RDP) is drawn by 8th Five-Year Development Plan coordinated with the efforts under the " Program for Transition to a Strengthened Economy " prepared as a part of the process for Turkey's accession to the European Union .
The project rests upon the philosophy of sustainable human development, which aims to create an environment in which future generations can benefit and develop. The basic strategies of the project include fairness in development, participation, environmental protection, jobs creation, spatial planning and infrastructure development. In reaching these goals the primary objective of GAP is to normalize levels of development, income, and living standards between the southeastern region and other regions of Turkey. GAP is transforming the region completely by creating economic and social opportunities and promoting business. Critical infrastructure, such as airports and highways, is being constructed to support the development of the region. GAP will provide jobs to an estimated 3.5 million people directly.
GAP is estimated to double Turkey's irrigable farmland. The increase of agricultural activity of GAP in its incomplete state is visible clearly on the USDA graph belove. Cotton production increased from 150,000 metric tons to 400,000 metric tons, making the region the top cotton producer. But at the same time other regions declined, which means that Turkey's overall output stayed relatively steady.
GAP is supposed to create 17,000 square kilometres (4.2 million acres) of farmland in the Harran plain alone, as visible on two USDA maps above.
Reports indicate that, due to irrigation from the Atatürk Dam , harvest yields of cotton , wheat , barley , lentils , and other grains in the Harran plain have tripled. A number of Agriculture Department backed initiatives are encouraging farmers to experiment with new varieties of fruits, vegetables, and nuts that did not exist in the region prior.
The amount of foreign trade of the region is continuously rising since 2002. In 2002, total export from the region was 689 million $ and total imports stood at 773 million $.According to TÜİK data, GAP's total exports are In 2023, total reached 13.657 billion $, while imports reached 9.330 billion $. Since 2004 the G.A.P. region is net exporter. [ 5 ]
GAP is being built in a region where water used to be a scarcity. With the vast number of lakes being formed, plans to use them as breeding spaces for commercial fishing are also underway. In the case of the Atatürk Dam the fishing industry in the region is already developing.
The GAP also consists of 19 hydroelectric power plants . These will supply the energy equivalent of 22% of the anticipated total nationwide energy consumption in 2010. Providing 8,900 gigawatt hours (32 PJ), it is one of the largest series of hydroelectric power plants in the world.
Southeastern Anatolia Project consists of 22 Dams (year of completion):
The reason for the sheer number of dams in the project, more than would at first appear needed, is maintenance. Dams need to be cleaned from the debris carried with the water flow. After a while the dam becomes obsolete as water flow slows down to inadequate levels. The dams will be shut down every 5 to 10 years for fall maintenance (also called fall cleanup). Water levels are normally lowest in fall. The extra dams are placed in service during this maintenance period.
In cases of natural disasters such as floods, the maintenance may be performed earlier. The plan is to have one or two dams spare in case an emergency shutdown of any dam is necessary. While shutting down a dam also shuts down irrigation channels linked to it, it can nevertheless continue providing power.
Providing electricity and irrigation is challenging in a region as large as the one targeted by GAP. A constant flow of water is imperative.
After a large body of water is collected behind the dam a constant flow of water is then available. The height of the dam allows the water to go at a high velocity through the turbines thus generating electricity. After the fast flowing water exits the dam it is slowed down by a concrete energy dissipator (pictured). Creation of electricity is only part of the usage of the tons of water collected at the dam.
When dealing with tons of water, it has to be distributed evenly and slowly. Occasionally main channels will need maintenance, or may be damaged due to external reasons. In order to even assess the problem, tons of water need to be removed from the main channel. The best way to do this is to slow the overall flow from the main dam and redirect all water flowing originally through the damaged channel to backup channels. Radial gates serve this purpose, they regulate the flow of water. It is imperative to keep water flowing. Lack of the flow will not only compromise all irrigation linked to that channel but also all cities linked will experience a power outage.
After leaving the energy dissipator, water flows into a set of main channels, which flow in different directions supplying water to a greater area. They are the most critical part of a dam project aside from the dam itself. This is as critical as high-voltage transmission lines in power grids.
Sluice gates regulate the flow of water. If water flows too fast it will overflow and probably damage one or more of the channels, or flood irrigation fields. Multiple sluice gates regulate the speed of the flow on different sections of the channel. They can also be used like radial gates to cut water in channels.
After leaving the radial gates on the main channel, water flows to canals which are smaller and can carry less water. Flow regulators divert water on canals to distribution canals. Just like radial gates and sluice gates, flow generators can stop water flow if necessary. Distribution canals are the last step as far as engineers are concerned. It delivers water to different sections of large fields, pretty much an artificial river.
It is up to farmers to get the water from distribution channels to their crops for irrigation . There are different methods to do this; any one or a combination of earth distribution channel, furrow, and drip tubes can be used.
The latest design of the project divides the GAP into smaller projects. Each project generates its own annual reports and activity sheets.
The water resources development component of the program envisages the construction of 22 dams and 19 hydraulic power plants and irrigation of 17,000 square kilometres of land. The total cost of the project is estimated at $32 billion USD . The total installed capacity of power plants is 7483 MW and projected annual energy production reaches 27 billion kWh. [ 7 ]
GAP contributes to the country's hydroelectric energy production. As of 2023, 91.2% physical realization of energy investments was achieved.The amount of government investment for 2023 was around 84 billion TL, which corresponds to 18.6% of Turkey 's total investment for same year. [ 8 ]
Completion of the Ilısu Dam would cause the flooding of the ancient city of Hasankeyf whose history stretches back over 10,000 years. Between 50 and 68 hamlets and villages will be flooded affecting approximately 25,000 local people. An additional 57 villages will have their land partially flooded.
Construction began on August 5, 2006, after a ceremony led by Prime Minister Recep Tayyip Erdoğan . [1] The dam entered into service in 2018.
Critics of the project say that the dam could effectively destroy the artifacts of ancient Kurdish, Armenian, and Assyrian habitation in the region. [ 9 ]
The environmental justice lense of the Human-environment geography allows us to explore the fair distribution of environmental benefits and burdens, especially with regard to vulnerable communities.In context of the Ilisu Dam environmental justice focuses attention on the fair treatment of different social groups and the potentially disproportionate impact of these projects on specific communities. This perspective highlights the ethical dimension of environmental decision-making and emphasises the need for fairness and social equity in the distribution of environmental goods and damage [ 10 ]
Environmental justice, for example, would highlight how dam construction can disproportionately affect certain communities, perhaps leading to the displacement of indigenous or economically disadvantaged groups. (As occurred recently in Hasankeyf) It prompts us to ask whether the benefits of hydropower and economic development are distributed fairly to all communities or whether certain groups are hit hardest by the negative impacts, such as loss of land, cultural heritage or livelihoods. By looking at environmental justice, we can assess whether the decision-making processes surrounding dam construction adhere to the principles of justice and fairness and ensure that burdens and benefits are distributed fairly across different social groups. [ 11 ]
TRT GAP, belonging to the Turkish Radio and Television Corporation , was established in 1989 to promote the Southeastern Anatolia Project in the region. In 1991, TRT GAP was put under the jurisdiction of TRT's Ankara facilities. [ 12 ] From 1989 to 2001 TRT GAP was broadcasting on TRT 2 before being revamped as a 24-hour news and culturally-oriented channel. TRT GAP's transmissions are realized through the same channel with the TRT 3 since 2001 (which broadcasts live footage of TBMM TV ) on a time-share basis. | https://en.wikipedia.org/wiki/Southeastern_Anatolia_Project |
The Southern African Institute of Steel Construction (SAISC) is an organization which helps building and construction in South Africa by serving to promote and develop companies providing steel-related products and services to the industry. [ 1 ]
The institute was founded on 24 March 1956 when South Africa was still a Union under the Nationalist Government. It was known as the Structural Steel Publicity and Advanced Association Limited . The first meeting of the association took place on 12 September 1956 in Johannesburg in the Barclay Bank building which stood on the corner of Commissioner and Market Streets. [ 2 ] The staff consisted on a single engineer offering his services on a part-time with a membership of 18 members. [ 3 ]
As a result of World War II , the cheapness of concrete enabled it to encroach upon work which until previously had been the domain of the steel industry. The institute was born to rectify this situation.
In 1958 the association started to receive copies of publications from Belgium and Luxemburg, and the American Institute of Steel started to send their journal. The association found themselves on the mailing list for Acier-Stahl-Steel a steel-structure based journal in three languages. The board management found this journal to be so informative that it sponsored the circulation of the journal to engineers and architects to promote publicity, something that continued until the demise of the journal.
In 1960 the institute employed an engineer, Mr Robert McHalfie-Clarke, on a part-time basis. Scottish and born in 1906 McHalfie-Clarke was a consulting engineer who specialised in structural steel design. Some of his structures including Iscor head office in Pretoria and Newcastle as well as the Norwich Union Building in Pretoria. He was to remain on the scene until 1976 when Dr. Hennie de Clercq took the over the reigns.
At the 5th annual general meeting a resolution was placed before members that the name of the company be changed. In 1961, the institute changed its name to the ' South African Institute of Steel Construction , and more recently the Southern African Institute of Steel Construction .
Today the institute has over 600 members. [ 4 ]
SASFA - Southern African Light Steel Frame Building Association The Southern African Light Steel Frame Building Association (SASFA), was formed in October 2006 as a division of the Southern African Institute of Steel Construction (SAISC). The founder members are ArcelorMittal (Steel), Everite (fibre cement cladding Saint-Gobain Construction Products)(gypsum board lining and insulation), and Lafarge (gypsum board lining).
An Executive committee, with representatives from the major material suppliers, manufactures, equipment suppliers and the Institute of Steel Construction, guides and monitors the activities of the Association. Technical and Training committees deal with technical and training matters.
SASFA has been established as the industry representative association for light steel frame building. It has more than 70 company members- see membership list on www.sasfa.co.za .
According to SASFA records, there are already 33 companies manufacturing light steel frames on profiling facilities in South Africa. They have a combined annual manufacturing capacity (single shift basis) of 55 million linear meters of light steel sections, or 56 000 tons/year of galvanized steel, of which a third is dedicated to the manufacture of light steel roof trusses. This means that South African has sufficient manufacturing capacity to produce light steel frames for 2,1 million m 2 and trusses for 2,0 million m 2 per year of floor area of building
Manufacturing facilities are also being established in neighbouring countries.
POLASA - Power Line Association of South Africa The Power Line Association of South Africa (POLASA), was formally established on 15 August 2013. The Southern African Institute of Steel Construction (SAISC]) hosted a breakfast function in launching the Power Line Association of SA on the day. [ 5 ]
Mr Gray Whalley, MD of Babcock Ntuthuko Powerlines is the first Chairman of the Association and he made a short presentation on the state of the industry and challenges that need to be faced. [ 5 ]
Power line construction is integral in the National Development Plan (NDT) where out of the 18 Presidential Infrastructure Coordinating Commission (PICC) Strategic Integrated Projects (SIP's), six contain transmission and distribution infrastructure. POLASA is involved in SIP number ten which is Electricity Transmission and Distribution for all. [ 5 ]
When the association was officially launched, there were about 16 members. There are now 32 members. The first annual meeting was held on 7 November 2013. [ 6 ]
SAMCRA - South African Metal Cladding and Roofing Association From the turn of the century there was a progressive decline in the quality of metal cladding products sold into the South African market. Professionals and developers were becoming increasingly concerned with the integrity of the industry both from the manufacturing and installation point of view. In October 2012 a group of concerned individuals called a meeting of the major players which included representatives from the producer mills, manufactures, installers, suppliers of ancillary items, professionals and other interested parties. At this meeting it was agreed to form a committee that would consolidate the ideas and proposals discussed during the meeting and to draft a basic structure for formal association to known as the Southern African Metal Cladding and Roofing Association (SAMCRA).
At the meeting SAMCRA had nine founder members plus three new members. The association now has a membership number of seventeen members.
The Founder members of SAMCRA are: [ 7 ]
During this process it was decided to approach the SAISC with the prospect of SAMCRA becoming a sub-association of the SAISC. An agreement was concluded and on 22 August 2013 SAMCRA held its inaugural meeting. During the inaugural meeting, Johann van der Westhuizen was elected as the Chairman of the association.
Both SAISC and SAMCRA jointly launched the Southern African Metal Cladding and roofing Association (SAMCRA) in Johannesburg in the SAISC boardroom on 30 October 2013. Newly elected SAMCRA Chairman, Johann van der Westhuizen, said that in an industry which uses, inter alia, 650 000 tons of metal and colour-coated coil per annum, the need for an industry association has become essential. [ 8 ]
ISF - International Steel Fabricators The International Steel Fabricators is a joint-venture marketing consortium representing the leading players in the South African structural steel construction industry whose objective are to increase their export sales by pooling their resources. [ 9 ] [ 10 ] The International Steel Fabricators (ISF) established in 1991 by the five big structural companies Genrec Engineering , Aveng Steel Fabrication , and the other three remaining companies no longer exist. The five structural companies were in Australia in a meeting bidding for one tender in Israel and they decided to form a partnership called International Steel Fabricators (ISF). The International Steel Fabricators work as a partnership until they get a request from the Minister of Trade and Industry to register the company, in 1999 International Steel Fabricators (ISF) was registered and became the formal independent exports company. [ 11 ]
ISF started with five members, today the company has over 50 members. In order to be an ISF member everyone has to satisfy the two rules from the ISF constitution, firstly have to be a member of Southern African Institute of Steel Construction and secondly pay the joining fees.
International Steel Fabricators members have a combined capacity in excess of 20 000 tons of steelwork a month and with their holding companies have combined turnover of billions per year. The ISF steel producers are AcrelorMittal South Africa and Evraz Highveld Steel & Vanadium . [ 9 ]
SAISC School of Draughting The SAISC/DSE School of Draughting is a division of the Southern African Institute of Steel Construction (SAISC). [ 12 ] The SAISC School of Draughting was launched in September 2007, and Howard Fox was appointed as draughtsperson to conduct the training. The school opened its doors on 15 October 2007, as a joint initiative between DSE now known as Aveng Grinaker-LTA Mechanical & Electrical DSE Fabrication. The objective being to train learners to become structural steelwork detailers, with ability to design simple connections and to have an all-round knowledge of the steelwork industry, and to address the need for trained structural steel detailers. The primary skills relates to the production of structural steel drawings for fabrication and erection of steel structures as well as the understanding of the steel construction industry and how to operate within the legislative, safety and quality systems which govern the industry. [ 12 ]
The Southern African Institute of Steel Construction (SAISC) set in motion the initiative to begin a specialist school. The process began by developing a course outline which, after 18 months of negotiation, was certified by the South African Qualification Authority (SAQA). At a later stage the course was registered as a learneship with the Department of Labour (DOF). To complete the process, the Construction Education and Training Authority (CETA) required that course material be developed. The course material was achieved after two years at a cost of about R 1.8-million, half of this amount was provided by the Southern African Institute of Steel Construction (SAISC) and the other half by the Construction Education and Training Authority (CETA). [ 12 ]
The next step was to set up the school and train staff. A part of Aveng Grinaker-LTA Mechanical & Electrical DSE Fabrication, DSE provided the solution to the premises issue. The school operated from the DSE premises in Germiston with 10 trainees. The school offered the National diploma on a full-time basis. On 1 April 2014, the SAISC School of Draughting was relocated to Genrec Engineering in Wadeville, Germiston. Genrec Engineering is a division of Murray & Roberts limited . It was an advantage for the school to be on the premises of structural steel fabricators. [ 12 ]
The SAISC School of Draughting offers the Diploma, Learnerships, Skill programmes and Shortage course on a full-time and part-time bases to companies and private individuals, for the whole of South African Steelwork Industry, and has a capacity for 25 trainees. It is a non profit, Section 21 Company with a board of directors, with members from the Southern African Institute of Steel Construction (SAISC), DSE as well as an executive committee. The course comprises many specialist Unit Standards, many of which have outcomes at National Qualifications Framework (NQF) Level 5, and will be a diploma qualification. [ 12 ] | https://en.wikipedia.org/wiki/Southern_African_Institute_of_Steel_Construction |
The Southern Local Supervoid is a tremendously large, nearly empty region of space (a void ).
It lies next to the Local Supercluster , which contains our galaxy the Milky Way . Its center is 96 megaparsecs away and the void is 112 megaparsecs in diameter across its narrowest width. [ 1 ] Its volume is very approximately 600 billion times that of the Milky Way. See volumes of similar orders of magnitude .
This astronomy -related article is a stub . You can help Wikipedia by expanding it .
This galaxy-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Southern_Local_Supervoid |
Southern Research is a not-for-profit US 501(c)(3) research organization that conducts basic and applied research for commercial and non-commercial organizations across four divisions: Drug development , Drug discovery , Energy & Environment, and Engineering . [ 1 ]
Southern Research was founded in Birmingham, Alabama , on October 11, 1941, by Thomas Martin as the Alabama Research Institute. [ 2 ]
Although Martin was named chairman of the newly chartered organization in December, 1941, activities were put on hold in the aftermath of the attack on Pearl Harbor and the beginning of US involvement in World War II . Two years later, in December 1943, with a promise of support from the Alabama Power Company , Martin reengaged the Alabama's industrial leaders and received over $100,000 in philanthropic donations. [ 3 ]
Alabama Power Company pledged an additional US$ 15,000 per year for five years, $75,000 total, and this was enough for the organization to finance laboratory space and hire researchers and staff. The following year, 1944, the decision was made to change the institute's name from Alabama Research Institute, to Southern Research Institute. [ 3 ]
Around this same time, Southern Research Institute hired its first director, Wilbur Lazier. Though he only stayed in this role for four years, Lazier is credited with recruiting many figures that shaped the history of the organization, including Howard E. Skipper . [ 4 ]
Southern Research celebrated its 75th anniversary in October 2016. [ 5 ] In celebration of this milestone the director of National Institutes of Health (NIH), Francis Collins , produced a video congratulating the organization on its anniversary. [ 6 ]
In June 2021, Josh Carpenter was named president and CEO of Southern Research. Before joining Southern Research, Carpenter served as director of the Innovation and Economic Opportunity Department for the City of Birmingham, where he led the city's efforts in workforce development, COVID recovery and business expansion. Previously, he worked as the director of External Affairs at the University of Alabama at Birmingham, as an assistant professor of economics at UAB and as a non-resident senior fellow at The Brookings Institution.
Southern Research's Drug Development division is the largest of the organization's four divisions. Set up like a contract research organization (CRO), Southern Research provides commercial and government clients with nonclinical and clinical trial support services. [ 7 ] They offer studies including both in vitro and in vivo testing of small molecule compounds, vaccines , biologics , and other test articles in therapeutic areas including infectious disease , CNS and cancer . Current service areas include: Bioanalytical Analysis; Anticancer Efficacy Services; Immunology ; Infectious Disease ; Pathology ; and Consulting .
Southern Research's Drug Discovery division conducts research focused on oncology , infectious disease , and neuroscience . Their current service areas include: High Throughput Screening (HTS), [ 8 ] Chemistry, Oncology, Infectious Disease, Neuroscience, and the Center for Neuromolecular Research.
Southern Research is a founding member of the Alabama Drug Discovery Alliance (ADDA) along with the University of Alabama at Birmingham School of Medicine (SOM). The UAB Center for Clinical and Translational Science (CCTS), and the UAB Comprehensive Cancer Center (CCC) are also crucial contributors to the ADDA. [ 9 ]
Mark J. Suto is vice president of Drug Discovery at Southern Research. [ 10 ] [ 11 ] He has been named a Fellow of the National Academy of Inventors (NAI) in recognition of his wide-ranging contributions to pharmaceutical research and drug discovery efforts. [ 12 ]
Southern Research cancer research program was started in 1946 with a $25,000 philanthropic donation from Mobile, AL businessman, Ben E. May . [ 13 ]
The organization's scientists are credited with the discovery of seven Food and Drug Administration (FDA) approved anti-cancer drugs, including carmustine , lomustine , dacarbazine developed by Y Fulmer Shealy, fludarabine , amifostine , clofarabine and the latest pralatrexate (approved in 2009). Notable cancer researchers who worked at the institute include Y Fulmer Shealy Howard E. Skipper , John Montgomery, Frank Schabel and Lee Bennett Jr.
Clofarabine [ 14 ] is a nucleoside discovered at Southern Research that eventually received FDA approval. Clofarabine , a second-generation nucleoside analogue received accelerated approval from the US FDA at the end of 2004 for the treatment of paediatric patients 1–21 years old with relapsed or refractory acute lymphoblastic leukaemia after at least two prior regimens. It is the first such drug to be approved for paediatric leukaemia in more than a decade, and the first to receive approval for paediatric use before adult use. [ 14 ]
Pralatrexate is another anticancer drug whose discovery was a result of contributions from medicinal chemists at Southern Research along with chemists from SRI International and Memorial Sloan-Kettering Cancer Center . The US FDA announced the approval of pralatrexate in 2009 for the treatment of relapsed or refractory peripheral T-cell lymphoma (PTCL). [ 15 ] Research on drugs of this class began at SRI International in the 1950s. Pralatrexate was first prepared there by Dr. Joseph DeGraw and Dr. William Colwell. Dr. Robert Piper at Southern Research synthesized the key starting material (a bromomethyl compound) which was used to prepare the intermediates needed to make multigram quantities of high purity final compound. Multiple issued patents on this compound are jointly owned by Southern Research, SRI International and Memorial Sloan Kettering and licensed to Allos Therapeutics.
[ 16 ] MLP was founded by the NIH to fund research aimed at identifying new chemical probes against biological targets that might be amenable for drug therapy. Southern Research was one of eight extramural institutes selected for this initiative along with the Broad Institute , Sanford-Burnham Medical Research Institute , Johns Hopkins University , Scripps Research Institute , Vanderbilt University , University of New Mexico and the University of Kansas . [ 17 ] In addition the MLP initiative also included an NIH intramural site: the National Center for Chemical Genomics (NCGC).
Southern Research's Energy & Environment division focuses on technology for clean energy , clean air, and clean water. Southern Research develops and tests air and water emissions control technologies for leading utilities, industrial manufacturers, municipal water utilities, and related trade organizations. The division has also historically partnered with private sector firms and government agencies to develop new technologies that transform energy generation, chemical synthesis , and air and water purification . [ 18 ]
Southern Research engineers have worked with the National Aeronautics and Space Administration (NASA), the U.S. Military and other organizations. [ 19 ]
Current areas include: Non destructive evaluation of materials; Chemistry and Physics of Materials; Electrical, EO/IR, and Mechanical Systems; Hypersonic Structures; Space Structures Characterization; Mechanical Testing of Materials Structures and Components; and Thermal Testing of Materials.
Michael D. Johns is the vice president of Engineering at Southern Research. [ 20 ] He also serves on NASA Space Technology Mission Directorate's Technology, Innovation and Engineering Committee. [ 21 ]
In 2014, Southern Research and the University of Alabama at Birmingham formed the Alliance for Innovative Medical Technology (AIMTech) to develop new medical devices to improve healthcare. [ 22 ]
The creation of medical devices are across all five specializations: Cardiology , Orthopedics , Ophthalmology , Rehabilitation and Trauma . The goal is for the first group of AIMTech-created medical devices to hit the market by 2020. By comparison, it can take 10 years to create an FDA approved drug. [ 23 ]
In 2016, AIMTech was awarded a $500,000 U.S. Department of Commerce grant to expand medical device innovation and commercialization. [ 24 ] [ 25 ] | https://en.wikipedia.org/wiki/Southern_Research |
The Southern States Energy Board (SSEB) is a multi-state regional organization created by an interstate compact approved by sixteen states and two United States territories. The board is committed to promoting economic development and quality of life in the Southern United States through innovations in energy and the environment. Constituent members include Alabama , Arkansas , Florida , Georgia , Kentucky , Louisiana , Maryland , Mississippi , Missouri , North Carolina , Oklahoma , Puerto Rico , South Carolina , Tennessee , Texas , United States Virgin Islands , Virginia , and West Virginia . [ 1 ]
The creation of the SSEB can be traced to the Southern Governors Conference meeting in Point Clear, Alabama , which on October 20, 1955 approved the "Point Clear Plan" whereby Southern states would coordinate the possible development of civilian uses of nuclear energy in the region. The agreement led to Florida Governor LeRoy Collins convening a preliminary energy conference on January 25, 1956 in Oak Ridge, Tennessee . Also attended by Tennessee Governor Frank Clement , representatives of fifteen Southern and Border states, as well as nuclear energy experts, additional meetings were held at Raleigh, North Carolina , Aiken, South Carolina and a March 1, 1956 meeting in Miami, Florida . Under the auspices of the Southern Regional Education Board (SREB), Gov. Collins convened a "Work Conference on Nuclear Energy" at Redington Beach, Florida on August 1, 1956, which urged Southern governors to create "statewide atomic energy citizens advisory committees."
These efforts resulted in the creation of a Regional Advisory Council on Nuclear Energy (RACNE) , which first convened in Atlanta on February 1–2, 1957, with representatives from 14 states in attendance. Administrative support for the Council, originally provided by SREB, was transferred to the Council of State Governments ' regional office.
By September 1961, with eight states having ratified a proposed interstate compact, RACNE became the "Southern Interstate Nuclear Board" (SINB), the precursor to the SSEB, which then was officially sanctioned by enactment of Public Law 87-563, filed by Tennessee Senator Albert Gore Sr. and signed into law by President John F. Kennedy on July 31, 1962.
Southern Interstate Nuclear Board
Southern States Energy Board
Southern States Energy Board: A Golden Anniversary History of Service to the Southern Region , by Dr. Canter Brown Jr. and Kenneth J. Nemeth, Published 2010 by Southern States Energy Board, ISBN 978-0-615-38187-9 | https://en.wikipedia.org/wiki/Southern_States_Energy_Board |
The Southern Textile Exposition (1915-2004) was an intermittent trade fair for textile manufacturers held in Greenville , South Carolina .
By the early 20th century, American textile production had moved into the Carolina Piedmont from its earlier center in New England. [ 1 ] By the second decade of the century, South Carolina ranked second only to Massachusetts in textile production; and Greenville, located between Charlotte and Atlanta , was central to the industry.
In 1914, the Southern Textile Association approved the bid of Greenville mill owners to host the first textile machinery trade fair in the South. [ 2 ] The first show, in 1915, was held in borrowed warehouses; but the trade fair was so successful that Greenville's Southern Textile Exposition, Inc. soon raised the money needed to build a permanent exhibition space, Textile Hall , on West Washington Street, which was effectively completed before the second exposition in 1917. [ 3 ] In succeeding years the exhibition was often held biennially. [ 4 ]
By 1946 Greenville could advertise itself as the "Textile Capital of the World," and by 1962 Textile Hall, even with nine annexes and additional leased space, proved inadequate to host the Textile Exposition. The Greenville corporation put up a larger building adjoining the Greenville Downtown Airport on the new U.S. Route 29 -Bypass. [ 5 ] In 1969 the Exposition joined with the American Textile Machinery Association to sponsor the American Textile Machinery Exhibition-International, the largest textile machinery show ever held in the United States. [ 6 ]
By the end of the 20th century, low wages and new production capacity in countries such as China, India, and Brazil dramatically reduced textile production in the United States, especially in the Southeast. [ 7 ] The Southern Textile Exposition was held in Greenville for a final time in 2004. [ 8 ] | https://en.wikipedia.org/wiki/Southern_Textile_Exposition |
Southern blot is a method used for detection and quantification of a specific DNA sequence in DNA samples. This method is used in molecular biology . Briefly, purified DNA from a biological sample (such as blood or tissue) is digested with restriction enzymes , and the resulting DNA fragments are separated by electrophoresis using an electric current to move them through a sieve-like gel or matrix, which allows smaller fragments to move faster than larger fragments. The DNA fragments are transferred out of the gel or matrix onto a solid membrane, which is then exposed to a DNA probe labeled with a radioactive, fluorescent, or chemical tag. The tag allows any DNA fragments containing complementary sequences with the DNA probe sequence to be visualized within the Southern blot. [ 1 ]
The Southern blotting combines the transfer of electrophoresis -separated DNA fragments to a filter membrane in a process called blotting , and the subsequent fragment detection by probe hybridization . [ 2 ]
The method is named after the British biologist Edwin Southern , who first published it in 1975. [ 3 ] Other blotting methods (i.e., western blot , [ 4 ] northern blot , eastern blot , southwestern blot ) that employ similar principles, but using RNA or protein, have later been named for compass directions as a sort of pun from Southern's name. As the label is eponymous , Southern is capitalized, as is conventional of proper nouns . The names for other blotting methods may follow this convention, by analogy. [ 5 ]
Southern invented Southern blot after combining three innovations. The first one is the restriction endonucleases, which were developed at Johns Hopkins University by Tom Kelly and Hamilton Smith . Those restriction endonucleases are used to cut the DNA at a specific sequence. Kenneth and Noreen Murray introduced this technique as Southern. The second innovation is the gel electrophoresis that is based on separation of mixtures of DNA, RNA, or proteins according to molecular size, which was also developed at Johns Hopkins University, by Daniel Nathans and Kathleen Danna in 1971. The third innovation is the blotting-through method which was developed by Frederick Sanger , when he transferred RNA molecules to DEAE paper. Southern blot was invented in 1973 but it was not published until 1975. Although it was published later the technique was disseminated when Southern introduced the Southern blot technique to a scientist at Cold Spring Harbor Laboratory called Michael Mathews by drawing this technique on a paper. [ 6 ]
The genomic DNA is digested with either one or more than one restriction enzyme, then the DNA fragments are size-fractionated by gel electrophoresis. Before the DNA fragments are transferred to a solid membrane which is either nylon or nitrocellulose membrane they are first denatured by alkaline treatment. [ 7 ] After the DNA fragments are immobilized on the membrane, prehybridization methods are used to reduce non-specific probe binding. Then the fragments on the membrane are hybridized with either radiolabeled or nonradioactive labeled DNA, RNA, or oligonucleotide probes that are complementary to the target DNA sequence. Then detection methods are used to visualize the target DNA. [ 8 ]
Hybridization of the probe to a specific DNA fragment on the filter membrane indicates that this fragment contains a DNA sequence that is complementary to the probe.
The transfer step of the DNA from the electrophoresis gel to a membrane permits easy binding of the labeled hybridization probe to the size-fractionated DNA. It also allows for the fixation of the target-probe hybrids, required for analysis by autoradiography or other detection methods.
Southern blots performed with restriction enzyme-digested genomic DNA may be used to determine the number of sequences (e.g., gene copies) in a genome . A probe that hybridizes only to a single DNA segment that has not been cut by the restriction enzyme will produce a single band on a Southern blot, whereas multiple bands will likely be observed when the probe hybridizes to several highly similar sequences (e.g., those that may be the result of sequence duplication). To improve specificity and reduce hybridization of the probe to sequences that are less than 100% identical, the hybridization parameters may be changed (for instance, by raising the hybridization temperature or lowering the salt content). Nylon membrane is more durable and has higher binding capacity to DNA fragments than nitrocellulose membrane, so the DNA fragments will be more fixed to the membrane even when the membrane is incubated in high temperatures. In addition, compared to the nitrocellulose membrane which requires a high ionic strength buffer to bind the DNA fragments to the membrane, nylon charged membranes use buffers with very low ionic strength to transfer even small fragments of DNA of about 50 bp to the membrane, usually the DNA to be transferred is separated by polyacrylamide gel. In the blotting step the most efficient method to transfer the DNA from the gel to the membrane is the vacuum transfer since it transfers the DNA more rapidly and quantitatively. [ 8 ] | https://en.wikipedia.org/wiki/Southern_blot |
The southern celestial hemisphere , also called the Southern Sky , is the southern half of the celestial sphere ; that is, it lies south of the celestial equator . This arbitrary sphere, on which seemingly fixed stars form constellations , appears to rotate westward around a polar axis as the Earth rotates .
At all times, the entire Southern Sky is visible from the geographic South Pole ; less of the Southern Sky is visible the further north the observer is located. The northern counterpart is the northern celestial hemisphere .
In the context of astronomical discussions or writing about celestial mapping , it may also simply then be referred to as the Southern Hemisphere.
For the purpose of celestial mapping, the sky is considered by astronomers as the inside of a sphere divided in two halves by the celestial equator . [ according to whom? ] The Southern Sky or Southern Hemisphere is, therefore, that half of the celestial sphere that is south of the celestial equator. Even if this one is the ideal projection of the terrestrial equatorial onto the imaginary celestial sphere, the Northern and Southern celestial hemispheres should not be confused with descriptions of the terrestrial hemispheres of Earth itself. [ according to whom? ]
From the South Pole , in good visibility conditions, the Southern Sky features over 2,000 fixed stars that are easily visible to the naked eye , while about 20,000 to 40,000 with the aided eye. [ citation needed ] [ dubious – discuss ] In large cities, about 300 to 500 stars can be seen depending on the extent of light and air pollution . [ citation needed ] The farther north, the fewer are visible to the observer. [ citation needed ]
The brightest star in the night sky is located in the southern celestial hemisphere and is larger than the Sun . Sirius in the constellation of Canis Major has the brightest apparent magnitude of −1.46; it has a radius twice that of the Sun and is 8.6 light-years away. Canopus and the next fixed star α Centauri , 4.2 light-years away, are also located in the Southern Sky, having declinations around −60°; too close to the south celestial pole for either to be visible from Central Europe . [ 1 ]
Of the 88 modern constellations , 45 are only visible from the Southern celestial hemisphere with 15 other constellations along the equator and have portions on the northern hemisphere. The southern constellations are: [ citation needed ] [ 2 ]
The first telescopic chart of the Southern Sky was made by the English astronomer Edmond Halley , [ 3 ] [ 4 ] from the island of St Helena in the South Atlantic Ocean and published by him in 1678. [ 5 ] | https://en.wikipedia.org/wiki/Southern_celestial_hemisphere |
The Southwell plot is a graphical method of determining experimentally a structure's critical load , without needing to subject the structure to near-critical loads. [ 1 ] The technique can be used for nondestructive testing of any structural elements that may fail by buckling . [ 2 ]
Consider a simply supported beam under a compressive load P . The differential equation of equilibrium is
d 4 v d x 4 + α 2 d 2 d x 2 ( v − v o ) = 0 {\displaystyle {\frac {d^{4}v}{dx^{4}}}+\alpha ^{2}{\frac {d^{2}}{dx^{2}}}(v-v^{o})=0} , α 2 = P E I {\displaystyle \alpha ^{2}={\frac {P}{EI}}}
where v o is the initial deflection, and the boundary conditions are
v ( 0 ) = v ″ ( 0 ) = v ( L ) = v ″ ( L ) = 0 {\displaystyle v(0)=v^{''}(0)=v(L)=v^{''}(L)=0}
Assuming that the deflected shape can be expressed as a Fourier series
v o ( x ) = ∑ 1 ∞ v n o sin n π x L {\displaystyle v^{o}(x)=\sum _{1}^{\infty }v_{n}^{o}\sin {\frac {n\pi x}{L}}} , v ( x ) = ∑ 1 ∞ v n sin n π x L {\displaystyle v(x)=\sum _{1}^{\infty }v_{n}\sin {\frac {n\pi x}{L}}}
Then after substitution into the differential equation,
v ( x ) = ∑ 1 ∞ v n o P n / P − 1 sin n π x L {\displaystyle v(x)=\sum _{1}^{\infty }{\frac {v_{n}^{o}}{P_{n}/P-1}}\sin {\frac {n\pi x}{L}}} , P n = n 2 π 2 E I L 2 {\displaystyle P_{n}={\frac {n^{2}\pi ^{2}EI}{L^{2}}}}
This relates the deflected shape to the initial imperfections and the applied load. Specifically, at x = L /2,
v ( L / 2 ) = V 1 − V 3 + V 5 + . . . {\displaystyle v(L/2)=V_{1}-V_{3}+V_{5}+...} , V n = v n o P n / P − 1 {\displaystyle V_{n}={\frac {v_{n}^{o}}{P_{n}/P-1}}}
As P approaches P 1 , v ( L /2) is dominated by V 1 . Therefore, when P ≈ {\displaystyle \approx } P 1 , then the fundamental mode will dominate, resulting in
v = V 1 = v 1 o P 1 / P − 1 o r v P = v P c + v i o P c {\displaystyle v=V_{1}={\frac {v_{1}^{o}}{P_{1}/P-1}}or{\frac {v}{P}}={\frac {v}{P_{c}}}+{\frac {v_{i}^{o}}{P_{c}}}}
Southwell plots v / P against v and obtains P 1 = P critical = P c from the slope of the predicted straight line graph. [ 3 ]
This analysis was done for a specific point on a simply supported beam , but the concept can be extended to arbitrary structures. With any problem whose mathematical analog is the same fourth order ordinary differential equation as above, with similar boundary conditions, the first eigenvalue of the associated homogeneous problem can be obtained from the slope of the graph. Therefore, a point of large deflection can be chosen, and it does not need to be the center of a simply supported beam. [ 3 ]
Strictly speaking, Southwell's Plot is applicable only to structures with a neutral post-buckling path. Initially created for stability problems in column buckling, the Southwell method has also been used to determine critical loads in frame and plate buckling experiments.
The method is particularly useful for field tests of structures that are likely to be damaged by applying loads near the critical load and beyond, such as reinforced concrete columns or advanced composite materials . [ 2 ] The method can also minimize parasitic effects in experiments and give values that are closer to the theoretically expected values. For example, in a real experiment setup it is impossible to reproduce any theoretical boundary condition perfectly. Additionally, the results of compressive tests can be very sensitive to imperfections and the actual boundary conditions. Therefore, the measured critical load during the experiment can be very different from what is predicted. [ 3 ] | https://en.wikipedia.org/wiki/Southwell_plot |
The South Wales West Local Section is one of 35 local sections of the Royal Society of Chemistry in the UK and Ireland. [ 1 ] It covers an area including the Local Authority areas of Bridgend, Carmarthenshire, Neath Port Talbot, Pembrokeshire and Swansea. [ 2 ]
The section was originally established in November 1918 as the South Wales Section of the Royal Institute of Chemistry following the decision to establish local sections to allow members to play a more prominent role in the Institute and develop communication between members in their own areas. [ 3 ] Members from the Munitions Factory Pembrey were the nucleus of the section. Despite its name, the South Wales Section served the majority of members in Wales but by 1935 the number of members in the southeast had increased sufficiently for them to form their own South East Wales Local Section [ 4 ] and in 1948 the South Wales Section successfully campaigned for a North Wales Local Section to be created. With the amalgamation of the RIC and the Chemical Society in 1971, it became the South Wales West Local Section.
Historically the chair comes alternately from the world of education and from the industry. Up to 1968, seven chairs came from Swansea University, seven from the Mond Nickel Company , three each from the Munitions Factory , local technical colleges and the Llandarcy oil refinery .
The local section holds a variety of lectures for members and the public. One of the largest meetings was in 1936 when 220 people attended a lecture given by Mr Davidson Pratt on Protecting the civil population from chemical gases . [ 11 ] A selected list of lectures is given below.
In former years a successful development was the Annual Lecture on the History of Chemistry associated with the name of Sir William Grove , the scientist from Swansea. One such lecture was by the Nobel Prize winner Archer Martin on his work on the invention of partition chromatography. At one time a Ladies Night were regularly organized lectures such as by Mr H. Armitage of British Nylon Spinners on Nylon in Industry and Fashion . [ 15 ]
For many years Mr Bill Williams and Dr Jim Ballantine conducted a series of demonstration lectures where the children carry out all the experiments themselves to show how energy is interconvertible. [ 16 ] [ 17 ]
Since 1983, each year the section awards a lectureship as part of the Hallam Memorial Fund in memory of the late Harry Evans Hallam. [ 18 ]
Since 1963, each year a prize has been awarded by Swansea University in memory of the late Ernest Edward Ayling, who had served the section as Hon Secretary for 21 years.
Science and Energy Lecture | https://en.wikipedia.org/wiki/Southwest_and_Central_Wales_Local_Section_(Royal_Society_of_Chemistry) |
The southwestern blot, is a lab technique that involves identifying as well as characterizing DNA-binding proteins [ 1 ] by their ability to bind to specific oligonucleotide probes. Determination of molecular weight of proteins binding to DNA is also made possible by the technique. The name originates from a combination of ideas underlying Southern blotting and Western blotting techniques of which they detect DNA and protein respectively. Similar to other types of blotting, proteins are separated by SDS-PAGE and are subsequently transferred to nitrocellulose membranes. Thereafter southwestern blotting begins to vary with regards to procedure as since the first blotting’s, many more have been proposed and discovered with goals of enhancing results. Former protocols were hampered by the need for large amounts of proteins and their susceptibility to degradation while being isolated.
Southwestern blotting was first described by Brian Bowen, Jay Steinberg, U.K. Laemmli, and Harold Weintraub in 1979. [ 2 ] During the time the technique was originally called "protein blotting". While there were existing techniques for purification of proteins associated with DNA, they often had to be used together to yield desired results. Thus, Bowen and colleagues sought to describe a procedure that could simplify the current methods of their time.
To begin, proteins of interest are prepared for the SDS-PAGE technique and subsequently loaded onto the gel for separation on the basis of molecular size. Large proteins will have difficulty navigating through the mesh-like structure of the gel as they can not fit through the pores with the ease that smaller proteins can. As a result, large proteins do not travel very far on the gel in comparison to smaller proteins that travel further. After enough time, this results in distinct bands that can be visualized from a number of post-gel electrophoresis staining procedures. The bands are at different positions on the gel relative to the well that they were loaded into.
Next, proteins are to be renatured followed by the gel being subjected to pressed between two nitrocellulose filters which rely on diffusion to transfer the proteins from the gel to the membrane filters. At this point replicas of the gel have been created of which each serves a particular purpose. One membrane filter can be stained to see the protein bands that were created from gel electrophoresis and the other is used in the actual process of hybridizing with prepared 32 P radioactively labeled specific oligonucleotide probes. [ 3 ] To detect any protein-DNA interactions, autoradiography is commonly used.
"Southwestern blot mapping" is a time-efficient way of identifying DNA-binding proteins and specific sites on the genomic DNA that they interact with.
After time is allowed for binding with the oligonucleotide probes, the hope is that some of the proteins on the membrane filter have bound to the probes. Any probe that was not able to bind a protein needs to be removed. Once unbound probe removal has been taken care of, to better visualize the membrane filter, it is subjected to further varying procedures. By corresponding the resulting membrane filter to the second membrane filter that the gel was sandwiched between, the position of the protein in comparison to the molecular weight ladder gives information about the weight of the protein that bound to the probe. | https://en.wikipedia.org/wiki/Southwestern_blot |
The South–North Water Transfer Project , also translated as the South-to-North Water Diversion Project , [ 1 ] is a multi-decade infrastructure mega-project in China that aims to channel 44.8 cubic kilometers (44.8 billion cubic meters) of fresh water each year [ 2 ] from the Yangtze River in southern China to the more arid and industrialized north through three canal systems: [ 3 ]
Construction began in 2003, and the first phases of the Eastern and Central routes became operational in late 2014. [ 5 ] The project is the largest water transfer scheme in the world, with an estimated investment exceeding 500 billion yuan (over $70 billion) to date. [ 6 ] The South–North Water Transfer Project is intended to alleviate chronic water shortages in northern China, support economic development, and curb over-extraction of groundwater. However, it faces significant engineering, environmental, and social challenges. [ 7 ]
The initial basis for this project was the lack of water in the Chinese north, which has a lot of agricultural land. [ 8 ] Mao Zedong discussed the idea for a mass engineering project as an answer to China's water problems as early as 1952. He reportedly said, "there's plenty of water in the south, not much water in the north. If at all possible, borrowing some water would be good". [ 9 ] Rapid industrial and agricultural growth since 1978 has resulted in a large increase of water in the north, raising water demand in comparison to supply. [ 8 ]
Engineer Wang Mengshu initially proposed transferring water from the Songhua River in Jilin, around 900 km from Beijing. Before the construction, it was predicted that the development of the Bohai Economic Rim was significantly constrained by lack of water resources. [ 10 ] [ 11 ] The decision to start the project was also based on the strategic need to safeguard Beijing's water supply, which could theoretically also be met at similar cost through desalinization. In addition, water has been strategically diverted to Beijing from the surrounding regions in Hebei, which themselves lack water resources.
The project's real concept began in 2002, with China's Ministry of Water Resources , which developed Blueprints and established the Office of the Construction Committee for the South North Water Transfer Project, to oversee building. [ 8 ] Construction of the project began in 2003. The East and Middle routes took nine and ten years to build, respectively. The East route began operating in 2013, and the West route saw waterflow by 2014. [ 8 ]
In 2024, it was reported that 76.7 km³ of water had been transported in the ten years since operation began. [ 12 ] Environmental impacts of the project have been monitored since its initiation, and it was found in 2020 that it greatly increased the water quality as well as the amount of groundwater in the north. [ 13 ]
The Eastern Route Project (ERP), or Jiangdu Hydro Project, consists of an upgrade to the Grand Canal and will be used to divert a fraction of the total flow of the Yangtze River to northern China. According to local hydrologists , the entire flow of the Yangtze at the point of its discharge into the East China Sea is, on average, 956 km 3 per year; the annual flow does not fall below approximately 600 km 3 per year, even in the driest years. [ 14 ] As the project progresses, the amount of water to be diverted to the north will increase from 8.9 km 3 /year to 10.6 km 3 /year to 14.8 km 3 /year. [ 14 ]
Water from the Yangtze River will be drawn into the canal in Jiangdu , where a giant 400 m 3 /s (12.6 km 3 /year if operated continuously) pumping station was built in the 1980s. The water will then be pumped by stations along the Grand Canal and through a tunnel under the Yellow River and down an aqueduct to reservoirs near Tianjin. Construction on the Eastern route officially began on 27 December 2002, and water was expected to reach Tianjin by 2013. However, in addition to construction delays, water pollution has affected the viability of the route. Initially, the route was expected to provide water for the provinces of Shandong , Jiangsu , and Hebei , with trial operations to begin in mid-2013. Water started arriving in Shandong in 2014, and it is expected one cubic kilometer of water will have been transferred in 2018. [ 15 ]
As of October 2017, water had reached Tianjin. Tianjin is expected to receive 1 km 3 /year. [ 16 ] The Eastern route is not expected to supply Beijing, which is to be supplied by the central route. [ 17 ]
The completed line will be slightly over 1,152 km (716 miles) long, equipped with 23 pumping stations with a power capacity of 454 megawatts. [ 18 ]
An important element of the Eastern Route will be a tunnel crossing under the Yellow River, on the border of Dongping and Dong'e counties of Shandong Province. The crossing will consist of two 9.3 m diameter horizontal tunnels, positioned 70 m under the bed of the Yellow River. [ 18 ] [ 14 ]
Due to the topography of the Yangtze Plain and the North China Plain , pumping stations will be needed to raise water from the Yangtze to the Yellow River crossing; farther north, the water will be flowing downhill in an aqueduct. [ 14 ]
The central route, known colloquially as the Grand Aqueduct, runs from Danjiangkou Reservoir on the Han River , a tributary of the Yangtze, to Beijing. This project involved raising the height of the Danjiangkou Dam by increasing the dam's crest elevation from 162 m to 176.6 m above sea level . This addition to the dam's height allows the water level in the reservoir to rise from 157 m to 170 m above sea level and thus permits the flow into the water diversion canal to begin downhill, pulled by gravity into the lower elevation of the canals. [ 19 ]
The central route crosses the North China Plain . The canal was constructed to create a continuous downhill flow all the way from the Danjiangkou Reservoir to Beijing without the need for pumping stations. [ 19 ] The greatest engineering challenge of the route was building two tunnels under the Yellow River to carry the canal's flow. Construction on the central route began in 2004. In 2008, the 307 km-long northern stretch of the central route was completed at a cost of $ 2 billion. Water in that stretch of the canal does not come from the Han River but from reservoirs in Hebei Province, south of Beijing. [ needs update ] Farmers and industries in Hebei had to cut back on water consumption to allow for water to be transferred to Beijing. [ 20 ]
On mapping services, one can see the canal's intake at the Danjiangkou Reservoir ( 32°40′26″N 111°42′32″E / 32.67389°N 111.70889°E / 32.67389; 111.70889 ); its crossing of the Baihe River north of Nanyang , Henan ( 33°6′41″N 112°37′30″E / 33.11139°N 112.62500°E / 33.11139; 112.62500 ); the Shahe River in Lushan County ( 33°42′49″N 112°56′40″E / 33.71361°N 112.94444°E / 33.71361; 112.94444 ); the Ying River in Yuzhou ( 34°11′05″N 113°26′18″E / 34.18472°N 113.43833°E / 34.18472; 113.43833 ); and the Yellow River northeast of Zhengzhou ( 34°52′55″N 113°13′14″E / 34.88194°N 113.22056°E / 34.88194; 113.22056 ); as well as its entrance into the southwestern suburbs of Beijing at the Juma River in Zhuozhou , Hebei ( 39°30′26″N 115°47′30″E / 39.50722°N 115.79167°E / 39.50722; 115.79167 ).
The whole project was expected to be completed around 2010. Final completion was on 12 December 2014, to allow for more environmental protection along the route. One problem was the impact of the project on the Han River below the Danjiangkou Dam, [ 21 ] from which approximately one-third of the route's total water is diverted. To mitigate this, another canal is being built to divert water from the Three Gorges Reservoir to the Danjiangkou Reservoir. [ 22 ] Construction of this project, named the Yinjiangbuhan tunnel, began in July 2022. It is set to take an estimated ten years to complete. [ 23 ] [ 24 ]
Another major challenge was the resettlement of around 330,000 people who lived near Danjiangkou Reservoir at its former lower elevation and along the route of the project. On 18 October 2009, Chinese officials began to relocate residents from the areas of Hubei and Henan provinces that would be affected by the project. [ 25 ] The completed route of the Grand Aqueduct is about 1,264 km long and initially provided 9.5 km 3 of water annually. By 2030, the project is slated to increase this transfer to 12–13 km 3 per year. [ 18 ] Although the transfer will be lower in dry years, it is projected that it will be able to provide a flow of at least 6.2 km 3 /year at all times with 95% confidence. [ 19 ]
Industries are prohibited from locating on the reservoir's watershed to keep its water drinkable . [ 26 ]
There are long-standing plans to divert about 200 cubic kilometers of water per year from the upstream sections of six rivers in southwestern China, including the Mekong (Lancang River), the Yarlung Zangbo (called Brahmaputra further downstream), and the Salween (Nu River), to the Yangtze River, the Yellow River, and ultimately to the dry areas of northern China through a system of reservoirs, tunnels, and natural rivers. [ 27 ]
In 2008, construction costs for the eastern and central routes was estimated to be 254.6 billion yuan ($37.44 billion). The government had budgeted only 53.87 billion yuan ($7.9 billion), less than a quarter of the total cost, at that time. This included 26 billion from the central government and special accounts, 8 billion from local governments, and almost 20 billion in loans. As of 2008, around 30 billion yuan had been spent on the construction of the eastern (5.66 billion yuan) and central routes (24.82 billion yuan). Costs of the projects have increased significantly. [ 28 ]
By 2014, more than 208.2 billion RMB (34 billion USD) had been spent, with construction on the western route not yet started. This was a significant amount, costing 3% of all government investment while it was being built. [ 8 ] By 2024, 500 billion RMB had been spent on the project. [ citation needed ]
Notwithstanding these developments, the SNWTP has drawn much criticism for its negative environmental effects. The project required resettling at least 330,000 people in central China. [ 29 ] Critics have warned the water diversion will cause environmental damage, and some villagers said officials had forced them to sign agreements to relocate. [ 29 ]
In 2013, Radio Free Asia reported that fish farmers on Dongping Lake , on the project's eastern route, in Shandong, claimed that the polluted Yangtze River water entering the lake was killing their fish. Subsequent scientific research showed that the water diversion improved the water environment of Dongping Lake. [ 29 ] [ 30 ]
Although the project recharged northern rivers, lakes, and aquifers, reversing groundwater depletion, [ 31 ] concerns remain over reduced downstream flows in source regions, which have been partially addressed by supplementary projects. [ 32 ]
Additionally, scientists have expressed concern that the project will increase water losses from open-canal evaporation, implying lower water transfer efficiency and possibly reducing both ecological and financial advantages. [ 33 ] The exact amount of evaporation loss is not known, but it may be improved in the future as more water is transferred and the flow rate increases. In terms of climate-change scenarios that can aggravate water shortage, these evaporation losses also raise questions over the project's long-term sustainability and environmental feasibility. [ 33 ]
Engineer Wang Mengshu has noted that a tunnel structure would have reduced the project's cost, as the ground-level canal required more excavation and land acquisition as well as the construction of 1,300 bridges. [ 34 ] | https://en.wikipedia.org/wiki/South–North_Water_Transfer_Project |
A Soxhlet extractor is a piece of laboratory apparatus [ 1 ] invented in 1879 by Franz von Soxhlet . [ 2 ] It was originally designed for the extraction of a lipid from a solid material. Typically, Soxhlet extraction is used when the desired compound has a limited solubility in a solvent , and the impurity is insoluble in that solvent. It allows for unmonitored and unmanaged operation while efficiently recycling a small amount of solvent to dissolve a larger amount of material.
A Soxhlet extractor has three main sections: a percolator (boiler and reflux) which circulates the solvent, a thimble (usually made of thick filter paper) which retains the solid to be extracted, and a siphon mechanism, which periodically empties the condensed solvent from the thimble back into the percolator.
The solvent is heated to reflux . The solvent vapour travels up a distillation arm, and floods into the chamber housing the thimble of solid. The condenser ensures that any solvent vapour cools, and drips back down into the chamber housing the solid material. The chamber containing the solid material slowly fills with warm solvent. Some of the desired compound dissolves in the cold solvent. When the Soxhlet chamber is almost full, the chamber is emptied by the siphon . The solvent is returned to the distillation flask. The thimble ensures that the rapid motion of the solvent does not transport any solid material to the still pot. This cycle may be allowed to repeat many times, over hours or days.
During each cycle, a portion of the non- volatile compound dissolves in the solvent. After many cycles the desired compound is concentrated in the distillation flask. The advantage of this system is that instead of many portions of warm solvent being passed through the sample, just one batch of solvent is recycled.
After extraction the solvent is removed, typically by means of a rotary evaporator , yielding the extracted compound. The non-soluble portion of the extracted solid remains in the thimble, and is usually discarded.
Like Soxhlet extractor, the Kumagawa extractor has a specific design where the thimble holder/chamber is directly suspended inside the solvent flask (having a vertical large opening) above the boiling solvent. The thimble is surrounded by hot solvent vapour and maintained at a higher temperature compared to the Soxhlet extractor, thus allowing better extraction for compounds with higher melting points such as bitumen . The removable holder/chamber is fitted with a small siphon side arm and, in the same way as for Soxhlet, a vertical condenser ensures that the solvent drips back down into the chamber which is automatically emptied at every cycle.
William B. Jensen notes that the earliest example of a continuous extractor is archaeological evidence for a Mesopotamian hot-water extractor for organic matter dating from approximately 3500 BC. [ 3 ] The same mechanism is present in the Pythagorean cup . Before Soxhlet, the French chemist Anselme Payen also pioneered with continuous extraction in the 1830s.
A Soxhlet apparatus has been proposed as an effective technique for washing mass standards . [ 4 ] | https://en.wikipedia.org/wiki/Soxhlet_extractor |
The Sołtan argument is an astrophysical theory outlined in 1982 by Polish astronomer Andrzej Sołtan [ pl ] . It maintains that if quasars were powered by accretion onto a supermassive black hole , then such supermassive black holes must exist in our local universe as "dead" quasars.
As early as 1969, Donald Lynden-Bell wrote a paper suggesting that "dead quasars" were found at the center of the Milky Way and nearby galaxies by arguing that given the quasar-number counts, luminosities, distances, and the efficiency of accretion into a "Schwarzschild throat" through the last stable circular orbit (note that the term black hole had been coined only two years earlier and was still gaining popular usage), roughly 10 10 quasars existed in the observable universe . This number density of "dead quasars" was attributed by Lynden-Bell to high mass-to-light ratio objects found at the center of galaxies. This is essentially the Sołtan argument, though the direct connection between black hole masses and quasar luminosity functions is missing. In the paper, Lynden-Bell also suggests some radical ideas that are now fully integrated into modern understanding of astrophysics including the model that accretion disks are supported by magnetic fields , that extragalactic cosmic rays are accelerated in them, and he estimates to within an order of magnitude the masses of several of the closest supermassive black holes including the ones in the Milky Way , M31 , M32 , M81 , M82 , M87 , and NGC 4151 . [ 1 ]
Thirteen years later, Sołtan explicitly showed that the luminosity ( L {\displaystyle L} ) of quasars was due to the accretion rate of mass onto black holes given by:
L = ϵ M ˙ c 2 {\displaystyle L=\epsilon {\dot {M}}c^{2}}
where
Given the number of observed quasars at various redshifts , he was able to derive an integrated energy density due to quasar output. Since observers on Earth are flux limited , there are always more quasars that exist than are observed and thus the energy density he derived is a lower bound . He obtained the value of approximately 10 −10 ergs per cubic meter . [ 3 ]
Sołtan calculated the mass density of accreted material as it is directly related to the energy density of quasar light. He derived a value of approximately 10 14 solar masses per cubic Gigaparsec . This mass would be discretely distributed (since quasars are single point sources); given an average mass of approximately ten million solar masses, it would be statistically likely for a "dead quasar" to be within a few megaparsecs of Earth. [ 3 ]
At this time, evidence was already accumulating that supermassive black holes were found at the center of large galaxies, which are distributed approximately on the order of a megaparsec apart from each other. This argument therefore made a reasonable case that supermassive black holes were at one time ultraluminous quasars.
The first quantitative estimates of the mass density in supermassive black holes were 5-10 times higher than Sołtan's estimate. [ 4 ] This discrepancy was resolved in 2000 via the discovery of the M–sigma relation , which showed that most of the previously-published black hole masses were in error. [ 5 ]
As of 2008, the best constraints for the supermassive black hole mass per cubic megaparsec in the local universe derived from the Sołtan argument is between 2 - 5 x 10 5 solar masses. This value is consistent with observations of the mass of local supermassive black holes. [ 6 ] | https://en.wikipedia.org/wiki/Sołtan_argument |
Spa is a brand of mineral water from Spa , Belgium , and is owned by the Spadel Group . Spa mineral water has been bottled since the end of the 16th century and is very common in Western Europe and especially in the Benelux countries. It is also exported to other parts of the world. Spa Mineral Water is distributed in the UK by Aqua Amore Ltd. Spa mineral water comes from the grounds of the Hautes Fagnes , of which the upper layers exists from heath land and peat .
Spa mineral water is available in bottles of three litres , two litres, one and a half liter, one liter, 75 cl, 50 cl, 30 cl and 25 cl. It is also available in 33 cl cans. There are several types of Spa mineral water.
The several types of Spa mineral water are instantly recognizable by their color of the label. These labels are blue, red or green.
The water comes from different sources which are characterised by their difference in minerals.
In the Dutch language in the Netherlands , the brand Spa has historically been so pervasive that it has become a generic term for mineral water in . Spa rood ( transl. Spa red ) is a generic term for sparkling water, as the label for sparkling Spa is red. Likewise, Spa blauw ( transl. Spa blue ) is a generic term for still (non-carbonated) mineral water, as the label for non-carbonated Spa is blue.
In a Dutch restaurant, for example, if a customer wishes sparkling mineral water, he will most commonly ask for " Spa Rood ". Generally, the waiter would not expect that the customer wants Spa brand specifically, nor would the customer expect Spa specifically. | https://en.wikipedia.org/wiki/Spa_(mineral_water) |
Space-based solar power ( SBSP or SSP ) is the concept of collecting solar power in outer space with solar power satellites (SPS) and distributing it to Earth . Its advantages include a higher collection of energy due to the lack of reflection and absorption by the atmosphere , the possibility of very little night, and a better ability to orient to face the Sun. Space-based solar power systems convert sunlight to some other form of energy (such as microwaves ) which can be transmitted through the atmosphere to receivers on the Earth's surface.
Solar panels on spacecraft have been in use since 1958, when Vanguard I used them to power one of its radio transmitters; however, the term (and acronyms) above are generally used in the context of large-scale transmission of energy for use on Earth.
Various SBSP proposals have been researched since the early 1970s, [ 1 ] [ 2 ] but as of 2014 [update] none is economically viable with the space launch costs. Some technologists propose lowering launch costs with space manufacturing or with radical new space launch technologies other than rocketry .
Besides cost, SBSP also introduces several technological hurdles, including the problem of transmitting energy from orbit. Since wires extending from Earth's surface to an orbiting satellite are not feasible with current technology, SBSP designs generally include the wireless power transmission with its associated conversion inefficiencies, as well as land use concerns for antenna stations to receive the energy at Earth's surface. The collecting satellite would convert solar energy into electrical energy, power a microwave transmitter or laser emitter, and transmit this energy to a collector (or microwave rectenna ) on Earth's surface. Contrary to appearances in fiction, most designs propose beam energy densities that are not harmful if human beings were to be inadvertently exposed, such as if a transmitting satellite's beam were to wander off-course. But the necessarily vast size of the receiving antennas would still require large blocks of land near the end users. The service life of space-based collectors in the face of long-term exposure to the space environment, including degradation from radiation and micrometeoroid damage, could also become a concern for SBSP.
As of 2020, SBSP is being actively pursued by Japan, China, [ 3 ] Russia, India, the United Kingdom, [ 4 ] and the US.
In 2008, Japan passed its Basic Space Law which established space solar power as a national goal. [ 5 ] JAXA has a roadmap to commercial SBSP.
In 2015, the China Academy for Space Technology (CAST) showcased its roadmap at the International Space Development Conference. In February 2019, Science and Technology Daily (科技日报, Keji Ribao), the official newspaper of the Ministry of Science and Technology of the People's Republic of China , reported that construction of a testing base had started in Chongqing's Bishan District. CAST vice-president Li Ming was quoted as saying China expects to be the first nation to build a working space solar power station with practical value. Chinese scientists were reported as planning to launch several small- and medium-sized space power stations between 2021 and 2025. [ 6 ] [ 7 ] In December 2019, Xinhua News Agency reported that China plans to launch a 200-tonne SBSP station capable of generating megawatts (MW) of electricity to Earth by 2035. [ 8 ]
In May 2020, the US Naval Research Laboratory conducted its first test of solar power generation in a satellite. [ 9 ] In August 2021, the California Institute of Technology (Caltech) announced that it planned to launch a SBSP test array by 2023, and at the same time revealed that Donald Bren and his wife Brigitte, both Caltech trustees, had been since 2013 funding the institute's Space-based Solar Power Project, donating over $100 million. [ 10 ] [ 11 ] A Caltech team successfully demonstrated beaming power to earth in 2023. [ 11 ]
In 1941, science fiction writer Isaac Asimov published the science fiction short story " Reason ", in which a space station transmits energy collected from the Sun to various planets using microwave beams. The SBSP concept, originally known as satellite solar-power system (SSPS), was first described in November 1968. [ 12 ] In 1973 Peter Glaser was granted U.S. patent number 3,781,647 for his method of transmitting power over long distances (e.g. from an SPS to Earth's surface) using microwaves from a very large antenna (up to one square kilometer) on the satellite to a much larger one, now known as a rectenna , on the ground. [ 13 ]
Glaser then was a vice president at Arthur D. Little , Inc. NASA signed a contract with ADL to lead four other companies in a broader study in 1974. They found that, while the concept had several major problems – chiefly the expense of putting the required materials in orbit and the lack of experience on projects of this scale in space – it showed enough promise to merit further investigation and research. [ 14 ]
Between 1978 and 1986, the Congress authorized the Department of Energy (DoE) and NASA to jointly investigate the concept. They organized the Satellite Power System Concept Development and Evaluation Program. [ 15 ] [ 16 ] The study remains the most extensive performed to date (budget $50 million). [ 17 ] Several reports were published investigating the engineering feasibility of such a project. They include:
The project was not continued with the change in administrations after the 1980 United States elections . The Office of Technology Assessment concluded that "Too little is currently known about the technical, economic, and environmental aspects of SPS to make a sound decision whether to proceed with its development and deployment. In addition, without further research an SPS demonstration or systems-engineering verification program would be a high-risk venture." [ 35 ]
In 1997, NASA conducted its "Fresh Look" study to examine the modern state of SBSP feasibility. In assessing "What has changed" since the DOE study, NASA asserted that the "US National Space Policy now calls for NASA to make significant investments in technology (not a particular vehicle) to drive the costs of ETO [Earth to Orbit] transportation down dramatically. This is, of course, an absolute requirement of space solar power." [ 36 ]
Conversely, Pete Worden of NASA claimed that space-based solar is about five orders of magnitude more expensive than solar power from the Arizona desert, with a major cost being the transportation of materials to orbit. Worden referred to possible solutions as speculative and not available for decades at the earliest. [ 37 ]
On November 2, 2012, China proposed a space collaboration with India that mentioned SBSP, "may be Space-based Solar Power initiative so that both India and China can work for long term association with proper funding along with other willing space faring nations to bring space solar power to earth." [ 38 ]
In 1999, NASA initiated its Space Solar Power Exploratory Research and Technology program (SERT) for the following purposes: [ 39 ] [ 40 ] [ 41 ] [ 42 ]
SERT went about developing a solar power satellite (SPS) concept for a future gigawatt space power system, to provide electrical power by converting the Sun's energy and beaming it to Earth's surface, and provided a conceptual development path that would utilize current technologies. SERT proposed an inflatable photovoltaic gossamer structure with concentrator lenses or solar heat engines to convert sunlight into electricity. The program looked both at systems in Sun-synchronous orbit and geosynchronous orbit . Some of SERT's conclusions:
The May 2014 IEEE Spectrum magazine carried a lengthy article "It's Always Sunny in Space" by Susumu Sasaki. [ 44 ] The article stated, "It's been the subject of many previous studies and the stuff of sci-fi for decades, but space-based solar power could at last become a reality—and within 25 years, according to a proposal from researchers at the Tokyo -based Japan Aerospace Exploration Agency (JAXA)."
JAXA announced on 12 March 2015 that they wirelessly beamed 1.8 kilowatts 50 meters to a small receiver by converting electricity to microwaves and then back to electricity. This is the standard plan for this type of power. [ 45 ] [ 46 ] On 12 March 2015 Mitsubishi Heavy Industries demonstrated transmission of 10 kilowatts (kW) of power to a receiver unit located at a distance of 500 meters (m) away. [ 47 ]
Aetherflux is a venture-funded company focused on beaming solar power, funded with US$50 million. It plans a constellation of small Low Earth Orbit satellites, using infrared lasers. Ground stations are about 5–10 m (16–33 ft) in diameter. It is partially supported this financial year by the US Department of Defense 's Operational Energy Capability Improvement Fund (OECIF). [ 48 ]
The SBSP concept is attractive because space has several major advantages over the Earth's surface for the collection of solar power:
The SBSP concept also has a number of problems:
Space-based solar power essentially consists of three elements: [ 2 ]
The space-based portion will not need to support itself against gravity (other than relatively weak tidal stresses). It needs no protection from terrestrial wind or weather, but will have to cope with space hazards such as micrometeors and solar flares . Two basic methods of conversion have been studied: photovoltaic (PV) and solar dynamic (SD). Most analyses of SBSP have focused on photovoltaic conversion using solar cells that directly convert sunlight into electricity. Solar dynamic uses mirrors to concentrate light on a boiler. The use of solar dynamic could reduce mass per watt. Wireless power transmission was proposed early on as a means to transfer energy from collection to the Earth's surface, using either microwave or laser radiation at a variety of frequencies.
William C. Brown demonstrated in 1964, during Walter Cronkite 's CBS News program, a microwave-powered model helicopter that received all the power it needed for flight from a microwave beam. Between 1969 and 1975, Bill Brown was technical director of a JPL Raytheon program that beamed 30 kW of power over a distance of 1 mile (1.6 km) at 9.6% efficiency. [ 68 ] [ 69 ]
The beam does spread out due to diffraction. At 2.45 GHz, a one km phased array transmitting antenna at GEO spreads to about 10 km diameter to the first zero ring. [ 70 ] The overall transmission efficiency is close to 50% depending on many factors. [1]
Microwave power transmission of tens of kilowatts has been well proven by existing tests at Goldstone in California (1975) [ 69 ] [ 71 ] [ 72 ] and Grand Bassin on Reunion Island (1997). [ 73 ]
More recently, microwave power transmission has been demonstrated, in conjunction with solar energy capture, between a mountaintop in Maui and the island of Hawaii (92 miles away), by a team under John C. Mankins . [ 74 ] [ 75 ] Technological challenges in terms of array layout, single radiation element design, and overall efficiency, as well as the associated theoretical limits are presently a subject of research, as it was demonstrated by the Special Session on "Analysis of Electromagnetic Wireless Systems for Solar Power Transmission" held during the 2010 IEEE Symposium on Antennas and Propagation. [ 76 ] In 2013, a useful overview was published, covering technologies and issues associated with microwave power transmission from space to ground. It includes an introduction to SPS, current research and future prospects. [ 77 ] Moreover, a review of current methodologies and technologies for the design of antenna arrays for microwave power transmission appeared in the Proceedings of the IEEE. [ 78 ]
Laser power beaming was envisioned by some at NASA as a stepping stone to further industrialization of space. In the 1980s, researchers at NASA worked on the potential use of lasers for space-to-space power beaming, focusing primarily on the development of a solar-powered laser. In 1989, it was suggested that power could also be usefully beamed by laser from Earth to space. In 1991, the SELENE project (SpacE Laser ENErgy) had begun, which included the study of laser power beaming for supplying power to a lunar base. The SELENE program was a two-year research effort, but the cost of taking the concept to operational status was too high, and the official project ended in 1993 before reaching a space-based demonstration. [ 79 ]
Laser Solar Satellites are smaller in size, meaning that they have to work as a group with other similar satellites. There are many pros to Laser Solar Satellites, specifically regarding their lower overall costs in comparison to other satellites. While the cost is lower than other satellites, there are various safety concerns, and other concerns regarding this satellite. [ 80 ] Laser-emitting solar satellites only need to venture about 400 km into space, but because of their small generation capacity, hundreds or thousands of laser satellites would need to be launched in order to create a sustainable impact. A single satellite launch can range from fifty to four hundred million dollars. Lasers could be helpful for the energy from the sun harvested in space, to be returned back to Earth in order for terrestrial power demands to be met. [ 81 ]
The main advantage of locating a space power station in geostationary orbit is that the antenna geometry stays constant, and so keeping the antennas lined up is simpler. Another advantage is that nearly continuous power transmission is immediately available as soon as the first space power station is placed in orbit, LEO requires several satellites before they are producing nearly continuous power.
Power beaming from geostationary orbit by microwaves carries the difficulty that the required 'optical aperture' sizes are very large. For example, the 1978 NASA SPS study required a 1 km diameter transmitting antenna and a 10 km diameter receiving rectenna for a microwave beam at 2.45 GHz . These sizes can be somewhat decreased by using shorter wavelengths, although they have increased atmospheric absorption and even potential beam blockage by rain or water droplets. Because of the thinned array curse , it is not possible to make a narrower beam by combining the beams of several smaller satellites. The large size of the transmitting and receiving antennas means that the minimum practical power level for an SPS will necessarily be high; small SPS systems will be possible, but uneconomic. [ original research? ]
A collection of LEO ( low Earth orbit ) space power stations has been proposed as a precursor to GEO ( geostationary orbit ) space-based solar power. [ 82 ]
The Earth-based rectenna would likely consist of many short dipole antennas connected via diodes . Microwave broadcasts from the satellite would be received in the dipoles with about 85% efficiency. [ 83 ] With a conventional microwave antenna, the reception efficiency is better, but its cost and complexity are also considerably greater. Rectennas would likely be several kilometers across.
A laser SBSP could also power a base or vehicles on the surface of the Moon or Mars, saving on mass costs to land the power source. A spacecraft or another satellite could also be powered by the same means. In a 2012 report presented to NASA on space solar power, the author mentions another potential use for the technology behind space solar power could be for solar electric propulsion systems that could be used for interplanetary human exploration missions. [ 84 ] [ 85 ] [ 86 ]
One problem with the SBSP concept is the cost of space launches and the amount of material that would need to be launched.
Much of the material launched need not be delivered to its eventual orbit immediately, which raises the possibility that high efficiency (but slower) engines could move SPS material from LEO to GEO at an acceptable cost. Examples include ion thrusters or nuclear propulsion . Infrastructure including solar panels, power converters, and power transmitters will have to be built in order to begin the process. This will be extremely expensive and maintaining them will cost even more.
To give an idea of the scale of the problem, assuming a solar panel mass of 20 kg per kilowatt (without considering the mass of the supporting structure, antenna, or any significant mass reduction of any focusing mirrors) a 4 GW power station would weigh about 80,000 metric tons , [ 87 ] all of which would, in current circumstances, be launched from the Earth. This is, however, far from the state of the art for flown spacecraft, which as of 2015 was 150 W/kg (6.7 kg/kW), and improving rapidly. [ 88 ] Very lightweight designs could likely achieve 1 kg/kW, [ 89 ] meaning 4,000 metric tons for the solar panels for the same 4 GW capacity station. Beyond the mass of the panels, overhead (including boosting to the desired orbit and stationkeeping) must be added.
To these costs must be added the environmental impact of heavy space launch missions, if such costs are to be used in comparison to earth-based energy production. For comparison, the direct cost of a new coal [ 90 ] or nuclear power plant ranges from $3 billion to $6 billion per GW (not including the full cost to the environment from CO 2 emissions or storage of spent nuclear fuel, respectively).
Gerard O'Neill , noting the problem of high launch costs in the early 1970s, proposed building the SPS's in orbit with materials from the Moon . [ 91 ] Launch costs from the Moon are potentially much lower than from Earth because of the lower gravity and lack of atmospheric drag . This 1970s proposal assumed the then-advertised future launch costing of NASA's space shuttle. This approach would require substantial upfront capital investment to establish mass drivers on the Moon. [ 92 ] Nevertheless, on 30 April 1979, the Final Report ("Lunar Resources Utilization for Space Construction") by General Dynamics' Convair Division, under NASA contract NAS9-15560, concluded that use of lunar resources would be cheaper than Earth-based materials for a system of as few as thirty solar power satellites of 10 GW capacity each. [ 93 ]
In 1980, when it became obvious NASA's launch cost estimates for the space shuttle were grossly optimistic, O'Neill et al. published another route to manufacturing using lunar materials with much lower startup costs. [ 94 ] This 1980s SPS concept relied less on human presence in space and more on partially self-replicating systems on the lunar surface under remote control of workers stationed on Earth. The high net energy gain of this proposal derives from the Moon's much shallower gravitational well .
Having a relatively cheap per pound source of raw materials from space would lessen the concern for low mass designs and result in a different sort of SPS being built. The low cost per pound of lunar materials in O'Neill's vision would be supported by using lunar material to manufacture more facilities in orbit than just solar power satellites. Advanced techniques for launching from the Moon may reduce the cost of building a solar power satellite from lunar materials. Some proposed techniques include the lunar mass driver and the lunar space elevator , first described by Jerome Pearson. [ 95 ] It would require establishing silicon mining and solar cell manufacturing facilities on the Moon . [ citation needed ]
Physicist Dr David Criswell suggests the Moon is the optimum location for solar power stations, and promotes lunar-based solar power. [ 96 ] [ 97 ] [ 98 ] The main advantage he envisions is construction largely from locally available lunar materials, using in-situ resource utilization , with a teleoperated mobile factory and crane to assemble the microwave reflectors, and rovers to assemble and pave solar cells, [ 99 ] which would significantly reduce launch costs compared to SBSP designs. Power relay satellites orbiting around earth and the Moon reflecting the microwave beam are also part of the project. A demo project of 1 GW starts at $50 billion. [ 100 ] The Shimizu Corporation use combination of lasers and microwave for the Luna Ring concept, along with power relay satellites. [ 101 ] [ 102 ]
Asteroid mining has also been seriously considered. A NASA design study [ 103 ] evaluated a 10,000-ton mining vehicle (to be assembled in orbit) that would return a 500,000-ton asteroid fragment to geostationary orbit. Only about 3,000 tons of the mining ship would be traditional aerospace-grade payload. The rest would be reaction mass for the mass-driver engine, which could be arranged to be the spent rocket stages used to launch the payload. Assuming that 100% of the returned asteroid was useful, and that the asteroid miner itself couldn't be reused, that represents nearly a 95% reduction in launch costs. However, the true merits of such a method would depend on a thorough mineral survey of the candidate asteroids; thus far, we have only estimates of their composition. [ 104 ] One proposal is to capture the asteroid Apophis into Earth orbit and convert it into 150 solar power satellites of 5 GW each or the larger asteroid 1999 AN10, which is 50 times the size of Apophis and large enough to build 7,500 5-gigawatt solar power satellites [ 105 ]
The potential exposure of humans and animals on the ground to the high power microwave beams is a significant concern with these systems. At the Earth's surface, a suggested SPSP microwave beam would have a maximum intensity at its center, of 23 mW/cm 2 . [ 106 ] While this is less than 1/4 the solar irradiation constant , microwaves penetrate much deeper into tissue than sunlight, and at this level would exceed the current United States Occupational Safety and Health Act (OSHA) workplace exposure limits for microwaves at 10 mW/cm 2 [ 107 ] At 23 mW/cm 2 , studies show humans experience significant deficits in spatial learning and memory. [ 108 ] If the diameter of the proposed SPSP array is increased by 2.5x, the energy density on the ground increases to 1 W/cm 2 . [ a ] At this level, the median lethal dose for mice is 30-60 seconds of microwave exposure. [ 109 ] While designing an array with 2.5x larger diameter should be avoided, the dual-use military potential of such a system is readily apparent.
With good array sidelobe design, outside the receiver may be less than the OSHA long-term levels [ 110 ] as over 95% of the beam energy will fall on the rectenna. However, any accidental or intentional mis-pointing of the satellite could be deadly to life on Earth within the beam.
Exposure to the beam can be minimized in various ways. On the ground, assuming the beam is pointed correctly, physical access must be controllable (e.g., via fencing). Typical aircraft flying through the beam provide passengers with a protective metal shell (i.e., a Faraday Cage ), which will intercept the microwaves. [ original research? ] Other aircraft ( balloons , ultralight , etc.) can avoid exposure by using controlled airspace, as is currently done for military and other controlled airspace. In addition, a design constraint is that the microwave beam must not be so intense as to injure wildlife, particularly birds. Suggestions have been made to locate rectennas offshore, [ 111 ] [ 112 ] but this presents serious problems, including corrosion, mechanical stresses, and biological contamination.
A commonly proposed approach to ensuring fail-safe beam targeting is to use a retrodirective phased array antenna/rectenna. A "pilot" microwave beam emitted from the center of the rectenna on the ground establishes a phase front at the transmitting antenna. There, circuits in each of the antenna's subarrays compare the pilot beam's phase front with an internal clock phase to control the phase of the outgoing signal. If the phase offset to the pilot is chosen the same for all elements, the transmitted beam should be centered precisely on the rectenna and have a high degree of phase uniformity; if the pilot beam is lost for any reason (if the transmitting antenna is turned away from the rectenna, for example) the phase control value fails and the microwave power beam is automatically defocused. [ 113 ] Such a system would not focus its power beam very effectively anywhere that did not have a pilot beam transmitter. The long-term effects of beaming power through the ionosphere in the form of microwaves has yet to be studied.
The typical reference system-of-systems involves a significant number (several thousand multi-gigawatt systems to service all or a significant portion of Earth's energy requirements) of individual satellites in GEO. The typical reference design for the individual satellite is in the 1-10 GW range and usually involves planar or concentrated solar photovoltaics (PV) as the energy collector / conversion. The most typical transmission designs are in the 1–10 GHz (2.45 or 5.8 GHz) RF band where there are minimum losses in the atmosphere. Materials for the satellites are sourced from, and manufactured on Earth and expected to be transported to LEO via re-usable rocket launch, and transported between LEO and GEO via chemical or electrical propulsion. In summary, the architecture choices are:
There are several interesting design variants from the reference system:
Alternate energy collection location: While GEO is most typical because of its advantages of nearness to Earth, simplified pointing and tracking, very small time in occultation, and scalability to meet all global demand several times over, other locations have been proposed:
Energy collection: The most typical designs for solar power satellites include photovoltaics. These may be planar (and usually passively cooled), concentrated (and perhaps actively cooled). However, there are multiple interesting variants.
Alternate satellite architecture: The typical satellite is a monolithic structure composed of a structural truss, one or more collectors, one or more transmitters, and occasionally primary and secondary reflectors. The entire structure may be gravity gradient stabilized. Alternative designs include:
Transmission: The most typical design for energy transmission is via an RF antenna at below 10 GHz to a rectenna on the ground. Controversy exists between the benefits of Klystrons, Gyrotrons, Magnetrons and solid state. Alternate transmission approaches include:
Materials and manufacturing: Typical designs make use of the developed industrial manufacturing system extant on Earth, and use Earth based materials both for the satellite and propellant. Variants include:
Method of installation / Transportation of Material to Energy Collection Location: In the reference designs, component material is launched via well-understood chemical rockets (usually fully reusable launch systems) to LEO, after which either chemical or electrical propulsion is used to carry them to GEO. The desired characteristics for this system is very high mass-flow at low total cost. Alternate concepts include:
The National Space Society maintains an extensive space solar power library Archived 2018-04-14 at the Wayback Machine of all major historical documents and studies associated with space solar power, and major news articles Archived 2016-05-29 at the Wayback Machine . | https://en.wikipedia.org/wiki/Space-based_solar_power |
In chemistry , a space-filling model , also known as a calotte model , is a type of three-dimensional (3D) molecular model where the atoms are represented by spheres whose radii are proportional to the radii of the atoms and whose center-to-center distances are proportional to the distances between the atomic nuclei , all in the same scale. Atoms of different chemical elements are usually represented by spheres of different colors.
Space-filling calotte models are also referred to as CPK models after the chemists Robert Corey , Linus Pauling , and Walter Koltun , who over a span of time developed the modeling concept into a useful form. [ 1 ] They are distinguished from other 3D representations, such as the ball-and-stick and skeletal models, by the use of the "full size" space-filling spheres for the atoms. The models are tactile and manually rotatable. They are useful for visualizing the effective shape and relative dimensions of a molecule, and (because of the rotatability) the shapes of the surface of the various conformers . On the other hand, these models mask the chemical bonds between the atoms, and make it difficult to see the structure of the molecule that is obscured by the atoms nearest to the viewer in a particular pose. For this reason, such models are of greater utility if they can be used dynamically, especially when used with complex molecules (e.g., see the greater understanding of the molecules shape given when the THC model is clicked on to rotate).
Space-filling models arise out of a desire to represent molecules in ways that reflect the electronic surfaces that molecules present, that dictate how they interact, one with another (or with surfaces, or macromolecules such as enzymes, etc.). Crystallographic data are the starting point for understanding static molecular structure, and these data contain the information rigorously required to generate space-filling representations (e.g., see these crystallographic models ); most often, however, crystallographers present the locations of atoms derived from crystallography via " thermal ellipsoids " whose cut-off parameters are set for convenience both to show the atom locations (with anisotropies ), and to allow representation of the covalent bonds or other interactions between atoms as lines. In short, for reasons of utility, crystallographic data historically have appeared in presentations closer to ball-and-stick models. Hence, while crystallographic data contain the information to create space-filling models, it remained for individuals interested in modeling an effective static shape of a molecule, and the space it occupied, and the ways in which it might present a surface to another molecule, to develop the formalism shown above.
In 1952, Robert Corey and Linus Pauling described accurate scale models of molecules which they had built at Caltech . [ 1 ] In their models, they envisioned the surface of the molecule as being determined by the van der Waals radius of each atom of the molecule, and crafted atoms as hardwood spheres of diameter proportional to each atom's van der Waals radius, in the scale 1 inch = 1 Å . To allow bonds between atoms a portion of each sphere was cut away to create a pair of matching flat faces, with the cuts dimensioned so that the distance between sphere centers was proportional to the lengths of standard types of chemical bonds. [ 1 ] A connector was designed—a metal bushing that threaded into each sphere at the center of each flat face. The two spheres were then firmly held together by a metal rod inserted into the pair of opposing bushing (with fastening by screws). The models also had special features to allow representation of hydrogen bonds . [ 1 ] [ verification needed ] [ 2 ]
In 1965, Walter L. Koltun designed and patented a simplified system with molded plastic atoms of various colours , which were joined by specially designed snap connectors; this simpler system accomplished essentially the same ends as the Corey-Pauling system, [ 4 ] [ 5 ] and allowed for the development of the models as a popular way of working with molecules in training and research environments. Such colour-coded, bond length-defined, van der Waals-type space-filling models are now commonly known as CPK models, after these three developers of the specific concept.
In modern research efforts, attention returned to use of data-rich crystallographic models in combination with traditional and new computational methods to provide space-filling models of molecules, both simple and complex, where added information such as which portions of the surface of the molecule were readily accessible to solvent , or how the electrostatic characteristics of a space-filling representation—which in the CPK case is almost fully left to the imagination—could be added to the visual models created. The two closing images give examples of the latter type of calculation and representation, and its utility. | https://en.wikipedia.org/wiki/Space-filling_model |
SpaceTEC® is one of the Advanced Technological Education (ATE) Centers [ 1 ] funded by the National Science Foundation (NSF) for developing partnerships between academic institutions and industry partners to promote improvement in the education of science and engineering technicians at the undergraduate and secondary school levels. [ 2 ] With an emphasis on two-year colleges, the ATE program focuses on the education of technicians for the high-technology fields that drive the world's economies. [ 3 ] Located in Titusville, Florida , SpaceTEC® supports the education and credentialing of aerospace technicians [ 4 ] in six core areas and three advanced disciplines: (1) space vehicle processing activities (2) aerospace manufacturing; and (3) composite materials. [ 5 ] SpaceTEC programs support a national consortium of community and technical colleges, universities, business and industry organizations, and government agencies promotes careers and educates candidates for technical employment. [ 6 ]
The organization has been accredited by the International Certification Accreditation Council [ 7 ] to ISO 17024 standards and offers performance-based examinations that result in industry-driven nationally recognized credentials reflecting the competencies employers demand. Successful candidates can qualify for college credits via transcripts provided by the American Council on Education . [ 8 ] The SpaceTEC® national credentialing program has earned a formal Safety Approval by the U.S. Federal Aviation Administration's Office of Commercial Space Transportation . [ 9 ]
SpaceTEC® was established in 2002 as an NSF National Center of Excellence funded in part by a three-year NSF Advanced Technological Education Program grant and renewed in 2005 for an additional four years. SpaceTEC® was awarded a four-year follow-on grant in 2009 as an NSF National Resource Center, and in April, 2013, it received a four-year renewal of its NSF grant. The center is now expanding operations to Science, Technology, Engineering, and Mathematics ( STEM fields ) technicians working in technical fields beyond aerospace through its ‘’’CertTEC®’’’ commercial industry credentials. [ 10 ]
The original consortium of industry, academia, and government representatives was known as the Community Colleges for Innovative Technology Transfer (CCITT), a not-for-profit Florida corporation founded in 1994 to provide technician education for geographic information systems . CCITT received one of the first National Science Foundation grants for two-year community and technical colleges. The founding partners were all located near NASA or Department of Defense locations, providing a consortium strongly linked to post-secondary education programs for the nation's technical workforce in aerospace and defense. Its credentials are widely recognized in academic circles [ 11 ] as well as within the U. S. aerospace industry. [ 12 ]
Community Colleges for Innovative Technology Transfer, was restructured in 2009 and renamed SpaceTEC Partners, Inc. (SPI). [ 13 ] to reflect a growing expansion of activities to technical education programs beyond aerospace. The primary mission of SPI was to create and implement an industry-driven, government-endorsed, technical education process to be shared with other educational venues. This role has now been expanded to include workforce development for aerospace, defense, advanced manufacturing and marine industries though Job Task Analyses, curriculum and coursework development and technician credentialing. SpaceTEC® programs to educate and credential STEM technicians have been adopted by educational institutions, [ 14 ] NASA and Department of Defense contractors [ 15 ] and for U. S. active duty personnel and veterans. [ 16 ]
Most recently, SpaceTEC® has obtained the NASA human spaceflight database of educational and credentialing activities for its NSF National Resource Center and all of its partners [ 17 ] and continues to support strong linkages between its industry and education partners. [ 18 ]
SpaceTEC provides third-party credentialing services to a wide array of industry trade groups, standards organizations and high schools across the country. In addition, through its CertTEC and Credential Testing Services platforms, SpaceTEC provides industry certifications for active duty military and veterans funded though Military COOL and VA WEAMS.
SpaceTEC is also host and fiscal agent for the Space Coast Consortium Apprenticeship Program (SCCAP) https://spacecoastconsortium.org/ offering 2.5 year dual (academic and On-the-Job training) apprenticeships in Mechatronics, CNC Machining, Advanced Composites, Additive Manufacturing, Aerospace Welding and Cybersecurity for East Central Florida employers.
In a recent venture, SpaceTEC Partners, Inc. is developing the Space Coast Aerospace and Defense Training Center (ADTC) https://adtcspacecoast.org/ as a means of providing accelerated skills training for non-traditional students and underserved populations as an entry into the region's aerospace and defense industries. | https://en.wikipedia.org/wiki/SpaceTEC_National_Resource_Center_for_Aerospace_Technical_Education |
SpaceTurk , founded in 1998 as the Turkish Space Research Group, is a non-profit and volunteer group dedicated to working on space research. The group's activities so far are: | https://en.wikipedia.org/wiki/SpaceTurk |
Starshield is a business unit of SpaceX creating purpose-built low-Earth-orbit (LEO) satellites designed to provide new military space capabilities to U.S. and allied governments. [ 1 ] [ 2 ] [ 3 ] [ 4 ] Starshield was adapted from the global communications network Starlink but brings additional capabilities such as target tracking, optical and radio reconnaissance , and early missile warning. [ 5 ] [ 6 ] [ 7 ] [ 8 ] Primary customers include the Space Development Agency (SDA), National Reconnaissance Office and the United States Space Force . [ 5 ] [ 9 ] [ 10 ] As of 2025, at least 118 Starshield satellites have been launched, with the latest batch of 22 satellites being launched in January 2025 as part of NROL-167 . [ 11 ] [ 12 ]
While SpaceX president and COO Gwynne Shotwell has indicated that there is little information she is allowed to disclose about Starshield, she has noted "very good collaboration" between the intelligence community and SpaceX on the program. [ 1 ] The U.S. Congressional Research Service reports that future satellites in Starshield's participating SDA program may wield interceptor missiles, hypersonic projectiles, or directed energy weapons , [ 8 ] with the program's founder [ 6 ] adding "since Reagan’s day, technology has advanced enough that putting both sensors and shooters in space is not only possible but relatively easy." [ 7 ] According to SDA director Derek Tournear , later satellites will take on the “extremely difficult” task of maintaining contact with missiles in flight. [ 13 ]
The former four-star general Terrence O'Shaughnessy , who previously ran U.S. Northern Command , is the vice president for SpaceX's Special Programs Group who is thought to be involved with Starshield. [ 1 ] The Wall Street Journal reported that Starshield's online job postings required people with top-secret clearances, as well as experience working with the Defense Department and intelligence community — such as representing Starshield to Pentagon combatant commands. [ 1 ] For weapons manufacturing, eight senior Starshield leaders formed an additional company Castelion , to develop mass produced hypersonic strike weapons, potentially for use as space-based interceptors [ 14 ] [ 15 ]
The first satellites were designed for the SDA and outfitted with advanced infrared sensors meant to detect and track ballistic and hypersonic missiles. [ 5 ] In 2021, Starshield had entered a $1.8 billion classified contract with the U.S. government, revealed in 2023, [ 1 ] to construct hundreds of spy satellites for continuous real-time monitoring of targets around the globe. [ 9 ] These began operations from May 2024, starting with NROL-146. These satellites are made in cooperation with Northrop Grumman . [ 16 ]
The Starshield name was publicly announced December 2022, [ 17 ] however in 2021, Starshield had already entered a $1.8 billion classified contract with the U.S. government, revealed in 2023. [ 1 ] In the documents of the contract, SpaceX says that funds from the contract were expected to become an important part of the revenue mix of the company after 2021. [ 1 ] Reuters revealed in 2024 that this contract was between the National Reconnaissance Office and SpaceX, and for a spy satellite network consisting of hundreds of satellites functioning as a swarm. [ 9 ] The satellites will have imaging capabilities, and the satellite network will enable the US government to have continuous surveillance of nearly anywhere around the globe. [ 9 ] Starshield also plans to be more resilient to attack from other powers. [ 9 ] Starshield's imaging capabilities are designed to have superior resolution over most existing U.S. government spying systems. Northrop Grumman was selected to partner with SpaceX, with insiders noting that "it is in the government's interest to not be totally invested in one company run by one person". [ 18 ]
As early as 2020, SpaceX was designing, building, and launching customized satellites based on variants of the Starlink satellite bus for the National Reconnaissance Office (NRO).
In October 2020, SDA awarded SpaceX an initial $150 million dual-use contract to develop 4 satellites to detect and track ballistic and hypersonic missiles. [ 5 ] The first batch of satellites were originally scheduled to launch September 2022 to form part of the Tracking Layer Tranche 0 of the Space Force's National Defense Space Architecture . [ 19 ] The launch was rescheduled multiple times but it eventually launched in April 2023. [ 20 ] [ 21 ]
In 2020, SpaceX hired retired four-star general Terrence J. O'Shaughnessy who according to some sources is associated with Starlink's military satellite development and according to one source is listed as a "chief operating officer" at SpaceX. [ 22 ] [ 23 ] While still in active duty, O'Shaughnessy advocated before the United States Senate Committee on Armed Services for a layered capability with lethal follow-on that incorporates machine learning and artificial intelligence to gather and act upon sensor data quickly. [ 24 ] As of 2024, Terrence O’Shaughnessy reportedly has had a high-level role at Starshield, though there is no indication that SpaceX is working on anything related to lethal weapons. [ 1 ]
SpaceX was not awarded a contract for the larger Tranche 1, with awards going to York Space Systems, Lockheed Martin Space, and Northrop Grumman Space Systems. [ 25 ]
As Starlink was being relied on in the Russo-Ukrainian war , expert on battlefield communications Thomas Wellington argued that Starlink signals, because they use narrow focused beams, are less vulnerable to interference and jamming by the enemy in wartime than satellites flying in higher orbits. [ 26 ] Although there is no lethal weapons being developed this technology is being used by the military and it "can be integrated onto partner satellites to enable incorporation into the Starshield network." [ 27 ] Therefore, if the military needed the use of SpaceX satellites through the Starshield program SpaceX "currently has over 3,000 satellites in low Earth orbit that beam the signal back to users' receiver dishes." [ 28 ]
Another Starshield contract was announced in September 2023, involving communications-focused services for U.S. Space Systems Command. [ 29 ] [ 30 ] This contract with the US Space Force plans to provide customized satellite communications for the military. [ 31 ] This is under the Space Force's new "Proliferated Low Earth Orbit" program for LEO satellites, where Space Force will allocate up to $900 million worth of contracts over the next 10 years. Although 16 vendors are competing for awards, the SpaceX contract is the only one to have been issued to date. [ 29 ] [ 31 ] The one-year Starshield contract was awarded on September 1, 2023. [ 10 ] The contract is expected to support 54 mission partners across the Army, Navy, Air Force, and Coast Guard. [ 10 ]
In February 2024, the United States House Select Committee on Strategic Competition between the United States and the Chinese Communist Party sent a letter to Elon Musk stating that the Starshield program was potentially in breach of contract for not providing access to U.S. troops stationed in Taiwan when "global access" was "possibly" required by the contract. [ 32 ] [ 33 ] SpaceX responded that they were in full compliance with their U.S. government contracts. SpaceX had notified the Select Committee a week earlier that they were misinformed, but the Select Committee "chose to contact media before seeking additional information [regarding Starshield military use in Taiwan]". [ 34 ]
In the context of military communication satellites, Col. Eric Felt, director of space architecture at the office of the assistant secretary of the Air Force for space acquisition and integration, said that there are plans to acquire at least 100 Starshield-branded satellites for this purpose by 2029. He said that while the military is an active user of SpaceX's commercial Starlink service, they also want to take advantage of the company's dedicated Starshield product line. Clare Hopper, head of the Space Force’s Commercial Satellite Communications Office (CSCO) stated that demand for Starlink's commercial service is "off the charts" and that currently all of their supported users are still using the commercial Starlink satellite constellation, but that the DoD has "unique service plans that contain privileged capabilities and features that are not available commercially". [ 35 ]
Between 2020 and March 2024, a dozen Starshield prototypes and operational satellites were launched on Falcon 9. [ 9 ] Reuters reported that these satellites have never been acknowledged by SpaceX or the US government and remain classified. [ 9 ]
Images were posted online [ 36 ] of the two SpaceX-built Space Development Agency Tranche 0 Flight 1 Tracking Layer infrared imaging satellites that launched on 2 April 2023. [ 37 ] After the launch of Starlink Group 7-16 , only 20 of a batch of 22 starlink satellites were catalogued, and the remaining two were later designated as USA-350 and USA-351. [ 38 ] | https://en.wikipedia.org/wiki/SpaceX_Starshield |
The SpaceX fairing recovery program was an experimental program by SpaceX , begun in 2017 in an effort to determine if it might be possible to economically recover and reuse expended launch vehicle payload fairings from suborbital space . The experimental program became an operational program as, by late 2020, the company was routinely recovering fairings from many flights, and by 2021 were successfully refurbishing and reflying previously flown fairings on the majority of their satellite launches.
During the early years of the program, SpaceX attempted to catch the descending payload fairings, under parachute , in a very large net on a moving ship in the Atlantic Ocean east of the Space Coast of Florida. Two former platform supply vessels — Ms. Tree , formerly known as Mr. Steven , [ 4 ] and its sister ship, Ms. Chief —were chartered by SpaceX and used 2018–2021 [ 5 ] as experimental platforms for recovery of rocket fairings from Falcon 9 orbital launch trajectories. These fast ships were retrofitted with large nets intended to catch fairings—and prevent the fairings from making contact with seawater—as part of an iterative development program to create technology that will eventually allow rocket payload fairings to be economically reused and reflown. Ms. Tree was used for SpaceX Falcon 9 fairing recovery experiments on a number of occasions in 2018 and early 2019, while named Mr. Steven . Ms. Tree first successfully caught a fairing on 25 June 2019 during Falcon Heavy launch 3, which carried the DoD's STP-2 mission. This was the ship's first fairing recovery voyage after its renaming, change of ownership, and net upgrade. [ 4 ] By 2020, the program reached operational status where fairings from most Falcon 9 satellite launches were recovered, either "in the net" or from the water, and for the first time, both fairing halves of a single flight were caught in the nets of two different ships. The final fairing that was successfully caught in a net was in October 2020. [ 6 ] In early 2021, the nets were removed from the two fast ships and SpaceX ended the ship leases, with both ships returned to their owner.
SpaceX found that recovery of the fairings floating on the ocean surface was adequate to support economic reuse of payload fairings on subsequent Falcon 9 launches. [ 5 ] After the end of the experimental "catch" recovery program, SpaceX entered an operational phase and as of April 2021 [update] was using the contracted [ 7 ] ships Shelia Bordelon and Hos Briarwood [ 8 ] to recover parachute-descended payload fairings that reached the sea surface in good condition using ship mounted cranes.
In May 2021, SpaceX purchased and began converting two offshore supply ships named Ella G and Ingrid for towing and supporting droneships as well as fairing recovery operations on the east coast. They are registered to Falcon Landing LLC, a SpaceX-linked company that also owns Elon Musk 's private jet. These two ships were renamed in honor of Demo-2 astronauts Doug Hurley and Bob Behnken as Doug [ 9 ] and Bob [ 10 ] respectively for their contribution to SpaceX's Crew Dragon development. [ 11 ] Currently, both support ships Bob and Doug are operating out of Port Canaveral, Florida along with other SpaceX recovery assets. To ease the recovery of these fairings out of water, SpaceX bought two small fast boats in February 2022, Maverick and Goose , named for Top Gun characters Pete "Maverick" Mitchell (Tom Cruise) and Nick "Goose" Bradshaw (Anthony Edwards), for both of these multipurpose ships. [ 12 ]
SpaceX performs some amount of cleaning and refurbishing before using the previously flown fairings on a subsequent flight. SpaceX has reflown fairing halves more than 300 times, with some being reflown for eleven or more times. [ 13 ]
Ms. Tree was originally built in 2014 for SeaTran as a platform supply vessel to support fast crew transport operations. The vessel was named Mr. Steven after Steven Miguez, the father of SeaTran CEO Blake J. Miguez . [ 14 ]
The vessel subsequently was chartered by SpaceX in 2018 for an experimental program to provide surface marine "catch and recovery" operations for a test program attempting to bring the large 5.2 by 13.2 meters (17 ft × 43 ft) [ 15 ] Falcon 9 launch vehicle satellite fairings—separated at high speed and high altitude—through atmospheric reentry and parachute descent to the ocean surface in a controlled way, and then recover them for evaluation and potential reuse. Since satellite fairings are traditionally expended into the ocean, the fairings used for these tests were somewhat modified test articles . As part of that effort, Mr. Steven was fitted in July 2018 with four large arms to support an elevated horizontal net, similar to a giant trampoline or trapeze net. [ 16 ]
In July 2018, Mr. Steven was upgraded and refitted with a much larger net with an area of 3,700 m 2 (0.91 acres), four times the original net size. [ 17 ] The upgrade included replacing the original rigid arms and fitting four new arms, which are each supported and positioned by two extendable shock-absorbing booms. [ 18 ] Each arm can be removed and disassembled into six subsections. [ 19 ]
In June 2019, Mr. Steven was renamed Ms. Tree (a play on the word mystery), after being purchased by Guice Offshore (GO), a company with a long-standing contractual relationship to SpaceX as a provider of a variety of marine services. [ 4 ] [ 20 ]
On June 25, 2019, SpaceX successfully caught its first fairing half on Ms. Tree in the Atlantic Ocean off the Florida coast as part of the Falcon Heavy STP-2 mission. [ 21 ]
On August 6, 2019, Ms. Tree was used to successfully catch another fairing half from a Falcon 9 that successfully launched Amos-17 . [ 22 ] SpaceX now had two complete fairing halves that have reentered from space and been recovered dry, without contacting the saltwater. [ 23 ] Although a dry recovery is preferable to maintain a cleaner environment inside the fairing to protect future payloads, eventually SpaceX would drop it as a requirement.
In August 2019, SpaceX chartered the sister ship to Ms. Tree , the Ms. Chief (a play on the word mischief), as the second fairing catcher vessel so that it could be possible to retrieve both halves of the same fairing on a Falcon 9 launch. [ 24 ] [ 20 ] This second ship is also operated by Guice Offshore, and is therefore titled "GO Ms. Chief" on the ship sides. Ms. Chief was outfitted with a matching set of four wide arms and a catch net by October 2019, in preparation for dual simultaneous fairing recovery attempts. [ 25 ]
On 11 November 2019, during the Starlink L1 mission both ships were sent to sea but were recalled due to rough seas so a recovery was not attempted. [ 26 ]
On 16 December 2019, both ships were positioned in the Atlantic Ocean for a recovery attempt, but both ships narrowly missed catching the fairing halves. [ 27 ]
On 29 January 2020, both ships were positioned for a recovery attempt for the Starlink 3 launch. Ms. Tree caught one fairing half, but Ms. Chief narrowly missed the other fairing half. [ 28 ]
On 20 July 2020, both fairing halves were successfully caught for the first time by both ships during the Anasis-2 mission. [ 29 ] The final payload fairing ever caught by SpaceX was in October 2020 on the Starlink v1.0 L13 mission. [ 6 ] In February 2021, both ships were taken out of service to have their catching arms removed . [ 6 ] On 6 April 2021, both ships departed Port Canaveral for the final time with a water salute . [ 30 ]
SpaceX abandoned the experimental program to recover descending-under-parachute payload fairings dry, in a net on a fast ship, by April 2021. SpaceX has decided to do "wet recovery" of fairings on future Falcon 9 flights, having found that they can clean, refurbish, and reuse such fairings more economically, and so their subordinate company, Falcon Landing LLC purchased two ships to support wet recovery and droneship operations and named them Bob and Doug . [ 11 ] Simultaneously with fairing recovery, they will also support booster towing and recovery missions along with their secondary fast boats, Maverick and Goose . [ citation needed ]
During the first six decades of spaceflight , payload fairings were expended by atmospheric reentry and allowed to drop into the ocean as debris.
In 2018, SpaceX began flight test experiments with fairings descending from sub-orbital trajectories above the atmosphere on its Falcon 9 rockets.
As a part of the SES-10 mission in March 2017, SpaceX successfully performed a controlled landing of the payload fairing into the ocean for the first time. SpaceX was able to recover the fairing half from the water after it landed, aided by attitude-control thrusters and a steerable parachute , gently on water. [ 31 ] [ 32 ] At the SES-10 news conference, the company announced its intent to land the fairings on a dry flexible structure, jokingly described by Elon Musk as a "floating bouncy castle ", with the goal of reusing the fairings. [ 33 ] [ 34 ] The cost of a fairing is about $6 million which accounts for 10 percent of overall Falcon 9 launch costs. [ 16 ]
The "bouncy castle" idea led to SpaceX contracting for the fast vessel Mr. Steven which was subsequently modified to facilitate a large net being strung between long arms that extend considerably beyond the width of the ship. Mr. Steven was equipped with a dynamic positioning system and was first tested after the launch of the Paz satellite from Vandenberg Air Force Base in February 2018. [ 35 ] [ 36 ] The test was not fully successful because the fairing missed the boat by a few hundred meters but landed safely in the water [ 37 ] before being recovered and taken back to port. [ 36 ] All four attempts in the first half of 2018 to land a fairing on the recovery ship failed, despite fitting Mr. Steven with larger nets before the July 2018 attempt. [ 38 ] [ 39 ]
In October 2018, to practice recovery outside mission situations, SpaceX performed drop tests of a fairing half from a helicopter with Mr. Steven below. [ 40 ] The outcome of the tests has not been publicly released. [ 41 ]
On the ArabSat-6A mission on April 11, 2019, SpaceX used the recovery boats GO Searcher and GO Navigator to recover both fairing halves quickly after they landed in the sea; Musk declared the recovery successful and reused the fairings in a later Starlink mission. [ 26 ] [ 42 ] SpaceX used the same recovery method in May 2019 on another Starlink launch. [ 43 ]
The first successful fairing catch was made as part of the STP-2 mission on 25 June 2019. [ 21 ] The final payload fairing ever caught in a net was in October 2020 on the Starlink v1.0 L13 mission, and fairings began more frequently to be scooped out of the ocean. [ 6 ]
By January 2021, SpaceX had modified the design of the fairing to better accommodate water recoveries. The ascent vents on the fairing halves were moved closer to the seam between the two fairing halves "so that water is less likely to enter the fairing through the holes when the halves are floating in the ocean." [ 6 ] By April 2021, the company had publicly abandoned net recovery and switched to water recovery as an ordinary operational practice. [ 5 ] | https://en.wikipedia.org/wiki/SpaceX_fairing_recovery_program |
Space is one of the elements of design of architecture , [ 1 ] as space is continuously studied for its usage. Architectural designs are created by carving space out of space, creating space out of space, and designing spaces by dividing this space using various tools, such as geometry , colours , and shapes . [ 2 ] | https://en.wikipedia.org/wiki/Space_(architecture) |
Space Data Integrator is a process/service platform or tool being developed by the US FAA to integrate space launch and reentry into the US National Airspace System . [ 1 ] It intends to oversee and manage airspace safety during space operations, ensuring the safety of vehicles more efficiently than manual processes. [ 2 ]
The project was initiated in 2015. [ 3 ] : 3
No funds for SDI were included in the FAA 2018 budget request. [ 4 ]
In March 2018 the FAA initiated a Market Survey on the requirements for SDI. [ 5 ]
This engineering-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Space_Data_Integrator |
The Space Nanotechnology Laboratory performs research in interference lithography and diffraction grating fabrication. It has fabricated the high energy transmission gratings for one of NASA 's Great Observatories, the Chandra X-Ray Observatory . It is also the home of the Nanoruler , a unique and high-precision grating patterning tool.
This nanotechnology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Space_Nanotechnology_Laboratory |
Space Power Facility ( SPF ) is a NASA facility used to test spaceflight hardware under simulated launch and spaceflight conditions. The SPF is part of NASA's Neil A. Armstrong Test Facility, which in turn is part of the Glenn Research Center . The Neil A. Armstrong Test Facility and the SPF are located near Sandusky, Ohio ( Oxford Township, Erie County, Ohio ).
The SPF is able to simulate a spacecraft's launch environment, as well as in-space environments. NASA has developed these capabilities under one roof to optimize testing of spaceflight hardware while minimizing transportation issues. Space Power Facility has become a "One Stop Shop" to qualify flight hardware for crewed space flight. This facility provides the capability to perform the following environmental testing:
This is a vacuum chamber built by NASA in 1969. It stands 122 feet (37 m) high and 100 feet (30 m) in diameter, enclosing a bullet -shaped space. It is the world's largest thermal vacuum chamber. It was originally commissioned for nuclear-electric power studies under vacuum conditions, but was later decommissioned. It was subsequently recommissioned for use in testing spacecraft propulsion systems. Recent uses include testing the airbag landing systems for the Mars Pathfinder and the Mars Exploration Rovers Spirit and Opportunity , under simulated Mars atmospheric conditions.
The facility was designed and constructed to test both nuclear and non-nuclear space hardware in a simulated low-Earth-orbiting environment. Although the facility was designed for testing nuclear hardware, only non-nuclear tests have been performed throughout its history. Test programs performed at the facility include high-energy experiments, rocket-fairing separation tests, Mars Lander system tests, deployable solar sail tests, and International Space Station hardware tests. The facility can sustain a high vacuum (10 −6 torr , 130 μPa), and simulate solar radiation via a 4 MW quartz heat lamp array, solar spectrum by a 400 kW arc lamp, and cold environments (−320 °F (−195.6 °C)) with a variable geometry cryogenic cold shroud.
The facility is available on a full-cost reimbursable basis to government, universities, and the private sector.
The aluminum test chamber is a vacuum-tight aluminum plate vessel that is 100 feet (30 m) in diameter and 122 feet (37 m) high. Designed for an external pressure of 2.5 psi (17 kPa) and internal pressure of 5 psi (34 kPa), the chamber is constructed of Type 5083 aluminum which is a clad on the interior surface with a 1 ⁄ 8 in (3.2 mm) thick type 3003 aluminum for corrosion resistance. This material was selected because of its low neutron absorption cross-section. The floor plate and vertical shell are 1 inch (25 mm) (total) thick, while the dome shell is 1 + 3 ⁄ 8 in (35 mm). Welded circumferentially to the exterior surface is aluminum structural T-section members that are 3 feet (0.9 m) deep and 2 feet (0.6 m) wide. The doors of the test chamber are 50 by 50 feet (15 by 15 m) in size and have double door seals to prevent leakage. The chamber floor was designed for a load of 300 tons.
The concrete chamber enclosure serves not only as a radiological shield but also as a primary vacuum barrier from atmospheric pressure. 130 feet (40 m) in diameter and 150 feet (46 m) in height, the chamber was designed to withstand atmospheric pressure outside of the chamber at the same time vacuum conditions are occurring within. The concrete thickness varies from 6 to 8 feet (1.8 to 2.4 m) and contains a leak-tight steel containment barrier embedded within. The chamber's doors are 50 by 50 feet (15 by 15 m) and have inflatable seals. The space between the concrete enclosure and the aluminum test chamber is pumped down to a pressure of 20 torrs (2.7 kPa) during a test.
Brian Cox of the BBC's Human Universe filmed a rock and feather drop episode at the Space Power Facility. [ 1 ]
Designed specifically as a large-scale thermal-vacuum test chamber for qualification testing of vehicles and equipment in outer-space conditions, it was discovered in the late 2000s that the unique construction of the SPF interior aluminum vacuum chamber also makes it an extremely large and electrically complex microwave or radio frequency cavity with excellent reverberant electro-magnetic characteristics. In 2009 these characteristics were measured by the National Institute of Standards and Technology and others [ 2 ] after which the facility was understood to be, not only the world's largest Vacuum chamber, but also the world's largest EMI/EMC test facility. In 2011, the Glenn Research Center successfully performed a calibration of the aluminum vacuum chamber [ 3 ] using IEC 61000-4-21 methodologies. [ 4 ] As a result of these activities, the SPF can perform radiated susceptibility EMI tests for vehicles and equipment per MIL-STD-461 , and can achieve MIL-STD-461F limits above approximately 80 MHz. In the spring of 2017 the low-power characterizations and calibrations from 2009 and 2011 were proven correct in a series of high-power tests performed in the chamber to validate its capabilities. The SPF chamber is currently being prepared for EMI radiated susceptibility testing of the crew module for the Artemis 1 of NASA's Orion spacecraft .
The Reverberant Acoustic Test Facility has 36 nitrogen-driven horns to simulate the high noise levels that are experienced during a space vehicle launch and supersonic ascent conditions. The RATF is capable of an overall sound pressure level of 163 dB within a 101,500-cubic-foot (2,870 m 3 ) chamber.
The Mechanical Vibration Test Facility (MVF) is a three-axis vibration system. It will apply vibration in each of the three orthogonal axes (not simultaneously) with one direction in parallel to the Earth-launch thrust axis (X) at 5–150 Hz, 0-1.25 g-pk vertical, and 5–150 Hz 0-1.0 g-pk for the horizontal axes.
Vertical, or the thrust axis, shaking is accomplished by using 16 vertical actuators manufactured by TEAM Corporation, [ 5 ] each capable of 30,000 lbf (130 kN). The 16 vertical actuators allow for testing of up to a 75,000 lb (34,000 kg) article at the previously stated frequency and amplitude limits.
Horizontal shaking is accomplished by four TEAM Corporation Horizontal Actuators. The horizontal actuators are used during vertical testing to counteract cross axis forces and overturning moments.
In addition to the sine vibe table, a fixed-base modal floor sufficient for the 20 ft (6.1 m) diameter test article is available. The fixed-base modal test facility is a 6 in (150 mm) thick steel floor on top of 19 ft (5.8 m) of concrete, that is tied to the earth using 50 ft (15 m) deep tensioned rock anchors.
There were over 21,000,000 pounds (9,500 t) of rock anchors, and 6,000,000 pounds (2,700 t) of concrete used in the construction of the fixed-base modal test facility and mechanical vibration test facility.
The SPF layout is ideal for performing multiple test programs. The facility has two large high bay areas adjacent to either side of the vacuum chamber. The advantage of having both areas available is that it allows for two complex tests to be prepared simultaneously. One can be prepared in a high bay while another is being conducted in the vacuum chamber. Large chamber doors provide access to the test chamber from either high bay. | https://en.wikipedia.org/wiki/Space_Power_Facility |
The Space Safety Programme, formerly the Space Situational Awareness ( SSA ) programme, is the European Space Agency 's (ESA) initiative to monitor hazards from space, determine their risk, make this data available to the appropriate authorities and where possible, mitigate the threat. [ 1 ]
The SSA Programme was designed to support Europe's independent space access and utilization through the timely and accurate information delivery regarding the space environment, particularly hazards to both in-orbit and ground infrastructure. [ 2 ] In 2019 it evolved into the present Space Safety Programme with an expanded focus, also including missions and activities to mitigate and prevent dangers from space. [ 3 ] The programme is split into four main segments: [ 4 ]
The Space Safety programme is being implemented as an optional ESA programme with financial participation by 14 Member States. The programme started in 2009 and its mandate was extended until 2019. The second phase of the programme received €46.5 million for the 2013–2016 period. [ 4 ]
The main objective of the space weather segment (SWE) is to detect and forecast of space weather events, avoid adverse effect on European space assets and ground-based infrastructure. To achieve that, the segment will focus on delivery of real-time space weather information, forecasts and warnings, supported by a data archive, applications and services. Assets currently available for the segment consist of multiple ground-based and spaceborne sensors monitoring the Sun, solar wind and Earth's magnetosphere , ionosphere and thermosphere . These include the PROBA2 satellite and the Kanzelhoehe Solar Observatory . The segment is jointly coordinated by the SWE Data Centre located at the ESTRACK Redu Station and the SSA Space Weather Coordination Centre (SSCC), both in Belgium . [ 10 ]
The near-Earth object segment aims to deliver monitoring and warning of potential Earth impactors and tracking of newly discovered objects. The segment's current assets consist of a mixture of professional and amateur telescopes, including the OGS Telescope , that are supported by tracking databases. The plans are to create a fully integrated system supporting alerts for civil authorities, including the NEOSTEL flyeye telescope due for completion in 2020. The segment is operated by the SSA NEO Coordination Centre located at the ESA Centre for Earth Observation , Italy. [ 11 ]
The SST segment's primary goal is the detection, cataloguing and orbit prediction of objects orbiting the Earth. It is part of an effort to avoid collisions between orbiting satellites and debris, provide safe reentries, detect on-orbit explosions, assist missions at launch, deployment and end-of-life and overall reduce cost of space access. The segment currently relies on existing European radar and optical systems. Some of its assets are existing radio and optical telescopes , with now serving a secondary role for tracking space debris. [ 12 ]
The radar-based SST assets are split into two categories: surveillance and tracking systems. SSA SST radar systems include: [ 13 ]
SSA SST optical surveillance and tracking assets include: [ 14 ]
As part of the SSA Programme new, dedicated surveillance radar supported by optical sensors systems will be developed. The segment is coordinated by the Space Surveillance Test & Validation (SSTC) Centre located at the ESAC in Spain . [ 12 ]
Close approaches of Near-Earth objects and near earth asteroids are reported by ESA through the space situational awareness center. [ 16 ] | https://en.wikipedia.org/wiki/Space_Situational_Awareness_Programme |
The Space Telescope Science Data Analysis System (STSDAS) is an IRAF -based suite of astronomical software for reducing and analyzing astronomical data. [ 1 ] It contains general purpose tools and packages for processing data from the Hubble Space Telescope . STSDAS is produced by Space Telescope Science Institute (STScI). The STSDAS software is generally in the public domain, however some routines were taken from the Numerical Recipes and other books and cannot freely distributed. [ 2 ]
In 2018, STScI stopped support of IRAF and STSDAS [ 3 ] and suggested migrating to Astropy . [ 4 ] For the support of the Gemini IRAF legacy pipeline, selected tasks of STSDAS are still maintained by NOIRLab in the st4gem package. [ 5 ]
This article about astronomy software is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Space_Telescope_Science_Data_Analysis_System |
The Space Variable Objects Monitor ( SVOM ) is a small X-ray telescope satellite developed by China National Space Administration (CNSA), Chinese Academy of Sciences (CAS) and the French Space Agency ( CNES ), [ 5 ] launched on 22 June 2024 (07:00:00 UTC). [ 2 ]
SVOM will study the explosions of massive stars by analysing the resulting gamma-ray bursts . The light-weight X-ray mirror for SVOM weighs just 1 kg (2.2 lb). [ 5 ] SVOM will add new capabilities to the work of finding gamma-ray bursts currently being done by the multinational satellite Swift Gamma-Ray Burst Mission . [ 5 ] Its anti-solar pointing strategy makes the Earth cross the field of view of its payload every orbit. [ 6 ]
Using synergy between space and ground instruments, the mission has these scientific objectives: [ 7 ]
The selected orbit is circular with an altitude of 600 km (370 mi) and an inclination angle of 30° with a precession period of 60 days. [ 8 ] The payload is composed of the following four main instruments: [ 8 ] [ 9 ]
The ground segment includes a set of three ground-based dedicated instruments – two robotic Ground Follow-up Telescopes (GFT) and an optical monitor, Ground Wide Angle Camera (GWAC) – which will complement the space borne instruments. A large fraction of GRB will have redshift determinations, an observing strategy optimized to facilitate follow-up observations by large ground-based spectroscopic telescopes.
A key elements of the SVOM mission are the Ground Wide Angle Cameras (GWACs) and the Ground Follow-up Telescopes (GFTs). [ 14 ] [ 15 ] | https://en.wikipedia.org/wiki/Space_Variable_Objects_Monitor |
Space architecture is the theory and practice of designing and building inhabited environments in outer space . [ 1 ] This mission statement for space architecture was developed in 2002 by participants in the 1st Space Architecture Symposium, organized at the World Space Congress in Houston, by the Aerospace Architecture Subcommittee, Design Engineering Technical Committee (DETC), American Institute of Aeronautics and Astronautics (AIAA) .
The subcommittee rose to the status of an independent Space Architecture Technical Committee (SATC) of the AIAA in 2008. The SATC routinely organizes technical sessions at several conferences, including AIAA ASCEND , the International Conference on Environmental Systems (ICES) , the International Astronautical Congress (IAC) , and the American Society of Civil Engineers (ASCE) Earth & Space conference.
SpaceArchitect.org is an outgrowth of the SATC that invites wider participation. Its membership is essentially a superset of the SATC's, and is independent of the AIAA .
The practice of involving architects in the space program grew out of the Space Race , although its origins can be seen much earlier. The need for their involvement stemmed from the push to extend space mission durations and address the needs of astronauts beyond minimum survival needs.
Much space architecture work has focused on design concepts for orbital space stations and lunar and Martian exploration ships and surface bases for the world's space agencies, including NASA , ESA , JAXA , CSA , Roscosmos , and CNSA .
Despite the historical pattern of large government-led space projects and university-level conceptual design, the advent of space tourism is shifting the outlook for space architecture work.
The architectural approach to spacecraft design addresses the total built environment. It combines the fields of architecture and engineering (especially aerospace engineering ), and also involves diverse disciplines such as industrial design , physiology , psychology , and sociology .
Like architecture on Earth, the attempt is to go beyond the component elements and systems and gain a broad understanding of the issues that affect design success. [ 2 ] Space architecture borrows from multiple forms of niche architecture to accomplish the task of ensuring human beings can live and work in space. These include the kinds of design elements one finds in “tiny housing, small living apartments / houses, vehicle design, capsule hotels, and more.” [ 3 ]
Specialized space-architecture education is currently offered in several institutions. The Sasakawa International Center for Space Architecture (SICSA) is an academic unit within the University of Houston that offers a Master of Science in Space Architecture. SICSA also works design contracts with corporations and space agencies. In Europe, The Vienna University of Technology (TU Wien) and the International Space University are involved in space architecture research. The TU Wien offers an EMBA in Space Architecture .
The word space in space architecture is referring to the outer space definition, which is from English outer and space . Outer can be defined as "situated on or toward the outside; external; exterior" and originated around 1350–1400 in Middle English . [ 4 ] Space is "an area, extent, expanse, lapse of time," the aphetic of Old French espace dating to 1300. Espace is from Latin spatium , "room, area, distance, stretch of time," and is of uncertain origin. [ 5 ] In space architecture, speaking of outer space usually means the region of the universe outside Earth's atmosphere, as opposed to outside the atmospheres of all terrestrial bodies. This allows the term to include such domains as the lunar and Martian surfaces.
Architecture , the concatenation of architect and -ure , dates to 1563, coming from Middle French architecte . This term is of Latin origin, formerly architectus , which came from Greek arkhitekton . Arkitekton means "master builder" and is from the combination of arkhi- "chief" and tekton "builder". [ 6 ] The human experience is central to architecture – the primary difference between space architecture and spacecraft engineering .
There is some debate over the terminology of space architecture. Some consider the field to be a specialty within architecture that applies architectural principles to space applications. Others such as Theodore W. Hall of the University of Michigan see space architects as generalists, with what is traditionally considered architecture (Earth-bound or terrestrial architecture) being a subset of a broader space architecture. [ 7 ] Any structures that fly in space will likely remain for some time highly dependent on Earth-based infrastructure and personnel for financing, development, construction, launch, and operation. Therefore, it is a matter of discussion how much of these earthly assets are to be considered part of space architecture. The technicalities of the term space architecture are open to some level of interpretation.
Ideas of people traveling to space were first published in science fiction stories, like Jules Verne's 1865 From the Earth to the Moon . In this story several details of the mission (crew of three, spacecraft dimensions, Florida launch site) bear striking similarity to the Apollo Moon landings that took place more than 100 years later. Verne's aluminum capsule had shelves stocked with equipment needed for the journey such as a collapsing telescope, pickaxes and shovels, firearms, oxygen generators, and even trees to plant. A curved sofa was built into the floor and walls and windows near the tip of the spacecraft were accessible by ladder. [ 8 ] The projectile was shaped like a bullet because it was gun-launched from the ground, a method infeasible for transporting man to space due to the high acceleration forces produced. It would take rocketry to get humans to the cosmos.
The first serious theoretical work published on space travel by means of rocket power was by Konstantin Tsiolkovsky in 1903. Besides being the father of astronautics he conceived such ideas as the space elevator (inspired by the Eiffel Tower), a rotating space station that created artificial gravity along the outer circumference, airlocks , space suits for extra-vehicular activity (EVA), closed ecosystems to provide food and oxygen, and solar power in space. [ 9 ] Tsiolkovsky believed human occupation of space was the inevitable path for our species. In 1952 Wernher von Braun published his own inhabited space station concept in a series of magazine articles. His design was an upgrade of earlier concepts, but he took the unique step in going directly to the public with it. The spinning space station would have three decks and was to function as a navigational aid, meteorological station, Earth observatory, military platform, and way point for further exploration missions to outer space. [ 10 ] It is said that the space station depicted in the 1968 film 2001: A Space Odyssey traces its design heritage to Von Braun's work. Wernher von Braun went on to devise mission schemes to the Moon and Mars, each time publishing his grand plans in Collier's Weekly .
The flight of Yuri Gagarin on April 12, 1961, was humanity's maiden spaceflight . While the mission was a necessary first step, Gagarin was more or less confined to a chair with a small view port from which to observe the cosmos – a far cry from the possibilities of life in space. Following space missions gradually improved living conditions and quality of life in low Earth orbit . Expanding room for movement, physical exercise regimens, sanitation facilities, improved food quality, and recreational activities all accompanied longer mission durations. Architectural involvement in space was realized in 1968 when a group of architects and industrial designers led by Raymond Loewy, over objections from engineers, prevailed in convincing NASA to include an observation window in the Skylab orbital laboratory. [ 11 ] This milestone represents the introduction of the human psychological dimension to spacecraft design. Space architecture was born. [ neutrality is disputed ]
The subject of architectural theory has much application in space architecture. Some considerations, though, will be unique to the space context.
In the first century BC, the Roman architect Vitruvius said all buildings should have three things: strength, utility, and beauty. [ 12 ] Vitruvius's work De Architectura , the only surviving work on the subject from classical antiquity, would have profound influence on architectural theory for thousands of years to come. Even in space architecture these are some of the first things we consider. However, the tremendous challenge of living in space has led to habitat design based largely on functional necessity with little or no applied ornament . In this sense space architecture as we know it shares the form follows function principle with modern architecture .
Some theorists [ who? ] link different elements of the Vitruvian triad . Walter Gropius writes:
'Beauty' is based on the perfect mastery of all the scientific, technological and formal prerequisites of the task ... The approach of Functionalism means to design the objects organically on the basis of their own contemporary postulates, without any romantic embellishment or jesting. [ 13 ]
As space architecture continues to mature as a discipline, dialogue on architectural design values will open up just as it has for Earth.
A starting point for space architecture theory is the search for extreme environments in terrestrial settings where humans have lived, and the formation of analogs between these environments and space. [ 14 ] For example, humans have lived in submarines deep in the ocean, in bunkers beneath the Earth's surface, and on Antarctica , and have safely entered burning buildings, radioactively contaminated zones, and the stratosphere with the help of technology. Aerial refueling enables Air Force One to stay airborne virtually indefinitely. [ 15 ] Nuclear powered submarines generate oxygen using electrolysis and can stay submerged for months at a time. [ 16 ] Many of these analogs can be very useful design references for space systems. In fact space station life support systems and astronaut survival gear for emergency landings bear striking similarity to submarine life support systems and military pilot survival kits, respectively.
Space missions, especially human ones, require extensive preparation. In addition to terrestrial analogs providing design insight, the analogous environments can serve as testbeds to further develop technologies for space applications and train astronaut crews. The Flashline Mars Arctic Research Station is a simulated Mars base, maintained by the Mars Society , on Canada's remote Devon Island . The project aims to create conditions as similar as possible to a real Mars mission and attempts to establish ideal crew size, test equipment "in the field", and determine the best extra-vehicular activity suits and procedures. [ 17 ] To train for EVAs in microgravity , space agencies make broad use of underwater and simulator training. The Neutral Buoyancy Laboratory , NASA's underwater training facility, contains full-scale mockups of the Space Shuttle cargo bay and International Space Station modules. Technology development and astronaut training in space-analogous environments are essential to making living in space possible.
Fundamental to space architecture is designing for physical and psychological wellness in space. What often is taken for granted on Earth – air, water, food, trash disposal – must be designed for in fastidious detail. Rigorous exercise regimens are required to alleviate muscular atrophy and other effects of space on the body . That space missions are (optimally) fixed in duration can lead to stress from isolation. This problem is not unlike that faced in remote research stations or military tours of duty, although non-standard gravity conditions can exacerbate feelings of unfamiliarity and homesickness. Furthermore, confinement in limited and unchanging physical spaces appears to magnify interpersonal tensions in small crews and contribute to other negative psychological effects. [ 18 ] These stresses can be mitigated by establishing regular contact with family and friends on Earth, maintaining health, incorporating recreational activities, and bringing along familiar items such as photographs and green plants. [ 19 ] The importance of these psychological measures can be appreciated in the 1968 Soviet 'DLB Lunar Base' design:
...it was planned that the units on the Moon would have a false window, showing scenes of the Earth countryside that would change to correspond with the season back in Moscow. The exercise bicycle was equipped with a synchronized film projector, that allowed the cosmonaut to take a 'ride' out of Moscow with return. [ 20 ]
The challenge of getting anything at all to space, due to launch constraints, has had a profound effect on the physical shapes of space architecture. [ 21 ] All space habitats to date have used modular architecture design. Payload fairing dimensions (typically the width but also the height) of modern launch vehicles limit the size of rigid components launched into space. This approach to building large scale structures in space involves launching multiple modules separately and then manually assembling them afterward. Modular architecture results in a layout similar to a tunnel system where passage through several modules is often required to reach any particular destination. It also tends to standardize the internal diameter or width of pressurized rooms, with machinery and furniture placed along the circumference. These types of space stations and surface bases can generally only grow by adding additional modules in one or more direction. Finding adequate working and living space is often a major challenge with modular architecture. As a solution, flexible furniture (collapsible tables, curtains on rails, deployable beds) can be used to transform interiors for different functions and change the partitioning between private and group space. For more discussion of the factors that influence shape in space architecture, see the Varieties section .
Eugène Viollet-le-Duc advocated different architectural forms for different materials. [ 22 ] This is especially important in space architecture. The mass constraints with launching push engineers to find ever lighter materials with adequate material properties. Moreover, challenges unique to the orbital space environment , such as rapid thermal expansion due to abrupt changes in solar exposure, and corrosion caused by particle and atomic oxygen bombardment, require unique materials solutions. Just as the industrial age produced new materials and opened up new architectural possibilities, advances in materials technology will change the prospects of space architecture. [ 23 ] Carbon-fiber is already being incorporated into space hardware because of its high strength-to-weight ratio. Investigations are underway to see whether carbon-fiber or other composite materials will be adopted for major structural components in space. The architectural principle that champions using the most appropriate materials and leaving their nature unadorned is called truth to materials .
A notable difference between the orbital context of space architecture and Earth-based architecture is that structures in orbit do not need to support their own weight. This is possible because of the microgravity condition of objects in free fall. In fact much space hardware, such as the Space Shuttle 's robotic arm , is designed only to function in orbit and would not be able to lift its own weight on the Earth's surface. [ 24 ] Microgravity also allows an astronaut to move an object of practically any mass, albeit slowly, provided he or she is adequately constrained to another object. Therefore, structural considerations for the orbital environment are dramatically different from those of terrestrial buildings, and the biggest challenge to holding a space station together is usually launching and assembling the components intact. Construction on extraterrestrial surfaces still needs to be designed to support its own weight, but its weight will depend on the strength of the local gravitational field .
Human spaceflight currently [ when? ] requires a great deal of supporting infrastructure on Earth. All human orbital missions to date have been government-orchestrated. The organizational body that manages space missions is typically a national space agency , NASA in the case of the United States and Roscosmos for Russia. These agencies are funded at the federal level. At NASA, flight controllers are responsible for real-time mission operations and work onsite at NASA Centers. Most engineering development work involved with space vehicles is contracted-out to private companies, who in turn may employ subcontractors of their own, while fundamental research and conceptual design is often done in academia through research funding .
Structures that cross the boundary of space but do not reach orbital speeds are considered suborbital architecture. For spaceplanes , the architecture has much in common with airliner architecture, especially those of small business jets .
On June 21, 2004, Mike Melvill reached space funded entirely by private means. The vehicle, SpaceShipOne , was developed by Scaled Composites as an experimental precursor to a privately operated fleet of spaceplanes for suborbital space tourism . The operational spaceplane model, SpaceShipTwo (SS2), will be carried to an altitude of about 15 kilometers by a B-29 Superfortress -sized carrier aircraft, WhiteKnightTwo . From there SS2 will detach and fire its rocket motor to bring the craft to its apogee of approximately 110 kilometers. Because SS2 is not designed to go into orbit around the Earth, it is an example of suborbital or aerospace architecture . [ 25 ]
The architecture of the SpaceShipTwo vehicle is somewhat different from what is common in previous space vehicles. Unlike the cluttered interiors with protruding machinery and many obscure switches of previous vehicles, this cabin looks more like something out of science fiction than a modern spacecraft. Both SS2 and the carrier aircraft are being built from lightweight composite materials instead of metal. [ 26 ] When the time for weightlessness has arrived on a SS2 flight, the rocket motor will be turned off, ending the noise and vibration. Passengers will be able to see the curvature of the Earth. [ 27 ] Numerous double-paned windows that encircle the cabin will offer views in nearly all directions. Cushioned seats will recline flat into the floor to maximize room for floating. [ 28 ] An always-pressurized interior will be designed to eliminate the need for space suits.
Orbital architecture is the architecture of structures designed to orbit around the Earth or another astronomical object . Examples of currently-operational orbital architecture are the International Space Station and the re-entry vehicles Space Shuttle , Soyuz spacecraft , and Shenzhou spacecraft . Historical craft include the Mir space station , Skylab , and the Apollo spacecraft . Orbital architecture usually addresses the condition of weightlessness, a lack of atmospheric and magnetospheric protection from solar and cosmic radiation, rapid day/night cycles, and possibly risk of orbital debris collision. In addition, re-entry vehicles must also be adapted both to weightlessness and to the high temperatures and accelerations experienced during atmospheric reentry .
The International Space Station (ISS) is the only permanently inhabited structure currently in space. It is the size of an American football field and has a crew of six. With a living volume of 358 m³, it has more interior room than the cargo beds of two American 18-wheeler trucks. [ 29 ] However, because of the microgravity environment of the space station, there are not always well-defined walls, floors, and ceilings and all pressurized areas can be used as living and working space. The International Space Station is still under construction. Modules were primarily launched using the Space Shuttle until its deactivation and were assembled by its crew with the help of the working crew on board the space station. ISS modules were often designed and built to barely fit inside the shuttle's payload bay, which is cylindrical with a 4.6 meter diameter. [ 30 ]
Life aboard the space station is distinct from terrestrial life in some very interesting ways. Astronauts commonly "float" objects to one another; for example they will give a clipboard an initial nudge and it will coast to its receiver across the room. In fact, an astronaut can become so accustomed to this habit that they forget that it doesn't work anymore when they return to Earth. [ 31 ] The diet of ISS spacefarers is a combination of participating nations' space food . Each astronaut selects a personalized menu before flight. Many food choices reflect the cultural differences of the astronauts, such as bacon and eggs vs. fish products for breakfast (for the United States and Russia, respectively). [ 32 ] More recently such delicacies as Japanense beef curry, kimchi, [ 33 ] and swordfish (Riviera style) have been featured on the orbiting outpost. [ 34 ] As much of ISS food is dehydrated or sealed in pouches MRE -style, astronauts are quite excited to get relatively fresh food from shuttle and Progress resupply missions. Food is stored in packages that facilitate eating in microgravity by
keeping the food constrained to the table. Spent packaging and trash must be collected to load into an available spacecraft for disposal. Waste management is not nearly as straight forward as it is on Earth. The ISS has many windows for observing Earth and space, one of the astronauts' favorite leisure activities. Since the Sun rises every 90 minutes, the windows are covered at "night" to help maintain the 24-hour sleep cycle.
When a shuttle is operating in low Earth orbit, the ISS serves as a safety refuge in case of emergency . The inability to fall back on the safety of the ISS during the latest Hubble Space Telescope Servicing Mission (because of different orbital inclinations ) was the reason a backup shuttle was summoned to the launch pad. So, ISS astronauts operate with the mindset that they may be called upon to give sanctuary to a Shuttle crew should something happen to compromise a mission. The International Space Station is a colossal cooperative project between many nations. The prevailing atmosphere on board is one of diversity and tolerance. This does not mean that it is perfectly harmonious. Astronauts experience the same frustrations and interpersonal quarrels as their Earth-based counterparts.
A typical day on the station might start with wakeup at 6:00 am inside a private soundproof booth in the crew quarters. [ 35 ] Astronauts would probably find their sleeping bags in an upright position tied to the wall, because orientation does not matter in space. The astronaut's thighs would be lifted about 50 degrees off the vertical. [ 36 ] This is the neutral body posture in weightlessness – it would be excessively tiring to "sit" or "stand" as is common on Earth. Crawling out of his booth, an astronaut may chat with other astronauts about the day's science experiments, mission control conferences, interviews with Earthlings, and perhaps even a space walk or space shuttle arrival.
Bigelow Aerospace took the unique step in securing two patents NASA held from development of the Transhab concept in regard to inflatable space structures. The company now has sole rights to commercial development of the inflatable module technology. [ 37 ] On July 12, 2006, the Genesis I experimental space habitat was launched into low Earth orbit. Genesis I demonstrated the basic viability of inflatable space structures, even carrying a payload of life science experiments. The second module, Genesis II , was launched into orbit on June 28, 2007, and tested out several improvements over its predecessor. Among these are reaction wheel assemblies, a precision measurement system for guidance, nine additional cameras, improved gas control for module inflation, and an improved on-board sensor suite. [ 38 ]
While Bigelow architecture is still modular, the inflatable configuration allows for much more interior volume than rigid modules. The BA-330 , Bigelow's full-scale production model, has more than twice the volume of the largest module on the ISS. Inflatable modules can be docked to rigid modules and are especially well suited for crew living and working quarters. In 2009 NASA began considering attaching a Bigelow module to the ISS, after abandoning the Transhab concept more than a decade before. [ 39 ] The modules will likely have a solid inner core for structural support. Surrounding usable space could be partitioned into different rooms and floors. The Bigelow Expandable Activity Module (BEAM) was transported to ISS arriving on April 10, 2016, inside the unpressurized cargo trunk of a SpaceX Dragon during the SpaceX CRS-8 cargo mission. [ 40 ]
Bigelow Aerospace may choose to launch many of their modules independently, leasing their use to a wide variety of companies, organizations, and countries that can't afford their own space programs. Possible uses of this space include microgravity research and space manufacturing . Or we may see a private space hotel composed of numerous Bigelow modules for rooms, observatories, or even a recreational padded gymnasium. There is the option of using such modules for habitation quarters on long-term space missions in the Solar System. One amazing aspect of spaceflight is that once a craft leaves an atmosphere, aerodynamic shape is a non-issue. For instance it's possible to apply a Trans Lunar Injection to an entire space station and send it to fly by the Moon. Bigelow has expressed the possibility of their modules being modified for lunar and Martian surface systems as well. However, it is out of business since March 2020. [ 41 ]
Lunar architecture exists both in theory and in practice. Today [ when? ] the archeological artifacts of temporary human outposts lay untouched on the surface of the Moon. Five Apollo Lunar Module descent stages stand upright in various locations across the equatorial region of the Near Side , hinting at the extraterrestrial endeavors of mankind. The leading hypothesis on the origin of the Moon did not gain its current status until after lunar rock samples were analysed. [ 42 ] The Moon is the furthest any humans have ever ventured from their home, and space architecture is what kept them alive and allowed them to function as humans.
On the cruise to the Moon, Apollo astronauts had two "rooms" to choose from – the Command Module (CM) or the Lunar Module (LM). This can be seen in the film Apollo 13 where the three astronauts were forced to use the LM as an emergency life boat. Passage between the two modules was possible through a pressurized docking tunnel, a major advantage over the Soviet design , which required donning a spacesuit to switch modules. The Command Module featured five windows made of three thick panes of glass. The two inner panes, made of aluminosilicate , ensured no cabin air leaked into space. The outer pane served as a debris shield and part of the heat shield needed for atmospheric reentry . The CM was a sophisticated spacecraft with all the systems required for successful flight but with an interior volume of 6.17 m 3 could be considered cramped for three astronauts. [ 43 ] It had its design weaknesses such as no toilet (astronauts used much-hated 'relief tubes' and fecal bags). The coming of the space station would bring effective life support systems with waste management and water reclamation technologies.
The Lunar Module had two stages. A pressurized upper stage, termed the ascent stage, was the first true spaceship as it could only operate in the vacuum of space. The descent stage carried the engine used for descent, landing gear and radar, fuel and consumables, the famous ladder, and the Lunar Roving Vehicle during later Apollo missions. The idea behind staging is to reduce mass later in a flight, and is the same strategy used in an Earth-launched multistage rocket . The LM pilot stood up during the descent to the Moon. Landing was achieved via automated control with a manual backup mode. There was no airlock on the LM so the entire cabin had to be evacuated (air vented to space) in order to send an astronaut out to walk on the surface. To stay alive, both astronauts in the LM would have to get in their space suits at this point. The Lunar Module worked well for what it was designed to do. However, a big unknown remained throughout the design process – the effects of lunar dust .
Every astronaut who walked on the Moon tracked in lunar dust, contaminating the LM and later the CM during Lunar Orbit Rendezvous . These dust particles can't be brushed away in a vacuum, and have been described by John Young of Apollo 16 as being like tiny razor blades. It was soon realized that for humans to live on the Moon, dust mitigation was one of many issues that had to be taken seriously.
The Exploration Systems Architecture Study that followed the Vision for Space Exploration of 2004 recommended the development of a new class of vehicles that have similar capabilities to their Apollo predecessors with several key differences. In part to retain some of the Space Shuttle program workforce and ground infrastructure, the launch vehicles were to use Shuttle-derived technologies. Secondly, rather than launching the crew and cargo on the same rocket, the smaller Ares I was to launch the crew with the larger Ares V to handle the heavier cargo. The two payloads were to rendezvous in low Earth orbit and then head to the Moon from there. The Apollo Lunar Module could not carry enough fuel to reach the polar regions of the Moon but the Altair lunar lander was intended to access any part of the Moon. While the Altair and surface systems would have been equally necessary for Constellation program to reach fruition, the focus was on developing the Orion spacecraft to shorten the gap in U.S. access to orbit following the retirement of the Space Shuttle in 2010.
Even NASA has described Constellation architecture as 'Apollo on steroids'. [ 44 ] Nonetheless, a return to the proven capsule design is a move welcomed by many. [ 45 ]
Martian architecture is architecture designed to sustain human life on the surface of Mars , and all the supporting systems necessary to make this possible. The direct sampling of water ice on the surface, [ 46 ] and evidence for geyser-like water flows within the last decade [ 47 ] have made Mars the most likely extraterrestrial environment for finding liquid water, and therefore alien life , in the Solar System. Moreover, some geologic evidence suggests that Mars could have been warm and wet on a global scale in its distant past. Intense geologic activity has reshaped the surface of the Earth, erasing evidence of our earliest history. Martian rocks can be even older than Earth rocks, though, so exploring Mars may help us decipher the story of our own geologic evolution including the origin of life on Earth . [ 48 ] Mars has an atmosphere, though its surface pressure is less than 1% of Earth's. Its surface gravity is about 38% of Earth's. Although a human expedition to Mars has not yet taken place, there has been significant work on Martian habitat design. Martian architecture would usually fall into one of two categories: architecture imported from Earth fully assembled and architecture making use of local resources.
Wernher von Braun was the first to come up with a technically comprehensive proposal for a crewed Mars expedition. Rather than a minimal mission profile like Apollo, von Braun envisioned a crew of 70 astronauts aboard a fleet of ten massive spacecraft. Each vessel would be constructed in low Earth orbit, requiring nearly 100 separate launches before one was fully assembled. Seven of the spacecraft would be for crew while three were designated as cargo ships. There were even designs for small "boats" to shuttle crew and supplies between ships during the cruise to the Red Planet, which was to follow a minimum-energy Hohmann transfer trajectory. This mission plan would involve one-way transit times on the order of eight months and a long stay at Mars, creating the need for long-term living accommodations in space. Upon arrival at the Red Planet, the fleet would brake into Mars orbit and would remain there until the seven human vessels were ready to return to Earth. Only landing gliders , which were stored in the cargo ships, and their associated ascent stages would travel to the surface. Inflatable habitats would be constructed on the surface along with a landing strip to facilitate further glider landings. All necessary propellant and consumables were to be brought from Earth in von Braun's proposal. Some crew remained in the passenger ships during the mission for orbit-based observation of Mars and to maintain the ships. [ 49 ] The passenger ships had habitation spheres 20 meters in diameter. Because the average crew member would spend much time in these ships (around 16 months of transit plus rotating shifts in Mars orbit), habitat design for the ships was an integral part of this mission.
Von Braun was aware of the threat posed by extended exposure to weightlessness. He suggested either tethering passenger ships together to spin about a common center of mass or including self-rotating, dumbbell-shaped "gravity cells" to drift alongside the flotilla to provide each crew member with a few hours of artificial gravity each day. [ 50 ] At the time of von Braun's proposal, little was known of the dangers of solar radiation beyond Earth and it was cosmic radiation that was thought to present the more formidable challenge. [ 49 ] The discovery of the Van Allen belts in 1958 demonstrated that the Earth was shielded from high energy solar particles. For the surface portion of the mission, inflatable habitats suggest the desire to maximize living space. It is clear von Braun considered the members of the expedition part of a community with much traffic and interaction between vessels.
The Soviet Union conducted studies of human exploration of Mars and came up with slightly less epic mission designs (though not short on exotic technologies) in 1960 and 1969. [ 51 ] The first of which used electric propulsion for interplanetary transit and nuclear reactors as the power plants. On spacecraft that combine human crew and nuclear reactors, the reactor is usually placed at a maximum distance from the crew quarters, often at the end of a long pole, for radiation safety. An interesting component of the 1960 mission was the surface architecture. A "train" with wheels for rough terrain was to be assembled of landed research modules, one of which was a crew cabin. The train was to traverse the surface of Mars from south pole to north pole, an extremely ambitious goal even by today's standards. [ 52 ] Other Soviet plans such as the TMK eschewed the large costs associated with landing on the Martian surface and advocated piloted (crewed) flybys of Mars. Flyby missions, like the lunar Apollo 8 , extend the human presence to other worlds with less risk than landings. Most early Soviet proposals called for launches using the ill-fated N1 rocket . They also usually involved fewer crew than their American counterparts. [ 53 ] Early Martian architecture concepts generally featured assembly in low Earth orbit, bringing all needed consumables from Earth, and designated work vs. living areas. The modern outlook on Mars exploration is not the same.
In every serious study of what it would take to land humans on Mars, keep them alive, and then return them to Earth, the total mass required for the mission is simply stunning. The problem lies in that to launch the amount of consumables (oxygen, food and water) even a small crew would go through during a multi-year Mars mission, it would take a very large rocket with the vast majority of its own mass being propellant. This is where multiple launches and assembly in Earth orbit come from. However even if such a ship stocked full of goods could be put together in orbit, it would need an additional (large) supply of propellant to send it to Mars. The delta-v , or change in velocity, required to insert a spacecraft from Earth orbit to a Mars transfer orbit is many kilometers per second. When we think of getting astronauts to the surface of Mars and back home we quickly realize that an enormous amount of propellant is needed if everything is taken from the Earth. This was the conclusion reached in the 1989 '90-Day Study' initiated by NASA in response to the Space Exploration Initiative .
Several techniques have changed the outlook on Mars exploration. The most powerful of which is in-situ resource utilization. Using hydrogen imported from Earth and carbon dioxide from the Martian atmosphere, the Sabatier reaction can be used to manufacture methane (for rocket propellant) and water (for drinking and for oxygen production through electrolysis ). Another technique to reduce Earth-brought propellant requirements is aerobraking . Aerobraking involves skimming the upper layers of an atmosphere, over many passes, to slow a spacecraft down. It's a time-intensive process that shows most promise in slowing down cargo shipments of food and supplies. NASA's Constellation program does call for landing humans on Mars after a permanent base on the Moon is demonstrated, but details of the base architecture are far from established. It is likely that the first permanent settlement will consist of consecutive crews landing prefabricated habitat modules in the same location and linking them together to form a base. [ 54 ]
In some of these modern, economy models of the Mars mission, we see the crew size reduced to a minimal 4 or 6. Such a loss in variety of social relationships can lead to challenges in forming balanced social responses and forming a complete sense of identity. [ 18 ] It follows that if long-duration missions are to be carried out with very small crews, then intelligent selection of crew is of primary importance. Role assignments is another open issue in Mars mission planning. The primary role of 'pilot' is obsolete when landing takes only a few minutes of a mission lasting hundreds of days, and when that landing will be automated anyway. Assignment of roles will depend heavily on the work to be done on the surface and will require astronauts to assume multiple responsibilities. As for surface architecture inflatable habitats, perhaps even provided by Bigelow Aerospace , remain a possible option for maximizing living space. In later missions, bricks could be made from a Martian regolith mixture for shielding or even primary, airtight structural components. [ 54 ] The environment on Mars offers different opportunities for space suit design, even something like the skin-tight Bio-Suit .
A number of specific habitat design proposals have been put forward, to varying degrees of architectural and engineering analysis. One recent proposal—and the winner of NASA's 2015 Mars Habitat Competition—is Mars Ice House . The design concept is for a Mars surface habitat, 3d-printed in layers out of water ice on the interior of an Earth-manufactured inflatable pressure-retention membrane. The completed structure would be semi-transparent, absorbing harmful radiation in several wavelengths, while admitting approximately 50 percent of light in the visible spectrum . The habitat is proposed to be entirely set up and built from an autonomous robotic spacecraft and bots, although human habitation with approximately 2–4 inhabitants is envisioned once the habitat is fully built and tested. [ 55 ] [ 56 ]
It is widely accepted that robotic reconnaissance and trail-blazer missions will precede human exploration of other worlds. Making an informed decision on which specific destinations warrant sending human explorers requires more data than what the best Earth-based telescopes can provide. For example, landing site selection for the Apollo Moon landings drew on data from three different robotic programs: the Ranger program , the Lunar Orbiter program , and the Surveyor program . Before a human was sent, robotic spacecraft mapped the lunar surface, proved the feasibility of soft landings, filmed the terrain up close with television cameras, and scooped and analysed the soil. [ 57 ]
A robotic exploration mission is generally designed to carry a wide variety of scientific instruments, ranging from cameras sensitive to particular wavelengths, telescopes, spectrometers , radar devices, accelerometers , radiometers , and particle detectors to name a few. The function of these instruments is usually to return scientific data but it can also be to give an intuitive "feel" of the state of the spacecraft, allowing a subconscious familiarization with the territory being explored, through telepresence . A good example of this is the inclusion of HDTV cameras on the Japanese lunar orbiter SELENE . While purely scientific instruments could have been brought in their stead, these cameras allow the use of an innate sense to perceive the exploration of the Moon.
The modern, balanced approach to exploring an extraterrestrial destination involves several phases of exploration, each of which needs to produce rationale for progressing to the next phase. The phase immediately preceding human exploration can be described as anthropocentric sensing, that is, sensing designed to give humans as realistic a feeling as possible of actually exploring in person. More, the line between a human system and a robotic system in space is not always going to be clear. As a general rule, the more formidable the environment, the more essential robotic technology is. Robotic systems can be broadly considered part of space architecture when their purpose is to facilitate the habitation of space or extend the range of the physiological senses into space.
The future of space architecture hinges on the expansion of human presence in space . Under the historical model of government-orchestrated exploration missions initiated by single political administrations , space structures are likely to be limited to small-scale habitats and orbital modules with design life cycles of only several years or decades. [ citation needed ] The designs, and thus architecture, will generally be fixed and without real time feedback from the spacefarers themselves. The technology to repair and upgrade existing habitats, a practice widespread on Earth, is not likely to be developed under short term exploration goals. If exploration takes on a multi-administration or international character, the prospects for space architecture development by the inhabitants themselves will be broader. Private space tourism is a way the development of space and a space transportation infrastructure can be accelerated. Virgin Galactic has indicated plans for an orbital craft , SpaceShipThree . The demand for space tourism is one without bound. It is not difficult to imagine lunar parks or cruises by Venus . Another impetus to become a spacefaring species is planetary defense .
The classic space mission is the Earth-colliding asteroid interception mission. Using nuclear detonations to split or deflect the asteroid is risky at best. Such a tactic could actually make the problem worse by increasing the amount of asteroid fragments that do end up hitting the Earth. Robert Zubrin writes:
If bombs are to be used as asteroid deflectors, they cannot just be launched willy-nilly. No, before any bombs are detonated, the asteroid will have to be thoroughly explored, its geology assessed, and subsurface bomb placements carefully determined and precisely located on the basis of such knowledge. A human crew, consisting of surveyors, geologists, miners, drillers, and demolition experts, will be needed on the scene to do the job right. [ 58 ]
If such a crew is to be summoned to a distant asteroid, there may be less risky ways to divert the asteroid. Another promising asteroid mitigation strategy is to land a crew on the asteroid well ahead of its impact date and to begin diverting some its mass into space to slowly alter its trajectory. This is a form of rocket propulsion by virtue of Newton's third law with the asteroid's mass as the propellant. Whether exploding nuclear weapons or diversion of mass is used, a sizable human crew may need to be sent into space for many months if not years to accomplish this mission. [ 59 ] Questions such as what the astronauts will live in and what the ship will be like are questions for the space architect.
When motivations to go into space are realized, work on mitigating the most serious threats can begin. One of the biggest threats to astronaut safety in space is sudden radiation events from solar flares . The violent solar storm of August 1972, which occurred between the Apollo 16 and Apollo 17 missions, could have produced fatal consequences had astronauts been caught exposed on the lunar surface. [ 60 ] The best known protection against radiation in space is shielding; an especially effective shield is water contained in large tanks surrounding the astronauts. [ 61 ] Unfortunately water has a mass of 1000 kilograms per cubic meter. A more practical approach would be to construct solar "storm shelters" that spacefarers can retreat to during peak events. [ 62 ] For this to work, however, there would need to be a space weather broadcasting system in place to warn astronauts of upcoming storms, much like a tsunami warning system warns coastal inhabitants of impending danger. Perhaps one day a fleet of robotic spacecraft will orbit close to the Sun, monitoring solar activity and sending precious minutes of warning before waves of dangerous particles arrive at inhabited regions of space.
Nobody knows what the long-term human future in space will be. Perhaps after gaining experience with routine spaceflight by exploring different worlds in the Solar System and deflecting a few asteroids, the possibility of constructing non-modular space habitats and infrastructure will be within capability. [ citation needed ] Such possibilities include mass drivers on the Moon, which launch payloads into space using only electricity, and spinning space colonies with closed ecological systems . A Mars in the early stages of terraformation , where inhabitants only need simple oxygen masks to walk out on the surface, may be seen. In any case, such futures require space architecture. | https://en.wikipedia.org/wiki/Space_architecture |
Space art, also known as astronomical art , is a genre of art that visually depicts the universe through various artistic styles. It may also refer to artworks sent into space . [ 1 ]
The development of space art was closely linked to advancements in telescope and imaging technology , which enabled more precise observations of the night sky . Some space artists work directly with scientists to explore new ways to expand the arts , humanities , and cultural expressions relative to space. Space art may communicate ideas about space, often including an artistic interpretation of cosmological phenomena and scientific discoveries . [ 2 ]
For many decades, visual artists have explored the topic of space using traditional painting media, followed recently by the use of digital media for the same purpose. Science-fiction magazines and picture essay magazines were some of the first major outlets for space art, often featuring planets, spaceships, and dramatic alien landscapes. Chesley Bonestell , R. A. Smith, Lucien Rudaux , David A. Hardy , and Ludek Pesek were some of the artists actively involved in visualizing topics such as space exploration and colonization in the early days of the genre. Astronomers and experts in rocketry also played roles in inspiring artists in this genre. [ 1 ]
NASA’s second administrator, James E. Webb , created the space agency's Space Art program in 1962, four years after its inception. [ 1 ] Bonestell's work in this program often depicted various celestial bodies and landscapes, highlighting both the destinations and the imagined technologies used to reach them.
Astronomical art is a genre of space art that focuses on visual representations of outer space . It encompasses various themes, including the space environment as a new frontier for humanity, depictions of alien worlds, representations of extreme phenomena like black holes , and artistic concepts inspired by astronomy .
Astronomical art emerged as a distinct genre in the 1940s and 1950s. Chesley Bonestell was recognized for his skills in addressing perspective challenges and creating visual representations of astronomical concepts. Contemporary artists continue to contribute to the visualization of ideas within the space community, such as depicting theoretical capabilities for interstellar travel and illustrating hypothetical deep-space phenomena. [ 3 ] [ 4 ]
Astronomical art is the most recent of several art movements that have explored ideas emerging from the ongoing exploration of Earth. Finding its roots in genres such as the Hudson River School or Luminism , most astronomical artists use traditional painting methods or digital equivalents in a way that brings the viewer to the frontiers of human knowledge gathered in the exploration of space. Such works usually portray things in the visual language of realism extrapolated to exotic environments, whose details reflect ongoing knowledge and educated guesswork. An example of the process of creating astronomical art would be studying and visiting desert environments to experience something of what it might be like on Mars and painting based on such experiences. Another would be to hear of an astronomical concept, and then seek out published articles or experts in the field. Usually, there is an artistic effort to emphasize the favourable visual elements, just as a photographer composes a picture. Notable astronomical art often reflects the artist's interpretation and imagination regarding the subject portrayed.
Science fiction magazines such as Fantasy and Science Fiction , Amazing , Astounding (later renamed Analog ), and Galaxy were platforms for space and astronomical art in the 1950s. Picture essay magazines of the time, such as Life , Collier's , and Coronet , were other major outlets for such art. Today, astronomical art can be seen in magazines such as Sky and Telescope , The Planetary Report , and occasionally in Scientific American . The NASA fine arts program has been an ongoing effort to hire artists to create works generally specific to a particular space project. The program documents historical events in recognizable form for professional artists. The NASA Fine Arts Program operated in an era of forward progress under its first head director, James Dean. [ 5 ] Even then, pictorial realism seemed a subset rather than a dominant visual influence.
The works that document space flight situations, such as those referenced above, are similar in concept to government efforts during World War II to send artists to battle zones for documentation. Much of which appeared in contemporary Life magazines. Most of today's widely published space and astronomical artists have belonged to the International Association of Astronomical Artists since 1983.
The first photographs of the entire Earth by satellites [ 6 ] and crewed Apollo missions [ 7 ] brought a new sense of Earth and promoted ideas of the unity of humanity. [ 8 ] Photographs taken by explorers on the Moon evoked the experience of being in another world. The Pillars of Creation [ 9 ] taken by the Hubble Space Telescope and other Hubble photos often evoke intense responses from viewers; for example, Hubble's planetary nebula images. [ 10 ]
Artists have experienced free-fall conditions during flights flown with NASA, the Russian and French Space Agencies , and the Zero Gravity Arts Consortium. Early efforts by artists to have art pieces placed in space have already been accomplished with painting, holography , micro-gravity mobiles, floating literary works , and sculpture . [ 11 ]
Early examples of space art are depictions of celestial bodies in ancient artifacts . The 'Land Grant to Ḫunnubat-Nanaya Kudurru,' a Babylonian limestone artifact from the 12th century BC, features early representations of Venus , the lunar crescent, and the solar disk .
Albrecht Altdorfer 's painting The Battle of Issus (1529) shows the curvature of the Earth from a great height. [ 12 ] Galileo 's sketches of the Moon from the Sidereus Nuncius (1610) were published among other early descriptions of the Moon's topography . In 1711, Donato Creti painted a series of astronomers viewing other planets of the Solar System through a telescope to interest the Vatican in establishing an astronomical observatory .
In the early 1870s-1900s, Étienne Léopold Trouvelot published a series of Chromolithographs of his pastels of astronomical subjects.
In 1874, James Carpenter and James Nasmyth 's work The Moon: Considered as a Planet, a World, and a Satellite included photographs of sculpted models of Lunar features , in the marked vertical exaggeration of the actual relief of the Moon.
In 1877, Paul Dominique Philippoteaux and engraver Laplante illustrated Jules Verne 's story Off on a Comet , including an imaginative view looking up at the rings of Saturn from the planet itself.
In 1918, Howard Russell Butler deliberately made use of the dynamic range of human vision in painting a total eclipse based on direct observation. [ 13 ]
In 1927, Scriven Bolten created lunar landscape images for the Illustrated London News using painted photos of plaster models.
In 1937, Lucien Rudaux painted many works for Sur Les Autres Mondes. [ 14 ] [ 15 ]
In 1944, Chesley Bonestell 's paintings of Saturn seen from its different moons appeared in Life magazine , introducing astronomical art to a wide American audience. Books featuring Bonestell's art include The Conquest Of Space (1949), The Exploration Of Mars (1956), and Life' s The World We Live In (1955).
The second Hayden Planetarium Symposium on Space Travel, held in New York in October 1952, resulted in a series of widely read space flight articles in Collier's magazine, illustrated by Bonestell and others.
In 1963, Ludek Pesek's paintings filled the large volumes of The Moon And the Planets , and the 1968 volume Our Planet Earth-From The Beginning .
The 1980 Cosmos PBS television show and book used the work of many space artists. Host Carl Sagan used such art in several of his books.
The 21st century expanded to sending art into space.
The first active artist in space was Alexei Leonov , who produced the first drawing in space onboard Voskhod 2 in 1965, depicting an orbital sunrise. [ 16 ]
An art conservation experiment from Vertical Horizons, [ 17 ] founded by Howard Wishnow and Ellery Kurtz, was flown aboard the Space Shuttle Columbia STS-61-C on January 12, 1986. Four original oil paintings by American artist Ellery Kurtz were flown in one of NASA's GetAway Special (G.A.S.) containers mounted to a bridge in the shuttle cargo bay. These original works of art are the first oil paintings to enter Earth's orbit. This NASA GAS canister, designated G-481, was the 46th such canister flown aboard a Space Shuttle. The Space Shuttle Columbia orbited the Earth 98 times during its mission duration of 6 days, 2 hours, 3 minutes, and 51 seconds. Columbia was launched from Kennedy Space Center , Cape Canaveral, Florida , on January 12, 1986, and landed at the Kennedy Space Center on January 18, 1986.
Small art objects have been carried on several Apollo missions, such as gold emblems and a small Fallen Astronaut figurine that was left on the Moon during the 1971 Apollo 15 mission. Visual observations have been recorded in drawings and commentary by earlier cosmonauts and astronauts of difficult-to-photograph phenomena such as the airglow , twilight colors, and outer details of the solar corona.
Another work, later brought to Earth orbit sometime in the mid-80s, was a study of the golden sunlight on a Soviet space station by Russian artist Andrei Sokolov, carried aboard the Soviet Mir space station starting with modules in February 1986. In 1984, Joseph McShane and Lowry Burgess had their conceptual artwork flown aboard the Space Shuttle utilizing NASA's 'Get Away Special' program. [ 18 ] The first sculpture specifically designed for human habitat in orbit was Arthur Woods' Cosmic Dancer [ 19 ] [ 20 ] which was sent to the Mir station in 1993. In 1995, Arthur Woods organized Ars ad Astra, the first art exhibition in Earth orbit. [ 21 ] consisting of 20 original artworks from 20 artists and an electronic archive also took place on the Mir space station as part of ESA's EUROMIR '95 mission. In 1998, Frank Pietronigro flew Research Project Number 33: Investigating the Creative Process in a Micro-gravity Environment, where he created 'drift paintings' and danced in microgravity space. In 2006, the artist returned to micro-gravity flight to create three new works, one in collaboration with Lowry Burgess ; Moments in the Infinite Absolute, Flags in Space!, and a new form of microgravity mobile.
The Slovenian theater director Dragan Živadinov staged a performance called Noordung Zero Gravity Biomechanical during a parabolic flight organized through the Yuri Gagarin Cosmonaut Training Center facility in Star City in 1999. The UK arts group The Arts Catalyst , with the MIR consortium (Arts Catalyst, Projekt Atol, V2 Organisation, Leonardo-Olats), organized a series of parabolic 'zero gravity' flights for artistic and cultural experimentation with the Gagarin Cosmonaut Training Centre, as well as with the European Space Agency , between 2000 and 2004, including Investigations in Microgravity, [ 22 ] MIR Flight 001, [ 23 ] and MIR Campaign 2003. [ 24 ] [ 25 ] [ 26 ] [ 27 ] Artists who participated in these flights and visits to Russia and ESA have included the Otolith Group, shortlisted in 2011 for the Turner Prize , Stefan Gec, Ansuman Biswas and Jem Finer , Kitsou Dubois, Yuri Leiderman , and Marcel·li Antunez Roca .
Richard Garriott visited the International Space Station , via the Soyuz TMA-13 on October 12, 2008, where he displayed an art exhibition, Celestial Matters , during his 12 days in orbit. Celestial Matters included works by ten American artists as well as work Garriott created himself while in orbit, honoring his heritage in art and science. The art was later exhibited at the Charles Bank Gallery in New York City in October 2011. [ 28 ] Garriott also exhibited Astrogeneris Mementos , two small works, somewhat reminiscent of memento mori or hairwork , containing locks of hair from Richard Garriott and Owen Garriott sealed in chambers by Steve Brudniak , the first assemblage sculptures exhibited in outer space. [ 29 ] [ 30 ] [ 31 ]
In 2009, NASA astronaut Nicole Stott having brought watercolor paint and watercolor paper with her for the long-duration Expedition 21 mission to the International Space Station became the first astronaut to paint in space. [ 32 ]
The Mexican artist and musician Nahum directed the art and science project Matters of Gravity ( La Gravedad de los Asuntos in Spanish), a project reflecting on gravity in its absence . The first mission consisting only of Latin American artists was executed in a zero-gravity flight at the Yuri Gagarin Cosmonaut Training Center in 2014. The participating artists include Tania Candiani , Ale de la Puente, Ivan Puig, Arcángelo Constantini, Fabiola Torres-Alzaga, Gilberto Esparza, Juan Jose Diaz Infante, Nahum , and Marcela Armas. The project included the participation of Mexican scientist Miguel Alcubierre and curators Rob La Frenais and Kerry Anne Doyle.
Performance art has also occurred in space, as with Chris Hadfield 's 2013, edited performance of David Bowie 's 1969 song " Space Oddity and Thomas Pesquet 's 2017 edited performance of "L'Art de la joie par les Spacelatorz" ." [ 33 ] [ 34 ]
In the Sojourner 2020 project from MIT , the Space Exploration Initiative took nine selected artists to develop art projects on board the International Space Station. Sojourner 2020 was a 1.5U size device (100mm x 100mm x 152.4mm) that was launched into low Earth orbit between March 7 and April 7 during the COVID-19 pandemic . It featured a three-layer telescoping structure that simulated three different "gravities": zero gravity , lunar gravity , and Martian gravity. Each layer of the structure rotated independently. The top layer remained still in weightlessness, while the middle and bottom layers spun at different speeds to produce centripetal accelerations that mimicked lunar gravity and Martian gravity respectively. Each layer carried six pockets that held the projects. Each pocket was a container with a diameter of 10 mm and a depth of 12 mm. The artist proposed and accomplished artworks in a variety of different mediums, including carved stone sculptures by Erin Genia, liquid pigment experiments by Andrea Ling and Levi Cai, sculptures made of transgender hormone replacement medicines by Adriana Knouf, and living organisms, like marine diatoms of the genus Phaeodactylum Tricornutum , by Luis Guzmán. [ 35 ]
The nine artist groups selected onboard Sojourner 2020 were:
Humans have engaged in many cultural activities in space, particularly on space stations, recontextualizing terrestrial culture and art. [ 40 ] | https://en.wikipedia.org/wiki/Space_art |
Space climate is the long-term variation in solar activity within the heliosphere , including the solar wind , the Interplanetary magnetic field (IMF), and their effects in the near-Earth environment, including the magnetosphere of Earth and the ionosphere , the upper and lower atmosphere, climate , and other related systems. The scientific study of space climate is an interdisciplinary field of space physics , solar physics , heliophysics , and geophysics . It is thus conceptually related to terrestrial climatology , and its effects on the atmosphere of Earth are considered in climate science. [ 1 ] [ 2 ] [ 3 ]
Space climatology considers long-term (longer than the latitudinally variable 27-day solar rotation period, through the 11-year solar cycle and beyond, up to and
exceeding millennia) variability of solar indices, cosmic ray , heliospheric parameters, and the induced geomagnetic, ionospheric, atmospheric, and climate effects. [ 1 ] It studies mechanisms and physical processes responsible for their variability in the past with projections onto future. [ 2 ] It is a broader and more general concept than space weather , to which it is related like the conventional climate and weather . [ 1 ]
In addition to real-time solar observations , the field of research also covers analysis of historical space climate data. This has included analysis and reconstruction that has allowed solar wind and heliospheric magnetic field strengths to be determined from back to 1611. [ 3 ]
The importance of space climate research has been recognized, in particular, by NASA which launched a special space mission Deep Space Climate Observatory (DSCOVR) [ 4 ] dedicated to monitoring of space climate. [ 5 ] New results, ideas and discoveries in the field of Space Climate are published in a focused peer-review research Journal of Space Weather and Space Climate (JSWSC). [ 6 ] Since 2013, research awards and medals in space weather and space climate are annually awarded by the European Space Weather Week. [ 7 ] Another recent space observatory platform is the Solar Radiation and Climate Experiment (SORCE).
Space climate research has three main aims: [ 1 ]
In the early 2000s, when the concept of space weather became common, a small initiative group, led by Kalevi Mursula and Ilya G. Usoskin the University of Oulu in Finland had realized that physical drivers of solar variability and its terrestrial effects can be better understood with a more general and broader view. The concept of Space Climate had been developed, and the corresponding research community formed, which presently includes a few hundred active members around the world. In particular, a series of International Space Climate Symposia (biennial since 2004) was organized, [ 8 ] with the first inaugural symposium being held in Oulu (Finland) in 2004, followed by those in Romania (2006), Finland (2009), India (2011), Finland (2013), Finland (2016), Canada (2019), Poland (2022) and Japan (2024) as well as topical space climate sessions are regularly held at the General Assemblies of the Committee on Space Research and Earth Science. [ 9 ] [ 10 ]
Research results related to Space Climate are published in a bunch of peer-reviewed journals, such as Astronomy & Astrophysics , Journal of Geophysical Research , Geophysical Research Letters , Solar Physics (journal) , Advances in Space Research . | https://en.wikipedia.org/wiki/Space_climate |
Space colonization (or extraterrestrial colonization ) is the settlement or colonization of outer space and astronomical bodies . The concept in its broad sense has been applied to any permanent human presence in space, such as a space habitat or other extraterrestrial settlements . [ 2 ] It may involve a process of occupation or control for exploitation, such as extraterrestrial mining .
Making territorial claims in space is prohibited by international space law , defining space as a common heritage . International space law has had the goal to prevent colonial claims and militarization of space , [ 3 ] [ 4 ] and has advocated the installation of international regimes to regulate access to and sharing of space, particularly for specific locations such as the limited space of geostationary orbit [ 3 ] or the Moon. To date, no permanent space settlement other than temporary space habitats have been established, nor has any extraterrestrial territory or land been internationally claimed . Currently there are also no plans for building a space colony by any government. However, many proposals, speculations, and designs, particularly for extraterrestrial settlements have been made through the years, and a considerable number of space colonization advocates and groups are active. Currently, the dominant private launch provider SpaceX , has been the most prominent organization planning space colonization on Mars , though having not reached a development stage beyond launch and landing systems. [ 5 ]
Space colonization raises numerous socio-political questions. Many arguments for and against space settlement have been made. The two most common reasons in favor of colonization are the survival of humans and life independent of Earth, making humans a multiplanetary species , [ 6 ] in the event of a planetary-scale disaster (natural or human-made) , and the commercial use of space particularly for enabling a more sustainable expansion of human society through the availability of additional resources in space, reducing environmental damage on and exploitation of Earth. [ 7 ] The most common objections include concerns that the commodification of the cosmos may be likely to continue pre-existing detrimental processes such as environmental degradation , economic inequality and wars , enhancing the interests of the already powerful, and at the cost of investing in solving existing major environmental and social issues . [ 8 ] [ 9 ] [ 10 ]
The mere construction of an extraterrestrial settlement, with the needed infrastructure, presents daunting technological, economic and social challenges. Space settlements are generally conceived as providing for nearly all (or all) the needs of larger numbers of humans. The environment in space is very hostile to human life and not readily accessible, particularly for maintenance and supply. It would involve much advancement of currently primitive technologies, such as controlled ecological life-support systems . With the high cost of orbital spaceflight (around $1400 per kg, or $640 per pound, to low Earth orbit by SpaceX Falcon Heavy ), a space settlement would currently be massively expensive, but ongoing progress in reusable launch systems aim to change that (possibly reaching $20 per kg to orbit), [ 11 ] and in creating automated manufacturing and construction techniques .
Space colonization has been in a broad sense referred to as space settlement, space humanization or space habitation. [ 12 ] Space colonization in a narrow sense refers to space settlements , as envisioned by Gerard K. O'Neill . [ 13 ] It is characterized by elements such as: settlement and exploitation, [ 14 ] as well as territorial claim. [ 15 ]
The concept in its broad sense has been applied to any permanent human presence, even robotic, [ 16 ] [ 17 ] [ 18 ] particularly along with the term "settlement", being imprecisely applied to any human space habitat , from research stations to self-sustaining communities in space . [ 2 ]
The words colony and colonization are terms rooted in colonial history on Earth, making them human geographic as well as particularly political terms. This broad use for any permanent human activity and development in space has been criticized, particularly as colonialist and undifferentiated (see below Objections ). [ 2 ]
In this sense, a colony is a settlement that claims territory and exploits it for the settlers or their metropole . Therefore, a human outpost , while possibly a space habitat or even a space settlement , does not automatically constitute a space colony. [ 19 ]
Therefore, any basing can be part of colonization, while colonization can be understood as a process that is open to more claims, beyond basing. The International Space Station , the longest-occupied extraterrestrial habitat thus far, does not claim territory and thus is not usually considered a colony. [ 20 ]
Moriba Jah has criticized existing approaches to orbital space as colonialist, such as for satellites, on the grounds that it involves claiming ownership instead of collaborative stewardship. [ 21 ]
Some advocates of peaceful human settlement of space have argued against use of the word "colony" and related terms, so as to avoid confusing their goals with colonialism on Earth. [ 2 ]
In the first half of the 17th century John Wilkins suggested in A Discourse Concerning a New Planet that future adventurers like Francis Drake and Christopher Columbus might reach the Moon and allow people to live there. [ 22 ] The first known work on space colonization was the 1869 novella The Brick Moon by Edward Everett Hale , about an inhabited artificial satellite. [ 23 ] In 1897, Kurd Lasswitz also wrote about space colonies. The Russian rocket science pioneer Konstantin Tsiolkovsky foresaw elements of the space community in his book Beyond Planet Earth written about 1900. Tsiolkovsky imagined his space travelers building greenhouses and raising crops in space. [ 24 ] Tsiolkovsky believed that going into space would help perfect human beings, leading to immortality and peace. [ 25 ] One of the first to speak about space colonization was Cecil Rhodes who in 1902 spoke about "these stars that you see overhead at night, these vast worlds which we can never reach", adding "I would annex the planets if I could; I often think of that. It makes me sad to see them so clear and yet so far". [ 26 ] In the 1920s John Desmond Bernal , Hermann Oberth , Guido von Pirquet and Herman Noordung further developed the idea. Wernher von Braun contributed his ideas in a 1952 Colliers magazine article. In the 1950s and 1960s, Dandridge M. Cole [ 27 ] published his ideas.
When orbital spaceflight was achieved in the 1950s colonialism was still a strong international project, e.g. easing the United States to advance its space program and space in general as part of a " New Frontier ". [ 8 ] As the Space Age was developing, decolonization gained again in force, producing many newly independent countries. These newly independent countries confronted spacefaring countries, demanding an anti-colonial stance and regulation of space activity when space law was raised and negotiated internationally. Fears of confrontations because of land grabs and an arms race in space between the few countries with spaceflight capabilities grew and were ultimately shared by the spacefaring countries themselves. [ 4 ] This produced the wording of the agreed on international space law, starting with the Outer Space Treaty of 1967, calling space a " province of all mankind " and securing provisions for international regulation and sharing of outer space.
The advent of geostationary satellites raised the case of limited space in outer space. In the 1960s and with an initial focus on communications spectrum management, the international community agreed to regulate the assignment of slots in the geosynchronous (GEO) belt through the International Telecommunication Union (ITU) . Today, any company or nation planning to launch a satellite to GEO must apply to the ITU for an orbital slot. [ 28 ] A group of equatorial countries, all of which were countries that were once colonies of colonial empires, but without spaceflight capabilities, signed in 1976 the Bogota Declaration . These countries declared that geostationary orbit is a limited natural resource and belongs to the equatorial countries directly below, seeing it not as part of outer space, humanity's common . Through this, the declaration challenged the dominance of geostationary orbit by spacefaring countries through identifying their dominance as imperialistic. [ 29 ] [ 30 ] [ 3 ]
Writers continued to address space colonization concepts by publishing books in the mid-1970s such as The High Frontier: Human Colonies in Space by Gerard K. O'Neill [ 31 ] and Colonies in Space by T. A. Heppenheimer . [ 32 ]
In 1975, the first international joint space mission occurred as a symbol of the policy of détente that the two superpowers were pursuing at the time. The U.S. Apollo and Soviet Soyuz spacecraft docked in earth orbit for almost two days. [ 33 ] In 1977, the first sustained space habitat, the Salyut 6 station, was put into Earth's orbit. Eventually the first space stations were succeeded by the ISS , today's largest human outpost in space and closest to a space settlement. Built and operated under a multilateral regime, it has become a blueprint for future stations, such as around and possibly on the Moon . [ 34 ] [ 35 ]
Additional discourse on living in space was generated by writers including Marianne J. Dyson who wrote Home on the Moon; Living on a Space Frontier in 2003; [ 36 ] Peter Eckart wrote Lunar Base Handbook in 2006 [ 37 ] and then Harrison Schmitt 's Return to the Moon written in 2007. [ 38 ]
An international regime for lunar activity was demanded by the international Moon Treaty , but is currently developed multilaterally as with the Artemis Accords . [ 39 ] Threats to existing treaties come in areas such as space debris because of the lack of regulation on disposition of assets by operators (and controlling sovereign power) once their mission is complete. The only habitation on a different celestial body so far have been the temporary habitats of the crewed lunar landers . Similar to the Artemis program, China is leading an effort to develop a lunar base called the International Lunar Research Station beginning in the 2030s.
A primary argument calling for space colonization is the long-term survival of human civilization and terrestrial life. [ 40 ] By developing alternative locations off Earth, the planet's species, including humans, could live on in the event of natural or human-made disasters on Earth . [ 41 ]
On two occasions, theoretical physicist and cosmologist Stephen Hawking argued for space colonization as a means of saving humanity. In 2001, Hawking predicted that the human race would become extinct within the next thousand years unless colonies could be established in space. [ 42 ] In 2010, he stated that humanity faces two options: either we colonize space within the next two hundred years, or we will face the long-term prospect of extinction . [ 43 ]
In 2005, then NASA Administrator Michael Griffin identified space colonization as the ultimate goal of current spaceflight programs, saying:
... the goal isn't just scientific exploration ... it's also about extending the range of human habitat out from Earth into the solar system as we go forward in time ... In the long run, a single-planet species will not survive ... If we humans want to survive for hundreds of thousands of millions of years, we must ultimately populate other planets. Now, today the technology is such that this is barely conceivable. We're in the infancy of it. ... I'm talking about that one day, I don't know when that day is, but there will be more human beings who live off the Earth than on it. We may well have people living on the Moon. We may have people living on the moons of Jupiter and other planets. We may have people making habitats on asteroids ... I know that humans will colonize the solar system and one day go beyond. [ 44 ]
Louis J. Halle Jr. , formerly of the United States Department of State , wrote in Foreign Affairs (Summer 1980) that the colonization of space will protect humanity in the event of global nuclear warfare . [ 45 ] The physicist Paul Davies also supports the view that if a planetary catastrophe threatens the survival of the human species on Earth, a self-sufficient colony could "reverse-colonize" Earth and restore human civilization . The author and journalist William E. Burrows and the biochemist Robert Shapiro proposed a private project, the Alliance to Rescue Civilization , with the goal of establishing an off-Earth " backup " of human civilization. [ 46 ]
Based on his Copernican principle , J. Richard Gott has estimated that the human race could survive for another 7.8 million years, but it is not likely to ever colonize other planets. However, he expressed a hope to be proven wrong, because "colonizing other worlds is our best chance to hedge our bets and improve the survival prospects of our species". [ 47 ]
In a theoretical study from 2019, a group of researchers have pondered the long-term trajectory of human civilization. [ 48 ] It is argued that due to Earth's finitude as well as the limited duration of the Solar System , mankind's survival into the far future will very likely require extensive space colonization. [ 48 ] : 8, 22f This 'astronomical trajectory' of mankind, as it is termed, could come about in four steps: First step, space colonies could be established at various habitable locations — be it in outer space or on celestial bodies away from Earth – and allowed to remain temporarily dependent on support from Earth. In the second step, these colonies could gradually become self-sufficient, enabling them to survive if or when the mother civilization on Earth fails or dies. Third step, the colonies could develop and expand their habitation by themselves on their space stations or celestial bodies, for example via terraforming . In the fourth step, the colonies could self-replicate and establish new colonies further into space, a process that could then repeat itself and continue at an exponential rate throughout the cosmos. However, this astronomical trajectory may not be a lasting one, as it will most likely be interrupted and eventually decline due to resource depletion or straining competition between various human factions, bringing about some 'star wars' scenario. [ 48 ] : 23–25
Resources in space, both in materials and energy, are enormous. The Solar System has enough material and energy to support anywhere from several thousand to over a billion times that of the current Earth-based human population, mostly from the Sun itself. [ 31 ] : 9 [ 49 ] [ 50 ]
Asteroid mining will likely be a key player in space colonization. Water and materials to make structures and shielding can be easily found in asteroids. Instead of resupplying on Earth, mining and fuel stations need to be established on asteroids to facilitate better space travel. [ 51 ] Optical mining is the term NASA uses to describe extracting materials from asteroids. NASA believes by using propellant derived from asteroids for exploration to the moon, Mars, and beyond will save $100 billion. If funding and technology come sooner than estimated, asteroid mining might be possible within a decade. [ 52 ]
Although some items of the infrastructure requirements above can already be easily produced on Earth and would therefore not be very valuable as trade items (oxygen, water, base metal ores, silicates, etc.), other high-value items are more abundant, more easily produced, of higher quality, or can only be produced in space. These could provide (over the long-term) a high return on the initial investment in space infrastructure. [ 53 ]
Some of these high-value trade goods include precious metals, [ 54 ] [ 55 ] gemstones, [ 56 ] power, [ 57 ] solar cells, [ 58 ] ball bearings, [ 58 ] semi-conductors, [ 58 ] and pharmaceuticals. [ 58 ]
The mining and extraction of metals from a small asteroid the size of 3554 Amun or (6178) 1986 DA , both small near-Earth asteroids, may yield 30 times as much metal as humans have mined throughout history. A metal asteroid this size would be worth approximately US$20 trillion at 2001 market prices. [ 59 ]
The main impediments to commercial exploitation of these resources are the very high cost of initial investment, [ 60 ] the very long period required for the expected return on those investments ( The Eros Project plans a 50-year development), [ 61 ] and the fact that the venture has never been carried out before—the high-risk nature of the investment.
Expansion of humans and technological progress has usually resulted in some form of environmental devastation, and destruction of ecosystems and their accompanying wildlife . In the past, expansion has often come at the expense of displacing many indigenous peoples , the resulting treatment of these peoples ranging anywhere from encroachment to genocide. Because space has no known life, this need not be a consequence, as some space settlement advocates have pointed out. [ 62 ] [ 63 ] However, on some bodies of the Solar System, there is the potential for extant native lifeforms and so the negative consequences of space colonization cannot be dismissed. [ 64 ]
Counterarguments state that changing only the location but not the logic of exploitation will not create a more sustainable future. [ 65 ]
An argument for space colonization is to mitigate proposed impacts of overpopulation of Earth , such as resource depletion . [ 66 ] If the resources of space were opened to use and viable life-supporting habitats were built, Earth would no longer define the limitations of growth. Although many of Earth's resources are non-renewable, off-planet colonies could satisfy the majority of the planet's resource requirements. With the availability of extraterrestrial resources, demand on terrestrial ones would decline. [ 31 ] [ 67 ] Proponents of this idea include Stephen Hawking [ 68 ] and Gerard K. O'Neill . [ 31 ]
Others including cosmologist Carl Sagan and science fiction writers Arthur C. Clarke , [ 69 ] and Isaac Asimov , [ 70 ] have argued that shipping any excess population into space is not a viable solution to human overpopulation. According to Clarke, "the population battle must be fought or won here on Earth". [ 69 ] The problem for these authors is not the lack of resources in space (as shown in books such as Mining the Sky [ 71 ] ), but the physical impracticality of shipping vast numbers of people into space to "solve" overpopulation on Earth.
Advocates for space colonization cite a presumed innate human drive to explore and discover, and call it a quality at the core of progress and thriving civilizations. [ 72 ] [ 73 ]
Nick Bostrom has argued that from a utilitarian perspective, space colonization should be a chief goal as it would enable a very large population to live for a very long time (possibly billions of years), which would produce an enormous amount of utility (or happiness). [ 74 ] He claims that it is more important to reduce existential risks to increase the probability of eventual colonization than to accelerate technological development so that space colonization could happen sooner. In his paper, he assumes that the created lives will have positive ethical value despite the problem of suffering .
In a 2001 interview with Freeman Dyson, J. Richard Gott and Sid Goldstein, they were asked for reasons why some humans should live in space. [ 75 ] Their answers were:
Biotic ethics is a branch of ethics that values life itself. For biotic ethics, and their extension to space as panbiotic ethics, it is a human purpose to secure and propagate life and to use space to maximize life.
Space colonization has been seen as a relief to the problem of human overpopulation as early as 1758, [ 76 ] and listed as one of Stephen Hawking's reasons for pursuing space exploration. [ 77 ] Critics note, however, that a slowdown in population growth rates since the 1980s has alleviated the risk of overpopulation. [ 76 ]
Critics also argue that the costs of commercial activity in space are too high to be profitable against Earth-based industries, and hence that it is unlikely to see significant exploitation of space resources in the foreseeable future. [ 78 ]
Other objections include concerns that the forthcoming colonization and commodification of the cosmos is likely to enhance the interests of the already powerful, including major economic and military institutions e.g. the large financial institutions, the major aerospace companies and the military–industrial complex , to lead to new wars , and to exacerbate pre-existing exploitation of workers and resources , economic inequality , poverty , social division and marginalization , environmental degradation, and other detrimental processes or institutions. [ 10 ] [ 79 ] [ 80 ]
Additional concerns include creating a culture in which humans are no longer seen as human, but rather as material assets. The issues of human dignity , morality , philosophy , culture , bioethics , and the threat of megalomaniac leaders in these new "societies" would all have to be addressed in order for space colonization to meet the psychological and social needs of people living in isolated colonies. [ 81 ]
As an alternative or addendum for the future of the human race, many science fiction writers have focused on the realm of the 'inner-space', that is the computer-aided exploration of the human mind and human consciousness —possibly en route developmentally to a Matrioshka Brain . [ 82 ]
Robotic spacecraft are proposed as an alternative to gain many of the same scientific advantages without the limited mission duration and high cost of life support and return transportation involved in human missions. [ 83 ]
A corollary to the Fermi paradox —"nobody else is doing it" [ 84 ] —is the argument that, because no evidence of alien colonization technology exists, it is statistically unlikely to even be possible to use that same level of technology ourselves. [ 85 ]
Space colonization has been discussed as postcolonial [ 89 ] continuation of imperialism and colonialism , [ 90 ] [ 91 ] [ 92 ] [ 8 ] calling for decolonization instead of colonization. [ 93 ] [ 92 ] Critics argue that the present politico-legal regimes and their philosophic grounding, advantage imperialist development of space, [ 8 ] that key decisionmakers in space colonization are often wealthy elites affiliated with private corporations, and that space colonization would primarily appeal to their peers rather than ordinary citizens. [ 94 ] [ 95 ] Furthermore, it is argued that there is a need for inclusive [ 96 ] and democratic participation and implementation of any space exploration, infrastructure or habitation. [ 97 ] [ 98 ] According to space law expert Michael Dodge, existing space law , such as the Outer Space Treaty , guarantees access to space, but does not enforce social inclusiveness or regulate non-state actors. [ 93 ]
Particularly the narrative of the " New Frontier " has been criticized as unreflected continuation of settler colonialism and manifest destiny , continuing the narrative of exploration as fundamental to the assumed human nature . [ 99 ] [ 100 ] [ 91 ] [ 94 ] [ 92 ] Joon Yun considers space colonization as a solution to human survival and global problems like pollution to be imperialist; [ 101 ] others have identified space as a new sacrifice zone of colonialism. [ 102 ]
Furthermore, the understanding of space as empty and separate is considered a continuation of terra nullius . [ 103 ] [ 104 ]
Natalie B. Trevino argues that not colonialism but coloniality will be carried into space if not reflected on. [ 105 ]
More specifically the advocacy for territorial colonization of Mars has been called surfacism , in contrast to habitation in the atmospheric space of Venus , [ 106 ] [ 107 ] a concept similar to Thomas Golds surface chauvinism .
More generally space infrastructure such as the Mauna Kea Observatories have also been criticized and protested against as being colonialist. [ 108 ] Guiana Space Centre has also been the site of anti-colonial protests, connecting colonization as an issue on Earth and in space. [ 89 ]
In regard to the scenario of extraterrestrial first contact , it has been argued that the employment of colonial language would endanger such first impressions and encounters. [ 93 ]
Furthermore, spaceflight as a whole and space law more particularly has been criticized as a postcolonial project by being built on a colonial legacy and by not facilitating the sharing of access to space and its benefits, too often allowing spaceflight to be used to sustain colonialism and imperialism, most of all on Earth instead. [ 89 ]
Agencies conducting interplanetary missions are guided by COSPAR 's planetary protection policies, to have at most 300,000 spores on the exterior of the craft—and more thoroughly sterilized if they contact "special regions" containing water, or it could contaminate life-detection experiments or the planet itself. [ 109 ] [ 110 ]
It is impossible to sterilize human missions to this level, as humans are host to typically a hundred trillion microorganisms of thousands of species of the human microbiome , and these cannot be removed while preserving the life of the human. Containment seems the only option, but it is a major challenge in the event of a hard landing (i.e. crash). [ 111 ] There have been several planetary workshops on this issue, but with no final guidelines yet for a way forward. [ 112 ] Human explorers could also inadvertently contaminate Earth if they return to the planet while carrying extraterrestrial microorganisms. [ 113 ]
Colonization beyond the Earth involves overcoming a number of difficult challenges.
The outer planets are much farther from Earth than the inner planets, and would therefore be harder and more time-consuming to reach. In addition, return voyages may well be prohibitive considering the time and distance. Even communication with Earth would be slow, with delays of 4 - 24 minutes for a message to mars , [ 114 ] and 35 - 52 minutes to Jupiter and it's moons. [ 115 ]
Extreme cold – due to the distance to the sun, temperatures are near absolute zero in many parts of the outer Solar System. [ 116 ] [ 117 ]
Power – Solar power is many times less concentrated in the outer Solar System than in the inner Solar System. It is unclear as to whether it would be usable there, using some form of concentration mirrors, or whether nuclear power would be necessary. [ 118 ] Use of geothermal systems to generate power may be practical on some of the planets and moons of the solar system. [ 119 ]
The health of the humans who may participate in a colonization venture would be subject to increased physical, mental and emotional risks.
Space colonization has been envisioned at many different locations inside and outside the Solar System , but most commonly at Mars and the Moon.
Geostationary orbit was an early issue of discussion about space colonization, with equatorial countries argueing for special rights to the orbit (see Bogota Declaration ). [ 89 ]
Space debris , particularly in low Earth orbit, has been characterized as a product of colonization by occupying space and hindering access to space through excessive pollution with debris, with drastic increases in the course of military activity and without a lack of management. [ 89 ]
Most of the delta- v budget , and thus propellant, of a launch is used bringing a spacecraft to low Earth orbit. [ 127 ] : 100 This is the main reason why Jerry Pournelle said "If you can get your ship into orbit, you're halfway to anywhere". [ 128 ] Therefore, the main advantages to constructing a space settlement in Earth orbit are accessibility to the Earth and already-existing economic motives such as space hotels and space manufacturing . However, a big disadvantage is that orbit does not host any materials that is available for exploitation. Space colonization altogether might eventually demand lifting vast amounts of payload into orbit, making thousands of daily launches potentially unsustainable. Various theoretical concepts, such as orbital rings and skyhooks , have been proposed to reduce the cost of accessing space. [ 127 ] : 142–147
The Moon is discussed as a target for colonization, due to its proximity to Earth and lower escape velocity . The Moon is reachable from Earth in three days, has a near-instant communication to Earth, with minable minerals, no atmosphere, and low gravity, making it extremely easy to ship materials and products to orbit. [ 127 ] : 175 Abundant ice is trapped in permanently shadowed craters near the poles, which could provide support for the water needs of a lunar colony, [ 129 ] though indications that mercury is also similarly trapped there may pose health concerns. [ 130 ] [ 131 ] Native precious metals , such as gold , silver , and probably platinum , are also concentrated at the lunar poles by electrostatic dust transport. [ 131 ] There are only a few materials on the Moon which have been identified to make economic sense to ship directly back to the Earth, which are helium-3 (for fusion power ) and rare-earth minerals (for electronics ). Instead, it makes more sense for these materials to be used in-space or being turned into valuable products for export. However, the Moon's lack of atmosphere provides no protection from space radiation or meteoroids, so lunar lava tubes have been proposed sites to gain protection. [ 132 ] The Moon's low surface gravity is also a concern, as it is unknown whether 1/6 g is enough to maintain human health for long periods. [ 133 ]
Since the Moon has extreme temperature swings and toxic lunar regolith , it is argued by some that the Moon will not become a place of habitation, but instead attract polluting extraction and manufacturing industries . Furthermore, it has been argued that moving these industries to the Moon could help protect the Earth's environment and allow poorer countries to be released from the shackles of neocolonialism by wealthier countries. In the space colonization framework, the Moon will be transformed into an industrial hub of the Solar System. [ 127 ] : 161–172
Interest in establishing a moonbase has increased in the 21st century as an intermediate to Mars colonization.
The European Space Agency (ESA) head Jan Woerner at the International Astronautical Congress in Bremen, Germany, in October, 2018 proposed cooperation among countries and companies on lunar capabilities, a concept referred to as Moon Village . [ 134 ]
In a December 2017 directive , the first Trump administration steered NASA to include a lunar mission on the pathway to other beyond Earth orbit (BEO) destinations. [ 135 ] [ 134 ]
In 2023, the U.S. Defense Department started a study of the necessary infrastructure and capabilities required to develop a moon-based economy over the following ten years. [ 136 ]
As of 2024, on one side, China , along with other partner countries, has announced its intention to establish the International Lunar Research Station . On the other side, the United States , in collaboration with international partners, is advancing its Artemis program , which includes plans to build Moonbases near the lunar poles, close to permanently shadowed craters , in the 2030s. The Chinese Lunar Exploration Program is seen as a means to bolster China's political influence and support its aspirations for superpower status, while the United States aims to maintain its position as the leading space power.
Another near-Earth possibility are the stable Earth–Moon Lagrange points L 4 and L 5 , at which point a space colony can float indefinitely. The L5 Society was founded to promote settlement by building space stations at these points. Gerard K. O'Neill suggested in 1974 that the stable region around L 5 could fit several thousand floating colonies, and would allow easy travel to and from the colonies due to the shallow effective potential at this point. [ 137 ]
The hypothetical colonization of Mars has received interest from public space agencies and private corporations and has received extensive treatment in science fiction writing, film, and art.
While there have been many plans for a human Mars mission , including affordable ones such as Mars Direct , none has been realized as of 2025. Both the United States and China have plans to send humans to Mars sometime in the 2040s, but these plans are not backed with hardware and funding. [ 127 ] : 219–223 However, SpaceX is currently developing Starship , a super-heavy-lift reusable launch vehicle , with a vision of sending humans to Mars. As of November 2024, the company plans to send five uncrewed Starships to Mars in either 2026 or 2028–2029 launch windows [ 138 ] and SpaceX's CEO Elon Musk has repeatingly stated his support for the Mars efforts, both financially and politically. [ 139 ]
Mars is more suitable for habitation than the Moon, with a stronger gravity, rich amount of materials needed for life, day/night cycle nearly identical to Earth, and a thin atmosphere to protect from micrometeroids . The main disadvantage of Mars compared to the Moon is the six-to-nine-month transit time and the lengthy launch window, which occurs approximately every two years. [ 127 ] : 175 Without in situ resource utilization , Mars colonization would be nearly impossible as it would require bringing thousands of tons of payload to sustain a handful of astronauts. If Martian materials can be used to make propellant (such as methane with the Sabatier process ) and supplies (such as oxygen for crews), the amount of supplies needed to bring to Mars can be greatly reduced. [ 140 ] [ 127 ] : 228–230 Even then, Mars colonies will not be economically viable in the near term, thus reasons for colonizing Mars will be mostly ideological and prestige-based, such as a desire for freedom . [ 127 ] : 267–270, 280
Mercury is rich of metals and volatiles, as well as solar energy. However, Mercury is the most energy-consuming body on the Solar System to land for spacecraft launching from Earth, and astronauts there must contend with the extreme temperature differential and radiation. [ 127 ] : 311–314
Once thought to be a volatile-depleted body like the Moon, Mercury is now known to be volatile-rich, surprisingly richer in volatiles than any other terrestrial body in the inner Solar System. [ 141 ] The planet also receives six and a half times the solar flux as the Earth/Moon system, [ 142 ] making solar energy an effective energy source; it could be harnessed through orbital solar arrays and beamed to the surface or exported to other planets. [ 143 ]
Geologist Stephen Gillett suggested in 1996, that this could make Mercury an ideal place to build and launch solar sail spacecraft, which could launch as folded "chunks" by a mass driver from Mercury's surface. Once in space, the solar sails would deploy. Solar energy for the mass driver should be easy to produce, and solar sails near Mercury would have 6.5 times the thrust they do near Earth. This could make Mercury an ideal place to acquire materials useful in building hardware to send to (and terraform) Venus. Vast solar collectors could also be built on or near Mercury to produce power for large-scale engineering activities such as laser-pushed light sails to nearby star systems. [ 144 ]
As Mercury has essentially no axial tilt, crater floors near its poles lie in eternal darkness , never seeing the Sun. They function as cold traps , trapping volatiles for geological periods. It is estimated that the poles of Mercury contain 10 14 –10 15 kg of water, likely covered by about 5.65×10 9 m 3 of hydrocarbons. This would make agriculture possible. It has been suggested that plant varieties could be developed to take advantage of the high light intensity and the long day of Mercury. The poles do not experience the significant day-night variations the rest of Mercury do, making them the best place on the planet to begin a colony. [ 142 ]
Another option is to live underground, where day-night variations would be damped enough that temperatures would stay roughly constant. There are indications that Mercury contains lava tubes , like the Moon and Mars, which would be suitable for this purpose. [ 143 ] Underground temperatures in a ring around Mercury's poles can reach room temperature on Earth, 22±1 °C; and this is achieved at depths starting from about 0.7 m. This presence of volatiles and abundance of energy has led Alexander Bolonkin and James Shifflett to consider Mercury preferable to Mars for colonization. [ 142 ] [ 145 ]
Yet a third option could be to continually move to stay on the night side, as Mercury's 176-day-long day-night cycle means that the terminator travels very slowly. [ 143 ]
Because Mercury is very dense, its surface gravity is 0.38g like Mars, even though it is a smaller planet. [ 142 ] This would be easier to adjust to than lunar gravity (0.16g), but presents advantages regarding lower escape velocity from Mercury than from Earth. [ 143 ] Mercury's proximity gives it advantages over the asteroids and outer planets, and its low synodic period means that launch windows from Earth to Mercury are more frequent than those from Earth to Venus or Mars. [ 143 ]
On the downside, a Mercury colony would require significant shielding from radiation and solar flares, and since Mercury is airless, decompression and temperature extremes would be constant risks. [ 143 ]
Though the surface of Venus is extremely hostile, habitats high above the atmosphere of Venus are fairly habitable, with temperatures ranging from 30 °C to 70 °C (86 to 158 °F) and a pressure similar to the Earth's sea level at an altitude of 50 kilometers (30 miles). [ 146 ] However, beside tourism opportunities, the economic benefit of a Venusian colony is minimal. [ 127 ] : 308–310
Asteroids can provide enough material in the form of water, air, fuel, metal, soil, and nutrients to support ten to a hundred trillion humans in space. Many asteroids contain minerals that are inheriently valuable, such as rare earths and precious metals. However, low gravity, distance from Earth and disperse nature of their orbits make it difficult to settle on small asteroids. [ 127 ] : 203, 204, 218
There have also been proposals to place robotic aerostats in the upper atmospheres of the Solar System's giant planets for exploration and possibly mining of helium-3 , which could have a very high value per unit mass as a thermonuclear fuel. [ 147 ] : 158–160 [ 148 ]
Robert Zubrin identified Saturn , Uranus and Neptune as "the Persian Gulf of the Solar System", as the largest sources of deuterium and helium-3 to drive a fusion economy, with Saturn the most important and most valuable of the three, because of its relative proximity, low radiation, and large system of moons. [ 147 ] : 161–163 On the other hand, planetary scientist John Lewis in his 1997 book Mining the Sky , insists that Uranus is the likeliest place to mine helium-3 because of its significantly shallower gravity well, which makes it easier for a laden tanker spacecraft to thrust itself away. Furthermore, Uranus is an ice giant , which would likely make it easier to separate the helium from the atmosphere.
Because Uranus has the lowest escape velocity of the four giant planets, it has been proposed as a mining site for helium-3 . [ 148 ] As Uranus is a gas giant without a viable surface, one of Uranus's natural satellites might serve as a base. [ 149 ]
It is hypothesized that one of Neptune 's satellites could be used for colonization. Triton 's surface shows signs of extensive geological activity that implies a subsurface ocean, perhaps composed of ammonia/water. [ 150 ] If technology advanced to the point that tapping such geothermal energy was possible, it could make colonizing a cryogenic world like Triton feasible, supplemented by nuclear fusion power. [ 151 ]
Human missions to the outer planets would need to arrive quickly due to the effects of space radiation and microgravity along the journey. [ 152 ] In 2012, Thomas B. Kerwick wrote that the distance to the outer planets made their human exploration impractical for now, noting that travel times for round trips to Mars were estimated at two years, and that the closest approach of Jupiter to Earth is over ten times farther than the closest approach of Mars to Earth. However, he noted that this could change with "significant advancement on spacecraft design". [ 153 ] Nuclear-thermal or nuclear-electric engines have been suggested as a way to make the journey to Jupiter in a reasonable amount of time. [ 154 ] Another possibility would be plasma magnet sails , a technology already suggested for rapidly sending a probe to Jupiter. [ 155 ] The cold would also be a factor, necessitating a robust source of heat energy for spacesuits and bases. [ 153 ] Most of the larger moons of the outer planets contain water ice , liquid water , and organic compounds that might be useful for sustaining human life. [ 156 ] [ 157 ]
Robert Zubrin has suggested Saturn, Uranus, and Neptune as advantageous locations for colonization because their atmospheres are good sources of fusion fuels, such as deuterium and helium-3 . Zubrin suggested that Saturn would be the most important and valuable as it is the closest and has an extensive satellite system. Jupiter's high gravity makes it difficult to extract gases from its atmosphere, and its strong radiation belt makes developing its system difficult. [ 158 ] On the other hand, fusion power has yet to be achieved, and fusion power from helium-3 is more difficult to achieve than conventional deuterium–tritium fusion . [ 159 ] Jeffrey Van Cleve, Carl Grillmair, and Mark Hanna instead focus on Uranus, because the delta-v required to get helium-3 from the atmosphere into orbit is half that needed for Jupiter, and because Uranus' atmosphere is five times richer in helium than Saturn's. [ 148 ]
Jupiter's Galilean moons (Io, Europa, Ganymede, and Callisto) and Saturn's Titan are the only moons that have gravities comparable to Earth's Moon. The Moon has a 0.17g gravity; Io, 0.18g; Europa, 0.13g; Ganymede, 0.15g; Callisto, 0.13g; and Titan, 0.14g. Neptune's Triton has about half the Moon's gravity (0.08g); other round moons provide even less (starting from Uranus' Titania and Oberon at about 0.04g). [ 153 ]
The Jovian system in general has particular disadvantages for colonization, including a deep gravity well . The magnetosphere of Jupiter bombards the moons of Jupiter with intense ionizing radiation [ 162 ] delivering about 36 Sv per day to unshielded colonists on Io and about 5.40 Sv per day on Europa . Exposure to about 0.75 Sv over a few days is enough to cause radiation poisoning , and about 5 Sv over a few days is fatal. [ 147 ] : 166–170
Jupiter itself, like the other gas giants, has further disadvantages. There is no accessible surface on which to land, and the light hydrogen atmosphere would not provide good buoyancy for some kind of aerial habitat as has been proposed for Venus.
Radiation levels on Io and Europa are extreme, enough to kill unshielded humans within an Earth day. [ 147 ] : 163–170 Therefore, only Callisto and perhaps Ganymede could reasonably support a human colony. Callisto orbits outside Jupiter's radiation belt. [ 153 ] Ganymede's low latitudes are partially shielded by the moon's magnetic field, though not enough to completely remove the need for radiation shielding. Both of them have available water, silicate rock, and metals that could be mined and used for construction. [ 153 ]
Although Io's volcanism and tidal heating constitute valuable resources, exploiting them is probably impractical. [ 153 ] Europa is rich in water (its subsurface ocean is expected to contain over twice as much water as all Earth's oceans together) [ 154 ] and likely oxygen, but metals and minerals would have to be imported. If alien microbial life exists on Europa, human immune systems may not protect against it. Sufficient radiation shielding might, however, make Europa an interesting location for a research base. [ 153 ] The private Artemis Project drafted a plan in 1997 to colonize Europa, involving surface igloos as bases to drill down into the ice and explore the ocean underneath, and suggesting that humans could live in "air pockets" in the ice layer. [ 163 ] [ 164 ] [ 154 ] Ganymede [ 154 ] and Callisto are also expected to have internal oceans. [ 165 ] It might be possible to build a surface base that would produce fuel for further exploration of the Solar System.
In 2003, NASA performed a study called HOPE (Revolutionary Concepts for Human Outer Planet Exploration) regarding the future exploration of the Solar System. [ 166 ] The target chosen was Callisto due to its distance from Jupiter, and thus the planet's harmful radiation. It could be possible to build a surface base that would produce fuel for further exploration of the Solar System. [ 167 ] : 21 HOPE estimated a round trip time for a crewed mission of about 2–5 years, assuming significant progress in propulsion technologies. [ 153 ]
Io is not ideal for colonization, due to its hostile environment. The moon is under influence of high tidal forces, causing high volcanic activity. Jupiter's strong radiation belt overshadows Io, delivering 36 Sv a day to the moon. The moon is also extremely dry. Io is the least ideal place for the colonization of the four Galilean moons.
Despite this, its volcanoes could be energy resources for the other moons, which are better suited to colonization.
Ganymede is the largest moon in the Solar System. Ganymede is the only moon with a magnetosphere , albeit overshadowed by Jupiter's magnetic field . Because of this magnetic field, Ganymede is one of only two Jovian moons where surface settlements would be feasible because it receives about 0.08 Sv of radiation per day. Ganymede could be terraformed. [ 161 ]
The Keck Observatory announced in 2006 that the binary Jupiter trojan 617 Patroclus , and possibly many other Jupiter trojans, are likely composed of water ice, with a layer of dust. This suggests that mining water and other volatiles in this region and transporting them elsewhere in the Solar System, perhaps via the proposed Interplanetary Transport Network , may be feasible in the not-so-distant future. This could make colonization of the Moon , Mercury and main-belt asteroids more practical.
Saturn's radiation belt is much weaker than Jupiter's, so radiation is less of an issue here. Dione, Rhea, Titan, and Iapetus all orbit outside the radiation belt, and Titan's thick atmosphere would adequately shield against cosmic radiation. [ 158 ]
Saturn has seven moons large enough to be round : in order of increasing distance from Saturn, they are Mimas , Enceladus , Tethys , Dione , Rhea , Titan , and Iapetus .
The small moon Enceladus is also of interest, having a subsurface ocean that is separated from the surface by only tens of meters of ice at the south pole, compared to kilometers of ice separating the ocean from the surface on Europa. Volatile and organic compounds are present there, and the moon's high density for an ice world (1.6 g/cm 3 ) indicates that its core is rich in silicates. [ 158 ]
On 9 March 2006, NASA 's Cassini space probe found possible evidence of liquid water on Enceladus . [ 168 ] According to that article, "pockets of liquid water may be no more than tens of meters below the surface." These findings were confirmed in 2014 by NASA. This means liquid water could be collected much more easily and safely on Enceladus than, for instance, on Europa (see above). Discovery of water, especially liquid water, generally makes a celestial body a much more likely candidate for colonization. An alternative model of Enceladus's activity is the decomposition of methane/water clathrates – a process requiring lower temperatures than liquid water eruptions. The higher density of Enceladus indicates a larger than Saturnian average silicate core that could provide materials for base operations.
Authors like Robert Zubrin have offered that Saturn is the most important and valuable of the four gas giants in the Solar System , because of its relative proximity, low radiation, and excellent system of moons. He named Titan as the best candidate on which to establish a base to exploit the resources of the Saturn system. [ 147 ] : 161–163 He pointed out that Titan possesses an abundance of all the elements necessary to support life, saying "In certain ways, Titan is the most hospitable extraterrestrial world within our solar system for human colonization." [ 147 ] : 163–166
To consider a colony on Saturn 's largest moon Titan , protection against the extreme cold must be a primary consideration. [ 169 ] Titan offers a gravity of approximately 1/7 of Earth gravity, in the same range as Earth's Moon. Atmospheric pressure at the surface of the planet is about 1.5x that of the surface of the Earth; there is however, no oxygen present in the environment. The atmosphere is about 95% nitrogen and 5% methane. [ 170 ] Some estimates suggest that abundant energy resources on Titan could power a colony with a population size of the United States. [ 171 ]
The dense atmosphere of Titan shields the surface from radiation and would make any structural failures problematic, rather than catastrophic. With an oxygen mask and thermal clothing protection, humans could roam Titan's surface in the dim sunlight. Or, given the low gravity and dense atmosphere, they could float above it in a balloon or on personal wings. [ 172 ] [ 173 ]
Beyond the Solar System colonization targets might be identified in the surrounding stars . The main difficulty is the vast distances to other stars.
To reach such targets travel times of millennia would be necessary, with current technology. At average speeds of even 0.1% of the speed of light ( c ) interstellar expansion across the entire Milky Way galaxy would take up to one-half of the Sun's galactic orbital period of ~240,000,000 years, which is comparable to the timescale of other galactic processes. [ 175 ] Due to fundamental energy and reaction mass consideration such speeds would be with current technology limited to small spaceships. If humanity would gain access to a large amount of energy, on the order of the mass-energy of entire planets, it may become possible to construct spaceships with Alcubierre drives . [ 176 ]
The following are plausible approaches with current technology:
The distances between galaxies are on the order of a million times farther than those between the stars, and thus intergalactic colonization would involve voyages of millions of years via special self-sustaining methods. [ 184 ] [ 185 ] [ 186 ]
Building colonies in space would require access to water, food, space, people, construction materials, energy, transportation, communications , life support , simulated gravity , radiation protection, migration, governance and capital investment. It is likely the colonies would be located near the necessary physical resources. The practice of space architecture seeks to transform spaceflight from a heroic test of human endurance to a normality within the bounds of comfortable experience. As is true of other frontier-opening endeavors, the capital investment necessary for space colonization would probably come from governments, [ 187 ] an argument made by John Hickman [ 188 ] and Neil deGrasse Tyson . [ 189 ]
In space settlements, a life support system must recycle or import all the nutrients without "crashing." The closest terrestrial analogue to space life support is possibly that of a nuclear submarine . Nuclear submarines use mechanical life support systems to support humans for months without surfacing, and this same basic technology could presumably be employed for space use. However, nuclear submarines run "open loop"—extracting oxygen from seawater, and typically dumping carbon dioxide overboard, although they recycle existing oxygen. [ 190 ] Another commonly proposed life-support system is a closed ecological system such as Biosphere 2 . [ 191 ]
Although there are many physical, mental, and emotional health risks for future colonists and pioneers, solutions have been proposed to correct these problems. Mars500 , HI-SEAS , and SMART-OP represent efforts to help reduce the effects of loneliness and confinement for long periods of time. Keeping contact with family members, celebrating holidays, and maintaining cultural identities all had an impact on minimizing the deterioration of mental health. [ 192 ] There are also health tools in development to help astronauts reduce anxiety, as well as helpful tips to reduce the spread of germs and bacteria in a closed environment. [ 193 ] Radiation risk may be reduced for astronauts by frequent monitoring and focusing work to minimize time away from shielding. [ 126 ] Future space agencies can also ensure that every colonist would have a mandatory amount of daily exercise to prevent degradation of muscle. [ 126 ]
Cosmic rays and solar flares create a lethal radiation environment in space. In orbit around certain planets with magnetospheres (including Earth), the Van Allen belts make living above the atmosphere difficult. To protect life, settlements must be surrounded by sufficient mass to absorb most incoming radiation, unless magnetic or plasma radiation shields are developed. [ 194 ] In the case of Van Allen belts, these could be drained using orbiting tethers [ 195 ] or radio waves. [ 196 ]
Passive mass shielding of four metric tons per square meter of surface area will reduce radiation dosage to several mSv or less annually, well below the rate of some populated high natural background areas on Earth. [ 197 ] This can be leftover material (slag) from processing lunar soil and asteroids into oxygen, metals, and other useful materials. However, it represents a significant obstacle to manoeuvering vessels with such massive bulk (mobile spacecraft being particularly likely to use less massive active shielding). [ 194 ] Inertia would necessitate powerful thrusters to start or stop rotation, or electric motors to spin two massive portions of a vessel in opposite senses. Shielding material can be stationary around a rotating interior.
The monotony and loneliness that comes from a prolonged space mission can leave astronauts susceptible to cabin fever or having a psychotic break. Moreover, lack of sleep, fatigue, and work overload can affect an astronaut's ability to perform well in an environment such as space where every action is critical. [ 198 ]
A range of different models of transplanetary or extraterrestrial governance have been sketched or proposed. Often envisioning the need for a fresh or independent extraterrestrial governance, particularly in the void left by the contemporarily criticized lack of space governance and inclusivity.
It has been argued that space colonialism would, similarly to terrestrial settler colonialism , produce colonial national identities. [ 199 ]
Federalism has been studied as a remedy of such distant and autonomous communities. [ 200 ]
Space activity is legally based on the Outer Space Treaty , the main international treaty. But space law has become a larger legal field, which includes other international agreements such as the significantly less ratified Moon Treaty and diverse national laws.
The Outer Space Treaty established the basic ramifications for space activity in article one: "The exploration and use of outer space, including the Moon and other celestial bodies, shall be carried out for the benefit and in the interests of all countries, irrespective of their degree of economic or scientific development, and shall be the province of all mankind." And continued in article two by stating: "Outer space, including the Moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means." [ 201 ]
The development of international space law has revolved much around outer space being defined as common heritage of mankind . The Magna Carta of Space presented by William A. Hyman in 1966 framed outer space explicitly not as terra nullius but as res communis , which subsequently influenced the work of the United Nations Committee on the Peaceful Uses of Outer Space . [ 89 ] [ 202 ]
Space colonization can roughly be said to be possible when the necessary methods of space colonization become cheap enough (such as space access by cheaper launch systems) to meet the cumulative funds that have been gathered for the purpose, in addition to estimated profits from commercial use of space . [ 203 ]
Although there are no immediate prospects for the large amounts of money required for space colonization to be available given traditional launch costs, [ 204 ] there is some prospect of a radical reduction to launch costs in the 2010s, which would consequently lessen the cost of any efforts in that direction. With a published price of US$56.5 million per launch of up to 13,150 kg (28,990 lb) payload [ 205 ] to low Earth orbit, SpaceX Falcon 9 rockets are already the "cheapest in the industry". [ 206 ] Advancements currently being developed as part of the SpaceX reusable launch system development program to enable reusable Falcon 9s "could drop the price by an order of magnitude, sparking more space-based enterprise, which in turn would drop the cost of access to space still further through economies of scale." [ 206 ] If SpaceX is successful in developing the reusable technology, it would be expected to "have a major impact on the cost of access to space", and change the increasingly competitive market in space launch services. [ 207 ]
The President's Commission on Implementation of United States Space Exploration Policy suggested that an inducement prize should be established, perhaps by government, for the achievement of space colonization, for example by offering the prize to the first organization to place humans on the Moon and sustain them for a fixed period before they return to Earth. [ 208 ]
Experts have debated on the possible use of money and currencies in societies that will be established in space. The Quasi Universal Intergalactic Denomination, or QUID, is a physical currency made from a space-qualified polymer PTFE for inter-planetary travelers. QUID was designed for the foreign exchange company Travelex by scientists from Britain's National Space Centre and the University of Leicester. [ 209 ] Other possibilities include the incorporation of cryptocurrency as the primary form of currency, as suggested by Elon Musk . [ 210 ]
Human spaceflight has enabled only temporarily relocating a few privileged people and no permanent space migrants.
The societal motivation for space migration has been questioned as rooted in colonialism, questioning the fundamentals and inclusivity of space colonization. Highlighting the need to reflect on such socio-economic issues beside the technical challenges for implementation. [ 211 ] [ 212 ]
Colonies on the Moon, Mars, asteroids, or the metal-rich planet Mercury , could extract local materials. The Moon is deficient in volatiles such as argon , helium and compounds of carbon , hydrogen and nitrogen . The LCROSS impacter was targeted at the Cabeus crater which was chosen as having a high concentration of water for the Moon. A plume of material erupted in which some water was detected. Mission chief scientist Anthony Colaprete estimated that the Cabeus crater contains material with 1% water or possibly more. [ 213 ] Water ice should also be in other permanently shadowed craters near the lunar poles. Although helium is present only in low concentrations on the Moon, where it is deposited into regolith by the solar wind, an estimated million tons of He-3 exists over all. [ 214 ] It also has industrially significant oxygen , silicon , and metals such as iron , aluminium , and titanium .
Launching materials from Earth is expensive, so bulk materials for colonies could come from the Moon, a near-Earth object (NEO), Phobos , or Deimos . The benefits of using such sources include: a lower gravitational force, no atmospheric drag on cargo vessels, and no biosphere to damage. Many NEOs contain substantial amounts of metals. Underneath a drier outer crust (much like oil shale ), some other NEOs are inactive comets which include billions of tons of water ice and kerogen hydrocarbons, as well as some nitrogen compounds. [ 215 ]
Farther out, Jupiter's Trojan asteroids are thought to be rich in water ice and other volatiles. [ 216 ]
Recycling of some raw materials would almost certainly be necessary.
Solar energy in orbit is abundant, reliable, and is commonly used to power satellites today. There is no night in free space, and no clouds or atmosphere to block sunlight. Light intensity obeys an inverse-square law . So the solar energy available at distance d from the Sun is E = 1367/ d 2 W/m 2 , where d is measured in astronomical units (AU) and 1367 watts/m 2 is the energy available at the distance of Earth's orbit from the Sun, 1 AU. [ 217 ]
In the weightlessness and vacuum of space, high temperatures for industrial processes can easily be achieved in solar ovens with huge parabolic reflectors made of metallic foil with very lightweight support structures. Flat mirrors to reflect sunlight around radiation shields into living areas (to avoid line-of-sight access for cosmic rays, or to make the Sun's image appear to move across their "sky") or onto crops are even lighter and easier to build.
Large solar power photovoltaic cell arrays or thermal power plants would be needed to meet the electrical power needs of the settlers' use. In developed parts of Earth, electrical consumption can average 1 kilowatt/person (or roughly 10 megawatt-hours per person per year.) [ 218 ] These power plants could be at a short distance from the main structures if wires are used to transmit the power, or much farther away with wireless power transmission .
A major export of the initial space settlement designs was anticipated to be large solar power satellites (SPS) that would use wireless power transmission (phase-locked microwave beams or lasers emitting wavelengths that special solar cells convert with high efficiency) to send power to locations on Earth, or to colonies on the Moon or other locations in space. For locations on Earth, this method of getting power is extremely benign, with zero emissions and far less ground area required per watt than for conventional solar panels. Once these satellites are primarily built from lunar or asteroid-derived materials, the price of SPS electricity could be lower than energy from fossil fuel or nuclear energy; replacing these would have significant benefits such as the elimination of greenhouse gases and nuclear waste from electricity generation. [ 219 ]
Transmitting solar energy wirelessly from the Earth to the Moon and back is also an idea proposed for the benefit of space colonization and energy resources. Physicist Dr. David Criswell, who worked for NASA during the Apollo missions, proposed the idea of using power beams to transfer energy from space. These beams, microwaves with a wavelength of about 12 cm, would be almost untouched as they travel through the atmosphere. They could also be aimed at more industrial areas to keep away from humans or animal activities. [ 220 ] This would allow for safer and more reliable methods of transferring solar energy.
In 2008, scientists were able to send a 20 watt microwave signal from a mountain on the island of Maui to the island of Hawaii. [ 221 ] Since then JAXA and Mitsubishi have been working together on a $21 billion project to place satellites in orbit which could generate up to 1 gigawatt of energy. [ 222 ] These are the next advancements being done today to transmit energy wirelessly for space-based solar energy.
However, the value of SPS power delivered wirelessly to other locations in space will typically be far higher than to Earth. Otherwise, the means of generating the power would need to be included with these projects and pay the heavy penalty of Earth launch costs. Therefore, other than proposed demonstration projects for power delivered to Earth, [ 223 ] the first priority for SPS electricity is likely to be locations in space, such as communications satellites, fuel depots or "orbital tugboat" boosters transferring cargo and passengers between low Earth orbit (LEO) and other orbits such as geosynchronous orbit (GEO), lunar orbit or highly-eccentric Earth orbit (HEEO). [ 71 ] : 132 The system will also rely on satellites and receiving stations on Earth to convert the energy into electricity. Because this energy can be transmitted easily from dayside to nightside, power would be reliable 24/7. [ 224 ]
Nuclear power is sometimes proposed for colonies located on the Moon or on Mars, as the supply of solar energy is too discontinuous in these locations; the Moon has nights of two Earth weeks in duration. Mars has nights, relatively high gravity, and an atmosphere featuring large dust storms to cover and degrade solar panels. Also, Mars' greater distance from the Sun (1.52 astronomical units, AU) means that only 1/1.52 2 or about 43% of the solar energy is available at Mars compared with Earth orbit. [ 225 ] Another method would be transmitting energy wirelessly to the lunar or Martian colonies from solar power satellites (SPSs) as described above; the difficulties of generating power in these locations make the relative advantages of SPSs much greater there than for power beamed to locations on Earth. In order to also be able to fulfill the requirements of a Moon base and energy to supply life support, maintenance, communications, and research, a combination of both nuclear and solar energy may be used in the first colonies. [ 220 ]
For both solar thermal and nuclear power generation in airless environments, such as the Moon and space, and to a lesser extent the very thin Martian atmosphere, one of the main difficulties is dispersing the inevitable heat generated . This requires fairly large radiator areas.
Space manufacturing could enable self-replication. Some consider it the ultimate goal because it would allow an exponential increase in colonies, while eliminating costs to, and dependence on, Earth. [ 226 ] It could be argued that the establishment of such a colony would be Earth's first act of self-replication . [ 227 ] Intermediate goals include colonies that expect only information from Earth (science, engineering, entertainment) and colonies that just require periodic supply of light weight objects, such as integrated circuits , medicines, genetic material and tools.
In 2002, the anthropologist John H. Moore estimated [ 228 ] that a population of 150–180 would permit a stable society to exist for 60 to 80 generations—equivalent to 2,000 years.
Assuming a journey of 6,300 years, the astrophysicist Frédéric Marin and the particle physicist Camille Beluffi calculated that the minimum viable population for a generation ship to reach Proxima Centauri would be 98 settlers at the beginning of the mission (then the crew will breed until reaching a stable population of several hundred settlers within the ship). [ 229 ] [ 230 ]
In 2020, Jean-Marc Salotti proposed a method to determine the minimum number of settlers to survive on an extraterrestrial world. It is based on the comparison between the required time to perform all activities and the working time of all human resources. For Mars, 110 individuals would be required. [ 231 ]
Several private companies have announced plans toward the colonization of Mars . Among entrepreneurs leading the call for space colonization are Elon Musk, Dennis Tito and Bas Lansdorp . [ 232 ] [ 233 ]
Organizations that advocate for space colonization include:
Many space agencies build "testbeds", which are facilities on Earth for testing advanced life support systems, but these are designed for long duration human spaceflight , not permanent colonization.
Space colonization is a recurring theme in science fiction . [ 245 ] NASA began to assess space colonization issues as early as 1975 with their Space Settlements Design Study. The report directly acknowledges the foundation of various ideas for colonization in science fiction. It quotes author Robert Salkeld and highlights the role of the precursors of science fiction alongside the founders of astronautics, where for example Jules Verne rubs shoulders with Constantin Tsiolkovsky. [ 246 ]
Indeed, colonization as a fictional theme and colonization as a research project are not independent. Research feeds fiction and fiction sometimes inspires research. Many of the most fascinating ideas in science originated not in the laboratory but in the minds of such science fiction writers as Arthur C. Clarke and Ray Bradbury. Clarke's 1945 article on communications satellites was the original idea behind modern communications satellites. [ 247 ] Bradbury's The Martian Chronicles explores the exploration and settlement of Mars and has been attributed as the main inspiration behind NASA's many missions to Mars. [ 248 ] Communicators and tricorders from the science fiction of Star Trek are said to be inspirations for cell phones and wireless medical triage devices. [ 249 ] [ 250 ] Fiction inspired innovation and invention to develop new technologies. Communications, governance principles, and advanced technological devices, all speculated by science fiction, are all precursors to survival of an extraterrestrial colony. [ 251 ] The European Space Agency ITSF project (Innovative Technologies in Science Fiction for Space Applications) study offers similar consideration for the cross-fertilization between fiction and science. [ 252 ]
Science fiction writer Norman Spinrad highlights the role of science fiction as a visionary force that spawned the conquest of space, a term he believes betrays its imperialist tendencies, and the colonization of space. [ 253 ] He also shows that political scientist and science fiction writer Jerry Pournelle, in wanting to revive the conquest of space for this purpose in the early 1980s, actually launched the Reagan administration 's Strategic Defense Initiative project, which he considers a failure, because instead of the military program reviving the space program, the opposite happens: the $40 billion cost of the program is actually taken away from the construction of a base on the Moon. [ 253 ]
One of the great names in science fiction, Arthur C. Clarke , a supporter of Marshall Savage's ideas, announced in a 2001 article, the date appearing in one of his most famous titles 2001: A Space Odyssey , that by 2057 there would be humans on the Moon, Mars , Europa, Ganymede, Titan and in orbit around Venus, Neptune and Pluto. [ 254 ] Contemporary science fiction has extended the colonization vision further. The TV series The Expanse which is based on a series of novels of the same name by James S. A. Corey, addresses the politics and conflict of humanity hundreds of years in the future after it has colonized the solar system and Mars has become an independent military power. In Theresa Hutchin's essay on the series in 2021, comparisons are drawn between the fiction of the story and the reality of current corporate led development of space exploration activities. [ 255 ]
Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion Arm → Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow ( → ) may be read as "within" or "part of". | https://en.wikipedia.org/wiki/Space_colonization |
A space command is a military organization with responsibility for space operations and warfare. A space command is typically a joint organization or organized within a larger military branch and is distinct from a fully independent space force . The world's first space command, the United States' Air Force Space Command was established in 1982 and later became the United States Space Force in 2019.
In the United States and Soviet Union, the early military space programs were managed by individual military services. In the United States, the Air Force and its various major commands were responsible for military space operations, however Air Defense Command was responsible for the majority of space operations. In 1967, it was redesignated Aerospace Defense Command to emphasize its increased space role. Following the inactivation of Aerospace Defense Command in 1980, U.S. space forces were briefly organized under Strategic Air Command , before being organized into Space Command , which was activated in 1982. Space Command, which was the first space command in the world, was redesignated Air Force Space Command in 1985 to distinguish it from the joint U.S. Space Command. The Army and Navy, both possessing smaller space capabilities, both had their own space commands, with Naval Space Command activated in 1983 and Army Space Command activated in 1988. [ 1 ]
Soviet space forces were organized under the Strategic Rocket Forces ' Central Directorate of Space Assets , which was activated in 1964, before being upgraded to the Main Directorate of Space Assets in 1970. [ 2 ] The Soviet Air Defense Forces ' Anti-Ballistic Missile and Anti-Space Defense Forces were activated in 1967 and remained a part from the Strategic Missile Forces' space forces. [ 3 ]
In 1959, fearing U.S. Air Force dominance of the military space program, the United States Navy 's chief of naval operations , Admiral Arleigh Burke , proposed the creation of a Defense Astronautical Agency to manage U.S. military space operations. The proposal of a joint space command did not come to pass until 1985, when United States Space Command was activated to manage U.S. military space activities, overseeing Air Force Space Command, Naval Space Command, and Army Space Command. [ 4 ] The Soviet Union also rose the profile of their space forces, moving the Main Directorate of Space Assets from the Strategic Missile Forces to the Soviet Armed Forces General Staff in 1982, before upgrading it into the Chief Directorate of Space Assets and placing it directly in the Ministry of Defence in 1986. [ 2 ] In 1981, the U.S.–Canadian North American Air Defense Command was redesignated as the North American Aerospace Defense Command , emphasizing its space role. [ 4 ]
Following the collapse of the Soviet Union, the Soviet space forces were reorganized into Russia's Military Space Forces and the Russian Air Defence Forces ' Rocket and Space Defence Troops . In 1997, both were merged into the Strategic Rocket Forces, before being split out in 2001 as the Russian Space Forces , which was an independent troops, but not a full independent service. [ 5 ] U.S. Army space forces also underwent reorganization, with the Army Space Command being merged with its missile defense forces to form Army Space and Strategic Defense Command in 1992, being redesignated as Army Space and Missile Defense Command in 1997. [ 6 ]
With the September 11 Attacks , U.S. space forces were sidelined with the change in focus to the War on Terror . In 2002, U.S. Space Command was inactivated and its joint space responsibilities were transferred to United States Strategic Command and Naval Space Command was inactivated, transferring most of its capabilities to Air Force Space Command. Starting in 2005, U.S. Strategic Command began to organize its space forces semi–independently, first as Joint Space Operations , then in 2006 as the Joint Functional Component Command for Space , and in 2017 the Joint Force Space Component Command . [ 7 ] In 2019, the United States reestablished United States Space Command , and in 2020, reorganized Air Force Space Command into the United States Space Force , becoming a full independent military branch, with Space Operations Command serving as its primary space command. To support U.S. Space Command, in 2020 the Navy created Navy Space Command , with United States Tenth Fleet as its operational arm, out of Fleet Cyber Command. [ 8 ]
Recognizing the growing importance of space operations, France created the Joint Space Command within the French Air Force in 2010 to manage its space capabilities, reorganizing it into the French Space Command as part of a larger transformation of the French Air Force into the French Air and Space Force in 2019. [ 9 ] Russia also reorganized their Space Forces, merging together their Space Forces and air defense elements of the Russian Air Force to form the Russian Aerospace Defense Forces in 2011, moving the space elements into the Aerospace Defense Forces' Russian Space Command . [ 10 ] In 2015, it reorganized its space forces again, merging the Russian Air Force and Russian Aerospace Defense Forces to form the Russian Aerospace Forces and recreating the Russian Space Forces as a sub-branch, replacing the Russian Space Command. [ 11 ] In 2015, the People's Liberation Army also centralized their space forces as part of the new Strategic Support Force 's Space Systems Department. [ 12 ] In 2018, India centralized its space forces in a tri-service Defence Space Agency , which is expected to become a full command in the coming years. [ 13 ] [ 14 ] In 2020, Iran also unveiled their own Space Command under the Islamic Revolutionary Guard Corps Aerospace Force . [ 15 ] In 2020, NATO also established a Space Centre as part of Allied Air Command . [ 16 ] In 2021, the British Armed Forces established United Kingdom Space Command as a joint command under the leadership of the Royal Air Force , taking over space responsibilities from United Kingdom Strategic Command . [ 17 ] In 2021, the Royal Australian Air Force Chief of Air Force announced the intended creation of an Australian Space Command. [ 18 ] | https://en.wikipedia.org/wiki/Space_command |
Space debris (also known as space junk , space pollution , [ 1 ] space waste , space trash , space garbage , or cosmic debris [ 2 ] ) are defunct human-made objects in space – principally in Earth orbit – which no longer serve a useful function. These include derelict spacecraft (nonfunctional spacecraft and abandoned launch vehicle stages), mission-related debris, and particularly numerous in-Earth orbit, fragmentation debris from the breakup of derelict rocket bodies and spacecraft. In addition to derelict human-made objects left in orbit, space debris includes fragments from disintegration, erosion , or collisions ; solidified liquids expelled from spacecraft; unburned particles from solid rocket motors; and even paint flecks. Space debris represents a risk to spacecraft. [ 3 ]
Space debris is typically a negative externality . It creates an external cost on others from the initial action to launch or use a spacecraft in near-Earth orbit, a cost that is typically not taken into account nor fully accounted for [ 4 ] [ 5 ] by the launcher or payload owner. [ 6 ] [ 1 ] [ 7 ]
Several spacecraft, both crewed and un-crewed, have been damaged or destroyed by space debris. The measurement, mitigation, and potential removal of debris is conducted by some participants in the space industry . [ 8 ]
As of April 2025 [update] , the European Space Agency 's Space Environment statistics reported 40230 artificial objects in orbit above the Earth regularly tracked by Space Surveillance Networks and maintained in their catalogue. [ 8 ]
However, these are just the objects large enough to be tracked and in an orbit that makes tracking possible. Satellite debris that is in a Molniya orbit , such as the Kosmos Oko series, might be too high above the Northern Hemisphere to be tracked. [ 9 ] As of January 2019 [update] , more than 128 million pieces of debris smaller than 1 cm (0.4 in), about 900,000 pieces of debris 1–10 cm, and around 34,000 of pieces larger than 10 cm (3.9 in) were estimated to be in orbit around the Earth. [ 8 ] When the smallest objects of artificial space debris (paint flecks, solid rocket exhaust particles, etc.) are grouped with micrometeoroids , they are together sometimes referred to by space agencies as MMOD (Micrometeoroid and Orbital Debris).
Collisions with debris have become a hazard to spacecraft. The smallest objects cause damage akin to sandblasting , especially to solar panels and optics like telescopes or star trackers that cannot easily be protected by a ballistic shield . [ 10 ]
Below 2,000 km (1,200 mi), pieces of debris are denser than meteoroids . Most are dust from solid rocket motors, surface erosion debris like paint flakes, and frozen coolant from Soviet nuclear-powered satellites . [ 11 ] [ 12 ] [ 13 ] For comparison, the International Space Station (ISS) orbits in the 300–400 kilometres (190–250 mi) range, while the two most recent large debris events, the 2007 Chinese antisatellite weapon test and the 2009 satellite collision , occurred at 800 to 900 kilometres (500 to 560 mi) altitude. [ 14 ] The ISS has Whipple shielding to resist damage from small MMOD. However, known debris with a collision chance over 1/10,000 are avoided by maneuvering the station.
According to a report published in January 2025, scientists are encouraging vigilance around closing airspace more often to avoid collisions between airline flights and space debris reentering the earth's atmosphere amid an increasing volume of both. [ 15 ] Following a destructive event, the explosion of SpaceX's Starship Flight 7 on January 16, 2025, the U.S. Federal Aviation Administration (FAA) slowed air traffic in the area where debris was falling. This prompted several aircraft to request diversion because of low fuel levels while they were holding outside the Debris Response Area. [ 16 ]
Space debris began to accumulate in Earth orbit with the launch of the first artificial satellite , Sputnik 1 , into orbit in October, 1957. But even before this event, humans might have produced ejecta that became space debris, as in the August 1957 Pascal B test . [ 17 ] [ 18 ] Going back further, natural ejecta from Earth has entered orbit.
After the launch of Sputnik, the North American Aerospace Defense Command (NORAD) began compiling a database (the Space Object Catalog ) of all known rocket launches and objects reaching orbit, including satellites, protective shields and upper-stages of launch vehicles . NASA later published modified versions of the database in two-line element sets , [ 19 ] and beginning in the early 1980s, they were republished in the CelesTrak bulletin board system . [ 20 ]
NORAD trackers who fed the database were aware of other objects in orbit, many of which were the result of in-orbit explosions. [ 21 ] Some were deliberately caused during anti-satellite weapon (ASAT) testing in the 1960s, and others were the result of rocket stages blowing up in orbit as leftover propellant expanded and ruptured their tanks. More detailed databases and tracking systems were gradually developed, including Gabbard diagrams, to improve the modeling of orbital evolution and decay. [ 22 ] [ 23 ]
When the NORAD database became publicly available during the 1970s, [ clarification needed ] techniques developed for the asteroid-belt were applied to the study [ by whom? ] of known artificial satellite objects. [ citation needed ]
Time and natural gravitational/atmospheric effects help to clear space debris. A variety of technological approaches have also been proposed, though most have not been implemented. A number of scholars have observed that systemic factors, political, legal, economic, and cultural, are the greatest impediment to the cleanup of near-Earth space. There has been little commercial incentive to reduce space debris since the associated cost does not accrue to the entity producing it. Rather, the cost falls to all users of the space environment who benefit from space technology and knowledge. A number of suggestions for increasing incentives to reduce space debris have been made. These would encourage companies to see the economic benefit of reducing debris more aggressively than existing government mandates require. [ 24 ] In 1979, NASA founded the Orbital Debris Program to research mitigation measures for space debris in Earth orbit. [ 25 ] [ 26 ]
During the 1980s, NASA and other U.S. groups attempted to limit the growth of debris. One trial solution was implemented by McDonnell Douglas in 1981 for the Delta launch vehicle by having the booster move away from its payload and vent any propellant remaining in its tanks. [ 27 ] This eliminated one source for pressure buildup in the tanks which had previously caused them to explode and create additional orbital debris. [ 28 ] Other countries were slower to adopt this measure and, due especially to a number of launches by the Soviet Union , the problem grew throughout the decade. [ 29 ]
A new battery of studies followed as NASA, NORAD, and others attempted to better understand the orbital environment, with each adjusting the number of pieces of debris in the critical-mass zone upward. Although in 1981 (when Schefter's article was published) the number of objects was estimated at 5,000, [ 21 ] new detectors in the Ground-based Electro-Optical Deep Space Surveillance system found new objects. By the late 1990s, it was thought that most of the 28,000 launched objects had already decayed and about 8,500 remained in orbit. [ 30 ] By 2005 this was adjusted upward to 13,000 objects, [ 31 ] and a 2006 study increased the number to 19,000 as a result of an ASAT and a satellite collision. [ 32 ] In 2011, NASA said that 22,000 objects were being tracked. [ 33 ]
A 2006 NASA model suggested that if no new launches took place, the environment would retain the then-known population until about 2055, when it would increase on its own. [ 34 ] [ 35 ] Richard Crowther of Britain's Defence Evaluation and Research Agency said in 2002 that he believed the cascade would begin about 2015. [ 36 ] The National Academy of Sciences, summarizing the professional view, noted widespread agreement that two bands of LEO space – 900 to 1,000 km (620 mi) and 1,500 km (930 mi) – were already past critical density. [ 37 ]
In the 2009 CEAS European Air and Space Conference, University of Southampton researcher Hugh Lewis predicted that the threat from space debris would rise 50 percent in the next decade and quadruple in the next 50 years. As of 2009 [update] , more than 13,000 close calls were tracked weekly. [ 38 ]
A 2011 report by the U.S. National Research Council warned NASA that the amount of orbiting space debris was at a critical level. According to some computer models, the amount of space debris "has reached a tipping point, with enough currently in orbit to continually collide and create even more debris, raising the risk of spacecraft failures." The report called for international regulations limiting debris and research of disposal methods. [ 39 ]
As of January 2019 [update] there were estimated to be over 128 million pieces of debris smaller than 1 cm (0.39 in), and approximately 900,000 pieces between 1 and 10 cm. The count of large debris (defined as 10 cm across or larger [ 46 ] ) was 34,000 in 2019, [ 8 ] and at least 37,000 by June 2023. [ 47 ] The technical measurement cut-off [ clarification needed ] is c. 3 mm (0.12 in). [ 48 ]
As of 2020 [update] , there were 8,000 metric tons of debris in orbit, a figure that is expected to increase. [ 49 ]
In the orbits nearest to Earth – less than 2,000 km (1,200 mi) orbital altitude , referred to as low-Earth orbit (LEO) – there have traditionally been few "universal orbits" that keep a number of spacecraft in particular rings (in contrast to GEO , a single orbit that is widely used by over 500 satellites ). There is currently 85% pollution in LEO (Low Earth Orbit). This was beginning to change in 2019, and several companies began to deploy the early phases of satellite internet constellations , which will have many universal orbits in LEO with 30 to 50 satellites per orbital plane and altitude. Traditionally, the most populated LEO orbits have been a number of Sun-synchronous satellites that keep a constant angle between the Sun and the orbital plane , making Earth observation easier with consistent sun angle and lighting. Sun-synchronous orbits are polar , meaning they cross over the polar regions. LEO satellites orbit in many planes, typically up to 15 times a day, causing frequent approaches between objects. The density of satellites – both active and derelict – is much higher in LEO. [ 50 ]
Orbits are affected by gravitational perturbations (which in LEO include unevenness of the Earth's gravitational field due to variations in the density of the planet), and collisions can occur from any direction. The average impact speed of collisions in Low Earth Orbit is 10 km/s with maximums reaching above 14 km/s due to orbital eccentricity . [ 51 ] The 2009 satellite collision occurred at a closing speed of 11.7 km/s (26,000 mph), [ 52 ] creating over 2,000 large debris fragments. [ 53 ] These debris cross many other orbits and increase debris collision risk.
It is theorized that a sufficiently large collision of spacecraft could potentially lead to a cascade effect, or even make some particular low Earth orbits effectively unusable for long term use by orbiting satellites, a phenomenon known as the Kessler syndrome . [ 54 ] The theoretical effect is projected to be a theoretical runaway chain reaction of collisions that could occur, exponentially increasing the number and density of space debris in low-Earth orbit, and has been hypothesized to ensue beyond some critical density. [ 55 ]
Crewed space missions are mostly at 400 km (250 mi) altitude and below, where air drag helps clear zones of fragments. The upper atmosphere is not a fixed density at any particular orbital altitude; it varies as a result of atmospheric tides and expands or contracts over longer time periods as a result of space weather . [ 56 ] These longer-term effects can increase drag at lower altitudes; the 1990s expansion was a factor in reduced debris density. [ 57 ] Another factor was fewer launches by Russia; the Soviet Union made most of their launches in the 1970s and 1980s. [ 58 ] : 7
At higher altitudes, where air drag is less significant, orbital decay takes longer. Slight atmospheric drag , lunar perturbations , Earth's gravity perturbations, solar wind , and solar radiation pressure can gradually bring debris down to lower altitudes (where it decays), but at very high altitudes this may take centuries. [ 59 ] Although high-altitude orbits are less commonly used than LEO and the onset of the problem is slower, the numbers progress toward the critical threshold more quickly. [ contradictory ] [ page needed ] [ 60 ]
Many communications satellites are in geostationary orbits (GEO), clustering over specific targets and sharing the same orbital path. Although velocities are low between GEO objects, when a satellite becomes derelict (such as Telstar 401 ) it assumes a geosynchronous orbit; its orbital inclination increases about 0.8° and its speed increases about 160 km/h (99 mph) per year. Impact velocity peaks at about 1.5 km/s (0.93 mi/s). Orbital perturbations cause longitude drift of the inoperable spacecraft and precession of the orbital plane. Close approaches (within 50 meters) are estimated at one per year. [ 61 ] The collision debris pose less short-term risk than from a LEO collision, but the satellite would likely become inoperable. Large objects, such as solar-power satellites , are especially vulnerable to collisions. [ 62 ]
Although the ITU now requires proof a satellite can be moved out of its orbital slot at the end of its lifespan, studies suggest this is insufficient. [ 63 ] Since GEO orbit is too distant to accurately measure objects under 1 m (3 ft 3 in), the nature of the problem is not well known. [ 64 ] Satellites could be moved to empty spots in GEO, requiring less maneuvering and making it easier to predict future motion. [ 65 ] Satellites or boosters in other orbits, especially stranded in geostationary transfer orbit , are an additional concern due to their typically high crossing velocity.
Despite efforts to reduce risk, spacecraft collisions have occurred. The European Space Agency telecom satellite Olympus-1 was struck by a meteoroid on 11 August 1993 and eventually moved to a graveyard orbit . [ 66 ] On 29 March 2006, the Russian Express-AM11 communications satellite was struck by an unknown object and rendered inoperable; [ 67 ] its engineers had enough contact time with the satellite to send it into a graveyard orbit.
In 1958, the United States of America launched Vanguard I into a medium Earth orbit (MEO). As of October 2009 [update] , it, the upper stage of Vanguard 1's launch rocket and associated piece of debris, are the oldest surviving artificial space objects still in orbit and are expected to be until after the year 2250. [ 70 ] [ 71 ] As of May 2022 [update] , the Union of Concerned Scientists listed 5,465 operational satellites from a known population of 27,000 pieces of orbital debris tracked by NORAD. [ 72 ] [ 73 ]
Occasionally satellites are left in orbit when they're no longer useful. Many countries require that satellites go through passivation at the end of their life. The satellites are then either boosted into a higher, graveyard orbit or a lower, short-term orbit. Nonetheless, satellites that have been properly moved to a higher orbit have an eight-percent probability of puncture and coolant release over a 50-year period. The coolant freezes into droplets of solid sodium-potassium alloy, creating more debris. [ 11 ] [ 74 ]
Despite the use of passivation, or prior to its standardization, many satellites and rocket bodies have exploded or broken apart on orbit. In February 2015, for example, the USAF Defense Meteorological Satellite Program Flight 13 (DMSP-F13) exploded on orbit, creating at least 149 debris objects, which were expected to remain in orbit for decades. [ 75 ] Later that same year, NOAA-16 which had been decommissioned after an anomaly in June 2014, broke apart on orbit into at least 275 pieces. [ 76 ] For older programs, such as the Soviet-era Meteor 2 and Kosmos satellites, design flaws resulted in numerous break-ups – at least 68 by 1994 – following decommissioning, resulting in more debris. [ 40 ]
In addition to the accidental creation of debris, some has been made intentionally through the deliberate destruction of satellites. This has been done as a test of anti-satellite or anti-ballistic missile technology, or to prevent a sensitive satellite from being examined by a foreign power. [ 40 ] The United States has conducted over 30 anti-satellite weapons tests (ASATs), the Soviet Union / Russia has performed at least 27, China has performed 10 and India has performed at least one. [ 77 ] [ 78 ] The most recent ASATs were the Chinese interception of FY-1C , Russian trials of its PL-19 Nudol , the American interception of USA-193 and India's interception of an unstated live satellite . [ 78 ]
Space debris includes a glove lost by astronaut Ed White on the first American space-walk (EVA), a camera lost by Michael Collins near Gemini 10 , a thermal blanket lost during STS-88, garbage bags jettisoned by Soviet cosmonauts during Mir 's 15-year life, [ 79 ] a wrench, and a toothbrush. [ 80 ] Sunita Williams of STS-116 lost a camera during an EVA. During an STS-120 EVA to reinforce a torn solar panel, a pair of pliers was lost, and in an STS-126 EVA, Heidemarie Stefanyshyn-Piper lost a briefcase-sized tool bag. [ 81 ]
A significant portion of debris is due to rocket upper stages (e.g. the Inertial Upper Stage ) breaking up due to decomposition of unvented fuel. [ 82 ] The first such instance involved the launch of the Transit-4a satellite in 1961. Two hours after insertion, the Ablestar upper stage exploded. Even boosters that don't break apart can be a problem. A major known impact event involved an (intact) Ariane booster. [ 58 ] : 2
Although NASA and the United States Air Force now require upper-stage passivation, other launchers – such as the Chinese and Russian space agencies – do not. Lower stages, like the Space Shuttle's solid rocket boosters or the Apollo program 's Saturn IB launch vehicles, do not reach orbit. [ 83 ]
Examples:
A former source of debris was anti-satellite weapons (ASATs) testing by the U.S. and Soviet Union during the 1960s and 1970s. North American Aerospace Defense Command (NORAD) only collected data for Soviet tests, and debris from U.S. tests were identified subsequently. [ 96 ] By the time the debris problem was understood, widespread ASAT testing had ended. The U.S. Program 437 was shut down in 1975. [ 97 ]
The U.S. restarted their ASAT programs in the 1980s with the Vought ASM-135 ASAT . A 1985 test destroyed a 1-tonne (2,200 lb) satellite orbiting at 525 km (326 mi), creating thousands of debris larger than 1 cm (0.39 in). At this altitude, atmospheric drag decayed the orbit of most debris within a decade. A de facto moratorium followed the test. [ 98 ]
China's government was condemned for the military implications and the amount of debris from the 2007 anti-satellite missile test, [ 99 ] the largest single space debris incident in history (creating over 2,300 pieces golf-ball size or larger, over 35,000 1 cm (0.4 in) or larger, and one million pieces 1 mm (0.04 in) or larger). The target satellite orbited between 850 km (530 mi) and 882 km (548 mi), the portion of near-Earth space most densely populated with satellites. [ 100 ] Since atmospheric drag is low at that altitude, the debris is slow to return to Earth, and in June 2007 NASA's Terra environmental spacecraft maneuvered to avoid impact from the debris. [ 101 ] Brian Weeden, U.S. Air Force officer and Secure World Foundation staff member, noted that the 2007 Chinese satellite explosion created an orbital debris of more than 3,000 separate objects that then required tracking. [ 102 ]
On 20 February 2008, the U.S. launched an SM-3 missile from the USS Lake Erie to destroy a defective U.S. spy satellite thought to be carrying 450 kg (1,000 lb) of toxic hydrazine propellant. The event occurred at about 250 km (155 mi), and the resulting debris has a perigee of 250 km (155 mi) or lower. [ 103 ] The missile was aimed to minimize the amount of debris, which (according to Pentagon Strategic Command chief Kevin Chilton) had decayed by early 2009. [ 104 ]
On 27 March 2019, Indian Prime Minister Narendra Modi announced that India shot down one of its own LEO satellites with a ground-based missile. He stated that the operation, part of Mission Shakti , would defend the country's interests in space. Afterwards, US Air Force Space Command announced they were tracking 270 new pieces of debris but expected the number to grow as data collection continues. [ 105 ]
On 15 November 2021, the Russian Defense Ministry destroyed Kosmos 1408 [ 106 ] orbiting at around 450 km, creating "more than 1,500 pieces of trackable debris and hundreds of thousands of pieces of un-trackable debris" according to the US State Department. [ 107 ]
The vulnerability of satellites to debris and the possibility of attacking LEO satellites to create debris clouds has triggered speculation that it is possible for countries unable to make a precision attack. [ clarification needed ] An attack on a satellite of 10 t (22,000 lb) or more would heavily damage the LEO environment. [ 98 ]
Space junk can be a hazard to active satellites and spacecraft. It has been suggested that Earth orbit could even become impassable if the risk of collision becomes too great. [ 108 ] [ failed verification ]
However, since the risk to spacecraft increases with exposure to high debris densities, it is more accurate to say that LEO would be rendered unusable by orbiting craft. The threat to craft passing through LEO to reach a higher orbit would be much lower owing to the short time span of the crossing.
Although spacecraft are typically protected by Whipple shields , solar panels, which are exposed to the Sun, wear from low-mass impacts. Even small impacts can produce a cloud of plasma which is an electrical risk to the panels. [ 109 ]
Satellites are believed to have been destroyed by micrometeorites and (small) orbital debris (MMOD). The earliest suspected loss was of Kosmos 1275 , which disappeared on 24 July 1981 (a month after launch). Kosmos contained no volatile fuel, therefore, there appeared to be nothing internal to the satellite which could have caused the destructive explosion which took place. However, the case has not been proven and another hypothesis forwarded is that the battery exploded. Tracking showed it broke up, into 300 objects. [ 110 ]
Many impacts have been confirmed since. For example, on 24 July 1996, the French microsatellite Cerise was hit by fragments of an Ariane 1 H-10 upper-stage booster which exploded in November 1986. [ 58 ] : 2 On 29 March 2006, the Russian Ekspress-AM11 communications satellite was struck by an unknown object and rendered inoperable. [ 67 ] On 13 October 2009, Terra suffered a single battery cell failure anomaly and a battery heater control anomaly which were subsequently considered likely the result of an MMOD strike. [ 111 ] On 12 March 2010, Aura lost power from one-half of one of its 11 solar panels and this was also attributed to an MMOD strike. [ 112 ] On 22 May 2013, GOES 13 was hit by an MMOD which caused it to lose track of the stars that it used to maintain an operational attitude. It took nearly a month for the spacecraft to return to operation. [ 113 ]
The first major satellite collision occurred on 10 February 2009. The 950 kg (2,090 lb) derelict satellite Kosmos 2251 and the operational 560 kg (1,230 lb) Iridium 33 collided, 500 mi (800 km) [ 114 ] over northern Siberia. The relative speed of impact was about 11.7 km/s (7.3 mi/s), or about 42,120 km/h (26,170 mph). [ 115 ] Both satellites were destroyed, creating thousands of pieces of new smaller debris, with legal and political liability issues unresolved even years later. [ 116 ] [ 117 ] [ 118 ] On 22 January 2013, BLITS (a Russian laser-ranging satellite) was struck by debris suspected to be from the 2007 Chinese anti-satellite missile test , changing both its orbit and rotation rate. [ 119 ]
Satellites sometimes [ clarification needed ] perform Collision Avoidance Maneuvers and satellite operators may monitor space debris as part of maneuver planning. For example, in January 2017, the European Space Agency altered the orbit of one of its three [ 120 ] Swarm mission spacecraft, based on data from the US Joint Space Operations Center , to lower the risk of collision from Cosmos-375, a derelict Russian satellite. [ 121 ]
Crewed flights are particularly vulnerable to space debris conjunctions in the orbital path of the spacecraft. Occasional avoidance maneuvers or longer-term space debris wear have affected the space shuttle, the MIR space station, and the International Space Station.
From the early shuttle missions, NASA used NORAD space monitoring capabilities to assess the shuttle's orbital path for debris. In the 1980s, this consumed a large proportion of NORAD capacity. [ 28 ] The first collision-avoidance maneuver occurred during STS-48 , in September,1991, [ 122 ] a seven-second thruster burn to avoid debris from the derelict satellite Kosmos 955 . [ 123 ] Similar maneuvers were executed on missions 53, 72 and 82. [ 122 ]
One of the earliest events to publicize the debris problem occurred on Space Shuttle Challenger 's second flight, STS-7. A fleck of paint struck its front window, creating a pit over 1 mm (0.04 in) wide. On STS-59 in 1994, Endeavour 's front window was pitted about half its depth. Minor debris impacts increased from 1998. [ 124 ]
Window chipping and minor damage to thermal protection system tiles (TPS) were already common by the 1990s. The Shuttle was later flown tail-first to take a greater proportion of the debris load on the engines and rear cargo bay, which are not used in orbit or during descent, and thus are less critical for post-launch operation. When flying attached to the ISS , a shuttle was flipped around so the better-armoured station shielded the orbiter. [ 125 ]
A NASA 2005 study concluded that debris accounted for approximately half of the overall risk to the Shuttle. [ 125 ] [ 126 ] Executive-level decision to proceed was required if the catastrophic impact was more likely than 1 in 200. On a normal (low-orbit) mission to the ISS, the risk was approximately 1 in 300, but the Hubble telescope repair mission was flown at the higher orbital altitude of 560 km (350 mi) where the risk was initially calculated at a 1-in-185 (due in part to the 2009 satellite collision). A re-analysis with better debris numbers reduced the estimated risk to 1 in 221, and the mission went ahead. [ 127 ]
Debris incidents continued on later Shuttle missions. During STS-115 in 2006, a fragment of circuit board bored a small hole through the radiator panels in Atlantis ' s cargo bay. [ 128 ] On STS-118 in 2007, debris blew a bullet-like hole through Endeavour ' s radiator panel. [ 129 ]
Impact wear was notable on the Soviet space station Mir , since it remained in space for long periods with its original solar module panels. [ 130 ] [ 131 ]
The ISS also uses Whipple shielding to protect its interior from minor debris. [ 132 ] However, exterior portions (notably its solar panels ) cannot be protected easily. In 1999, the ISS panels were predicted to degrade approximately 0.23% in four years due to the "sandblasting" effect of impacts with small orbital debris. [ 133 ] An avoidance maneuver is typically performed for the ISS if "there is a greater than one-in-10,000 chance of a debris strike". [ 134 ] As of January 2014 [update] , there have been sixteen maneuvers in the fifteen years the ISS had been in orbit. [ 134 ] By 2019, over 1,400 meteoroid and orbital debris (MMOD) impacts had been recorded on the ISS. [ 135 ]
As another method to reduce the risk to humans on board, ISS operational management asked the crew to shelter in the Soyuz on three occasions due to late debris-proximity warnings. In addition to the sixteen thruster firings and three Soyuz-capsule shelter orders, one attempted maneuver was not completed due to not having the several days' warning necessary to upload the maneuver timeline to the station's computer. [ 134 ] [ 136 ] [ 137 ] A March 2009 event involved debris believed to be a 10 cm (3.9 in) piece of the Kosmos 1275 satellite. [ 138 ] In 2013, the ISS operations management did not make a maneuver to avoid any debris, after making a record four debris maneuvers the previous year. [ 134 ]
The Kessler syndrome, [ 140 ] [ 141 ] proposed by NASA scientist Donald J. Kessler in 1978, is a theoretical scenario in which the density of objects in low Earth orbit (LEO) is high enough that collisions between objects could cause a cascade effect where each collision generates space debris that increases the likelihood of further collisions. [ 142 ] He further theorized that one implication, if this were to occur, is that the distribution of debris in orbit could render space activities and the use of satellites in specific orbital ranges economically impractical for many generations. [ 142 ]
The growth in the number of objects as a result of the late-1990s studies sparked debate in the space community on the nature of the problem and the earlier dire warnings. According to Kessler's 1991 derivation and 2001 updates, [ 143 ] the LEO environment in the 1,000 km (620 mi) altitude range should be cascading. However, only one major satellite collision incident occurred: the 2009 satellite collision between Iridium 33 and Cosmos 2251. The lack of obvious short-term cascading has led to speculation that the original estimates overstated the problem. [ 144 ] According to Kessler in 2010 however, a cascade may not be obvious until it is well advanced, which might take years. [ 145 ]
Although most debris burns up in the atmosphere, larger debris objects can reach the ground intact. According to NASA, an average of one cataloged piece of debris has fallen back to Earth each day for the past 50 years. Despite their size, there has been no significant property damage from the debris. [ 146 ] Burning up in the atmosphere contributes to air pollution. [ 147 ] Numerous small cylindrical tanks from space objects have been found, designed to hold fuel or gasses. [ 148 ]
Radar and optical detectors such as lidar are the main tools for tracking space debris. Although objects under 10 cm (4 in) have reduced orbital stability, debris as small as 1 cm can be tracked, [ 149 ] [ 150 ] however determining orbits to allow re-acquisition is difficult. Most debris remain unobserved. The NASA Orbital Debris Observatory tracked space debris with a 3 m (10 ft) liquid mirror transit telescope . [ 151 ] FM Radio waves can detect debris, after reflecting off them onto a receiver. [ 152 ] Optical tracking may be a useful early-warning system on spacecraft. [ 153 ]
The U.S. Strategic Command keeps a catalog of known orbital objects, using ground-based radar and telescopes, and a space-based telescope (originally to distinguish from hostile missiles). The 2009 edition listed about 19,000 objects. [ 154 ] Other data come from the ESA Space Debris Telescope , TIRA , [ 155 ] the Goldstone , Haystack , [ 156 ] and EISCAT radars and the Cobra Dane phased array radar, [ 157 ] to be used in debris-environment models like the ESA Meteoroid and Space Debris Terrestrial Environment Reference (MASTER).
Returned space hardware is a valuable source of information on the directional distribution and composition of the (sub-millimetre) debris flux. The LDEF satellite deployed by mission STS-41-C Challenger and retrieved by STS-32 Columbia spent 68 months in orbit to gather debris data. The EURECA satellite, deployed by STS-46 Atlantis in 1992 and retrieved by STS-57 Endeavour in 1993, was also used for debris study. [ 158 ]
The solar arrays of Hubble were returned by missions STS-61 Endeavour and STS-109 Columbia , and the impact craters studied by the ESA to validate its models. Materials returned from Mir were also studied, notably the Mir Environmental Effects Payload (which also tested materials intended for the ISS [ 159 ] ). [ 160 ] [ 161 ]
A debris cloud resulting from a single event is studied with scatter plots known as Gabbard diagrams, where the perigee and apogee of fragments are plotted with respect to their orbital period . Gabbard diagrams of the early debris cloud prior to the effects of perturbations, if the data were available, are reconstructed. They often include data on newly observed, as yet uncatalogued fragments. Gabbard diagrams can provide insights into the features of the fragmentation, the direction and point of impact. [ 23 ] [ 162 ]
An average of about one tracked object per day has been dropping out of orbit for the past 50 years, [ 163 ] averaging almost three objects per day at solar maximum (due to the heating and expansion of the Earth's atmosphere), but one about every three days at solar minimum , usually five and a half years later. [ 163 ] In addition to natural atmospheric effects, corporations, academics and government agencies have proposed plans and technology to deal with space debris, but as of November 2014 [update] , most of these are theoretical, and there is no business plan for debris reduction. [ 24 ]
A number of scholars have also observed that institutional factors – political, legal, economic, and cultural "rules of the game" – are the greatest impediment to the cleanup of near-Earth space. There is little commercial incentive to act, since costs are not assigned to polluters , though a number of technological solutions have been suggested. [ 24 ] However, effects to date are limited. In the US, governmental bodies have been accused of backsliding on previous commitments to limit debris growth, "let alone tackling the more complex issues of removing orbital debris." [ 164 ] The different methods for removal of space debris have been evaluated by the Space Generation Advisory Council , including French astrophysicist Fatoumata Kébé . [ 165 ]
In May 2024, a NASA report from the Office of Technology, Policy, and Strategy (OTPS) introduced new methods for addressing orbital debris. The report, titled Cost and Benefit Analysis of Mitigating, Tracking, and Remediating Orbital Debris , [ 166 ] provided a comprehensive analysis comparing the cost-effectiveness of over ten different actions, including shielding spacecraft, tracking smaller debris, and removing large debris. By evaluating these measures in economic terms, the study aims to inform cost-effective strategies for debris management, highlighting that methods like rapid deorbiting of defunct spacecraft can significantly reduce risks in space.
There is no international treaty minimizing space debris. However, the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) published voluntary guidelines in 2007, [ 167 ] using a variety of earlier national regulatory attempts at developing standards for debris mitigation. As of 2008, the committee was discussing international "rules of the road" to prevent collisions between satellites. [ 168 ] By 2013, a number of national legal regimes existed, [ 169 ] [ 170 ] [ 171 ] typically instantiated in the launch licenses that are required for a launch in all spacefaring nations . [ 172 ]
The U.S. issued a set of standard practices for civilian (NASA) and military ( DoD and USAF) orbital-debris mitigation in 2001. [ 173 ] [ 174 ] [ 170 ] The standard envisioned disposal for final mission orbits in one of three ways: 1) atmospheric reentry where even with "conservative projections for solar activity, atmospheric drag will limit the lifetime to no longer than 25 years after completion of mission;" 2) maneuver to a "storage orbit:" move the spacecraft to one of four very broad parking orbit ranges (2,000–19,700 km (1,200–12,200 mi), 20,700–35,300 km (12,900–21,900 mi), above 36,100 km (22,400 mi), or out of Earth orbit completely and into any heliocentric orbit ; 3) "Direct retrieval: Retrieve the structure and remove it from orbit as soon as practicable after completion of mission." [ 169 ] The standard articulated in option 1, which is the standard applicable to most satellites and derelict upper stages, has come to be known as the "25-year rule". [ 175 ] The US updated the Orbital Debris Mitigation Standard Practices (ODMSP) in December 2019, but made no change to the 25-year rule even though "[m]any in the space community believe that the timeframe should be less than 25 years." [ 176 ] There is no consensus however on what any new timeframe might be. [ 176 ]
In 2002, the European Space Agency (ESA) worked with an international group to promulgate a similar set of standards, also with a "25-year rule" applying to most Earth-orbit satellites and upper stages. Space agencies in Europe began to develop technical guidelines in the mid-1990s, and ASI , UKSA , CNES , DLR and ESA signed a "European Code of Conduct" in 2006, [ 171 ] which was a predecessor standard to the ISO international standard work that would begin the following year. In 2008, ESA further developed "its own "Requirements on Space Debris Mitigation for Agency Projects" which "came into force on 1 April 2008." [ 171 ]
Germany and France have posted bonds to safeguard property from debris damage. [ clarification needed ] [ 177 ] The "direct retrieval" option (option no. 3 in the US "standard practices" above) has rarely been done by any spacefaring nation (exception, USAF X-37 ) or commercial actor since the earliest days of spaceflight due to the cost and complexity of achieving direct retrieval, but the ESA has scheduled a 2026 demonstration mission ( ClearSpace-1 ) to do this with a single small 94 kg (207 lb) satellite ( PROBA-1 ) [ 178 ] at a projected cost of €120 million not including the launch costs. [ 179 ]
By 2006, the Indian Space Research Organization (ISRO) had developed a number of technical means of debris mitigation (upper stage passivation, propellant reserves for movement to graveyard orbits, etc.) for ISRO launch vehicles and satellites, and was actively contributing to inter-agency debris coordination and the efforts of the UN COPUOS committee. [ 180 ]
In 2007, the ISO began preparing an international standard for space-debris mitigation. [ 181 ] By 2010, ISO had published "a comprehensive set of space system engineering standards aimed at mitigating space debris. [with primary requirements] defined in the top-level standard, ISO 24113 ." By 2017, the standards were nearly complete. However, these standards are not binding on any party by ISO or any international jurisdiction. They are simply available for use in voluntary ways. They "can be adopted voluntarily by a spacecraft manufacturer or operator, or brought into effect through a commercial contract between a customer and supplier, or used as the basis for establishing a set of national regulations on space debris mitigation." [ 175 ]
The voluntary ISO standard also adopted the "25-year rule" for the "LEO protected region" below 2,000 km (1,200 mi) altitude that has been previously (and still is, as of 2019 [update] ) used by the US, ESA, and UN mitigation standards, and identifies it as "an upper limit for the amount of time that a space system shall remain in orbit after its mission is completed. Ideally, the time to deorbit should be as short as possible (i.e., much shorter than 25 years)". [ 175 ]
Holger Krag of the European Space Agency states that as of 2017 there is no binding international regulatory framework with no progress occurring at the respective UN body in Vienna. [ 108 ]
As of the 2010s, several technical approaches to the mitigation of the growth of space debris are typically undertaken, yet no comprehensive legal regime or cost assignment structure is in place to reduce space debris in the way that terrestrial pollution has reduced since the mid-20th century.
To avoid excessive creation of artificial space debris, many – but not all – satellites launched to above-low-Earth-orbit are launched initially into elliptical orbits with perigees inside Earth's atmosphere so the orbit will quickly decay and the satellites then will be destroyed upon reentry into the atmosphere. Other methods are used for spacecraft in higher orbits. These include passivation of the spacecraft at the end of its useful life; as well as the use of upper stages that can reignite to decelerate the stage to intentionally deorbit it, often on the first or second orbit following payload release; satellites that can, if they remain healthy for years, deorbit themselves from the lower orbits around Earth. Other satellites (such as many CubeSats) in low orbits below approximately 400 km (250 mi) orbital altitude depend on the energy-absorbing effects of the upper atmosphere to reliably deorbit a spacecraft within weeks or months.
Increasingly, spent upper stages in higher orbits – orbits for which low-delta-v deorbit is not possible, or not planned for – and architectures that support satellite passivation, are passivated at end of life. This removes any internal energy contained in the vehicle at the end of its mission or useful life. While this does not remove the debris of the now derelict rocket stage or satellite itself, it does substantially reduce the likelihood of the spacecraft destructing and creating many smaller pieces of space debris, a phenomenon that was common in many of the early generations of US and Soviet [ 74 ] spacecraft.
Upper stage passivation (e.g. of Delta boosters [ 28 ] ) achieved by releasing residual propellants reduces debris from orbital explosions; however even as late as 2011, not all upper stages implement this practice. [ 183 ] SpaceX used the term "propulsive passivation" for the final maneuver of their six-hour demonstration mission ( STP-2 ) of the Falcon 9 second stage for the US Air Force in 2019, but did not define what all that term encompassed. [ 184 ]
With a "one-up, one-down" launch-license policy for Earth orbits, launchers would rendezvous with, capture, and de-orbit a derelict satellite from approximately the same orbital plane. [ 185 ] Another possibility is the robotic refueling of satellites. Experiments have been flown by NASA, [ 186 ] and SpaceX is developing large-scale on-orbit propellant transfer technology. [ 187 ]
Another approach to debris mitigation is to explicitly design the mission architecture to leave the rocket second-stage in an elliptical geocentric orbit with a low-perigee, thus ensuring rapid orbital decay and avoiding long-term orbital debris from spent rocket bodies. Such missions will often complete the payload placement in a final orbit by the use of low-thrust electric propulsion or with the use of a small kick stage to circularize the orbit. The kick stage itself may be designed with the excess-propellant capability to be able to self-deorbit. [ 188 ]
Although the ITU requires geostationary satellites to move to a graveyard orbit at the end of their lives, the selected orbital areas do not sufficiently protect GEO lanes from debris. [ 63 ] Rocket stages (or satellites) with enough propellant may make a direct, controlled de-orbit, or if this would require too much propellant, a satellite may be brought to an orbit where atmospheric drag would cause it to eventually de-orbit. This was done with the French Spot-1 satellite , reducing its atmospheric re-entry time from a projected 200 years to about 15 by lowering its altitude from 830 km (516 mi) to about 550 km (342 mi). [ 189 ] [ 190 ]
The Iridium constellation – 95 communication satellites launched during the five-year period between 1997 and 2002 – provides a set of data points on the limits of self-removal. The satellite operator – Iridium Communications – remained operational over the two-decade life of the satellites (albeit with a company name change through a corporate bankruptcy during the period) and, by December 2019, had "completed disposal of the last of its 65 working legacy satellites." [ 191 ] However, this process left 30 satellites with a combined mass of (20,400 kg (45,000 lb), or nearly a third of the mass of this constellation) in LEO orbits at approximately 700 km (430 mi) altitude, where self-decay is quite slow. Of these satellites, 29 simply failed during their time in orbit and were thus unable to self-deorbit, while one – Iridium 33 – was involved in the 2009 satellite collision with the derelict Russian military satellite Kosmos-2251 . [ 191 ] No contingency plan was laid for the removal of satellites that were unable to remove themselves. In 2019, the CEO of Iridium, Matt Desch, said that Iridium would be willing to pay an active-debris-removal company to deorbit its remaining first-generation satellites if it were possible for an unrealistically low cost, say " US$10,000 per deorbit, but [he] acknowledged that price would likely be far below what a debris-removal company could realistically offer. 'You know at what point [it's] a no-brainer, but [I] expect the cost is really in the millions or tens of millions, at which price I know it doesn't make sense. ' " [ 191 ]
Passive methods of increasing the orbital decay rate of spacecraft debris have been proposed. Instead of rockets, an electrodynamic tether could be attached to a spacecraft at launch; at the end of its lifetime, the tether would be rolled out to slow the spacecraft. [ 192 ] Other proposals include a booster stage with a sail-like attachment [ 193 ] and a large, thin, inflatable balloon envelope. [ 194 ]
In late December 2022, ESA successfully carried out a demonstration of a breaking sail-based satellite deorbiter, ADEO , which could be used by mitigation measures and is part of ESA's Zero Debris Initiative. Around one year earlier, China also tested a drag sail. [ 195 ] [ 196 ]
A variety of approaches have been proposed, studied, or had ground subsystems built to use other spacecraft to remove existing space debris.
A consensus of speakers at a meeting in Brussels in October 2012, organized by the Secure World Foundation (a U.S. think tank) and the French International Relations Institute, [ 197 ] reported that removal of the largest debris would be required to prevent the risk to spacecraft becoming unacceptable in the foreseeable future (without any addition to the inventory of dead spacecraft in LEO). To date in 2019, removal costs and legal questions about ownership and the authority to remove defunct satellites have stymied national or international action. Current space law retains ownership of all satellites with their original operators, even debris or spacecraft which are defunct or threaten active missions. [ 198 ]
Multiple companies made plans in the late 2010s to conduct external removal on their satellites in mid-LEO orbits. For example, OneWeb planned to use onboard self-removal as "plan A" for satellite deorbiting at the end of life, but if a satellite were unable to remove itself within one year of end of life, OneWeb would implement "plan B" and dispatch a reusable (multi-transport mission) space tug to attach to the satellite at an already built-in capture target via a grappling fixture, to be towed to a lower orbit and released for re-entry. [ 199 ] [ 200 ]
A well-studied solution uses a remotely controlled vehicle to rendezvous with, capture, and return debris to a central station. [ 201 ] One such system is Space Infrastructure Servicing, a commercially developed refueling depot and service spacecraft for communications satellites in geosynchronous orbit originally scheduled for a 2015 launch. [ 202 ] The SIS would be able to "push dead satellites into graveyard orbits." [ 203 ] The Advanced Common Evolved Stage family of upper stages is being designed with a high leftover-propellant margin (for derelict capture and de-orbit) and in-space refueling capability for the high delta-v required to de-orbit heavy objects from geosynchronous orbit. [ 185 ] A tug-like satellite to drag debris to a safe altitude for it to burn up in the atmosphere has been researched. [ 204 ] When debris is identified the satellite creates a difference in potential between the debris and itself, then using its thrusters to move itself and the debris to a safer orbit.
A variation of this approach is for the remotely controlled vehicle to rendezvous with debris, capture it temporarily to attach a smaller de-orbit satellite and drag the debris with a tether to the desired location. The "mothership" would then tow the debris-smallsat combination for atmospheric entry or move it to a graveyard orbit. One such system is the proposed Busek ORbital DEbris Remover (ORDER) , which would carry over 40 SUL (satellite on umbilical line) de-orbit satellites and propellant sufficient for their removal. [ 24 ]
On 7 January 2010 Star, Incorporated reported that it received a contract from the Space and Naval Warfare Systems Command for a feasibility study of the ElectroDynamic Debris Eliminator (EDDE) propellantless spacecraft for space-debris removal. [ 205 ] In February 2012 the Swiss Space Center at École Polytechnique Fédérale de Lausanne announced the Clean Space One project, a nanosatellite demonstration project for matching orbit with a defunct Swiss nanosatellite, capturing it and de-orbiting together. [ 206 ] The mission has seen several evolutions to reach a pac-man inspired capture model. [ 207 ] In 2013, Space Sweeper with Sling-Sat (4S), a grappling satellite which captures and ejects debris was studied. [ 208 ] [ needs update ] In 2022, a Chinese satellite, SJ-21, grabbed an unused satellite and "threw" it into an orbit with a lower risk for it to collide. [ 209 ] [ 210 ]
In December 2019, the European Space Agency awarded the first contract to clean up space debris. The €120 million mission dubbed ClearSpace-1 (a spinoff from the EPFL project) is slated to launch in 2026. It aims to remove the 94 kg PROBA-1 satellite from orbit. [ 178 ] A "chaser" will grab the junk with four robotic arms and drag it down to Earth's atmosphere where both will burn up. [ 179 ]
The laser broom uses a ground-based laser to ablate the front of the debris, producing a rocket-like thrust that slows the object. With continued application, the debris would fall enough to be influenced by atmospheric drag. [ 211 ] [ 212 ] During the late 1990s, the U.S. Air Force's Project Orion was a laser-broom design. [ 213 ] Although a test-bed device was scheduled to launch on a Space Shuttle in 2003, international agreements banning powerful laser testing in orbit limited its use to measurements. [ 214 ] The 2003 Space Shuttle Columbia disaster postponed the project and according to Nicholas Johnson, chief scientist and program manager for NASA's Orbital Debris Program Office, "There are lots of little gotchas in the Orion final report. There's a reason why it's been sitting on the shelf for more than a decade." [ 215 ]
The momentum of the laser-beam photons could directly impart a thrust on the debris sufficient to move small debris into new orbits out of the way of working satellites. NASA research in 2011 indicates that firing a laser beam at a piece of space junk could impart an impulse of 1 mm (0.039 in) per second, and keeping the laser on the debris for a few hours per day could alter its course by 200 m (660 ft) per day. [ 216 ] One drawback is the potential for material degradation; the energy may break up the debris, adding to the problem. [ 217 ] A similar proposal places the laser on a satellite in Sun-synchronous orbit, using a pulsed beam to push satellites into lower orbits to accelerate their reentry. [ 24 ] A proposal to replace the laser with an Ion Beam Shepherd has been made, [ 218 ] and other proposals use a foamy ball of aerogel or a spray of water, [ 219 ] inflatable balloons, [ 220 ] electrodynamic tethers , [ 221 ] electroadhesion , [ 222 ] and dedicated anti-satellite weapons. [ 223 ]
On 28 February 2014, Japan Aerospace Exploration Agency (JAXA) launched a test "space net" satellite. The launch was an operational test only. [ 224 ] In December 2016 the country sent a space junk collector via Kounotori 6 to the ISS by which JAXA scientists experimented to pull junk out of orbit using a tether. [ 225 ] [ 226 ] The system failed to extend a 700-meter tether from a space station resupply vehicle that was returning to Earth. [ 227 ] [ 228 ] On 6 February the mission was declared a failure and leading researcher Koichi Inoue told reporters that they "believe the tether did not get released". [ 229 ]
Between 2012 and 2018, the European Space Agency was working on the design of a mission to remove large space debris from orbit using mechanical tentacles or nets. The mission, e.Deorbit , had an objective to remove debris heavier than 4,000 kilograms (8,800 lb) from LEO. [ 230 ] Several capture techniques were studied, including a net, a harpoon, and a combination robot arm and clamping mechanism. [ 231 ] Funding of the mission was stopped in 2018 in favor of the ClearSpace-1 mission, which is currently under development.
The RemoveDEBRIS mission plan is to test the efficacy of several ADR technologies on mock targets in low Earth orbit. In order to complete its planned experiments the platform is equipped with a net, a harpoon, a laser ranging instrument, a dragsail, and two CubeSats (miniature research satellites). [ 232 ] The mission was launched on 2 April 2018. [ 233 ]
Metal processing technologies to melt space debris and transform it into other useful form factors are developed by CisLunar Industries . Their system uses electromagnetic heating to melt metal and shape it into metal wire, sheet metal, and metal fuel. [ 234 ]
A propulsion system dubbed the Neumann Drive has been developed in Adelaide , South Australia , and first sent into space in June 2023. Metal space junk is converted into fuel rods , which can be plugged into the Neumann Drive, "basically converting the solid metal propellant into plasma". The Drive will be used by American space companies which already carry nets or robotic arms to capture orbital waste. The thruster enables these satellites to return to Earth with the waste they have collected, allowing it to be melted down to make more fuel. [ 47 ]
With the rapid development of the computer and digitalization industries, more countries and companies have engaged in space activities since the turn of the 21st century. The tragedy of the commons is an economic theory referring to a situation where maximizing self-interest through using a shared resource can lead to the resource degradation shared by all. [ 235 ] Based on the theory, individuals' rational action in space will lead to an irrational collective result: orbits crowded with debris. As a common-pool resource , the Earth's orbits, especially LEO and GEO that accommodate most satellites, are nonexcludable and rivalrous . [ 236 ]
To address the tragedy and ensure space sustainability , many technical approaches have been developed. In terms of governance mechanisms, a top-down centralized one is less suitable to tackle the complex debris problem due to the increasing number of space actors. [ 237 ] Instead, a polycentric form of governance developed by Elinor Ostrom may work in space. [ 238 ] In the process of promoting the polycentric network, there are some existing barriers needed to be dealt with.
As orbital debris is a global problem affecting both spacefaring and non-spacefaring nations, it is necessary to be handled in a worldwide context. [ 235 ] Because of the complexity and dynamics of object movements like spacecraft, debris, meteorites, etc., many countries and regions including the United States, Europe, Russia, and China have developed their space situational awareness (SSA) to avoid potential threats in space or plan actions in advance. [ 239 ] To an extent, SSA plays a role in tracking space debris. In order to build a powerful SSA system, there are two prerequisites: international cooperation and exchange of information and data. [ 239 ] However, limitations exist in spite of the improving data quality over the past decades. Some space powers are not willing to share the information that they have collected, and those, such as the U.S., that have shared the data keep parts of it secret. [ 240 ] Instead of joining in a coordinated way, a great deal of SSA programs and national databases run parallel to each other with some overlaps, hindering the formation of a collaborative monitoring system. [ 240 ]
Some private actors are also trying to establish SSA systems. For example, the Space Data Association (SDA) formed in 2009 is a non-governmental entity. It currently consists of 21 global satellite operators and 4 executive members: Eutelsat , Inmarsat , Intelsat , and SES . SDA is a non-profit platform, aiming to avoid radio interference and space collisions through pooling data from operators independently. [ 239 ] Researchers suggest that it is essential to establish an international center for exchanging information on space debris because SSA networks do not completely equal debris tracking systems – the former ones focus more on active and threatening objects in space. [ 241 ] In terms of debris populations and defunct satellites, few operators have provided data. [ 241 ]
In a polycentric governance network, a resource that cannot be holistically monitored is less likely to be well managed. [ 240 ] Both insufficient transnational cooperation and information sharing bring resistance to addressing the debris problem. There is a long way to go to build a global network that covers complete data and has strong interconnection and interoperability.
With the commercialization of satellites and space, the private sector is getting more interested in space activities. For example, SpaceX is planning to create a network of around 12,000 small satellites that can transmit high-speed internet to any place in the world. [ 242 ] The proportion of commercial spacecraft has increased from 4.6% in the 1980s to 55.6% in the 2010s. [ 243 ] Despite the high participation rate of commercial entities, UN COPUOS once deliberately excluded them from having a voice in discussions unless being formally invited by a member state. [ 237 ] Ostrom said that the involvement of all relevant stakeholders in the rule-design and implementation process is one of the critical elements of successful governance. [ 244 ] The exclusion of private actors largely reduces the effectiveness of the committee's role in making collective-choice arrangements that reflect the interests of all space users. [ 237 ]
The limited engagement of private actors slows the process of addressing space debris. [ 245 ] Ties between dissimilar stakeholders in the governance network offer access to diverse resources. [ 246 ] Different competence among stakeholders can help allocate the tasks more reasonably. In that case, the expertise and experience of private operators are critical to help the world achieve space sustainability. [ 245 ] The complementary strengths of different stakeholders enable the governance network to be more adaptable to changes and reach common goals more effectively. [ 246 ] In recent years, many private actors have seen commercial opportunities of eliminating space debris. It is estimated that by 2022 the global market for debris monitoring and removal will generate a revenue of around $2.9 billion. [ 247 ] For example, Astroscale has contracted with European and Japanese space agencies to develop the capacity of removing orbital debris. [ 248 ] Despite that, they are still in small quantity compared to the number of those who have placed satellites in space. Privateer Space , a Hawaiian-based startup company by American engineer Alex Fielding , space environmentalist Moriba Jah , and Apple co-founder Steve Wozniak , announced plans in September 2021 to launch hundreds of satellites into orbit in order to study space debris. [ 249 ] However, the company stated it is in "stealth mode" and no such satellites have been launched. [ 249 ]
Fortunately, the current space exploration is not completely driven by competition, and there still exists a chance for dialogues and cooperation among all stakeholders in both developed and developing countries, to reach an agreement on tackling space debris and assure an equitable and orderly exploration. [ 250 ] Besides private actors, network governance does not necessarily exclude the states from playing a role. Instead, the different functions of states might promote the governance process. [ 251 ] To improve the polycentric governance network of space debris, researchers suggest: encourage data-sharing among different national and organizational databases at the political level; develop shared standards for data collection systems to improve interoperability; and enhance the participation of private actors through involving them in national and international discussions. [ 240 ]
The issue of space debris has been raised as a mitigation challenge for missions around the Moon with the danger of increasing space debris around it. [ 252 ] [ 253 ]
It is thought that on 4 March 2022, for the first time, human space debris—most likely a spent rocket body , Long March 3C third stage from the 2014 Chang'e 5 T1 mission—unintentionally hit the lunar surface , creating an unexpected double crater. [ 254 ] [ 255 ]
In 2022, several elements of space debris were found on Mars: Perseverance ' s backshell was found on the surface of Jezero Crater, [ 256 ] and a piece of a thermal blanket which may have come from the descent stage of the rover. [ 257 ] [ 258 ]
As of February 2024 [update] , Mars is littered with about seven tons of human-made debris. Most of it consists of crashed and inactive spacecraft as well as discarded components. [ 259 ] [ 260 ]
Until the End of the World (1991) is a French sci-fi drama set under the backdrop of an out-of-control Indian nuclear satellite, predicted to re-enter the atmosphere, threatening vast populated areas of the Earth. [ 261 ]
Gravity , a 2013 survival film directed by Alfonso Cuaron , is about a disaster on a space mission caused by Kessler syndrome. [ 262 ]
In season 1 of Love, Death & Robots (2019), episode 11, "Helping Hand", revolves around an astronaut being struck by a screw from space debris which knocks her off a satellite in orbit. [ 263 ]
Manga and anime Planetes tells a story about a crew of Space Debris station that collects and disposes of space debris. [ 264 ]
Beside space debris as an issue of science-fiction stories other stories feature it as a reservoir for the story, as in stories about space junk scavengers like Space Sweepers (2021), or as a result or environment of the story.
The episode Conflict from Gerry and Sylvia Anderson's U.F.O. sci-fi TV series shows how small alien spaceships could use Terrestrial space debris such as orbital boosters to become undetectable by SHADO' s orbital Space Intruder Detector ( S.I.D. ). [ 265 ] | https://en.wikipedia.org/wiki/Space_debris |
Space domain awareness is the study and monitoring of satellites orbiting the Earth . It involves the detection, tracking, cataloging and identification of artificial objects, i.e. active/inactive satellites , spent rocket bodies, or fragmentation debris .
Space domain awareness accomplishes the following:
Systems include: | https://en.wikipedia.org/wiki/Space_domain_awareness |
Space dust measurement refers to the study of small particles of extraterrestrial material, known as micrometeoroids or interplanetary dust particles (IDPs), that are present in the Solar System . These particles are typically of micrometer to sub-millimeter size and are composed of a variety of materials including silicates, metals, and carbon compounds . The study of space dust is important as it provides insight into the composition and evolution of the Solar System , as well as the potential hazards posed by these particles to spacecraft and other space-borne assets. The measurement of space dust requires the use of advanced scientific techniques such as secondary ion mass spectrometry (SIMS) , optical and atomic force microscopy (AFM) , and laser-induced breakdown spectroscopy (LIBS) to accurately characterize the physical and chemical properties of these particles.
From the ground, space dust is observed as scattered sun light from myriads of interplanetary dust particles and as meteoroids entering the atmosphere . By observing a meteor from several positions on the ground, the trajectory and the entry speed can be determined by triangulation . Atmospheric entry speeds of up to 72,000 m/s have been observed for Leonid meteors.
Even sub-millimeter sized meteoroids hitting spacecraft at speeds around 300 m/s (much faster than bullets ) can cause significant damage. Therefore, the early US Explorer 1 , Vanguard 1 , and the Soviet Sputnik 3 satellites carried simple 0.001 m 2 sized microphone dust detectors in order to detect impacts of micron sized meteoroids. [ 1 ] [ 2 ] [ 3 ] The obtained fluxes were orders of magnitude higher than those estimated from zodiacal light measurements. [ 4 ] However, the latter determination had big uncertainties in the assumed size and heliocentric radial dust density distributions. Thermal studies in the lab with microphone detectors [ 5 ] suggested that the high count-rates recorded were due to noise generated by temperature variations in Earth orbit.
An excellent review of the early days of space dust research was given by Fechtig, H., Leinert, Ch., and Berg, O. [ 6 ] in the book Interplanetary Dust . [ 7 ]
A dust accelerator is a critical facility to develop, test, and calibrate space dust instruments. [ 8 ] Classic guns have muzzle velocities between just a few 100 m/s and 1 km/s, whereas meteoroid speeds range from a few km/s to several 100 km/s for nanometer sized dust particles. Only experimental light-gas guns (e.g. at NASA's Johnson Space Center , JSC [ 9 ] ) reach projectile speeds of several km/s up to 10 km/s in the laboratory. By exchanging the projectile with a sabot [ 10 ] containing dust particles, high speed dust projectiles can be used for impact cratering and dust sensor calibration experiments.
The workhorse for hypervelocity dust impact experiments is the electrostatic dust accelerator. [ 11 ] Nanometer to micrometer sized conducting dust particles are electrically charged and accelerated by an electrostatic particle accelerator to speeds up to 100 km/s. Currently, operational dust accelerators exist at IRS [ 12 ] in Stuttgart, Germany (formally at Max Planck Institute for Nuclear Physics in Heidelberg [ 13 ] ), and at the Laboratory for Atmospheric and Space Physics (LASP) in Boulder, Colorado. [ 14 ] The LASP dust accelerator facility has been operational since 2011, and has been used for basic impact studies, as well as for the development of dust instruments. The facility is available for the planetary and space science communities. [ 15 ]
Dust accelerators are used for impact cratering studies, [ 16 ] calibration of impact ionization dust detectors, [ 17 ] and meteor studies. [ 18 ] Only electrically conducting particles can be used in an electrostatic dust accelerator because the dust source is located in the high-voltage terminal. James F. Vedder, [ 19 ] at Ames Research Center , ARC, used a linear particle accelerator by charging dust particles by an ion beam in a quadrupole ion trap under visual control. This way, a wide range of dust materials could be accelerated to high speeds. [ 20 ]
Tennis court sized (200 m 2 ) penetration detectors on the Pegasus satellites [ 21 ] determined a much lower flux of 100 micron sized particles that would not pose a significant hazard to the crewed Apollo missions. The first reliable dust detections of micron sized meteoroids were obtained by the dust detectors on board the Pioneer 8 and 9 [ 22 ] and HEOS 2 [ 23 ] spacecraft. Both instruments were impact ionization detectors using coincident signals from ions and electrons released upon impact. The detectors had sensitive areas of approximately 0.01 m 2 and detected outside the Earth's magnetosphere on average one impact per ten days.
Microcraters on lunar samples provide an extensive record of impacts onto the lunar surface. Uneroded glass splashes from big impacts covering crystalline lunar rocks preserve microcraters well.
The number of microcraters was measured on a single rock sample using microscopic and scanning electron microscopic analyses. [ 24 ] [ 25 ] The craters ranged in size from 10 −8 to 10 −3 m, and were correlated to the mass of meteoroids based on impact simulations. [ 26 ] The impact speed onto the lunar surface was assumed to be 20 km/s. The age of the rocks on the surface could not be determined through traditional methods (counting the solar flare track densities), so spacecraft measurements by the Pegasus satellites were used to determine the interplanetary dust flux, specifically the crater production flux at 100 μm size. [ 27 ] The flux of smaller meteoroids was found to be smaller than the observed cratering flux on the lunar surface due to fast ejecta from impacts of bigger meteoroids. The flux was adjusted using data from the HEOS-2 and Pioneer 8/9 space probes.
From April 1984 to January 1990, NASA 's Long Duration Exposure Facility exposed several passive impact collectors (each a few square meters in area) to the space dust environment in low Earth orbit . After recovery of LDEF by the Space Shuttle Columbia , the instrument trays were analyzed. The results [ 28 ] [ 29 ] generally confirmed the earlier analysis of lunar microcraters. [ 27 ]
Zodiacal light observations at different heliocentric distances were performed by the Zodiacal light photometer instruments on Helios 1 and 2 [ 30 ] and the Pioneer 10 and Pioneer 11 [ 31 ] space probes, ranging between 0.3 AU and 3.3 AU from the sun. This way, the heliocentric radial profile was determined, and shown to vary by a factor of about 100 over that distance. The Asteroid Meteoroid Detector (AMD) [ 32 ] on Pioneer 10 and Pioneer 11 used the optical detection and triangulation of individual meteoroids to get information on their sizes and trajectories. Unfortunately, the trigger threshold was set too low, and noise corrupted the data. [ 33 ] Zodiacal light observations at visible light wavelengths use the light scattered by interplanetary dust particles, which constitute only a few percent of the incoming light. The remainder (over 90%) is absorbed and reradiated at infrared wavelengths.
The zodiacal dust cloud is much brighter at infrared wavelengths than visible wavelengths. However, on the ground, most of these infrared wavelengths are blocked by atmospheric absorption bands. Therefore, most infrared astronomy observations are done from space observatory satellites. The Infrared Astronomical Satellite (IRAS) mapped the sky at wavelengths of 12, 25, 60, and 100 micrometers. Between wavelengths of 12 and 60 microns, zodiacal dust was a prominent feature. Later, the Diffuse Infrared Background Experiment (DIRBE) on NASA's COBE mission provided a complete high-precision survey of the zodiacal dust cloud [ 34 ] at the same wavelengths. [ 35 ]
IRAS sky maps showed structure in the sky brightness at infrared wavelengths. In addition to the wide, general zodiacal cloud and a broad, central asteroidal band, there were several narrow cometary trails . [ 36 ] Follow-up observations using the Spitzer Space Telescope showed that at least 80% of all Jupiter family comets had trails. [ 37 ] When the Earth passes through a comet trail, a meteor shower is observed from the ground. Due to the enhanced risk to spacecraft in such meteoroid streams, the European Space Agency developed the IMEX model, [ 38 ] which follows the evolution of cometary particles [ 39 ] and hence allows us to determine the risk of collision at specific positions and times in the inner Solar System.
In the early 1960s, pressurized cell micrometeorite detectors were flown on the Explorer 16 and Explorer 23 satellites. Each satellite carried more than 200 individual gas-filled pressurized cells with metal walls of 25 and 50 microns thick. A puncture of a cell by a meteoroid impact could be detected by a pressure sensor. These instruments provided important measurements of the near-Earth meteoroid flux. [ 40 ] In 1972 and 1973, the Pioneer 10 and Pioneer 11 interplanetary spacecraft carried 234 pressurized cell detectors each, mounted on the back of the main dish antenna. The stainless-steel wall thickness was 25 microns on Pioneer 10, and 50 microns on Pioneer 11. The two instruments characterized the meteoroid environment in the outer Solar System as well as near Jupiter and near Saturn. [ 41 ]
In preparation for the Apollo Missions to the moon, three Pegasus satellites were launched by the Saturn 1 rocket into near-Earth orbit. Each satellite carried 416 individual meteoroid detectors with a total detection surface of about 200 m 2 . The detectors consisted of aluminum penetration sheets of various thicknesses: 171 m 2 of 400 micron-thick, 16 m 2 of 200 micron-thick, and 7.5 m 2 of 40 micron-thick. Placed behind these penetration sheets were 12 micron-thick mylar capacitor detectors that recorded penetrations of the overlying sheet. [ 42 ] The results showed that the meteoroid hazard is significant and meteoroid protection methods must be implemented for large space vehicles. [ 40 ]
In 1986, the Vega 1 and Vega 2 missions were equipped with a new dust detector, developed by John Simpson , which used polyvinylidene difluoride PVDF films. [ 43 ] This material responds to dust impacts by generating electrical charge due to impact cratering or penetration. [ 44 ] Since PVDF detectors are also sensitive to mechanical vibrations and energetic particles, detectors using PVDF work acceptably well as high-rate dust detectors in very dusty environments, like cometary comae or planetary rings (as was the case for the Cassini–Huygens Cosmic Dust Analyzer ). [ 45 ] For example, on the Stardust mission, the Dust Flux Monitor Instrument (DFMI) used PVDF detectors to study dust in the coma of Comet Wild 2 . However, in low-dust environments such as interplanetary space, this sensitivity makes the detectors susceptible to noise. Because of this, the PVDF detectors on the Venetia Burney Student Dust Counter also needed shielded reference detectors in order to determine the background noise rate. [ 46 ]
During its flyby of Halley's Comet at a distance of 600 km, the Giotto spacecraft was protected from space dust by a 1 mm-thick front Whipple shield (1.85 m diameter) and a 12 mm-thick rear Kevlar shield. Mounted on the front dust shield were three piezoelectric momentum sensors of the Dust Impact Detection System (DIDSY). [ 47 ] A fourth momentum sensor was mounted on the rear shield. These microphone detectors, together with other detectors, measured the dust distribution within the inner coma of the comet. [ 48 ] These instruments also measured dust during Giotto 's encounter with the comet 26P/Grigg–Skjellerup . [ 49 ]
On the Mercury Magnetospheric Orbiter [ 50 ] of the BepiColombo mission, the Mercury Dust Monitor (MDM) [ 51 ] will measure the dust environments of interplanetary space and Mercury . [ 52 ] MDM is composed of four piezoelectric ceramic sensors made of lead zirconate titanate , from which impact signals will be recorded and analyzed.
Most instruments on a spacecraft flying through a dense dust environment will experience effects of dust impacts. A prominent example of such an instrument was the Plasma Wave Subsystem (PWS) on the Voyager 1 and Voyager 2 spacecraft. PWS provided useful information on the local dust environment. Initially, the Asteroid Meteoroid Detector (AMD) previously flown on Pioneer 10 and 11 was preliminarily selected for the Voyager payload. However, because there were doubts about its performance, [ 33 ] the instrument was deselected and, hence, no dedicated dust instrument was carried by either Voyager 1 or 2.
During the Voyager 2 flythrough of the Saturn system, PWS detected intense impulse noise centered on the ring plane at 2.88 Saturn radii distance, slightly outside of the G ring. [ 53 ] This noise was attributed to micron sized particles hitting the spacecraft. In-situ dust detections by the Cassini Cosmic Dust Analyzer [ 54 ] and camera observations of the outer rings confirmed the existence of an extended G ring. Also during Voyager 's flybys of Uranus and Neptune , dust concentrations in the equatorial planes were observed. [ 55 ] [ 56 ]
During the flyby of comet 21P/Giacobini–Zinner by the International Cometary Explorer , dust impacts were observed by the plasma wave instrument. [ 57 ]
Though plasma wave instruments on various spacecraft claimed to detect dust, it was only in 2021 that a model for the generation of signals on plasma wave antennas by dust impacts was presented, based on dust accelerator tests. [ 58 ]
Impact ionization detectors are the most successful dust detectors in space. With these detectors, the interplanetary dust environment between Venus and Jupiter has been explored.
Impact ionization detectors use the simultaneous detection of positive ions and electrons upon dust impact on a solid target. This coincidence provides a means to discriminate from noise on a single channel. The first successful dust detector in interplanetary space at about 1 AU was flown on the Pioneer 8 and Pioneer 9 space probes. [ 59 ] The Pioneer 8 and 9 detectors had sensitive target areas of 0.01 m 2 . Besides interplanetary dust on eccentric orbits, it detected dust on hyperbolic orbits—that is, dust leaving the Solar System. [ 60 ] The HEOS 2 dust detector [ 61 ] was the first detector that employed a hemispherical geometry, like all the subsequent detectors of the Galileo and Ulysses spacecraft, and the LDEX detectors on the LADEE mission. The hemispherical target of 0.01 m 2 area collected electrons from the impact and the ions were collected by the central ion collector. These signals served to determine the mass and speed of the impacted meteoroid. The HEOS 2 dust detector explored the Earth dust environment within 10 Earth radii. [ 62 ]
The twin Galileo and Ulysses dust detectors were optimized for interplanetary dust measurements in the outer Solar System. The sensitive target areas were increased ten-fold to 0.1 m 2 in order to cope with the expected low dust fluxes. In order to provide reliable dust impact data even within the harsh Jovian environment, an electron channeltron was added in the center of the ion grid collector. This way, an impact was detected by triple coincidence of three charge signals. The 2.5-ton Galileo spacecraft was launched in 1989 and cruised for 6 years in interplanetary space between Venus’ and Jupiter's orbit and measured interplanetary dust. [ 63 ] The 370 kg Ulysses spacecraft was launched a year later and went on a direct trajectory to Jupiter, which it reached in 1992 for a swing-by maneuver that put the spacecraft on a heliocentric orbit of 80 degrees inclination. In 1995, Galileo started its 7-year path through the Jovian system with several flybys of all the Galilean moons . After its Jupiter flyby, Ulysses identified a flow of interstellar dust sweeping through the Solar System and hyper-velocity streams of nano-dust [ 64 ] which are emitted from Jupiter and then couple to the solar magnetic field. In addition, the Galileo instrument detected ejecta clouds around the Galilean moons. [ 65 ]
The Lunar Dust Experiment (LDEX) [ 66 ] on board the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission is a smaller version of the Galileo and Ulysses dust detectors. The most sensitive impact charge detector is a microchannel plate (MCP) behind the central focusing grid. LDEX has a sensitive area of 0.012 m 2 . The objective of the instrument was the detection and analysis of the lunar dust environment. From 16 October 2013 to 18 April 2014, LDEX detected about 140,000 dust hits at an altitude of 20–100 km above the lunar surface. It found a tenuous and permanent, asymmetric ejecta cloud around the Moon that is caused by meteoroid impacts onto the lunar surface. [ 67 ] From this data it was found that approximately 40 μm/Myr of lunar regolith is redistributed due to meteoritic bombardment. [ 68 ] Besides a continuous meteoroid bombardment, meteoroid streams cause temporary enhancements of the ejecta cloud. [ 69 ]
The Helios Micrometeoroid Analyzer was the in-situ instrument to analyze the composition of cosmic dust. In 1974, the instrument was carried by the Helios spacecraft from the Earth's orbit down to 0.3 AU from the Sun. The goal of the Micrometeoroid Analyzer was to determine the spatial distribution of the dust in the inner planetary system, and to search for variations in the compositional and physical properties of micrometeoroids . [ 70 ] The instrument consisted of two impact ionization time-of-flight mass spectrometers (Ecliptic and South sensor) with a total target area of about 0.01 m 2 . One sensor was shielded by the spacecraft rim from direct sunlight, whereas the other sensor was protected by a thin aluminized parylene film from intense solar radiation. These Micrometeoroid Analyzers were calibrated with a wide range of materials [ 71 ] at the dust accelerators of the Max Planck Institute for Nuclear Physics in Heidelberg and the Ames Research Center in Moffet Field. The mass resolution of the mass spectra of the Helios sensors was low: R = M Δ M ≈ 10 {\displaystyle R={\cfrac {M}{\Delta M}}\approx 10} . There was an excess of impacts recorded by the South sensor compared to the Ecliptic sensor. On the basis of the penetration studies with the Helios film, [ 72 ] this excess was interpreted to be due to low density ( ρ {\displaystyle \rho } < 1000 kg/m 3 ) meteoroids that were shielded from entering the Ecliptic sensor. [ 73 ] The mass spectra range from those with dominant low masses (up to 30 m u ), compatible with silicates, to those with dominant high masses (between 50 and 60 m u ), compatible with iron and molecular ions. Meteoroid streams [ 74 ] and even interstellar dust [ 75 ] particles were identified in the data.
Twin dust mass analyzers were flown on the 1986 Halley's Comet missions Vega 1 , Vega 2 , and Giotto . These spacecraft flew by the comet at a distance of 600–1,000 km with a speed of 70–80 km/s. The PUMA ( Vega ) and PIA ( Giotto ) instruments were developed by Jochen Kissel of the Max Planck Institute for Nuclear Physics in Heidelberg . Dust particle hitting the small (approximately 5 cm 2 ) impact target generated ions by impact ionization . The instruments were high mass resolution ( R ≈ 100) reflectron type time-of-flight mass spectrometers . The instruments could record up to 500 impacts per second. [ 76 ] During comet flybys, the instruments recorded an abundance of small particles of mass less than 10 −14 grams. Besides unequilibrated silicates, many of the particles were rich in light elements such as hydrogen , carbon , nitrogen , and oxygen . [ 77 ] [ 78 ] [ 79 ] This suggests that most particles consisted of a predominantly chondritic core with a refractory organic mantle. [ 80 ]
The Cometary and Interstellar Dust Analyzer (CIDA) was flown on the Stardust mission. In January 2004, Stardust flew by comet Comet Wild 2 at a distance of 240 km with a relative speed of 6.1 km/s. In February 2011, Stardust flew by comet Tempel 1 at a distance of 181 km with a speed of 10.9 km/s. During the interplanetary cruise between the comet encounters, there were favorable opportunities to analyze the interstellar dust stream discovered earlier by Ulysses . [ 64 ] CIDA is a derivative of the impact ionization mass spectrometers flown on the Giotto , Vega 1 , and Vega 2 missions. The impact target peeks out to the side of the spacecraft while the main part of the instrument is protected from the high-speed dust. It has a sensitive area of approximately 100 cm 2 and a mass resolution R ≈ 250. Besides the positive ion mode, CIDA has also a negative ion mode for better sensitivity for organic molecules. [ 81 ] The 75 spectra obtained during the comet flybys [ 82 ] indicate a dominance of organic matter; sulfur ions were also detected in one spectrum. In the 45 spectra obtained during the cruise phase favorable for the detection of interstellar particles, derivates of quinone were suggested as constituents of the organic component. [ 83 ]
The Cosmic Dust Analyzer (CDA) was flown on the Cassini mission to Saturn . CDA is a large-area (0.1 m 2 total sensitive area) multi-sensor dust instrument that includes a 0.01 m 2 medium resolution ( R ≈ 20–50) chemical dust analyzer , a 0.09 m 2 highly-reliable impact ionization detector, and two high-rate polarized polyvinylidene fluoride (PVDF) detectors with sensitive areas of 0.005 m 2 and 0.001 m 2 , respectively. [ 84 ] During its 6-year cruise to Saturn , CDA analyzed interplanetary dust , [ 85 ] the stream of interstellar dust , [ 86 ] and Jupiter dust streams. [ 87 ] A highlight was the detection of electrical dust charges in interplanetary space and in Saturn's magnetosphere . [ 88 ] [ 89 ] During the following 13 years, Cassini completed 292 orbits around Saturn (2004–2017) and measured several million dust impacts which characterize dust primarily in Saturn's E ring . [ 90 ] [ 91 ] In 2005, during Cassini 's close flyby of Enceladus within 175 km from the surface, CDA discovered active ice geysers. [ 92 ] Detailed compositional analyses found salt-rich water ice grains close to Enceladus, which led to the discovery of large reservoirs of liquid water oceans below the icy crust of the moon. [ 93 ] Analyses of interstellar grains at Saturn's distance suggest magnesium-rich grains of silicate and oxide composition, some with iron inclusions. [ 94 ]
A Dust Telescope is an instrument to perform dust astronomy . It not only analyses the signals and ions that are generated by a dust impact on the sensitive target, but also determines the dust trajectory prior to the impact. [ 95 ] [ 96 ] The latter is based on the successful measurement of the dust electric charge by Cassini 's Cosmic Dust Analyzer (CDA). [ 88 ] [ 89 ] A Dust Trajectory Sensor consists of four planes of parallel position sensing wire electrodes. [ 97 ] Dust accelerator tests show that dust trajectories can be determined to an accuracy of 1% in velocity and 1° in direction. [ 98 ] The second element of a Dust Telescope is a Large-area Mass Analyzer: [ 99 ] a reflectron type time-of-flight mass analyzer with a sensitive area of up to 0.2 m 2 [ 100 ] and a mass resolution R > 150. It consists of a circular plate target with the ion detector behind the center hole. In front of the target is an acceleration grid. Ions generated by an impact are reflected by a paraboloid shaped grid onto the center ion detector. Prototypes of dust telescope have been built at the Laboratory for Atmospheric and Space Physics (LASP) of the University of Colorado, Boulder , USA [ 101 ] and at the Institute of Space Systems [ 102 ] of the University of Stuttgart , Germany, and tested at their respective dust accelerators. [ 103 ]
The Surface Dust Analyser (SUDA) on board the Europa Clipper mission is being developed by Sacha Kempf and colleagues at LASP. SUDA will collect spatially resolved compositional maps of Jupiter's moon Europa along the ground tracks of the Europa orbiter, and search for plumes. The instrument is capable of identifying traces of organic and inorganic compounds in the ice ejecta. [ 104 ] The launch of the Europa Clipper mission is planned for 2024. [ 105 ]
The DESTINY + Dust Analyzer (DDA) will fly on the Japanese – German space mission DESTINY + to asteroid 3200 Phaethon . [ 106 ] [ 107 ] Phaethon is believed to be the origin of the Geminids meteor stream that can be observed from the ground every December. DDA [ 108 ] development is led by Ralf Srama and colleagues from the Institute of Space Systems (IRS) [ 109 ] at the University of Stuttgart in cooperation with von Hoerner & Sulger GmbH (vH&S) company. [ 110 ] DDA will analyze interstellar and interplanetary dust on cruise to Phaethon [ 111 ] and will study its dust environment during the encounter; of particular interest is the proportion of organic matter. Its launch is planned for 2024.
The Interstellar Dust Experiment (IDEX), [ 112 ] developed by Mihaly Horanyi and colleagues at LASP, will fly on the Interstellar Mapping and Acceleration Probe (IMAP) in orbit about the Sun–Earth L1 Lagrange point . IDEX is a large-area (0.07 m 2 ) dust analyzer that provides the mass distribution and elemental composition of interstellar and interplanetary dust particles. A laboratory version of the IDEX instrument was used at the dust accelerator facility [ 113 ] operated at University of Colorado to collect impact ionization mass spectra for a range of dust samples of known composition. [ 114 ] Its launch is planned for 2025.
The importance of lunar samples and lunar soil for dust science was that they provided a meteoroid impact cratering record. Even more important are the cosmochemical aspects—from their isotopic , elemental , molecular , and mineralogical compositions, important conclusions can be drawn, such as concerning the giant-impact hypothesis of the Moon's formation. [ 115 ] From 1969 to 1972, six Apollo missions collected 382 kilograms of lunar rocks and soil . These samples are available for research and teaching projects. [ 116 ] From 1970 to 1976, three Luna spacecraft returned 301 grams of lunar material. In 2020, Chang'e 5 collected 1.7 kg of lunar material.
In 1950, Fred Whipple showed that micrometeoroids smaller than a critical size (~100 micrometers) are decelerated at altitudes above 100 km slowly enough to radiate their frictional energy away without melting. [ 117 ] Such micrometeorites sediment through the atmosphere and ultimately deposit on the ground. The most efficient method to collect micrometeorites is by high (~20 km) flying aircraft with special silicon oil covered collectors that capture this dust. At lower altitudes, these micrometeorites become mixed with Earth dust. Don Brownlee first reliably identified the extraterrestrial nature of collected dust particles by their chondritic composition . [ 118 ] These stratospheric dust samples are available for further research. [ 119 ]
Stardust was the first mission to return samples from a comet and from interstellar space. In January 2004, Stardust flew by Comet Wild 2 at a distance of 237 km with a relative velocity of 6.1 km/s. Its dust collector consisted of 0.104 m 2 aerogel and 0.015 m 2 aluminium foil; [ 120 ] one side of the detector was exposed to the flow of cometary dust. The Stardust cometary samples were a mix of different components, including presolar grains like 13 C-rich silicon carbide grains, a wide range of chondrule-like fragments, and high-temperature condensates like calcium-aluminum inclusions found in primitive meteorites that were transported to cold nebular regions. [ 121 ] During March–May 2000 and July–December 2002, the spacecraft was in a favorable position to collect interstellar dust on the back side of the sample collector. Once the sample capsule was returned in January 2006, the collector trays were inspected and thousands of grains from Comet Wild 2 [ 122 ] and seven probable interstellar grains [ 123 ] were identified. These grains are available for teaching and research from the NASA Astromaterials Curation Office. [ 124 ]
The first asteroid samples were returned by the JAXA Hayabusa missions. Hayabusa encountered asteroid 25143 Itokawa in November 2005, picked up surface samples, and returned to Earth in June 2010. Despite some problems during sample collection, thousands of 10–100 micron sized particles were collected and are available for research in the laboratories. [ 125 ] The second Hayabusa2 mission rendezvoused with asteroid 162173 Ryugu in June 2018. About 5 g of surface and sub-surface material from this primitive C-type asteroid were returned. [ 126 ] JAXA shares about 10% of the collected samples with NASA sample curation. [ 127 ] [ 128 ]
The Rosetta space probe orbited comet 67P/Churyumov–Gerasimenko from August 2014 to September 2016. During this time, Rosetta's instruments analyzed the nucleus, dust, gas, and plasma environments. Rosetta carried a suite of miniaturized sophisticated lab instruments to study collected cometary dust particles. Among them was the high-resolution secondary ion mass spectrometer COSIMA (Cometary Secondary Ion Mass Analyzer) that analyzed the rocky and organic composition of collected dust particles, [ 129 ] [ 130 ] an atomic force microscope MIDAS (Micro-Imaging Dust Analysis System) that investigated morphology and physical properties of micrometer-sized dust particles that were deposited on a collector plate, [ 131 ] and the double-focus magnetic mass spectrometer (DFMS) and the reflectron type time of flight mass spectrometer (RTOF) of ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) to analyze cometary gas and the volatile components of cometary particulates. [ 132 ] [ 133 ] Rosetta 's Philae lander carried the gas chromatography–mass spectrometry COSAC experiment to analyze organic molecules in the comet's atmosphere and on its surface. [ 134 ] | https://en.wikipedia.org/wiki/Space_dust_measurement |
Space environment is a branch of astronautics , aerospace engineering and space physics that seeks to understand and address conditions existing in space that affect the design and operation of spacecraft. A related subject, space weather , deals with dynamic processes in the solar-terrestrial system that can give rise to effects on spacecraft, but that can also affect the atmosphere, ionosphere and geomagnetic field , giving rise to several other kinds of effects on human technologies.
Effects on spacecraft can arise from radiation , space debris and meteoroid impact, upper atmospheric drag and spacecraft electrostatic charging . Various mitigation strategies have been adopted.
Radiation in space usually comes from three main sources:
For long-duration missions, the high doses of radiation can damage electronic components and solar cells. A major concern is also radiation-induced "single-event effects" such as single event upset . Crewed missions usually avoid the radiation belts and the International Space Station is at an altitude well below the most severe regions of the radiation belts. During solar energetic events ( solar flares and coronal mass ejections ) particles can be accelerated to very high energies and can reach the Earth in times as short as 30 minutes (but usually take some hours). These particles are mainly protons and heavier ions that can cause radiation damage, disruption to logic circuits, and even hazards to astronauts. Crewed missions to return to the Moon or to travel to Mars will have to deal with the major problems presented by solar particle events to radiation safety, in addition to the important contribution to doses from the low-level background cosmic rays . In near-Earth orbits, the Earth's geomagnetic field screens spacecraft from a large part of these hazards - a process called geomagnetic shielding .
Space debris and meteoroids can impact spacecraft at high speeds, causing mechanical or electrical damage. The average speed of space debris is 10 km/s (22,000 mph; 36,000 km/h) [ 1 ] while the average speed of meteoroids is much greater. For example, the meteoroids associated with the Perseid meteor shower travel at an average speed of 58 km/s (130,000 mph; 210,000 km/h). [ 2 ] Mechanical damage from debris impacts have been studied through space missions including LDEF , which had over 20,000 documented impacts through its 5.7-year mission. [ 3 ] Electrical anomalies associated with impact events include ESA 's Olympus spacecraft, which lost attitude control during the 1993 Perseid meteor shower. [ 4 ] A similar event occurred with the Landsat 5 spacecraft [ 5 ] during the 2009 Perseid meteor shower. [ 6 ]
Spacecraft electrostatic charging is caused by the hot plasma environment around the Earth. The plasma encountered in the region of the geostationary orbit becomes heated during geomagnetic substorms caused by disturbances in the solar wind. "Hot" electrons (with energies in the kilo- electron volt range) collect on surfaces of spacecraft and can establish electrostatic potentials of the order of kilovolts. As a result, discharges can occur and are known to be the source of many spacecraft anomalies.
Solutions devised by scientists and engineers include, but are not limited to, spacecraft shielding, special " hardening " of electronic systems, various collision detection systems. Evaluation of effects during spacecraft design includes application of various models of the environment, including radiation belt models, spacecraft-plasma interaction models and atmospheric models to predict drag effects encountered in lower orbits and during reentry.
The field often overlaps with the disciplines of astrophysics , atmospheric science , space physics , and geophysics , albeit usually with an emphasis on application.
The United States government maintains a Space Weather Prediction Center at Boulder, Colorado . The Space Weather Prediction Center (SWPC) is part of the National Oceanic and Atmospheric Administration ( NOAA ). SWPC is one of the National Weather Service 's (NWS) National Centers for Environmental Prediction (NCEP).
Environmental law in space law is being considered but lacks establishment, [ 7 ] but has become an issue in light of increased space debris . [ 8 ]
Space environmentalism is an advocacy that sees space as not devoid of needing regulation and protection, and has gained attention by an increasing number of academics, [ 9 ] such as Moriba Jah . [ 10 ] | https://en.wikipedia.org/wiki/Space_environment |
Space ethics, astroethics or astrobioethics [ 1 ] is a discipline of applied ethics that discusses the moral and ethical implications arising from astrobiological research , space exploration and space flight . [ 2 ] It deals with practical contemporary issues like the protection of the space environment [ 3 ] and hypothetical future issues pertaining to our interaction with extraterrestrial life forms.
Specific issues of space ethics include space debris mitigation, the militarization of space and the ethics of SETI and METI , but also more theoretical topics like space colonization , [ 4 ] terraforming , directed panspermia and space mining . The field also concerns itself with more fundamental moral questions, such as the value of abiotic environments in space, the intrinsic value of extraterrestrial life , and how humans should treat extraterrestrial non-intelligent life (like microbes ) and extraterrestrial intelligent life (and whether this distinction should be made in the first place).
Astroethical issues are often discussed as elements of broader issues such as general environmental protection and imperialism . [ 5 ] Astroethics have been described as an emerging discipline gaining in attention, a "necessity for astrobiology " and a "true issue for the future of astrobiology". [ 1 ]
A guiding principle in astroethics is that of Planetary Protection (PP), which seeks to prevent the introduction of lifeforms from Earth to other celestial bodies (forward contamination) [ 6 ] and vice versa (back contamination), and thereby possible adverse consequences on existing ecospheres resulting from such contamination. This principle is anchored in the UN Outer Space Treaty , which was established in 1967 and has since been signed and ratified by all space-faring nations.
The precautionary principle was defined in the 1998 Wingspread Conference on the Precautionary Principle . This approach is supposed to guide decisions in the face of a lack of scientific knowledge or consensus on a matter. In a 2010 COSPAR workshop at Princeton University , 26 experts embraced the precautionary principle and concluded that "further investigations before interference that is likely to be harmful to Earth and other extraterrestrial bodies, including extraterrestrial life and the contamination and disturbance of celestial environments", are to be conducted. [ 7 ]
SETI astrobiologist Margaret Race and Methodist theologian Richard Randolph have outlined 4 principles for the search for extra-terrestrial life within the Solar System : [ 8 ]
A wide range of concrete issues is discussed in astroethics. Some of them are herein elaborated.
Assumptions about outer space, particularly regarding space colonization , have characterized outer space as sterile and therefore a terra nullius . This assumption does not hold true, particularly considering that Earth is part of it. [ 9 ]
Millions of pieces of space debris , defunct artificial objects in space, are orbiting Earth. [ 10 ] On average, one cataloged piece of space debris falls back onto the planet every day, potentially posing a risk to organisms and property. [ 11 ] In total, an estimated 80 tons of space debris re-enter Earth's atmosphere every year. Due to the high friction with the atmospheric gases, the debris burns up, causing the release of its chemical components, which may contribute to atmospheric pollution and ozone depletion . [ 12 ] Additionally, space debris orbits the Earth at extremely high velocity. In Low Earth Orbit , where all crewed space stations and many satellites are located, debris typically reaches speeds of around 8 km/s (approximately 18,000 mph or 29,000 km/h). [ 10 ] [ 13 ] As a result, even tiny pieces of debris can severely damage or destroy satellites and spacecraft in the event of a collision. This could pose a threat to the lives of astronauts on crewed missions and lead to the phenomenon of Kessler syndrome , where a collision of objects in space produces new fragments of space debris that could set off a chain reaction of more collisions. This could render the space around Earth untraversable for space missions and unsuitable for the use of satellites.
As of March 2022, there are no legally binding international laws about who is responsible for the extraction of space debris, or mandating a reduction of new space debris brought into Earth's orbit. [ 14 ] However, space agencies of several countries have implemented their own standards and policies to reduce introduction of new space debris, and the Inter-Agency Space Debris Coordination Committee (IADC) has been founded to address issues regarding orbital debris. [ 11 ] Additionally, JAXA is researching an electromagnetic tether that could be used to pull debris down into the atmosphere. [ 15 ]
The moral problem is that those in power (space agencies) can launch material into the Earth's orbit for their own gains without being held accountable for it, while the general public has to bear the consequences (such as atmospheric pollution or the risk of being hit by space debris). [ citation needed ]
Reconnaissance satellites are used for a variety of military and intelligence purposes, such as optical imaging and signals intelligence . It has been noted that such data could infringe on people's privacy and thereby lead to ethical and legal issues. It could also turn into a source of national security threats if such information got into malevolent hands. [ 16 ] In order to ensure ethically correct obtainment and use of satellite data, leading researchers in law, meteorology and atmospheric science have called for new policy which would lead to more transparency and security. [ 16 ]
In 1967, the Outer Space Treaty was signed, spurred by the development of intercontinental ballistic missiles , the Soviet Union's launch of Sputnik , the first artificial satellite, and the following arms race with the United States. The treaty outlaws all kinds of military action (including weapon tests) in space, limits the use of space to peaceful purposes only and ensures that all nations on Earth are free to explore space.
This treaty has since been called into question multiple times, especially by President of the United States Donald Trump . On June 18, 2018, Trump announced plans to establish a space force, which would constitute a new, sixth branch of the United States military. [ 17 ] He expressed that "When it comes to defending America, it is not enough to merely have an American presence in space. We must have American dominance in space". [ 18 ] On December 20, 2019, the United States Space Force Act was signed into law with votes from both Democratic and Republican senators and House members. [ 19 ] As a result, the United States Space Force was founded.
This was seen by some as an American contestation of the Outer Space Treaty. Viktor Bondarev , chair of the Federation Council Committee on Defense and Security , [ 20 ] responded by saying that if the US were to go further and withdraw from the 1967 treaty, there would be "a tough response aimed at ensuring world security." [ 21 ] This is despite Russia itself having a space force branch in their military .
The emergence of space tourism gives rise to a number of ethical concerns. Future frequent and large-scale landings on celestial bodies like the moon may damage or pollute landing sites and the areas around them. While scientific activity in space is benign, this cannot be guaranteed for actions by private people. If, how, by what criteria and by whom laws should be made to ensure that space tourism doesn't negatively impact other celestial bodies is a question of astroethics.
Terraforming is a controversial astroethical matter. Proponents of terraforming, like Robert Zubrin , argue that humans, being the only technologically advanced and intelligent species on Earth, have a moral obligation to make other celestial bodies habitable for Earth's lifeforms to ensure their survival after the inevitable destruction of our planet. [ 22 ] The other, ecocentrist and biocentrist side of the debate criticizes this position as anthropocentrism and argues that other celestial bodies may already contain life which always has intrinsic value , no matter how advanced it may be. They oppose the interplanetary contamination and changes to the other world that would stem from terraforming, as they could endanger the indigenous life and alter its evolutionary trajectory.
SETI and especially METI (Active SETI) are not uncontroversial and come with their own ethical implications. METI has been criticized as incompatible with the precautionary principle because it could reveal the location of our planet to potentially malevolent alien species. It therefore also potentially puts all of humanity at risk without the need for their individual prior consent , which violates the basic scientific rule of informed consent that all other science must abide by. [ 23 ] Reflecting on human history , some authors even fear the enslavement of humanity, should we be discovered by a more advanced species. [ citation needed ] Similarly, Stephen Hawking , one of the most prominent METI critics, warned of the potential consequences of a meeting with such a species, citing the near-extinction of Aboriginal Tasmanians as an equivalent case from human history. [ 24 ]
Concerns regarding the ethicality of METI might be a solution to the Fermi paradox . It is proposed that extraterrestrial life forms may abstain from attempting interstellar communication due to the potential danger it may pose to them, in line with the precautionary principle. [ 24 ]
Other astroethical considerations regarding METI are the lack of legally enforceable protocols about the steps that should be taken once extraterrestrial life is discovered, [ 25 ] the unpredictability of cultural consequences of that discovery (potential paradigm changes in policy, nations, religions, etc.), [ 26 ] who will get to speak for humanity in case contact is made, how and by whom that person or group of people should be selected, and what the contents of the messages should be.
A further point of contention in the field is whether extraterrestrial life has intrinsic value and therefore if humans have a moral obligation to protect it. This becomes even more difficult when considering the wide span of possible extraterrestrial life forms and whether our treatment of them should differ based on criteria such as their advancement and intelligence . As former NASA chief historian Steven J. Dick put it, "Does Mars belong to the Martians, even if the Martians are only microbes?" [ 25 ] Dick argues that the first step in deciding how we should interact with life forms is to assess their moral status , which is complicated by our ambiguous relations with animals on earth, sheltering some species as pets while eating and exterminating others. [ 25 ] The principle of planetary protection provides that all life on other celestial bodies is worthy of protection from harm (also in the form of contamination ) and therefore confers rights even on hypothetical extraterrestrial microbes, a situation that contrasts with our treatment of microbes and even most higher-developed organisms on Earth. This difference in treatment is hardly justifiable. Therefore, according to Dick, astroethical considerations will broaden our current ethical horizon: they will unveil such inconsistencies and double standards and move humanity from an anthropocentric ethic (ascribing intrinsic value only to rationing beings) to a cosmocentric or biocentric one that values all living things. In fact, Dick says that the finding of extraterrestrial life would "necessitate" a transition away from the anthropocentric approach because it would no longer be consistently applicable to a cosmos that harbors life beyond Earth . [ 25 ]
The decision to include several grams of human cremains onboard Peregrine Lunar Lander flight 01 was criticized by the Navajo Nation , [ 27 ] whose president, Buu Nygren , argued that the Moon is sacred to the Navajo and other American Indian nations, [ 28 ] saying "As stewards of our culture and traditions, it is our responsibility to voice our grievances when actions are taken that could desecrate sacred spaces and disregard deeply held cultural beliefs". Celestis CEO Charles Chafer responded that "[the company] reject[s] the whole premise that this is somehow desecration" and that "nobody owns the Moon". [ 29 ] The launch was not successful in reaching the Moon. | https://en.wikipedia.org/wiki/Space_ethics |
Space exploration utilizes astronomy and space technology to investigate outer space. [ 1 ] While the exploration of space is currently carried out mainly by astronomers with telescopes , its physical exploration is conducted both by uncrewed robotic space probes and human spaceflight . Space exploration, like its classical form astronomy , is one of the main sources for space science .
While the observation of objects in space, known as astronomy , predates reliable recorded history , it was the development of large and relatively efficient rockets during the mid-twentieth century that allowed physical space exploration to become a reality. Common rationales for exploring space include advancing scientific research, national prestige, uniting different nations, ensuring the future survival of humanity, and developing military and strategic advantages against other countries. [ 2 ]
The early era of space exploration was driven by a " Space Race " between the Soviet Union and the United States . A driving force of the start of space exploration was during the Cold War. After the ability to create nuclear weapons, the narrative of defense/offense left land and the power to control the air the focus. Both the Soviet Union and the U.S. were racing to prove their superiority in technology through exploring space. In fact, the reason NASA was created was as a response to Sputnik I. [ 3 ]
The launch of the first human-made object to orbit Earth , the Soviet Union's Sputnik 1 , on 4 October 1957, and the first Moon landing by the American Apollo 11 mission on 20 July 1969 are often taken as landmarks for this initial period. The Soviet space program achieved many of the first milestones, including the first living being in orbit in 1957, the first human spaceflight ( Yuri Gagarin aboard Vostok 1 ) in 1961, the first spacewalk (by Alexei Leonov ) on 18 March 1965, the first automatic landing on another celestial body in 1966, and the launch of the first space station ( Salyut 1 ) in 1971. After the first 20 years of exploration, focus shifted from one-off flights to renewable hardware, such as the Space Shuttle program , and from competition to cooperation as with the International Space Station (ISS).
With the substantial completion of the ISS [ 4 ] following STS-133 in March 2011, plans for space exploration by the U.S. remained in flux. The Constellation program aiming for a return to the Moon by 2020 [ 5 ] was judged unrealistic by an expert review panel reporting in 2009. [ 6 ] Constellation ultimately was replaced with the Artemis Program , of which the first mission occurred in 2022 , with a planned crewed landing to occur with Artemis III . [ 7 ] The rise of the private space industry also began in earnest in the 2010s with the development of private launch vehicles, space capsules and satellite manufacturing.
In the 2000s, China initiated a successful crewed spaceflight program while India launched the Chandrayaan programme , while the European Union and Japan have also planned future crewed space missions. The two primary global programs gaining traction in the 2020s are the Chinese-led International Lunar Research Station and the US-led Artemis Program, with its plan to build the Lunar Gateway and the Artemis Base Camp , each having its own set of international partners.
The first telescope is said to have been invented in 1608 in the Netherlands by an eyeglass maker named Hans Lippershey , but their first recorded use in astronomy was by Galileo Galilei in 1609. [ 8 ] In 1668 Isaac Newton built his own reflecting telescope , the first fully functional telescope of this kind, and a landmark for future developments due to its superior features over the previous Galilean telescope . [ 9 ]
A string of discoveries in the Solar System (and beyond) followed, then and in the next centuries : the mountains of the Moon , the phases of Venus , the main satellites of Jupiter and Saturn , the rings of Saturn , many comets , the asteroids , the new planets Uranus and Neptune , and many more satellites .
The Orbiting Astronomical Observatory 2 was the first space telescope launched 1968, [ 10 ] but the launching of Hubble Space Telescope in 1990 [ 11 ] set a milestone. As of 1 December 2022, there were 5,284 confirmed exoplanets discovered. The Milky Way is estimated to contain 100–400 billion stars [ 12 ] and more than 100 billion planets . [ 13 ] There are at least 2 trillion galaxies in the observable universe . [ 14 ] [ 15 ] HD1 is the most distant known object from Earth, reported as 33.4 billion light-years away. [ 16 ] [ 17 ] [ 18 ] [ 19 ] [ 20 ] [ 21 ]
MW 18014 was a German V-2 rocket test launch that took place on 20 June 1944, at the Peenemünde Army Research Center in Peenemünde . It was the first human-made object to reach outer space , attaining an apogee of 176 kilometers, [ 22 ] which is well above the Kármán line . [ 23 ] It was a vertical test launch. Although the rocket reached space, it did not reach orbital velocity , and therefore returned to Earth in an impact, becoming the first sub-orbital spaceflight . [ 24 ] In 1949, the Bumper-WAC reached an altitude of 393 kilometres (244 mi), becoming the first human-made object to enter space, according to NASA . [ 25 ]
The first successful orbital launch was of the Soviet uncrewed Sputnik 1 ("Satellite 1") mission on 4 October 1957. The satellite weighed about 83 kg (183 lb), and is believed to have orbited Earth at a height of about 250 km (160 mi). It had two radio transmitters (20 and 40 MHz), which emitted "beeps" that could be heard by radios around the globe. Analysis of the radio signals was used to gather information about the electron density of the ionosphere, while temperature and pressure data was encoded in the duration of radio beeps. The results indicated that the satellite was not punctured by a meteoroid . Sputnik 1 was launched by an R-7 rocket. It burned up upon re-entry on 3 January 1958.
The first successful human spaceflight was Vostok 1 ("East 1"), carrying the 27-year-old Russian cosmonaut , Yuri Gagarin , on 12 April 1961. The spacecraft completed one orbit around the globe, lasting about 1 hour and 48 minutes. Gagarin's flight resonated around the world; it was a demonstration of the advanced Soviet space program and it opened an entirely new era in space exploration: human spaceflight .
The first artificial object to reach another celestial body was Luna 2 reaching the Moon in 1959. [ 26 ] The first soft landing on another celestial body was performed by Luna 9 landing on the Moon on 3 February 1966. [ 27 ] Luna 10 became the first artificial satellite of the Moon, entering in a lunar orbit on 3 April 1966. [ 28 ]
The first crewed landing on another celestial body was performed by Apollo 11 on 20 July 1969, landing on the Moon. There have been a total of six spacecraft with humans landing on the Moon starting from 1969 to the last human landing in 1972.
The first interplanetary flyby was the 1961 Venera 1 flyby of Venus , though the 1962 Mariner 2 was the first flyby of Venus to return data (closest approach 34,773 kilometers). Pioneer 6 was the first satellite to orbit the Sun , launched on 16 December 1965. The other planets were first flown by in 1965 for Mars by Mariner 4 , 1973 for Jupiter by Pioneer 10 , 1974 for Mercury by Mariner 10 , 1979 for Saturn by Pioneer 11 , 1986 for Uranus by Voyager 2 , 1989 for Neptune by Voyager 2 . In 2015, the dwarf planets Ceres and Pluto were orbited by Dawn and passed by New Horizons , respectively. This accounts for flybys of each of the eight planets in the Solar System , the Sun , the Moon , and Ceres and Pluto (two of the five recognized dwarf planets ).
The first interplanetary surface mission to return at least limited surface data from another planet was the 1970 landing of Venera 7 , which returned data to Earth for 23 minutes from Venus . In 1975, Venera 9 was the first to return images from the surface of another planet, returning images from Venus. In 1971, the Mars 3 mission achieved the first soft landing on Mars returning data for almost 20 seconds. Later, much longer duration surface missions were achieved, including over six years of Mars surface operation by Viking 1 from 1975 to 1982 and over two hours of transmission from the surface of Venus by Venera 13 in 1982, the longest ever Soviet planetary surface mission. Venus and Mars are the two planets outside of Earth on which humans have conducted surface missions with uncrewed robotic spacecraft .
Salyut 1 was the first space station of any kind, launched into low Earth orbit by the Soviet Union on 19 April 1971. The International Space Station (ISS) is currently the largest and oldest of the 2 current fully functional space stations, inhabited continuously since the year 2000. The other, Tiangong space station built by China, is now fully crewed and operational.
Voyager 1 became the first human-made object to leave the Solar System into interstellar space on 25 August 2012. The probe passed the heliopause at 121 AU to enter interstellar space . [ 29 ]
The Apollo 13 flight passed the far side of the Moon at an altitude of 254 kilometers (158 miles; 137 nautical miles) above the lunar surface, and 400,171 km (248,655 mi) from Earth, marking the record for the farthest humans have ever traveled from Earth in 1970.
As of 9 February 2025 [update] Voyager 1 was at a distance of 166.4 AU (24.89 billion km; 15.47 billion mi) from Earth. [ 30 ] It is the most distant human-made object from Earth. [ 31 ]
Starting in the mid-20th century probes and then human missions were sent into Earth orbit, and then on to the Moon. Also, probes were sent throughout the known Solar System, and into Solar orbit. Uncrewed spacecraft have been sent into orbit around Saturn, Jupiter, Mars, Venus, and Mercury by the 21st century, and the most distance active spacecraft, Voyager 1 and 2 traveled beyond 100 times the Earth-Sun distance. The instruments were enough though that it is thought they have left the Sun's heliosphere, a sort of bubble of particles made in the Galaxy by the Sun's solar wind .
The Sun is a major focus of space exploration. Being above the atmosphere in particular and Earth's magnetic field gives access to the solar wind and infrared and ultraviolet radiations that cannot reach Earth's surface. The Sun generates most space weather , which can affect power generation and transmission systems on Earth and interfere with, and even damage, satellites and space probes. Numerous spacecraft dedicated to observing the Sun, beginning with the Apollo Telescope Mount , have been launched and still others have had solar observation as a secondary objective. Parker Solar Probe , launched in 2018, will approach the Sun to within 1/9th the orbit of Mercury.
Mercury remains the least explored of the Terrestrial planets . As of May 2013, the Mariner 10 and MESSENGER missions have been the only missions that have made close observations of Mercury. MESSENGER entered orbit around Mercury in March 2011, to further investigate the observations made by Mariner 10 in 1975 (Munsell, 2006b). A third mission to Mercury, scheduled to arrive in 2025, BepiColombo is to include two probes . BepiColombo is a joint mission between Japan and the European Space Agency . MESSENGER and BepiColombo are intended to gather complementary data to help scientists understand many of the mysteries discovered by Mariner 10's flybys .
Flights to other planets within the Solar System are accomplished at a cost in energy, which is described by the net change in velocity of the spacecraft, or delta-v . Due to the relatively high delta-v to reach Mercury and its proximity to the Sun, it is difficult to explore and orbits around it are rather unstable.
Venus was the first target of interplanetary flyby and lander missions and, despite one of the most hostile surface environments in the Solar System, has had more landers sent to it (nearly all from the Soviet Union) than any other planet in the Solar System. The first flyby was the 1961 Venera 1 , though the 1962 Mariner 2 was the first flyby to successfully return data. Mariner 2 has been followed by several other flybys by multiple space agencies often as part of missions using a Venus flyby to provide a gravitational assist en route to other celestial bodies. In 1967, Venera 4 became the first probe to enter and directly examine the atmosphere of Venus. In 1970, Venera 7 became the first successful lander to reach the surface of Venus and by 1985 it had been followed by eight additional successful Soviet Venus landers which provided images and other direct surface data. Starting in 1975, with the Soviet orbiter Venera 9 , some ten successful orbiter missions have been sent to Venus, including later missions which were able to map the surface of Venus using radar to pierce the obscuring atmosphere.
Space exploration has been used as a tool to understand Earth as a celestial object. Orbital missions can provide data for Earth that can be difficult or impossible to obtain from a purely ground-based point of reference.
For example, the existence of the Van Allen radiation belts was unknown until their discovery by the United States' first artificial satellite, Explorer 1 . These belts contain radiation trapped by Earth's magnetic fields, which currently renders construction of habitable space stations above 1000 km impractical. Following this early unexpected discovery, a large number of Earth observation satellites have been deployed specifically to explore Earth from a space-based perspective. These satellites have significantly contributed to the understanding of a variety of Earth-based phenomena. For instance, the hole in the ozone layer was found by an artificial satellite that was exploring Earth's atmosphere, and satellites have allowed for the discovery of archeological sites or geological formations that were difficult or impossible to otherwise identify.
The Moon was the first celestial body to be the object of space exploration. It holds the distinctions of being the first remote celestial object to be flown by, orbited, and landed upon by spacecraft, and the only remote celestial object ever to be visited by humans.
In 1959, the Soviets obtained the first images of the far side of the Moon , never previously visible to humans. The U.S. exploration of the Moon began with the Ranger 4 impactor in 1962. Starting in 1966, the Soviets successfully deployed a number of landers to the Moon which were able to obtain data directly from the Moon's surface; just four months later, Surveyor 1 marked the debut of a successful series of U.S. landers. The Soviet uncrewed missions culminated in the Lunokhod program in the early 1970s, which included the first uncrewed rovers and also successfully brought lunar soil samples to Earth for study. This marked the first (and to date the only) automated return of extraterrestrial soil samples to Earth. Uncrewed exploration of the Moon continues with various nations periodically deploying lunar orbiters. China's Chang'e 4 in 2019 and Chang'e 6 in 2024 achieved the world's first landing and sample return on the far side of the Moon . India's Chandrayaan-3 in 2023 achieved the world's first landing on the lunar south pole region.
Crewed exploration of the Moon began in 1968 with the Apollo 8 mission that successfully orbited the Moon, the first time any extraterrestrial object was orbited by humans. In 1969, the Apollo 11 mission marked the first time humans set foot upon another world. Crewed exploration of the Moon did not continue for long. The Apollo 17 mission in 1972 marked the sixth landing and the most recent human visit. Artemis II is scheduled to complete a crewed flyby of the Moon in 2025, and Artemis III will perform the first lunar landing since Apollo 17 with it scheduled for launch no earlier than 2026. Robotic missions are still pursued vigorously.
The exploration of Mars has been an important part of the space exploration programs of the Soviet Union (later Russia), the United States, Europe, Japan and India. Dozens of robotic spacecraft , including orbiters , landers , and rovers , have been launched toward Mars since the 1960s. These missions were aimed at gathering data about current conditions and answering questions about the history of Mars. The questions raised by the scientific community are expected to not only give a better appreciation of the Red Planet but also yield further insight into the past, and possible future, of Earth.
The exploration of Mars has come at a considerable financial cost with roughly two-thirds of all spacecraft destined for Mars failing before completing their missions, with some failing before they even began. Such a high failure rate can be attributed to the complexity and large number of variables involved in an interplanetary journey, and has led researchers to jokingly speak of The Great Galactic Ghoul [ 32 ] which subsists on a diet of Mars probes. This phenomenon is also informally known as the " Mars Curse ". [ 33 ] In contrast to overall high failure rates in the exploration of Mars, India has become the first country to achieve success of its maiden attempt. India's Mars Orbiter Mission (MOM) [ 34 ] [ 35 ] [ 36 ] is one of the least expensive interplanetary missions ever undertaken with an approximate total cost of ₹ 450 Crore ( US$73 million ). [ 37 ] [ 38 ] The first mission to Mars by any Arab country has been taken up by the United Arab Emirates. Called the Emirates Mars Mission , it was launched on 19 July 2020 and went into orbit around Mars on 9 February 2021. The uncrewed exploratory probe was named "Hope Probe" and was sent to Mars to study its atmosphere in detail. [ 39 ]
The Russian space mission Fobos-Grunt , which launched on 9 November 2011, experienced a failure leaving it stranded in low Earth orbit . [ 40 ] It was to begin exploration of the Phobos and Martian circumterrestrial orbit, and study whether the moons of Mars, or at least Phobos, could be a "trans-shipment point" for spaceships traveling to Mars. [ 41 ]
Until the advent of space travel , objects in the asteroid belt were merely pinpricks of light in even the largest telescopes, their shapes and terrain remaining a mystery. Several asteroids have now been visited by probes, the first of which was Galileo , which flew past two: 951 Gaspra in 1991, followed by 243 Ida in 1993. Both of these lay near enough to Galileo' s planned trajectory to Jupiter that they could be visited at acceptable cost. The first landing on an asteroid was performed by the NEAR Shoemaker probe in 2000, following an orbital survey of the object, 433 Eros . The dwarf planet Ceres and the asteroid 4 Vesta , two of the three largest asteroids, were visited by NASA's Dawn spacecraft , launched in 2007.
Hayabusa was a robotic spacecraft developed by the Japan Aerospace Exploration Agency to return a sample of material from the small near-Earth asteroid 25143 Itokawa to Earth for further analysis. Hayabusa was launched on 9 May 2003 and rendezvoused with Itokawa in mid-September 2005. After arriving at Itokawa, Hayabusa studied the asteroid's shape, spin, topography, color, composition, density, and history. In November 2005, it landed on the asteroid twice to collect samples. The spacecraft returned to Earth on 13 June 2010.
The exploration of Jupiter has consisted solely of a number of automated NASA spacecraft visiting the planet since 1973. A large majority of the missions have been "flybys", in which detailed observations are taken without the probe landing or entering orbit; such as in Pioneer and Voyager programs. The Galileo and Juno spacecraft are the only spacecraft to have entered the planet's orbit. As Jupiter is believed to have only a relatively small rocky core and no real solid surface, a landing mission is precluded.
Reaching Jupiter from Earth requires a delta-v of 9.2 km/s, [ 42 ] which is comparable to the 9.7 km/s delta-v needed to reach low Earth orbit. [ 43 ] Fortunately, gravity assists through planetary flybys can be used to reduce the energy required at launch to reach Jupiter, albeit at the cost of a significantly longer flight duration. [ 42 ]
Jupiter has 95 known moons , many of which have relatively little known information about them.
Saturn has been explored only through uncrewed spacecraft launched by NASA, including one mission ( Cassini–Huygens ) planned and executed in cooperation with other space agencies. These missions consist of flybys in 1979 by Pioneer 11 , in 1980 by Voyager 1 , in 1982 by Voyager 2 and an orbital mission by the Cassini spacecraft, which lasted from 2004 until 2017.
Saturn has at least 62 known moons , although the exact number is debatable since Saturn's rings are made up of vast numbers of independently orbiting objects of varying sizes. The largest of the moons is Titan , which holds the distinction of being the only moon in the Solar System with an atmosphere denser and thicker than that of Earth. Titan holds the distinction of being the only object in the Outer Solar System that has been explored with a lander, the Huygens probe deployed by the Cassini spacecraft.
The exploration of Uranus has been entirely through the Voyager 2 spacecraft, with no other visits currently planned. Given its axial tilt of 97.77°, with its polar regions exposed to sunlight or darkness for long periods, scientists were not sure what to expect at Uranus. The closest approach to Uranus occurred on 24 January 1986. Voyager 2 studied the planet's unique atmosphere and magnetosphere . Voyager 2 also examined its ring system and the moons of Uranus including all five of the previously known moons, while discovering an additional ten previously unknown moons.
Images of Uranus proved to have a uniform appearance, with no evidence of the dramatic storms or atmospheric banding evident on Jupiter and Saturn. Great effort was required to even identify a few clouds in the images of the planet. The magnetosphere of Uranus, however, proved to be unique, being profoundly affected by the planet's unusual axial tilt. In contrast to the bland appearance of Uranus itself, striking images were obtained of the Moons of Uranus, including evidence that Miranda had been unusually geologically active.
The exploration of Neptune began with the 25 August 1989 Voyager 2 flyby, the sole visit to the system as of 2025. The possibility of a Neptune Orbiter has been discussed, but no other missions have been given serious thought.
Although the extremely uniform appearance of Uranus during Voyager 2 ' s visit in 1986 had led to expectations that Neptune would also have few visible atmospheric phenomena, the spacecraft found that Neptune had obvious banding, visible clouds, auroras , and even a conspicuous anticyclone storm system rivaled in size only by Jupiter's Great Red Spot . Neptune also proved to have the fastest winds of any planet in the Solar System, measured as high as 2,100 km/h. [ 44 ] Voyager 2 also examined Neptune's ring and moon system . It discovered 900 complete rings and additional partial ring "arcs" around Neptune. In addition to examining Neptune's three previously known moons, Voyager 2 also discovered five previously unknown moons, one of which, Proteus , proved to be the last largest moon in the system. Data from Voyager 2 supported the view that Neptune's largest moon, Triton , is a captured Kuiper belt object. [ 45 ]
The dwarf planet Pluto presents significant challenges for spacecraft because of its great distance from Earth (requiring high velocity for reasonable trip times) and small mass (making capture into orbit difficult at present). Voyager 1 could have visited Pluto, but controllers opted instead for a close flyby of Saturn's moon Titan, resulting in a trajectory incompatible with a Pluto flyby. Voyager 2 never had a plausible trajectory for reaching Pluto. [ 46 ]
After an intense political battle, a mission to Pluto dubbed New Horizons was granted funding from the United States government in 2003. [ 47 ] New Horizons was launched successfully on 19 January 2006. In early 2007 the craft made use of a gravity assist from Jupiter . Its closest approach to Pluto was on 14 July 2015; scientific observations of Pluto began five months prior to closest approach and continued for 16 days after the encounter.
The New Horizons mission also performed a flyby of the small planetesimal Arrokoth , in the Kuiper belt , in 2019. This was its first extended mission. [ 48 ]
Although many comets have been studied from Earth sometimes with centuries-worth of observations, only a few comets have been closely visited. In 1985, the International Cometary Explorer conducted the first comet fly-by ( 21P/Giacobini-Zinner ) before joining the Halley Armada studying the famous comet. The Deep Impact probe smashed into 9P/Tempel to learn more about its structure and composition and the Stardust mission returned samples of another comet's tail. The Philae lander successfully landed on Comet Churyumov–Gerasimenko in 2014 as part of the broader Rosetta mission .
Deep space exploration is the branch of astronomy , astronautics and space technology that is involved with the exploration of distant regions of outer space. [ 49 ] Physical exploration of space is conducted both by human spaceflights (deep-space astronautics) and by robotic spacecraft .
Some of the best candidates for future deep space engine technologies include anti-matter , nuclear power and beamed propulsion . [ 50 ] Beamed propulsion, appears to be the best candidate for deep space exploration presently available, since it uses known physics and known technology that is being developed for other purposes. [ 51 ]
Breakthrough Starshot is a research and engineering project by the Breakthrough Initiatives to develop a proof-of-concept fleet of light sail spacecraft named StarChip , [ 52 ] to be capable of making the journey to the Alpha Centauri star system 4.37 light-years away. It was founded in 2016 by Yuri Milner , Stephen Hawking , and Mark Zuckerberg . [ 53 ] [ 54 ]
An article in the science magazine Nature suggested the use of asteroids as a gateway for space exploration, with the ultimate destination being Mars. In order to make such an approach viable, three requirements need to be fulfilled: first, "a thorough asteroid survey to find thousands of nearby bodies suitable for astronauts to visit"; second, "extending flight duration and distance capability to ever-increasing ranges out to Mars"; and finally, "developing better robotic vehicles and tools to enable astronauts to explore an asteroid regardless of its size, shape or spin". Furthermore, using asteroids would provide astronauts with protection from galactic cosmic rays, with mission crews being able to land on them without great risk to radiation exposure.
The Artemis program is an ongoing crewed spaceflight program carried out by NASA , U.S. commercial spaceflight companies , and international partners such as ESA , [ 55 ] with the goal of landing "the first woman and the next man" on the Moon, specifically at the lunar south pole region. Artemis would be the next step towards the long-term goal of establishing a sustainable presence on the Moon, laying the foundation for private companies to build a lunar economy, and eventually sending humans to Mars .
In 2017, the lunar campaign was authorized by Space Policy Directive 1 , using various ongoing spacecraft programs such as Orion , the Lunar Gateway , Commercial Lunar Payload Services , and adding an undeveloped crewed lander. The Space Launch System will serve as the primary launch vehicle for Orion, while commercial launch vehicles are planned for use to launch other elements of the campaign. [ 56 ] NASA requested $1.6 billion in additional funding for Artemis for fiscal year 2020, [ 57 ] while the U.S. Senate Appropriations Committee requested from NASA a five-year budget profile [ 58 ] which is needed for evaluation and approval by the U.S. Congress . [ 59 ] [ 60 ] As of 2024, the first Artemis mission was launched in 2022 with the second mission, a crewed lunar flyby planned for 2025. [ 61 ] Construction on the Lunar Gateway is underway with initial capabilities set for the 2025–2027 timeframe. [ 62 ] The first CLPS lander landed in 2024, marking the first US spacecraft to land since Apollo 17 . [ 63 ]
The research that is conducted by national space exploration agencies, such as NASA and Roscosmos , is one of the reasons supporters cite to justify government expenses. Economic analyses of the NASA programs often showed ongoing economic benefits (such as NASA spin-offs ), generating many times the revenue of the cost of the program. [ 64 ] It is also argued that space exploration would lead to the extraction of resources on other planets and especially asteroids, which contain billions of dollars worth of minerals and metals. Such expeditions could generate substantial revenue. [ 65 ] In addition, it has been argued that space exploration programs help inspire youth to study in science and engineering. [ 66 ] Space exploration also gives scientists the ability to perform experiments in other settings and expand humanity's knowledge. [ 67 ]
Another claim is that space exploration is a necessity to humankind and that staying on Earth will eventually lead to extinction . Some of the reasons are lack of natural resources, comets, nuclear war, and worldwide epidemic. Stephen Hawking , renowned British theoretical physicist, said, "I don't think the human race will survive the next thousand years, unless we spread into space. There are too many accidents that can befall life on a single planet. But I'm an optimist. We will reach out to the stars." [ 68 ] Author Arthur C. Clarke (1950) presented a summary of motivations for the human exploration of space in his non-fiction semi-technical monograph Interplanetary Flight . [ 69 ] He argued that humanity's choice is essentially between expansion off Earth into space, versus cultural (and eventually biological) stagnation and death.
These motivations could be attributed to one of the first rocket scientists in NASA, Wernher von Braun , and his vision of humans moving beyond Earth. The basis of this plan was to:
Develop multi-stage rockets capable of placing satellites, animals, and humans in space.
Development of large, winged reusable spacecraft capable of carrying humans and equipment into Earth orbit in a way that made space access routine and cost-effective.
Construction of a large, permanently occupied space station to be used as a platform both to observe Earth and from which to launch deep space expeditions.
Launching the first human flights around the Moon, leading to the first landings of humans on the Moon, with the intent of exploring that body and establishing permanent lunar bases.
Assembly and fueling of spaceships in Earth orbit for the purpose of sending humans to Mars with the intent of eventually colonizing that planet. [ 70 ]
Known as the Von Braun Paradigm, the plan was formulated to lead humans in the exploration of space. Von Braun's vision of human space exploration served as the model for efforts in space exploration well into the twenty-first century, with NASA incorporating this approach into the majority of their projects. [ 70 ] The steps were followed out of order, as seen by the Apollo program reaching the moon before the space shuttle program was started, which in turn was used to complete the International Space Station. Von Braun's Paradigm formed NASA's drive for human exploration, in the hopes that humans discover the far reaches of the universe.
NASA has produced a series of public service announcement videos supporting the concept of space exploration. [ 71 ]
Overall, the U.S. public remains largely supportive of both crewed and uncrewed space exploration. According to an Associated Press Poll conducted in July 2003, 71% of U.S. citizens agreed with the statement that the space program is "a good investment", compared to 21% who did not. [ 72 ]
Space advocacy and space policy [ 73 ] regularly invokes exploration as a human nature . [ 74 ]
Spaceflight is the use of space technology to achieve the flight of spacecraft into and through outer space.
Spaceflight is used in space exploration, and also in commercial activities like space tourism and satellite telecommunications . Additional non-commercial uses of spaceflight include space observatories , reconnaissance satellites and other Earth observation satellites .
A spaceflight typically begins with a rocket launch , which provides the initial thrust to overcome the force of gravity and propels the spacecraft from the surface of Earth. Once in space, the motion of a spacecraft—both when unpropelled and when under propulsion—is covered by the area of study called astrodynamics . Some spacecraft remain in space indefinitely, some disintegrate during atmospheric reentry , and others reach a planetary or lunar surface for landing or impact.
Satellites are used for a large number of purposes. Common types include military (spy) and civilian Earth observation satellites, communication satellites, navigation satellites, weather satellites, and research satellites. Space stations and human spacecraft in orbit are also satellites.
The commercialization of space first started out with the launching of private satellites by NASA or other space agencies. Current examples of the commercial satellite use of space include satellite navigation systems , satellite television, satellite communications (such as internet services) and satellite radio . The next step of commercialization of space was seen as human spaceflight. Flying humans safely to and from space had become routine to NASA and Russia. [ 75 ] Reusable spacecraft were an entirely new engineering challenge, something only seen in novels and films like Star Trek and War of the Worlds. Astronaut Buzz Aldrin supported the use of making a reusable vehicle like the space shuttle. Aldrin held that reusable spacecraft were the key in making space travel affordable, stating that the use of "passenger space travel is a huge potential market big enough to justify the creation of reusable launch vehicles". [ 76 ] Space tourism is a next step in the use of reusable vehicles in the commercialization of space. The purpose of this form of space travel is personal pleasure.
Private spaceflight companies such as SpaceX and Blue Origin , and commercial space stations such as the Axiom Space and the Bigelow Commercial Space Station have changed the cost and overall landscape of space exploration, and are expected to continue to do so in the near future.
Astrobiology is the interdisciplinary study of life in the universe, combining aspects of astronomy , biology and geology. [ 77 ] It is focused primarily on the study of the origin , distribution and evolution of life. It is also known as exobiology (from Greek: έξω, exo , "outside"). [ 78 ] [ 79 ] [ 80 ] The term "Xenobiology" has been used as well, but this is technically incorrect because its terminology means "biology of the foreigners". [ 81 ] Astrobiologists must also consider the possibility of life that is chemically entirely distinct from any life found on Earth. [ 82 ] In the Solar System, some of the prime locations for current or past astrobiology are on Enceladus, Europa, Mars, and Titan. [ 83 ]
To date, the longest human occupation of space is the International Space Station which has been in continuous use for 24 years, 199 days. Valeri Polyakov 's record single spaceflight of almost 438 days aboard the Mir space station has not been surpassed. The health effects of space have been well documented through years of research conducted in the field of aerospace medicine . Analog environments similar to those experienced in space travel (like deep sea submarines), have been used in this research to further explore the relationship between isolation and extreme environments. [ 84 ] It is imperative that the health of the crew be maintained as any deviation from baseline may compromise the integrity of the mission as well as the safety of the crew, hence the astronauts must endure rigorous medical screenings and tests prior to embarking on any missions. However, it does not take long for the environmental dynamics of spaceflight to commence its toll on the human body; for example, space motion sickness (SMS) – a condition which affects the neurovestibular system and culminates in mild to severe signs and symptoms such as vertigo, dizziness, fatigue, nausea, and disorientation – plagues almost all space travelers within their first few days in orbit. [ 84 ] Space travel can also have an impact on the psyche of the crew members as delineated in anecdotal writings composed after their retirement. Space travel can adversely affect the body's natural biological clock ( circadian rhythm ); sleep patterns causing sleep deprivation and fatigue; and social interaction; consequently, residing in a Low Earth Orbit (LEO) environment for a prolonged amount of time can result in both mental and physical exhaustion. [ 84 ] Long-term stays in space reveal issues with bone and muscle loss in low gravity, immune system suppression, problems with eyesight, and radiation exposure. The lack of gravity causes fluid to rise upward which can cause pressure to build up in the eye, resulting in vision problems; the loss of bone minerals and densities; cardiovascular deconditioning; and decreased endurance and muscle mass. [ 85 ]
Radiation is an insidious health hazard to space travelers as it is invisible and can cause cancer. When above the Earth's magnetic field, spacecraft are no longer protected from the sun's radiation; the danger of radiation is even more potent in deep space. The hazards of radiation can be ameliorated through protective shielding on the spacecraft, alerts, and dosimetry . [ 86 ]
Fortunately, with new and rapidly evolving technological advancements, those in Mission Control are able to monitor the health of their astronauts more closely using telemedicine . One may not be able to completely evade the physiological effects of space flight, but those effects can be mitigated. For example, medical systems aboard space vessels such as the International Space Station (ISS) are well equipped and designed to counteract the effects of lack of gravity and weightlessness; on-board treadmills can help prevent muscle loss and reduce the risk of developing premature osteoporosis . [ 84 ] [ 86 ] Additionally, a crew medical officer is appointed for each ISS mission and a flight surgeon is available 24/7 via the ISS Mission Control Center located in Houston, Texas. [ 86 ] Although the interactions are intended to take place in real time, communications between the space and terrestrial crew may become delayed – sometimes by as much as 20 minutes [ 86 ] – as their distance from each other increases when the spacecraft moves further out of low Earth orbit; because of this the crew are trained and need to be prepared to respond to any medical emergencies that may arise on the vessel as the ground crew are hundreds of miles away.
Many past and current concepts for the continued exploration and colonization of space focus on a return to the Moon as a "steppingstone" to the other planets, especially Mars. At the end of 2006, NASA announced they were planning to build a permanent Moon base with continual presence by 2024. [ 87 ]
Beyond the technical factors that could make living in space more widespread, it has been suggested that the lack of private property , the inability or difficulty in establishing property rights in space, has been an impediment to the development of space for human habitation. Since the advent of space technology in the latter half of the twentieth century, the ownership of property in space has been murky, with strong arguments both for and against. In particular, the making of national territorial claims in outer space and on celestial bodies has been specifically proscribed by the Outer Space Treaty , which had been, as of 2012 [update] , ratified by all spacefaring nations . [ 88 ] Space colonization, also called space settlement and space humanization, would be the permanent autonomous (self-sufficient) human habitation of locations outside Earth, especially of natural satellites or planets such as the Moon or Mars , using significant amounts of in-situ resource utilization .
Participation and representation of humanity in space is an issue ever since the first phase of space exploration. [ 89 ] Some rights of non-spacefaring countries have been mostly secured through international space law , declaring space the " province of all mankind ", understanding spaceflight as its resource, though sharing of space for all humanity is still criticized as imperialist and lacking. [ 89 ] Additionally to international inclusion, the inclusion of women and people of colour has also been lacking. To reach a more inclusive spaceflight, some organizations like the Justspace Alliance [ 89 ] and IAU featured Inclusive Astronomy [ 90 ] have been formed in recent years.
The first woman to go to space was Valentina Tereshkova . She flew in 1963 but it was not until the 1980s that another woman entered space again. All astronauts were required to be military test pilots at the time and women were not able to join this career. This is one reason for the delay in allowing women to join space crews. [ 91 ] After the rule changed, Svetlana Savitskaya became the second woman to go to space, she was also from the Soviet Union . Sally Ride became the next woman in space and the first woman to fly to space through the United States program.
Since then, eleven other countries have allowed women astronauts. The first all-female space walk occurred in 2018, including Christina Koch and Jessica Meir . They had both previously participated in space walks with NASA. The first woman to go to the Moon is planned for 2026.
Despite these developments, women are underrepresented among astronauts and especially cosmonauts. Issues that block potential applicants from the programs, and limit the space missions they are able to go on, include:
Artistry in and from space ranges from signals, capturing and arranging material like Yuri Gagarin 's selfie in space or the image The Blue Marble , over drawings like the first one in space by cosmonaut and artist Alexei Leonov , music videos like Chris Hadfield's cover of Space Oddity on board the ISS, to permanent installations on celestial bodies like on the Moon .
Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion Arm → Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow ( → ) may be read as "within" or "part of". | https://en.wikipedia.org/wiki/Space_exploration |
A space force is a military branch of a nation's armed forces that conducts military operations in outer space and space warfare . The world's first space force was the Russian Space Forces , established in 1992 as an independent military service. However, it lost its independence twice, first being absorbed into the Strategic Rocket Forces from 1997–2001 and 2001–2011, then it merged with the Russian Air Force to form the Russian Aerospace Forces in 2015, where it now exists as a sub-branch. [ 1 ] As of 2025 [update] , there are two independent space forces: the United States Space Force and China's People's Liberation Army Aerospace Force .
Countries with smaller or developing space forces may combine their air and space forces under a single military branch, such as the Russian Aerospace Forces , Spanish Air and Space Force , French Air and Space Force , or Iranian Islamic Revolutionary Guard Corps Aerospace Force , or put them in an independent defense agency, such as the Indian Defence Space Agency . Countries with nascent military space capabilities usually organize them within their air forces . [ 1 ]
The first artificial object to cross the Kármán line , the boundary between air and space, was MW 18014 , an A-4 rocket launched by the German Heer on 20 June 1944 from the Peenemünde Army Research Center . The A4, more commonly known as the V-2, was the world's first ballistic missile , used by the Wehrmacht to launch long-range attacks on the Allied Forces on the Western Front during the Second World War . The designer of the A4, Wernher von Braun , had aspirations to use them as space launch vehicles. In both the United States and the Soviet Union, military space development began immediately after the Second World War concluded, with Wernher von Braun defecting to the Allies and both superpowers gathering V-2 rockets, research materials, and German scientists to jumpstart their own ballistic missile and space programs. [ 2 ]
In the United States, there was a fierce interservice rivalry between the U.S. Air Force and U.S. Army over which service would gain responsibility for the military space program. The Air Force, which had started developing its space program while it was still the Army Air Forces in 1945, saw space operations as an extension of its strategic airpower mission, while the Army argued that ballistic missiles were an extension of artillery . In 1946, the Navy began developing rockets primarily for Naval Research Laboratory projects rather than seeking to actively develop an operational space capability. Ultimately, the Air Force's space rivals in the Army Ballistic Missile Agency , Naval Research Laboratory , and Advanced Research Projects Agency were absorbed by NASA when it was created in 1958, leaving it as the only major military space organization within the U.S. Department of Defense. In 1954, General Bernard Schriever established the Western Development Division within Air Research and Development Command , becoming the U.S. military's first space organization, which continues to exist in the U.S. Space Force as the Space Systems Command , its research and development center. [ 3 ] [ 4 ]
During the 1960s and 1970s, Air Force space forces were organized within Aerospace Defense Command for missile defense and space surveillance forces, Strategic Air Command for weather reconnaissance satellites, and Air Force Systems Command for satellite communications, space launch, and space development systems. In 1982, U.S. Air Force space forces were centralized in Air Force Space Command , the first direct predecessor to the U.S. Space Force. U.S. space forces were first employed in the Vietnam War , and continued to provide satellite communications, weather, and navigation support during the 1982 Falklands War , 1983 United States invasion of Grenada , 1986 United States bombing of Libya , and 1989 United States invasion of Panama . The first major employment of space forces culminated in the Gulf War , where they proved so critical to the U.S.-led coalition, that it is sometimes referred to as the first space war. The first discussions of creating a military space service in the United States occurred in 1958, with the idea being floated by President Reagan as well in 1982. The 2001 Space Commission argued for the creation of a Space Corps between 2007 and 2011 and a bipartisan proposal in the U.S. Congress would have created a Space Corps in 2017. Then on 20 December 2019, the United States Space Force Act, part of the National Defense Authorization Act for 2020 , was signed, creating an independent space service by renaming and reorganizing Air Force Space Command into the United States Space Force. [ 5 ]
In the Soviet Union, the early space program was led by the OKB-1 design bureau, led by Sergei Korolev . Unlike in the United States, where the U.S. Air Force held preeminence in missile and space development, the Soviet Ground Forces , and specifically the Artillery of the Reserve of the Supreme High Command (RVGK), was responsible for missile and military space programs, with the RVGK responsible for the launch of Sputnik 1 , the world's first artificial satellite on 4 October 1957. [ 6 ] In 1960, Soviet military space forces were reorganized into the 3rd Department of the Main Missile Directorate of the Ministry of Defence , before in 1964 becoming a part of the new Soviet Strategic Rocket Forces Central Directorate of Space Assets. [ 7 ] [ 8 ] The Strategic Rocket Forces Central Directorate of Space Assets would be renamed the Main Directorate of Space Assets in 1970, being transferred to directly report to the Soviet Ministry of Defense in 1982, and in 1986 became the Chief Directorate of Space Assets. [ 7 ] Established in 1967, the Anti-Ballistic Missile and Anti-Space Defense Forces of the Soviet Air Defense Forces were responsible for space surveillance and defense operations. [ 9 ]
When the Soviet Union collapsed in 1991, the Russian Federation gained its space forces, with the Chief Directorate of Space Assets was reorganized into the Military Space Forces , an independent troops ( vid ) under the Russian Ministry of Defense, but not a military service ( vid ). The Soviet Air Defense Forces' Anti-Ballistic Missile and Anti-Space Defense Forces were reorganized into the Russian Air Defense Forces' Rocket and Space Defence Troops [ ru ] . [ 9 ] In 1997, the Rocket and Space Defence Troops and Military Space Forces were merged into the Strategic Missile Forces; it subordinated the priorities of the space troops to the missile forces, resulting in the establishment of the Russian Space Forces as independent troops in 2001. [ 10 ] [ 11 ] In 2011, the Russian Space Forces became the Russian Space Command , part of the Russian Aerospace Defense Forces , which merged Russia's space and air defense forces into one service. [ 12 ] In 2015, the Russian Air Force and Russian Aerospace Defense Forces were merged to form the Russian Aerospace Forces , which reestablished the Russian Space Forces as one of its three sub-branches, although it is no longer an independent entity. [ 1 ]
In 1998, the Chinese People's Liberation Army began creating its space forces under the General Armaments Department , before being reorganized and renamed as the People's Liberation Army Strategic Support Force Space Systems Department in 2015. [ 13 ] [ 14 ] The PLASSF was eventually dissolved in April 2024, with the space force element of the SSF becoming the People's Liberation Army Aerospace Force . [ 15 ]
In 2010, the French Armed Forces created the Joint Space Command, a joint organism under the authority of the Chief of the Defence Staff . In 2019, the French President Emmanuel Macron announced that the Joint Space Command would become the Space Command and the newest major command of the Air Force, which would be renamed to reflect an "evolution of its mission" into the area of outer space . [ 16 ] The Space Command is effective since 2019 and the Air Force was renamed Air and Space Force on 24 July 2020, with its new logo unveiled on 11 September 2020. [ 17 ]
In June 2022, the Spanish Government announced the Spanish Air Force would be renamed as the Spanish Air and Space Force . [ 18 ]
The following list outlines the independent space forces currently in operation: | https://en.wikipedia.org/wiki/Space_force |
A space fountain is a proposed form of an extremely tall tower extending into space. As known materials cannot support a static tower with this height, a space fountain has to be an active structure : A stream of pellets is accelerated upwards from a ground station. At the top it is deflected downwards. The necessary force for this deflection supports the station at the top and payloads going up the structure. [ 1 ] A spacecraft could launch from the top without having to deal with the atmosphere. This could reduce the cost of placing payloads into orbit. Its largest downside is that the tower will re-enter the atmosphere if the accelerator fails and the stream stops. This risk could be reduced by several redundant streams. [ 2 ]
The lower part of a pellet stream has to be in a vacuum tube to avoid excessive drag in the atmosphere. Similar to the top station, this tube can be supported by its own system of transferring momentum from a space-bound stream to a surface-bound stream. If the tube itself also accelerates the station-supporting stream, it would have to transfer additional momentum to an earth-bound stream in order to keep itself supported. The tube-supporting streams could also be designed to integrate with the station-supporting streams. [ 3 ]
Unlike a space elevator , this concept does not need extremely strong materials anywhere, and unlike space elevators and orbital rings , it does not need a 40,000-kilometre (25,000 mi) long structure. [ 3 ]
This engineering-related article is a stub . You can help Wikipedia by expanding it .
This article about futures studies is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Space_fountain |
In architecture and structural engineering , a space frame or space structure ( 3D truss ) is a rigid, lightweight, truss-like structure constructed from interlocking struts in a geometric pattern . Space frames can be used to span large areas with few interior supports. Like the truss, a space frame is strong because of the inherent rigidity of the triangle; flexing loads (bending moments ) are transmitted as tension and compression loads along the length of each strut.
Chief applications include buildings and vehicles.
Alexander Graham Bell from 1898 to 1908 developed space frames based on tetrahedral geometry. [ 1 ] [ 2 ] Bell's interest was primarily in using them to make rigid frames for nautical and aeronautical engineering, with the tetrahedral truss being one of his inventions.
Max Mengeringhausen developed the space grid system called MERO (acronym of ME ngeringhausen RO hrbauweise ) in 1943 in Germany, thus initiating the use of space trusses in architecture. [ 3 ] The commonly used method, still in use [ as of? ] , has individual tubular members connected at node joints (ball shaped) and variations such as the space deck system, octet truss system, and cubic system.
Stéphane de Chateau in France invented the Tridirectional SDC system (1957), Unibat system (1959), and Pyramitec (1960). [ 4 ] [ 5 ] A method of tree supports was developed to replace the individual columns. [ 6 ]
Buckminster Fuller patented the octet truss ( U.S. patent 2,986,241 ) in 1961 [ 7 ] while focusing on architectural structures.
Gilman's Tetrahedral Truss of 1980 was developed by John J. Gilman , a material scientist known for his work on the molecular matrices of crystalline solids. Gilman was an admirer of Buckminster Fuller's architectural trusses, and developed a stronger matrix, in part by rotating an alignment of tetrahedral nodes in relation to each other.
Space frames are typically designed using a rigidity matrix. The special characteristic of the stiffness matrix in an architectural space frame is the independence of the angular factors. If the joints are sufficiently rigid, then the angular deflections can be neglected, simplifying the calculations.
The simplest form of space frame is a horizontal slab of interlocking square pyramids and tetrahedra built from Aluminium or tubular steel struts. In many ways this looks like the horizontal jib of a tower crane repeated many times to make it wider. A stronger form is composed of interlocking tetrahedra in which all the struts have unit length. More technically this is referred to as an isotropic vector matrix or, in a single unit width, an octet truss. More complex variations change the lengths of the struts to curve the overall structure or may incorporate other geometrical shapes.
Within the meaning of space frame, we can find three systems clearly different between them: [ 8 ]
Curvature classification
Classification by the arrangement of its elements
Other examples classifiable as space frames are these:
Chief space frame applications include:
Buildings
Vehicles :
Architectural design elements
Space frames are a common feature in modern building construction; they are often found in large roof spans in modernist commercial and industrial buildings.
Examples of buildings based on space frames include:
Large portable stages and lighting gantries are also frequently built from space frames and octet trusses.
The CAC CA-6 Wackett and Yeoman YA-1 Cropmaster 250R aircraft were built using roughly the same welded steel-tube fuselage frame.
Many early "whirlybird"-style exposed-boom helicopters had tubular space-frame booms, such as the Bell 47 series.
Space frames are sometimes used in the chassis designs of automobiles and motorcycles . In both a space-frame and a tube-frame chassis, the suspension, engine, and body panels are attached to a skeletal frame of tubes, and the body panels have little or no structural function. By contrast, in a unibody or monocoque design, the body serves as part of the structure.
Tube-frame chassis pre-date space frame chassis and are a development of the earlier ladder chassis . The advantage of using tubes rather than the previous open-channel sections is that they resist torsional forces better. Some tube chassis were little more than a ladder chassis made with two large-diameter tubes, or even a single tube as a backbone chassis . Although many tubular chassis developed additional tubes and were even described as "space frames", their design was rarely correctly stressed as a space frame, and they behaved mechanically as a tube-ladder chassis, with additional brackets to support the attached components. The distinction of the true space frame is that all the forces in each strut are either tensile or compressive, never bending. [ 10 ] Although these additional tubes did carry some extra load, they were rarely diagonalised into a rigid space frame. [ 10 ]
An earlier contender for the first true space-frame chassis is the one-off Chamberlain 8 race "special" built by brothers Bob and Bill Chamberlain in Melbourne , Australia, in 1929. [ 11 ] Others attribute vehicles were produced in the 1930s by designers such as Buckminster Fuller and William Bushnell Stout (the Dymaxion and the Stout Scarab ) who understood the theory of the true space frame from either architecture or aircraft design. [ 12 ]
A post-WW2 attempt to build a racing car space frame was the Cisitalia D46 of 1946. [ 12 ] This used two small-diameter tubes along each side, but they were spaced apart by vertical smaller tubes, and so were not diagonalised in any plane. A year later, Porsche designed their Type 360 for Cisitalia . As this included diagonal tubes, it can be considered a true space frame and arguably the first mid-rear engined design. [ 12 ]
The Maserati Tipo 61 of 1959 (Birdcage) is often thought of as the first, but in 1949, Robert Eberan von Eberhorst designed the Jowett Jupiter exhibited at that year's London Motor Show ; the Jowett went on to take a class win at the 1950 Le Mans 24hr. Later, TVR , the small British car manufacturers, developed the concept and produced an alloy-bodied two-seater on a multi-tubular chassis, which appeared in 1949.
Colin Chapman of Lotus introduced his first "production" car, the Mark VI , in 1952. This was influenced by the Jaguar C-Type chassis, another with four tubes of two different diameters, separated by narrower tubes. Chapman reduced the main tube diameter for the lighter Lotus, but did not reduce the minor tubes any further, possibly because he considered that this would appear flimsy to buyers. [ 10 ] Although widely described as a space frame, Lotus did not build a true space-frame chassis until the Mark VIII , with the influence of other designers, with experience from the aircraft industry. [ 10 ]
A large number of kit cars use space frame construction, because manufacturing them in small quantity requires only simple and inexpensive jigs , and it is relatively easy for an amateur designer to achieve good stiffness with a space frame.
A drawback of the space-frame chassis is that it encloses much of the working volume of the car and can make access for both the driver and to the engine difficult. The Mercedes-Benz 300 SL "Gullwing" received its iconic upward-opening doors when its tubular space frame made using regular doors impossible.
Some space frames have been designed with removable sections, joined by bolted pin joints. Such a structure had already been used around the engine of the Lotus Mark III . [ 13 ] Although somewhat inconvenient, an advantage of the space frame is that the same lack of bending forces in the tubes that allow it to be modeled as a pin-jointed structure also means that creating such a removable section need not reduce the strength of the assembled frame.
Italian motorbike manufacturer Ducati extensively uses tube-frame chassis on its models.
Space frames have also been used in bicycles , which readily favor stressed triangular sectioning. | https://en.wikipedia.org/wiki/Space_frame |
Space geodesy is geodesy by means of sources external to Earth, mainly artificial satellites (in satellite geodesy ) but also quasars (in very-long-baseline interferometry , VLBI), visible stars (in stellar triangulation ), and the retroreflectors on the Moon (in lunar laser ranging , LLR).
This geodesy -related article is a stub . You can help Wikipedia by expanding it .
This space - or spaceflight -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Space_geodesy |
In mathematics , physics and chemistry , a space group is the symmetry group of a repeating pattern in space, usually in three dimensions . [ 1 ] The elements of a space group (its symmetry operations ) are the rigid transformations of the pattern that leave it unchanged. In three dimensions, space groups are classified into 219 distinct types, or 230 types if chiral copies are considered distinct. Space groups are discrete cocompact groups of isometries of an oriented Euclidean space in any number of dimensions. In dimensions other than 3, they are sometimes called Bieberbach groups .
In crystallography , space groups are also called the crystallographic or Fedorov groups , and represent a description of the symmetry of the crystal. A definitive source regarding 3-dimensional space groups is the International Tables for Crystallography Hahn (2002) .
Space groups in 2 dimensions are the 17 wallpaper groups which have been known for several centuries, though the proof that the list was complete was only given in 1891, after the much more difficult classification of space groups had largely been completed. [ 2 ]
In 1879 the German mathematician Leonhard Sohncke listed the 65 space groups (called Sohncke groups) whose elements preserve the chirality . [ 3 ] More accurately, he listed 66 groups, but both the Russian mathematician and crystallographer Evgraf Fedorov and the German mathematician Arthur Moritz Schoenflies noticed that two of them were really the same. The space groups in three dimensions were first enumerated in 1891 by Fedorov [ 4 ] (whose list had two omissions (I 4 3d and Fdd2) and one duplication (Fmm2)), and shortly afterwards in 1891 were independently enumerated by Schönflies [ 5 ] (whose list had four omissions (I 4 3d, Pc, Cc, ?) and one duplication (P 4 2 1 m)). The correct list of 230 space groups was found by 1892 during correspondence between Fedorov and Schönflies. [ 6 ] William Barlow ( 1894 ) later enumerated the groups with a different method, but omitted four groups (Fdd2, I 4 2d, P 4 2 1 d, and P 4 2 1 c) even though he already had the correct list of 230 groups from Fedorov and Schönflies; the common claim that Barlow was unaware of their work is incorrect. [ citation needed ] Burckhardt (1967) describes the history of the discovery of the space groups in detail.
The space groups in three dimensions are made from combinations of the 32 crystallographic point groups with the 14 Bravais lattices , each of the latter belonging to one of 7 lattice systems . What this means is that the action of any element of a given space group can be expressed as the action of an element of the appropriate point group followed optionally by a translation. A space group is thus some combination of the translational symmetry of a unit cell (including lattice centering ), the point group symmetry operations of reflection , rotation and improper rotation (also called rotoinversion), and the screw axis and glide plane symmetry operations. The combination of all these symmetry operations results in a total of 230 different space groups describing all possible crystal symmetries.
The number of replicates of the asymmetric unit in a unit cell is thus the number of lattice points in the cell times the order of the point group. This ranges from 1 in the case of space group P1 to 192 for a space group like Fm 3 m, the NaCl structure .
The elements of the space group fixing a point of space are the identity element, reflections, rotations and improper rotations , including inversion points .
The translations form a normal abelian subgroup of rank 3, called the Bravais lattice (so named after French physicist Auguste Bravais ). There are 14 possible types of Bravais lattice. The quotient of the space group by the Bravais lattice is a finite group which is one of the 32 possible point groups .
A glide plane is a reflection in a plane, followed by a translation parallel with that plane. This is noted by a {\displaystyle a} , b {\displaystyle b} , or c {\displaystyle c} , depending on which axis the glide is along. There is also the n {\displaystyle n} glide, which is a glide along the half of a diagonal of a face, and the d {\displaystyle d} glide, which is a fourth of the way along either a face or space diagonal of the unit cell. The latter is called the diamond glide plane as it features in the diamond structure. In 17 space groups, due to the centering of the cell, the glides occur in two perpendicular directions simultaneously, i.e. the same glide plane can be called b or c , a or b , a or c . For example, group Abm2 could be also called Acm2, group Ccca could be called Cccb. In 1992, it was suggested to use symbol e for such planes. The symbols for five space groups have been modified:
A screw axis is a rotation about an axis, followed by a translation along the direction of the axis. These are noted by a number, n , to describe the degree of rotation, where the number is how many operations must be applied to complete a full rotation (e.g., 3 would mean a rotation one third of the way around the axis each time). The degree of translation is then added as a subscript showing how far along the axis the translation is, as a portion of the parallel lattice vector. So, 2 1 is a twofold rotation followed by a translation of 1/2 of the lattice vector.
The general formula for the action of an element of a space group is
where M is its matrix, D is its vector, and where the element transforms point x into point y . In general, D = D ( lattice ) + D ( M ), where D ( M ) is a unique function of M that is zero for M being the identity. The matrices M form a point group that is a basis of the space group; the lattice must be symmetric under that point group, but the crystal structure itself may not be symmetric under that point group as applied to any particular point (that is, without a translation). For example, the diamond cubic structure does not have any point where the cubic point group applies.
The lattice dimension can be less than the overall dimension, resulting in a "subperiodic" space group. For (overall dimension, lattice dimension):
The 65 "Sohncke" space groups, not containing any mirrors, inversion points, improper rotations or glide planes, yield chiral crystals, not identical to their mirror image; whereas space groups that do include at least one of those give achiral crystals. Achiral molecules sometimes form chiral crystals, but chiral molecules always form chiral crystals, in one of the space groups that permit this.
Among the 65 Sohncke groups are 22 that come in 11 enantiomorphic pairs.
Only certain combinations of symmetry elements are possible in a space group. Translations are always present, and the space group P1 has only translations and the identity element. The presence of mirrors implies glide planes as well, and the presence of rotation axes implies screw axes as well, but the converses are not true. An inversion and a mirror implies two-fold screw axes, and so on.
There are at least ten methods of naming space groups. Some of these methods can assign several different names to the same space group, so altogether there are many thousands of different names.
The viewing directions of the 7 crystal systems are shown as follows.
There are (at least) 10 different ways to classify space groups into classes. The relations between some of these are described in the following table. Each classification system is a refinement of the ones below it. To understand an explanation given here it may be necessary to understand the next one down.
Arithmetic crystal classes may be interpreted as different orientations of the point groups in the lattice, with the group elements' matrix components being constrained to have integer coefficients in lattice space. This is rather easy to picture in the two-dimensional, wallpaper group case. Some of the point groups have reflections, and the reflection lines can be along the lattice directions, halfway in between them, or both.
These correspond to conjugacy classes of lattice point groups in GL n ( Z ), where the lattice point group is the group of symmetries of the underlying lattice that fix a point of the lattice, and contains the point group.
Conway , Delgado Friedrichs, and Huson et al. ( 2001 ) gave another classification of the space groups, called a fibrifold notation , according to the fibrifold structures on the corresponding orbifold . They divided the 219 affine space groups into reducible and irreducible groups. The reducible groups fall into 17 classes corresponding to the 17 wallpaper groups , and the remaining 35 irreducible groups are the same as the cubic groups and are classified separately.
In n dimensions, an affine space group, or Bieberbach group, is a discrete subgroup of isometries of n -dimensional Euclidean space with a compact fundamental domain. Bieberbach ( 1911 , 1912 ) proved that the subgroup of translations of any such group contains n linearly independent translations, and is a free abelian subgroup of finite index, and is also the unique maximal normal abelian subgroup. He also showed that in any dimension n there are only a finite number of possibilities for the isomorphism class of the underlying group of a space group, and moreover the action of the group on Euclidean space is unique up to conjugation by affine transformations. This answers part of Hilbert's eighteenth problem . Zassenhaus (1948) showed that conversely any group that is the extension [ when defined as? ] of Z n by a finite group acting faithfully is an affine space group. Combining these results shows that classifying space groups in n dimensions up to conjugation by affine transformations is essentially the same as classifying isomorphism classes for groups that are extensions of Z n by a finite group acting faithfully.
It is essential in Bieberbach's theorems to assume that the group acts as isometries; the theorems do not generalize to discrete cocompact groups of affine transformations of Euclidean space. A counter-example is given by the 3-dimensional Heisenberg group of the integers acting by translations on the Heisenberg group of the reals, identified with 3-dimensional Euclidean space. This is a discrete cocompact group of affine transformations of space, but does not contain a subgroup Z 3 .
This table gives the number of space group types in small dimensions, including the numbers of various classes of space group. The numbers of enantiomorphic pairs are given in parentheses.
In addition to crystallographic space groups there are also magnetic space groups (also called two-color (black and white) crystallographic groups or Shubnikov groups). These symmetries contain an element known as time reversal. They treat time as an additional dimension, and the group elements can include time reversal as reflection in it. They are of importance in magnetic structures that contain ordered unpaired spins, i.e. ferro- , ferri- or antiferromagnetic structures as studied by neutron diffraction . The time reversal element flips a magnetic spin while leaving all other structure the same and it can be combined with a number of other symmetry elements. Including time reversal there are 1651 magnetic space groups in 3D ( Kim 1999 , p.428). It has also been possible to construct magnetic versions for other overall and lattice dimensions ( Daniel Litvin's papers , ( Litvin 2008 ), ( Litvin 2005 )). Frieze groups are magnetic 1D line groups and layer groups are magnetic wallpaper groups, and the axial 3D point groups are magnetic 2D point groups. Number of original and magnetic groups by (overall, lattice) dimension:( Palistrant 2012 )( Souvignier 2006 )
Table of the wallpaper groups using the classification of the 2-dimensional space groups:
For each geometric class, the possible arithmetic classes are
Note: An e plane is a double glide plane, one having glides in two different directions. They are found in seven orthorhombic, five tetragonal and five cubic space groups, all with centered lattice. The use of the symbol e became official with Hahn (2002) .
The lattice system can be found as follows. If the crystal system is not trigonal then the lattice system is of the same type. If the crystal system is trigonal, then the lattice system is hexagonal unless the space group is one of the seven in the rhombohedral lattice system consisting of the 7 trigonal space groups in the table above whose name begins with R. (The term rhombohedral system is also sometimes used as an alternative name for the whole trigonal system.) The hexagonal lattice system is larger than the hexagonal crystal system, and consists of the hexagonal crystal system together with the 18 groups of the trigonal crystal system other than the seven whose names begin with R.
The Bravais lattice of the space group is determined by the lattice system together with the initial letter of its name, which for the non-rhombohedral groups is P, I, F, A or C, standing for the principal, body centered, face centered, A-face centered or C-face centered lattices. There are seven rhombohedral space groups, with initial letter R. | https://en.wikipedia.org/wiki/Space_group |
In computational complexity theory , the space hierarchy theorems are separation results that show that both deterministic and nondeterministic machines can solve more problems in (asymptotically) more space, subject to certain conditions. For example, a deterministic Turing machine can solve more decision problems in space n log n than in space n . The somewhat weaker analogous theorems for time are the time hierarchy theorems .
The foundation for the hierarchy theorems lies in the intuition that with either more time or more space comes the ability to compute more functions (or decide more languages). The hierarchy theorems are used to demonstrate that the time and space complexity classes form a hierarchy where classes with tighter bounds contain fewer languages than those with more relaxed bounds. Here we define and prove the space hierarchy theorem.
The space hierarchy theorems rely on the concept of space-constructible functions . The deterministic and nondeterministic space hierarchy theorems state that for all space-constructible functions f ( n ) {\displaystyle f(n)} and all g ( n ) ∈ o ( f ( n ) ) {\displaystyle g(n)\in o(f(n))} ,
where SPACE stands for either DSPACE or NSPACE , and o refers to the little o notation.
Formally, a function f : N ⟶ N {\displaystyle f:\mathbb {N} \longrightarrow \mathbb {N} } is space-constructible if f ( n ) ≥ log n {\displaystyle f(n)\geq \log ~n} and there exists a Turing machine
which computes the function f ( n ) {\displaystyle f(n)} in space O ( f ( n ) ) {\displaystyle O(f(n))} when starting
with an input 1 n {\displaystyle 1^{n}} , where 1 n {\displaystyle 1^{n}} represents a string of n consecutive 1s. Most of the common functions that we work with are space-constructible, including polynomials, exponents, and logarithms.
For every space-constructible function f : N ⟶ N {\displaystyle f:\mathbb {N} \longrightarrow \mathbb {N} } , there exists a language L that is decidable in space O ( f ( n ) ) {\displaystyle O(f(n))} but not in space o ( f ( n ) ) {\displaystyle o(f(n))} .
The goal is to define a language that can be decided in space O ( f ( n ) ) {\displaystyle O(f(n))} but not space o ( f ( n ) ) {\displaystyle o(f(n))} . The language is defined as L :
L = { ( ⟨ M ⟩ , 10 k ) : M uses space ≤ f ( | ⟨ M ⟩ , 10 k | ) and time ≤ 2 f ( | ⟨ M ⟩ , 10 k | ) and M does not accept ( ⟨ M ⟩ , 10 k ) } {\displaystyle L=\{~(\langle M\rangle ,10^{k}):M{\mbox{ uses space }}\leq f(|\langle M\rangle ,10^{k}|){\mbox{ and time }}\leq 2^{f(|\langle M\rangle ,10^{k}|)}{\mbox{ and }}M{\mbox{ does not accept }}(\langle M\rangle ,10^{k})~\}}
For any machine M that decides a language in space o ( f ( n ) ) {\displaystyle o(f(n))} , L will differ in at least one spot from the language of M . Namely, for some large enough k , M will use space ≤ f ( | ⟨ M ⟩ , 10 k | ) {\displaystyle \leq f(|\langle M\rangle ,10^{k}|)} on ( ⟨ M ⟩ , 10 k ) {\displaystyle (\langle M\rangle ,10^{k})} and will therefore differ at its value.
On the other hand, L is in S P A C E ( f ( n ) ) {\displaystyle {\mathsf {SPACE}}(f(n))} . The algorithm for deciding the language L is as follows:
Note on step 3: Execution is limited to 2 f ( | x | ) {\displaystyle 2^{f(|x|)}} steps in order to avoid the case where M does not halt on the input x . That is, the case where M consumes space of only O ( f ( x ) ) {\displaystyle O(f(x))} as required, but runs for infinite time.
The above proof holds for the case of PSPACE, but some changes need to be made for the case of NPSPACE. The crucial point is that while on a deterministic TM, acceptance and rejection can be inverted (crucial for step 4), this is not possible on a non-deterministic machine.
For the case of NPSPACE, L needs to be redefined first:
L = { ( ⟨ M ⟩ , 10 k ) : M uses space ≤ f ( | ⟨ M ⟩ , 10 k | ) and M accepts ( ⟨ M ⟩ , 10 k ) } {\displaystyle L=\{~(\langle M\rangle ,10^{k}):M{\mbox{ uses space }}\leq f(|\langle M\rangle ,10^{k}|){\mbox{ and }}M{\mbox{ accepts }}(\langle M\rangle ,10^{k})~\}}
Now, the algorithm needs to be changed to accept L by modifying step 4 to:
L can not be decided by a TM using o ( f ( n ) ) {\displaystyle o(f(n))} cells. Assuming L can be decided by some TM M using o ( f ( n ) ) {\displaystyle o(f(n))} cells, and following from the Immerman–Szelepcsényi theorem , L ¯ {\displaystyle {\overline {L}}} can also be determined by a TM (called M ¯ {\displaystyle {\overline {M}}} ) using o ( f ( n ) ) {\displaystyle o(f(n))} cells. Here lies the contradiction, therefore the assumption must be false:
The space hierarchy theorem is stronger than the analogous time hierarchy theorems in several ways:
It seems to be easier to separate classes in space than in time. Indeed, whereas the time hierarchy theorem has seen little remarkable improvement since its inception, the nondeterministic space hierarchy theorem has seen at least one important improvement by Viliam Geffert in his 2003 paper "Space hierarchy theorem revised". This paper made several generalizations of the theorem:
If space is measured as the number of cells used regardless of alphabet size, then S P A C E ( f ( n ) ) = S P A C E ( O ( f ( n ) ) ) {\displaystyle {\mathsf {SPACE}}(f(n))={\mathsf {SPACE}}(O(f(n)))} because one can achieve any linear compression by switching to a larger alphabet. However, by measuring space in bits, a much sharper separation is achievable for deterministic space. Instead of being defined up to a multiplicative constant, space is now defined up to an additive constant. However, because any constant amount of external space can be saved by storing the contents into the internal state, we still have S P A C E ( f ( n ) ) = S P A C E ( f ( n ) + O ( 1 ) ) {\displaystyle {\mathsf {SPACE}}(f(n))={\mathsf {SPACE}}(f(n)+O(1))} .
Assume that f is space-constructible. SPACE is deterministic.
The proof is similar to the proof of the space hierarchy theorem, but with two complications: The universal Turing machine has to be space-efficient, and the reversal has to be space-efficient. One can generally construct universal Turing machines with O ( log ( s p a c e ) ) {\displaystyle O(\log(space))} space overhead, and under appropriate assumptions, just O ( 1 ) {\displaystyle O(1)} space overhead (which may depend on the machine being simulated). For the reversal, the key issue is how to detect if the simulated machine rejects by entering an infinite (space-constrained) loop. Simply counting the number of steps taken would increase space consumption by about f ( n ) {\displaystyle f(n)} . At the cost of a potentially exponential time increase, loops can be detected space-efficiently as follows: [ 2 ]
Modify the machine to erase everything and go to a specific configuration A on success. Use depth-first search to determine whether A is reachable in the space bound from the starting configuration. The search starts at A and goes over configurations that lead to A. Because of determinism, this can be done in place and without going into a loop.
It can also be determined whether the machine exceeds a space bound (as opposed to looping within the space bound) by iterating over all configurations about to exceed the space bound and checking (again using depth-first search) whether the initial configuration leads to any of them.
For any two functions f 1 {\displaystyle f_{1}} , f 2 : N ⟶ N {\displaystyle f_{2}:\mathbb {N} \longrightarrow \mathbb {N} } , where f 1 ( n ) {\displaystyle f_{1}(n)} is o ( f 2 ( n ) ) {\displaystyle o(f_{2}(n))} and f 2 {\displaystyle f_{2}} is space-constructible, S P A C E ( f 1 ( n ) ) ⊊ S P A C E ( f 2 ( n ) ) {\displaystyle {\mathsf {SPACE}}(f_{1}(n))\subsetneq {\mathsf {SPACE}}(f_{2}(n))} .
This corollary lets us separate various space complexity classes.
For any natural number k, the function n k {\displaystyle n^{k}} is space-constructible. Therefore for any two natural numbers k 1 < k 2 {\displaystyle k_{1}<k_{2}} we can
prove S P A C E ( n k 1 ) ⊊ S P A C E ( n k 2 ) {\displaystyle {\mathsf {SPACE}}(n^{k_{1}})\subsetneq {\mathsf {SPACE}}(n^{k_{2}})} .
Savitch's theorem shows that N L ⊆ S P A C E ( log 2 n ) {\displaystyle {\mathsf {NL}}\subseteq {\mathsf {SPACE}}(\log ^{2}n)} , while the space hierarchy theorem shows that S P A C E ( log 2 n ) ⊊ S P A C E ( n ) {\displaystyle {\mathsf {SPACE}}(\log ^{2}n)\subsetneq {\mathsf {SPACE}}(n)} . The result is this corollary along with the fact that TQBF ∉ NL
since TQBF is PSPACE-complete.
This could also be proven using the non-deterministic space hierarchy theorem to show that NL ⊊ NPSPACE, and using Savitch's theorem to show that PSPACE = NPSPACE.
This last corollary shows the existence of decidable problems that are intractable. In other words, their decision procedures must use more than polynomial space.
There are problems in PSPACE requiring an arbitrarily large exponent to solve; therefore PSPACE does not collapse to DSPACE ( n k ) for some constant k .
To see it, assume the contrary, thus any problem decided in space O ( n ) {\displaystyle O(n)} is decided in time O ( n c ) {\displaystyle O(n^{c})} , and any problem L {\displaystyle L} decided in space O ( n b ) {\displaystyle O(n^{b})} is decided in time O ( ( n b ) c ) = O ( n b c ) {\displaystyle O((n^{b})^{c})=O(n^{bc})} . Now P := ⋃ k ∈ N D T I M E ( n k ) {\displaystyle {\mathsf {P}}:=\bigcup _{k\in \mathbb {N} }{\mathsf {DTIME}}(n^{k})} , thus P is closed under such a change of bound, that is ⋃ k ∈ N D T I M E ( n b k ) ⊆ P {\displaystyle \bigcup _{k\in \mathbb {N} }{\mathsf {DTIME}}(n^{bk})\subseteq {\mathsf {P}}} , so L ∈ P {\displaystyle L\in {\mathsf {P}}} . This implies that for all b , S P A C E ( n b ) ⊆ P ⊆ S P A C E ( n ) {\displaystyle b,{\mathsf {SPACE}}(n^{b})\subseteq {\mathsf {P}}\subseteq {\mathsf {SPACE}}(n)} , but the space hierarchy theorem implies that S P A C E ( n 2 ) ⊈ S P A C E ( n ) {\displaystyle {\mathsf {SPACE}}(n^{2})\not \subseteq {\mathsf {SPACE}}(n)} , and Corollary 6 follows. Note that this argument neither proves that P ⊈ S P A C E ( n ) {\displaystyle {\mathsf {P}}\not \subseteq {\mathsf {SPACE}}(n)} nor that S P A C E ( n ) ⊈ P {\displaystyle {\mathsf {SPACE}}(n)\not \subseteq {\mathsf {P}}} , as to reach a contradiction we used the negation of both sentences, that is we used both inclusions, and can only deduce that at least one fails. It is currently unknown which fail(s) but conjectured that both do, that is that S P A C E ( n ) {\displaystyle {\mathsf {SPACE}}(n)} and P {\displaystyle {\mathsf {P}}} are incomparable -at least for deterministic space. [ 3 ] This question is related to that of the time complexity of (nondeterministic) linear bounded automata which accept the complexity class N S P A C E ( n ) {\displaystyle {\mathsf {NSPACE}}(n)} (aka as context-sensitive languages , CSL); so by the above CSL is not known to be decidable in polynomial time -see also Kuroda's two problems on LBA . | https://en.wikipedia.org/wiki/Space_hierarchy_theorem |
Solar mirrors in space can be used to change the amount of sunlight that reaches the Earth. The concept was first theorised in 1923 by physicist Hermann Oberth [ 1 ] [ 2 ] [ 3 ] [ 4 ] and later developed in the 1980s by other scientists. [ 5 ] Space mirrors can be used to increase or decrease the amount of solar energy that reaches a specific point of the earth for various purposes.
There have been several proposed implementations of the space mirror concept but none have been implemented thus far other than the Znamya experiment by Russia, due to logistical concerns and challenges of deployment. [ 5 ] [ 6 ] Znamya successfully tested reflecting more sunlight to Earth.
They were theorised as a method of climate engineering through shading the Earth by creating a space sunshade to deflect sunlight and counter global warming . [ 5 ] [ 7 ]
The concept of constructing space mirrors as a method of climate engineering dates to the years 1923, 1929, 1957 and 1978 by the physicist Hermann Oberth and the 1980s by other scientists. In 1923, Hermann Oberth first described his space mirrors with a diameter of 100 to 300 km in his book „Die Rakete zu den Planetenräumen“, [ 1 ] which are said to consist of a grid network of individually adjustible facets.
Space mirrors in orbit around the Earth, as designed by Hermann Oberth , are intended to focus sunlight on individual regions of the earth's surface or deflect it into space.
It is therefore not a question of the weakening of the solar radiation on the entire exposed surface of the Earth, as would be the case when considering the establishment of shading areas at Lagrange point between the Sun and the Earth. These giant mirrors in orbit could be used to illuminate individual cities, as a means of protection against natural disasters, to control weather and climate, to create additional living space for tens of billions of people, Hermann Oberth writes. The fact that this could influence the trajectories of the barometric high and low pressure areas with these spatial mirrors seemed most important to Oberth. [ citation needed ]
The physicist Hermann Oberth followed his first suggestion in 1923 [ 1 ] with further publications, in which he took into account the technical progress achieved up to that point: 1929 „ Wege zur Raumschiffahrt “ (Ways to Spaceflight), [ 2 ] 1957 „Menschen im Weltraum. Neue Projekte für Raketen- und Raumfahrt“ (People in Space. New Projects for Rocket and Space Travel) [ 3 ] and 1978 „Der Weltraumspiegel“ (The Space Mirror). [ 4 ] For cost reasons, Hermann Oberth's concept envisages that the components should be produced from lunar minerals on the Moon, because its lower gravitational pull requires less energy to launch the components into lunar Orbit. In addition, the earth's atmosphere is not burdened by many rocket launches. From the lunar surface, the components would be launched into the lunar orbit by an electromagnetic lunar slingshot and „stacked“ at a 60° libration point. From there, the components could be transported into orbit with the electric spaceships he had designed [ 4 ] with little recoil, and there they would be assembled into mirrors with a diameter of 100 to 300 km. In 1978 he estimated that the realization could be expected between 2018 and 2038. [ citation needed ]
Other scientists proposed in the 1980s to cool Venus’ climate to provide for a theoretical future where humans occupy other planets. [ 8 ] In 1989, James Early, working at the Lawrence Livermore National Laboratory , proposed using a "space shade" 2,000 kilometres (1,200 miles) in diameter orbiting at Lagrangian Point L1 . He estimated the cost at between one and ten trillion US dollars and suggested manufacturing it on the Moon using Moon rock. [ 8 ]
Space mirrors are designed either to increase or decrease the amount of energy that reaches a planet from the sun with the goal of changing the impact of UV radiation; or, to reflect light onto or deflect light off of a planet in order to change the sun's lighting conditions. [ 9 ] [ 10 ] [ failed verification ] Space mirrors are an example of Solar Radiation Management (SRM), which is a "theoretical approach to reducing some of the impacts of climate change by reflecting a small amount of inbound sunlight back out into space." [ 11 ] [ unreliable source? ] [ 2 ] [ need quotation to verify ] The concept is to reflect enough sunlight to reduce the Earth's temperature thereby balancing out the warming effect of greenhouse gases. [ 11 ] [ unreliable source? ] [ 2 ] [ need quotation to verify ]
Most past proposals for the development of space mirrors are specifically to slow the progression of global warming on Earth. [ 9 ] [ failed verification ] Deflecting a small amount of the sun's energy from the Earth's atmosphere would reduce the amount of energy entering the ecosystem of the Earth.
Some proposals for the development of space mirrors also focus on the ability to change localized lighting conditions on the surface of the Earth by shading certain sections or reflecting sunlight onto small sections. [ 9 ] [ 2 ] Doing this could allow for differentiated climates in local areas and potentially additional sunlight for enhanced crop growth. [ 12 ] A first practical attempt at reflecting sunlight was made in the 1990s by the Russian Agency project name Znamya .
Geoengineering research efforts to mitigate or reverse global warming can be separated into two different categories, carbon dioxide removal and solar radiation management . [ 7 ] Carbon dioxide is the main source for climate change on Earth as it causes an increase in the atmospheric temperature and acidification of the oceans. Although CO 2 removal from the atmosphere would reverse climate changes thus far, removing carbon is a slower and more difficult process compared to solar radiation management. [ 7 ]
Solar radiation management works to directly mitigate the effects of atmospheric warming due to the burning of fossil fuels and subsequent release of greenhouse gases. [ 7 ] Space mirrors fall under this category of geoengineering as they work to block solar radiation and lower the warming effects from the Sun. [ 7 ]
There has been a range of proposals to reflect or deflect solar radiation from space, before it even reaches the atmosphere, commonly described as a space sunshade . [ 13 ] The most straightforward is to have mirrors orbiting around the Earth—an idea first suggested even before the wider awareness of climate change , with rocketry pioneer Hermann Oberth considering it a way to facilitate terraforming projects in 1923. [ 14 ] [ need quotation to verify ] and this was followed by other books in 1929, 1957 and 1978. [ 15 ] [ 16 ] [ 17 ] By 1992, the U.S. National Academy of Sciences described a plan to suspend 55,000 mirrors with an individual area of 100 square meters in a Low Earth orbit . [ 18 ] Another contemporary plan was to use space dust to replicate Rings of Saturn around the equator , although a large number of satellites would have been necessary to prevent it from dissipating. A 2006 variation on this idea suggested relying entirely on a ring of satellites electromagnetically tethered in the same location. In all cases, sunlight exerts pressure which can displace these reflectors from orbit over time, unless stabilized by enough mass. Yet, higher mass immediately drives up launch costs. [ 18 ]
In an attempt to deal with this problem, other researchers have proposed Inner lagrangian point between the Earth and the Sun as an alternative to near-Earth orbits, even though this tends to increase manufacturing or delivery costs instead. In 1989, a paper suggested founding a lunar colony , which would produce and deploy diffraction grating made out of a hundred million tonnes of glass . [ 19 ] In 1997, a single, very large mesh of aluminium wires "about one millionth of a millimetre thick" was also proposed. [ 20 ] [ self-published source? ] Two other proposals from the early 2000s advocated the use of thin metallic disks 50–60 cm in diameter, which would either be launched from the Earth at a rate of once per minute over several decades, or be manufactured from asteroids directly in orbit. [ 18 ]
When summarizing these options in 2009, the Royal Society concluded that their deployment times are measured in decades and costs in the trillions of USD , meaning that they are "not realistic potential contributors to short-term, temporary measures for avoiding dangerous climate change", and may only be competitive with the other geoengineering approaches when viewed from a genuinely long (a century or more) perspective, as the long lifetime of L1-based approaches could make them cheaper than the need to continually renew atmospheric-based measures over that timeframe. [ 18 ]
In 2021, researchers in Sweden considered building solar sails in the near-Earth orbit, which would then arrive to L1 point over 600 days one by one. Once they all form an array in situ, the combined 1.5 billion sails would have total area of 3.75 million square kilometers, while their combined mass is estimated in a range between 83 million tons (present-day technology) and 34 million tons (optimal advancements). This proposal would cost between five and ten trillion dollars, but only once launch cost has been reduced to US$50/kg, which represents a massive reduction from the present-day costs of $4400–2700/kg [ 21 ] for the most widely used launch vehicles. [ 22 ]
In 2002, the aerospace consulting company STAR Technology and Research proposed a concept which, like Hermann Oberth's concept, uses the near-Earth orbit. Star's experts calculated that a network of steerable space mirrors orbiting Earth's equator, like one of the rings of Saturn, could lower the average air temperature by up to 3 degrees Celsius (5.4 degrees Fahrenheit) while simultaneously generating power from onboard solar panels and beaming it to Earth. But such an approach could generate problems. Report author and Star Technology president Jerome Pearson calculated it would take 5 million spacecraft to achieve the desired result, and even if each individual craft could last 100 years, that means 137 ships would have to be replaced or repaired per day. And the craft would produce "stars" that would be visible from the ground. (Pearson's other hypothetical proposal, a ring of reflective rocks in the same position, would light the night sky with the equivalent of 12 full moons.). [ 5 ] [ 23 ]
In the 1980s there were more theoretical proposals for space mirrors as scientists attempted to discover a feasible way to partially reflect sunlight and slow down the warming of the Earth's atmosphere using space mirrors. [ 5 ] In 1989, engineer James Early proposed a 2,000 km glass shield. [ 24 ] The glass shield would need to be constructed on the Moon using moon rock due to its sheer mass. [ 24 ] Lowell Wood, a researcher at the Lawrence Livermore National Laboratory, proposed sending a single, massive mirror into orbit at Lagrange point L1, approximately one million miles away from Earth. [ 5 ] [ 25 ] While orbiting at the Lagrange point 1 , the space mirror would be able to remain in orbit without any additional energy supplies and continue to block sunlight. [ 25 ] In 2006, Roger Angel, a researcher at the University of Arizona, proposed sending millions of smaller space mirrors as opposed to one large mirror to reduce costs and increase feasibility as a single mirror would need to be approximately 600,000 square miles to block just one percent of sunlight. [ 5 ]
The Znamya project was a series of orbital mirror experiments in the 1990s that intended to beam solar power to Earth by reflecting sunlight . It consisted of three experiments the Znamya 1, Znamya 2 experiment, and the failed Znamya 2.5. The Znamya 1 was a ground experiment that never was launched. [ 26 ] The Znamya 2 was the first successful launch the Znamya project had. It was attached to the unmanned Progress M-15. [ 26 ] The deployment resulted in a bright light of a width of 5km and with the intensity of a Full Moon being shined. [ 26 ] The Znamya 3 was proposed but never acted upon because of the failure of the Znamya 2.5. [ 26 ] The project was abandoned by the Russian Federal Space Agency after the failed deployment of the Znamya 2.5. [ 6 ]
After the Russian Znamya space mirror experiment in 1993, there has not been any active development of space mirrors due to the sheer challenges involved in their deployment and the potential consequences that follow their operation.
Climate experts have cautioned that geoengineering proposals like space mirrors, while potentially being able to cool the planet, would not provide any benefit for other climate related problems like high acidity levels in the ocean due to the build up of carbon. [ 9 ] In the past, many scientists have also resisted the idea of using geoengineering to curb climate change, as the risks of causing adverse effects were too great and they worried it would encourage people to continue to use fossil fuels that contribute to that change. [ 9 ]
In 2007 the US government recommended that research on sunlight deflection, including space mirrors, be continued in line with the next United Nations Report on Climate Change. [ 27 ] [ 28 ] In addition to the space mirror, suggested sunlight-reducing techniques included launching thousands of highly reflective balloons and pumping sulphate droplets into the upper atmosphere to emulate volcanic emissions. [ 8 ] [ 27 ]
Andrew Yang , a Democratic US presidential candidate in 2020, revived the space mirror movement with his expandable space mirror initiative. [ 29 ] According to Yang's proposal, US researchers need to create satellites, similar to those already in orbit, equipped with retractable space mirrors with the ability to deploy and retract quickly and easily in case of an emergency. [ 29 ]
The deployment and maintenance of a fleet of small space mirrors that can create a shade of around 100,000 kilometers in space would include necessary factors such as energy, construction, transportation, and ground support operations. [ 30 ] Overall, the estimated cost of constructing and sending a fleet of space mirrors to space is around 750 billion dollars. [ 30 ] If the space mirrors are able to achieve a 50-year lifetime, the annual maintenance cost estimates to around 100 billion dollars. [ 30 ] Furthermore, if any individual satellite needed to be replaced at the end of their lifetime, the costs of the entire operation would amount to 5 trillion dollars. [ 30 ]
The deployment of either one large space mirror or a fleet of smaller mirror will also have to take into consideration of the millions of space debris within the Earth's orbit. Most debris is small, weighing around 1 gram. [ 30 ] However, depending on their speed, such debris can be catastrophic for satellites if they were to collide. Therefore, orbital satellites would need to maneuver out of the path of tracked space debris from the space mirror. Additionally, if one very large space mirror were to be deployed, its massive surface area will be a very large target for space debris. Therefore, maneuvering hundreds of space mirrors or one very large space mirror will prove to be very difficult due to the space debris and the potential size of the space mirror. [ 30 ] | https://en.wikipedia.org/wiki/Space_mirror |
A space station (or orbital station ) is a spacecraft which remains in orbit and hosts humans for extended periods of time. It therefore is an artificial satellite featuring habitation facilities . The purpose of maintaining a space station varies depending on the program. Most often space stations have been research stations , but they have also served military or commercial uses , such as hosting space tourists .
Space stations have been hosting the only continuous presence of humans in space . The first space station was Salyut 1 (1971), hosting the first crew, of the ill-fated Soyuz 11 . Consecutively space stations have been operated since Skylab (1973) and occupied since 1987 with the Salyut successor Mir . Uninterrupted occupation has been sustained since the operational transition from the Mir to the International Space Station (ISS), with its first occupation in 2000.
Currently there are two fully operational space stations – the ISS and China 's Tiangong Space Station (TSS), which have been occupied since October 2000 with Expedition 1 and since June 2022 with Shenzhou 14 . The highest number of people at the same time on one space station has been 13, first achieved with the eleven day docking to the ISS of the 127th Space Shuttle mission in 2009. The record for most people on all space stations at the same time has been 17, first on May 30, 2023, with 11 people on the ISS and 6 on the TSS. [ 1 ]
Space stations are often modular , featuring docking ports , through which they are built and maintained, allowing the joining or movement of modules and the docking of other spacecrafts for the exchange of people, supplies and tools. While space stations generally do not leave their orbit, they do feature thrusters for station keeping .
The first mention of anything resembling a space station occurred in Edward Everett Hale 's 1868 " The Brick Moon ". [ 2 ] The first to give serious, scientifically grounded consideration to space stations were Konstantin Tsiolkovsky and Hermann Oberth about two decades apart in the early 20th century. [ 3 ]
In 1929, Herman Potočnik 's The Problem of Space Travel was published, the first to envision a "rotating wheel" space station to create artificial gravity . [ 2 ] Conceptualized during the Second World War , the " sun gun " was a theoretical orbital weapon orbiting Earth at a height of 8,200 kilometres (5,100 mi). No further research was ever conducted. [ 4 ] In 1951, Wernher von Braun published a concept for a rotating wheel space station in Collier's Weekly , referencing Potočnik's idea. However, development of a rotating station was never begun in the 20th century. [ 3 ]
The first human flew to space and concluded the first orbit on April 12, 1961, with Vostok 1 .
The Apollo program had in its early planning instead of a lunar landing a crewed lunar orbital flight and an orbital laboratory station in orbit of Earth, at times called Project Olympus , as two different possible program goals, until the Kennedy administration sped ahead and made the Apollo program focus on what was originally planned to come after it, the lunar landing. The Project Olympus space station, or orbiting laboratory of the Apollo program, was proposed as an in-space unfolded structure with the Apollo command and service module docking. [ 5 ] While never realized, the Apollo command and service module would perform docking maneuvers and eventually become a lunar orbiting module which was used for station-like purposes.
But before that the Gemini program paved the way and achieved the first space rendezvous (undocked) with Gemini 6 and Gemini 7 in 1965. Subsequently in 1966 Neil Armstrong performed on Gemini 8 the first ever space docking, while in 1967 Kosmos 186 and Kosmos 188 were the first spacecrafts that docked automatically.
In January 1969, Soyuz 4 and Soyuz 5 performed the first docked, but not internal, crew transfer, and in March, Apollo 9 performed the first ever internal transfer of astronauts between two docked spaceships.
In 1971, the Soviet Union developed and launched the world's first space station, Salyut 1 . [ 6 ] The Almaz and Salyut series were eventually joined by Skylab , Mir , and Tiangong-1 and Tiangong-2 . The hardware developed during the initial Soviet efforts remains in use, with evolved variants comprising a considerable part of the ISS, orbiting today. Each crew member stays aboard the station for weeks or months but rarely more than a year.
Early stations were monolithic designs that were constructed and launched in one piece, generally containing all their supplies and experimental equipment. A crew would then be launched to join the station and perform research. After the supplies had been consumed, the station was abandoned. [ 6 ]
The first space station was Salyut 1 , which was launched by the Soviet Union on April 19, 1971. The early Soviet stations were all designated "Salyut", but among these, there were two distinct types: civilian and military. The military stations, Salyut 2 , Salyut 3 , and Salyut 5 , were also known as Almaz stations. [ 7 ]
The civilian stations Salyut 6 and Salyut 7 were built with two docking ports, which allowed a second crew to visit, bringing a new spacecraft with them; the Soyuz ferry could spend 90 days in space, at which point it needed to be replaced by a fresh Soyuz spacecraft. [ 8 ] This allowed for a crew to man the station continually. The American Skylab (1973–1979) was also equipped with two docking ports, like second-generation stations, but the extra port was never used. The presence of a second port on the new stations allowed Progress supply vehicles to be docked to the station, meaning that fresh supplies could be brought to aid long-duration missions. This concept was expanded on Salyut 7, which "hard docked" with a TKS tug shortly before it was abandoned; this served as a proof of concept for the use of modular space stations. The later Salyuts may reasonably be seen as a transition between the two groups. [ 7 ]
Unlike previous stations, the Soviet space station Mir had a modular design ; a core unit was launched, and additional modules, generally with a specific role, were later added. This method allows for greater flexibility in operation, as well as removing the need for a single immensely powerful launch vehicle . Modular stations are also designed from the outset to have their supplies provided by logistical support craft, which allows for a longer lifetime at the cost of requiring regular support launches. [ 9 ]
The ISS is divided into two main sections, the Russian Orbital Segment (ROS) and the US Orbital Segment (USOS). The first module of the ISS, Zarya , was launched in 1998. [ 10 ]
The Russian Orbital Segment's "second-generation" modules were able to launch on Proton , fly to the correct orbit, and dock themselves without human intervention. [ 11 ] Connections are automatically made for power, data, gases, and propellants. The Russian autonomous approach allows the assembly of space stations prior to the launch of crew.
The Russian "second-generation" modules are able to be reconfigured to suit changing needs. As of 2009, RKK Energia was considering the removal and reuse of some modules of the ROS on the Orbital Piloted Assembly and Experiment Complex after the end of mission is reached for the ISS. [ 12 ] However, in September 2017, the head of Roscosmos said that the technical feasibility of separating the station to form OPSEK had been studied, and there were now no plans to separate the Russian segment from the ISS. [ 13 ]
In contrast, the main US modules launched on the Space Shuttle and were attached to the ISS by crews during EVAs . Connections for electrical power, data, propulsion, and cooling fluids are also made at this time, resulting in an integrated block of modules that is not designed for disassembly and must be deorbited as one mass. [ 14 ]
Axiom Station is a planned commercial space station that will begin as a single module docked to the ISS. Axiom Space gained NASA approval for the venture in January 2020. The first module, the Payload Power Transfer Module (PPTM), is expected to be launched to the ISS no earlier than 2027. [ 15 ] PPTM will remain at the ISS until the launch of Axiom's Habitat One (Hab-1) module about one year later, after which it will detach from the ISS to join with Hab-1. [ 15 ]
China's first space laboratory, Tiangong-1 was launched in September 2011. [ 16 ] The uncrewed Shenzhou 8 then successfully performed an automatic rendezvous and docking in November 2011. The crewed Shenzhou 9 then docked with Tiangong-1 in June 2012, followed by the crewed Shenzhou 10 in 2013. [ citation needed ]
According to the China Manned Space Engineering Office , Tiangong-1 reentered over the South Pacific Ocean , northwest of Tahiti , on 2 April 2018 at 00:15 UTC. [ 17 ] [ 18 ]
A second space laboratory Tiangong-2 was launched in September 2016, while a plan for Tiangong-3 was merged with Tiangong-2. [ 19 ] The station made a controlled reentry on 19 July 2019 and burned up over the South Pacific Ocean. [ 20 ]
The Tiangong Space Station ( Chinese : 天宫 ; pinyin : Tiāngōng ; lit. 'Heavenly Palace'), the first module of which was launched on 29 April 2021, [ 21 ] is in low Earth orbit, 340 to 450 kilometres above the Earth at an orbital inclination of 42° to 43°. The core module was extended in 2022 with two laboratory modules, bringing the total station capacity to six crew members. The station was completed on 5 November 2022. [ 22 ] [ 23 ] [ 24 ]
These space stations have been announced by their host entity and are currently in planning, development or production. The launch date listed here may change as more information becomes available.
(14,126 cu ft)
(~23,548 cu ft)
(29,000 cu ft)
(~15892 cu ft)
While originally Lockheed Martin was included in the project, as of 2024, it appears their primary role has been filled by Airbus , to provide the main habitat for the station. [ 40 ] As of 2024, they are no longer listed as a partner on Starlab's website. [ 41 ]
[ 26 ]
Two types of space stations have been flown: monolithic and modular. Monolithic stations consist of a single vehicle and are launched by one rocket. Modular stations consist of two or more separate vehicles that are launched independently and docked on orbit. Modular stations are currently preferred due to lower costs and greater flexibility. [ 48 ] [ 49 ]
A space station is a complex vehicle that must incorporate many interrelated subsystems, including structure, electrical power, thermal control, attitude determination and control , orbital navigation and propulsion, automation and robotics, computing and communications, environmental and life support, crew facilities, and crew and cargo transportation. Stations must serve a useful role, which drives the capabilities required. [ citation needed ]
Space stations are made from durable materials that have to weather space radiation , internal pressure, micrometeoroids , thermal effects of the sun and cold temperatures for long periods of time. They are typically made from stainless steel , titanium and high-quality aluminum alloys , with layers of insulation such as Kevlar as a ballistics shield protection. [ 50 ]
The International Space Station (ISS) has a single inflatable module, the Bigelow Expandable Activity Module , which was installed in April 2016 after being delivered to the ISS on the SpaceX CRS-8 resupply mission. [ 51 ] [ 52 ] This module, based on NASA research in the 1990s, weighs 1,400 kilograms (3,100 lb) and was transported while compressed before being attached to the ISS by the space station arm and inflated to provide a 16 cubic metres (21 cu yd) volume. Whilst it was initially designed for a 2 year lifetime it was still attached and being used for storage in August 2022. [ 53 ] [ 54 ]
The space station environment presents a variety of challenges to human habitability, including short-term problems such as the limited supplies of air, water, and food and the need to manage waste heat , and long-term ones such as weightlessness and relatively high levels of ionizing radiation . These conditions can create long-term health problems for space-station inhabitants, including muscle atrophy , bone deterioration , balance disorders , eyesight disorders , and elevated risk of cancer . [ 55 ]
Future space habitats may attempt to address these issues, and could be designed for occupation beyond the weeks or months that current missions typically last. Possible solutions include the creation of artificial gravity by a rotating structure , the inclusion of radiation shielding , and the development of on-site agricultural ecosystems. Some designs might even accommodate large numbers of people, becoming essentially "cities in space" where people would reside semi-permanently. [ 56 ]
Molds that develop aboard space stations can produce acids that degrade metal, glass, and rubber. Despite an expanding array of molecular approaches for detecting microorganisms, rapid and robust means of assessing the differential viability of the microbial cells, as a function of phylogenetic lineage, remain elusive. [ 57 ]
Like uncrewed spacecraft close to the Sun, space stations in the inner Solar System generally rely on solar panels to obtain power. [ 58 ]
Space station air and water is brought up in spacecraft from Earth before being recycled. Supplemental oxygen can be supplied by a solid fuel oxygen generator . [ 59 ]
The last military-use space station was the Soviet Salyut 5 , which was launched under the Almaz program and orbited between 1976 and 1977. [ 60 ] [ 61 ] [ 62 ]
Space stations have harboured so far the only long-duration direct human presence in space. After the first station, Salyut 1 (1971), and its tragic Soyuz 11 crew, space stations have been operated consecutively since Skylab (1973–1974), having allowed a progression of long-duration direct human presence in space. Long-duration resident crews have been joined by visiting crews since 1977 ( Salyut 6 ), and stations have been occupied by consecutive crews since 1987 with the Salyut successor Mir . Uninterrupted occupation of stations has been achieved since the operational transition from the Mir to the ISS , with its first occupation in 2000. The ISS has hosted the highest number of people in orbit at the same time, reaching 13 for the first time during the eleven day docking of STS-127 in 2009. [ 63 ]
The duration record for a single spaceflight is 437.75 days, set by Valeri Polyakov aboard Mir from 1994 to 1995. [ 64 ] As of 2021 [update] , four cosmonauts have completed single missions of over a year, all aboard Mir .
Many spacecraft are used to dock with the space stations. Soyuz flight T-15 in March to July 1986 was the first and as of 2016, only spacecraft to visit two different space stations, Mir and Salyut 7 . [ 65 ]
The International Space Station has been supported by many different spacecraft.
The Tiangong space station is supported by the following spacecraft:
The Tiangong program relied on the following spacecraft.
The Mir space station was in orbit from 1986 to 2001 and was supported and visited by the following spacecraft:
Research conducted on the Mir included the first long term space based ESA research project EUROMIR 95 which lasted 179 days and included 35 scientific experiments. [ 104 ]
During the first 20 years of operation of the International Space Station, there were around 3,000 scientific experiments in the areas of biology and biotech, technology development, educational activities, human research, physical science, and Earth and space science. [ 105 ] [ 106 ]
Space stations provide a useful platform to test the performance, stability, and survivability of materials in space. This research follows on from previous experiments such as the Long Duration Exposure Facility , a free flying experimental platform which flew from April 1984 until January 1990. [ 107 ] [ 108 ]
On the International Space Station , guests sometimes pay $50 million to spend the week living as an astronaut . Later, space tourism is slated to expand once launch costs are lowered sufficiently. By the end of the 2020s, space hotels may become relatively common. [ citation needed ]
As it currently costs on average $10,000 to $25,000 per kilogram to launch anything into orbit, space stations remain the exclusive province of government space agencies, which are primarily funded by taxation . In the case of the International Space Station , space tourism makes up a small portion of money to run it.
Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion Arm → Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow ( → ) may be read as "within" or "part of". | https://en.wikipedia.org/wiki/Space_station |
A space sunshade or sunshield is something that diverts or otherwise reduces some of the Sun's radiation , preventing it from hitting the Earth and thereby reducing its insolation , which results in reduced heating. Light can be diverted by different methods. The concept of the construction of sunshade as a method of climate engineering dates back to the years 1923, 1929, 1957 and 1978 by the physicist Hermann Oberth . [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ need quotation to verify ] Space mirrors in orbit around the Earth with a diameter of 100 to 300 km, as designed by Hermann Oberth, were intended to focus sunlight on individual regions of the Earth’s surface or deflect it into space so that the solar radiation is weakened in a specifically controlled manner for individual regions on the Earth’s surface.
First proposed in 1989, another space sunshade concept involves putting a large occulting disc, or technology of equivalent purpose, between the Earth and Sun.
A sunshade could potentially be one climate engineering method for mitigating global warming through solar radiation management , because internationally negotiated reductions in carbon emissions may be insufficient to stem climate change. [ 5 ] [ 6 ] Sunshades could also be used to produce space solar power , acting as solar power satellites . Proposed shade designs include a single-piece shade and a shade made by a great number of small objects. Most such proposals contemplate a blocking element at the Sun-Earth L1 Lagrangian point .
Modern proposals are based on some form of distributed sunshade composed of lightweight transparent elements or inflatable "space bubbles" manufactured in space to reduce the cost of launching massive objects to space. [ 7 ] [ 8 ] However it would cost trillions of dollars and no prototype has yet been launched. [ 9 ] Critics also argue that building it would be too slow to prevent dangerous levels of global warming. [ 10 ]
One proposed sunshade would be composed of 16 trillion small disks at the Sun-Earth L1 Lagrangian point , 1.5 million kilometers from Earth and between it and the Sun. Each disk is proposed to have a 0.6-meter diameter and a thickness of about 5 micrometers. The mass of each disk would be about a gram, adding up to a total of almost 20 million tonnes. [ 11 ] Such a group of small sunshades that blocks 2% of the sunlight, deflecting it off into space, would be enough to halt global warming. [ 12 ] If 100 tonnes of disks were launched to low Earth orbit every day, it would take 550 years to launch all of them.
The individual autonomous flyers building up the cloud of sunshades are proposed not to reflect the sunlight but rather to be transparent lenses, deflecting the light slightly so it does not hit Earth. This minimizes the effect of solar radiation pressure on the units, requiring less effort to hold them in place at the L1 point. An optical prototype has been constructed by Roger Angel with funding from NIAC . [ 13 ]
The remaining solar pressure and the fact that the L1 point is one of unstable equilibrium , easily disturbed by the wobble of the Earth due to gravitational effects from the Moon, requires the small autonomous flyers to be capable of maneuvering themselves to hold position. A suggested solution is to place mirrors capable of rotation on the surface of the flyers. By using the solar radiation pressure on the mirrors as solar sails and tilting them in the right direction, the flyer will be capable of altering its speed and direction to keep in position. [ 14 ]
Such a group of sunshades would need to occupy an area of about 3.8 million square kilometers if placed at the L1 point [ 14 ] (see other lower disc size estimates below).
It would still take years to launch enough of the disks into orbit to have any effect. This means a long lead time . Roger Angel of the University of Arizona [ 11 ] presented the idea for a sunshade at the U.S. National Academy of Sciences in April 2006 and won a NASA Institute for Advanced Concepts grant for further research in July 2006. Creating this sunshade in space was estimated to cost in excess of US$130 billion over 20 years with an estimated lifetime of 50-100 years. [ 15 ] Thus leading Professor Angel to conclude that "the sunshade is no substitute for developing renewable energy , the only permanent solution. A similar massive level of technological innovation and financial investment could ensure that. But if the planet gets into an abrupt climate crisis that can only be fixed by cooling, it would be good to be ready with some shading solutions that have been worked out." [ 14 ] [ 16 ]
Researchers from the University of Stuttgart, Institute of Space Systems described a roadmap for the development, construction and transport of an international planetary sun shield (IPSS) at the Lagrange point 1 in 2021, which would also be a photovoltaic plant. Here, too, as with Hermann Oberth, production on the Moon, the use of an electromagnetic Moon slingshot (lunar coilgun) and the transport of the components from the Moon to the Lagrange point 1 between the Earth and the Sun are discussed by means of electric spaceships (alternatively with sun sails) assumed. The authors refer to the many international activities and the chance to put the sunlight shield into operation by 2060. [ 17 ]
A more recent design has been proposed by Olivia Borgue and Andreas M. Hein in 2022, proposing a distributed sunshade with a mass on the order of 100,000 tons, composed of ultra-thin polymeric films and SiO2 nanotubes. [ 7 ] The author estimated that launching such mass would require 399 yearly launches of a vehicle such as SpaceX Starship for 10 years. [ 7 ]
A 2022 concept by MIT Senseable City Lab proposes using thin-film structures ("space bubbles") manufactured in outer space to solve the problem of launching the required mass to space. [ 18 ] MIT scientists led by Carlo Ratti believe deflecting 1.8 percent of solar radiation can fully reverse climate change. The full raft of inflatable bubbles would be roughly the size of Brazil and include a control system to regulate its distance from the Sun and optimise its effects. [ 19 ] The shell of the thin-film bubbles would be made of silicon , tested in outer space-like conditions at a pressure of .0028 atm and at -50 degrees Celsius. [ 19 ] They plan to investigate low vapor-pressure materials to rapidly inflate the bubbles, such as a silicon-based melt or a graphene-reinforced ionic liquid. [ 19 ]
In July 2022, a pair of researchers from MIT Senseable City Lab , Olivia Borgue and Andreas M. Hein, have instead proposed integrating nanotubes made out of silicon dioxide into ultra-thin polymeric films (described as "space bubbles" in the media [ 20 ] ), whose semi-transparent nature would allow them to resist the pressure of solar wind at L1 point better than any alternative with the same weight. The use of these "bubbles" would limit the mass of a distributed sunshade roughly the size of Brazil to about 100,000 tons, much lower than the earlier proposals. However, it would still require between 399 and 899 yearly launches of a vehicle such as SpaceX Starship for a period of around 10 years, even though the production of the bubbles themselves would have to be done in space. The flights would not begin until research into production and maintenance of these bubbles is completed, which the authors estimate would require a minimum of 10–15 years. After that, the space shield may be large enough by 2050 to prevent crossing of the 2 °C (3.6 °F) threshold. [ 21 ] [ 20 ] [ 22 ]
In 2023, three astronomers revisited the space dust concept, instead advocating for a lunar colony which would continuously mine the Moon in order to eject lunar dust into space on a trajectory where it would interfere with sunlight streaming towards the Earth. Ejections would have to be near-continuous, as since the dust would scatter in a matter of days, and about 10 million tons would have to be dug out and launched annually. [ 23 ] The authors admit that they lack a background in either climate or rocket science, and the proposal may not be logistically feasible. [ 24 ]
Several authors have proposed dispersing light before it reaches the Earth by putting a very large lens in space, perhaps at the L1 point between the Earth and the Sun. This plan was proposed in 1989 by J. T. Early. [ 25 ] His design involved making a large glass (2,000 km) occulter from lunar material and placing at the L1 point. Issues included the large amount of material needed to make the disc and also the energy to launch it to its orbit. [ 6 ]
In 2004, physicist and science fiction author Gregory Benford calculated that a concave rotating Fresnel lens 1000 kilometres across, yet only a few millimeters thick, floating in space at the L 1 point, would reduce the solar energy reaching the Earth by approximately 0.5% to 1%. [ 26 ]
The cost of such a lens has been disputed. At a science fiction convention in 2004, Benford estimated that it would cost about US$ 10 billion up front, and another $10 billion in supportive cost during its lifespan. [ 26 ]
A similar approach involves placing a very large diffraction grating (thin wire mesh) in space, perhaps at the L1 point between the Earth and the Sun. A proposal for a 3,000 ton diffraction mesh was made in 1997 by Edward Teller , Lowell Wood , and Roderick Hyde , [ 27 ] although in 2002 these same authors argued for blocking solar radiation in the stratosphere rather than in orbit given then-current space launch technologies. [ 28 ]
Other Lower Disc Size Estimates
Recent work by Feinberg (2022) [ 29 ] illustrate that lower disc area sizes (factor of approximately 3.5 reduction) are feasible when the background climate response is considered. For example, the background Earth climate would yield less re-radiation and feedback. In addition, disc area sizes can be further reduced by 50 times using an Annual Solar Geoengineering approach as indicated by Feinberg (2024). [ 30 ] | https://en.wikipedia.org/wiki/Space_sunshade |
Space sustainability aims to maintain the safety and health of the space environment , [ 1 ] as well as planetary environments. [ 2 ]
Similar to sustainability initiatives on Earth, space sustainability seeks to use the environment of space to meet the current needs of society without compromising the needs of future generations. [ 3 ] [ 4 ] [ 5 ] It usually focuses on space closest to Earth, Low Earth Orbit (LEO), since this environment is the one most used and therefore most relevant to humans. [ 6 ] It also considers Geostationary Equatorial Orbit (GEO) as this orbit is another popular choice for Earth-orbiting mission designs. [ 7 ]
The issue of space sustainability is a new phenomenon that is gaining more attention in recent years as the launching of satellites and other space objects has increased. [ 8 ] These launches have resulted in more space debris orbiting Earth, hindering the ability of nations to operate in the space environment while increasing the risk of a future launch-related accident that could disrupt its proper use. [ 9 ] [ 10 ] Space weather also acts as an outstanding factor for spacecraft failure. [ 7 ] The current protocol for spacecraft disposal at end-of-life has, at large, not been followed in mission designs and demands extraneous amounts of time for disposal. [ 11 ] [ 12 ]
Precedent created through prior policy initiatives has facilitated initial mitigation of space pollution and created a foundation for space sustainability efforts. [ 11 ] To further mitigation, international and transdisciplinary consortia have stepped forward to analyze existing operations, develop standards, and incentivize future procedures to prioritize a sustainable approach. [ 13 ] A shift towards sustainable interactions with the space environment is growing in urgency due to the implications of climate change and increasing risk to spacecraft as time presses on. [ 12 ] [ 14 ]
Space sustainability requires all space participants to have three consensuses. The space field should be used peacefully, jointly protect the space field from harm, and maximize space utilization through environmental, economic, and security exploration of space. [ 15 ] These consensuses also clarify the relationship between space sustainability and international security, that states and individuals explore space for various purposes. Their reliance on space needs to be guided by rules, order, and policies and obtain more benefits without negatively affecting the space environment and space activities. [ 15 ]
However, striking an agreement remains challenging even with such demands in place. In the discussions between countries on long-term sustainability, technical improvements are given more importance than introducing and applying new legal regimes. [ 16 ] Specifically, technical approaches to space debris have been proposed, such as debris removal. [ 17 ] Specific data on space debris is also being explored to help study its impact on sustainability and promote further cooperation between countries. [ 16 ]
Space sustainability comes into play to address the pressing current state of near-Earth orbits and its high amounts of orbital debris. [ 17 ] Spacecraft collisions with orbital debris, space weather, overcrowding in low Earth orbit (LEO) makes spacecraft susceptible to higher rates of failure. [ 17 ] [ 12 ] The current end-of-life protocol for spacecraft exacerbates the space sustainability crisis; many spacecraft are not properly disposed, which increasing the likelihood of further collisions. [ 17 ]
Orbital debris is defined as unmanned, inoperate objects that exist in space. [ 18 ] This orbital debris breaks down further as time progresses as a result of naturally occurring events, such as high-velocity collisions with micrometeoroids , and forced events, such as a controlled release of a launch vehicle. [ 18 ] In LEO, these collisions can take place at speeds anywhere between an average velocity of 9 kilometers per second (km/s) and 14 km/s relative to the debris and spacecraft. [ 18 ] In GEO, however, these high-speed collisions are a much lower risk as the average relative velocity between the debris and spacecraft is typically between 0 km/s and 2.5 km/s. [ 18 ] As of 2012, the United States Joint Space Operations Center tracked 21,000 pieces of orbital debris larger than 10 cm in Earth's nearby orbits (LEO, GEO, and Sun-synchronous ), where 16,000 of these pieces are catalogued. Space debris can be categorized into three categories: small, medium, and large. [ 17 ] Small debris is for pieces that are less than 10 centimeters (cm). [ 17 ] Medium-sized debris is for pieces larger than 10 cm, but not an entire spacecraft. [ 17 ] Large-sized debris has no official classification, but typically refers to entire spacecraft, such as an out of use satellite or launch vehicle. [ 17 ] It is difficult to track small-sized debris in LEO, and challenging to track small and medium-sized debris in GEO. [ 18 ] Yet this statement is not to discount the abilities of LEO and GEO tracking capabilities, the smallest piece of tracked debris can weigh as low as ten grams. [ 18 ] If the size of the debris prohibits it from being tracked, it also cannot be avoided by the spacecraft and does not allow the spacecraft to lower its risk of collisions. [ 18 ] The likelihood of the Kessler syndrome , which essentially states that each collision produces more debris, grows larger as the amount of orbital debris multiplies, increasing the amount of further collisions until space cannot be used entirely. [ 17 ]
Space weather poses a risk to satellite health, consequently, resulting in greater amounts of orbital debris. [ 7 ] Space weather impacts satellite health in a variety of ways. Firstly, surface charging from the Sun's surface facilitates electrical discharges, damaging on-orbit electronics, posing a threat to mission failure. [ 7 ] Single Event Upsets (SEUs) can also damage electronics. [ 7 ] Dielectric charging and bulk charging can also occur, causing energy problems within the spacecraft. [ 7 ] Additionally, at altitudes less than one thousand kilometers, atmospheric drag can increase during solar storms by increasing the altitude of the spacecraft, only adding more drag onto the spacecraft. [ 7 ] These factors degrade performance over the spacecraft's lifetime, leaving the spacecraft more susceptible to further system and mission failures. [ 7 ]
There has been a dramatic increase in the use of LEO and GEO orbits over the last sixty years since the first satellite launch in 1957. To date, there have been approximately ten thousand satellite launches, whereas only approximately 2000 are still active. [ 17 ] These satellites can be used for a variety of purposes, which are telecommunications, navigation, weather monitoring, and exploration. Within the coming decade, companies like SpaceX are predicted to launch an additional fifteen thousand satellites into LEO and GEO orbits. [ 17 ] Microsatellites built by universities or research organizations have also increased in popularity, contributing to the overcrowding of near earth orbits. [ 12 ] This overcrowding of LEO and GEO orbits increases the likelihood of potential collisions among satellites and orbital debris, contributing further to the large amount of orbital debris present in space. [ 17 ]
The current end of life protocol is that at the end of mission, spacecraft are either added to the graveyard orbit or at a low enough altitude that drag will allow the spacecraft to burn up upon reentry and fall back to Earth. [ 12 ] Approximately twenty satellites are put into the graveyard orbit each year. [ 12 ] There is no current process to return satellites to Earth after entering the graveyard orbit. [ 17 ] The process of a spacecraft returning to Earth via drag can take between ten and one hundred years. [ 17 ] This protocol is critical to reduce overcrowding in near-Earth orbits. [ 17 ]
The impact of constellations on the space environment has also been studied, such as the probability of collisions of mega constellations in the presence of large amounts of space debris . Although studies have shown that the predictors of mega constellations are highly variable, specific information related to mega constellations is not transparent. [ 19 ]
But any catastrophic collision, as in the case of Kessler syndrome , has consequences for people and the environment. Putting this thinking into mega constellations, mega constellations existence may have potential benefits, but it will not bring adequate help to the governance of space debris. [ 17 ] At the same time, the space debris situation cannot be underestimated or ignored because of the existence of mega constellations. [ 17 ]
Atmospheric entry has a measurable impact on Earth's atmosphere , particularly the stratosphere .
Atmospheric entry by spacecrafts accounted for 3% of all atmospheric entries by 2021, but in a scenario in which the number of satellites since 2019 are doubled, artificial entries would make 40% of all entries, [ 20 ] which would cause atmospheric aerosols to be 94% artificial. [ 21 ] The impact of spacecrafts burning up in the atmosphere during artificial atmospheric entry is different to meteors due to the spacecrafts' generally larger size and different composition. The atmospheric pollutants produced by artificial atmospheric burning-up have been traced in the atmosphere and identified as reacting and possibly negatively impacting the composition of the atmosphere and particularly the ozone layer . [ 20 ]
Considering space sustainability in regard to atmospheric impact of re-entry is by 2022 just developing [ 22 ] and has been identified in 2024 as suffering from "atmosphere-blindness", causing global environmental injustice . [ 23 ] This is identified as a result of the current end-of life spacecraft management, which favors the station keeping practice of controlled re-entry. [ 23 ] This is mainly done to prevent the dangers from uncontrolled atmospheric entries and space debris . [ 23 ]
The existence of orbital debris has caused great trouble to the conduct of space activities. The development of space sustainability has not given sufficient political attention, although some warnings and discussions have made this abundantly clear. [ 12 ] Debris management is still voluntary on the part of the state, and there are no laws mandating debris management practices, including the amount of debris to be managed. [ 12 ] Although the UN Space Debris Mitigation Guidelines were promulgated in 2007 as an initial measure of space debris governance, there is still no broad consensus or action on further limits on space debris after that.
The difficulties for individuals wishing to participate in debris management initiatives cannot be ignored. Any individual or sector desiring to participate in space debris operations needs to obtain permission from the launching state, which is difficult for the launching state to do. [ 12 ] This is because the process of space debris management inevitably has a negative impact on other space objects, and there is a lot of subsequent liability in terms of financial consumption. [ 12 ] Therefore, the launching state would argue that space debris management requires the joint efforts of all states. [ 24 ] However, it is difficult to determine what actions can be taken to gain acceptance between countries.
Current space sustainability efforts rely heavily on the precedent set by regulatory agreements and conventions of the twentieth century. [ 11 ] Much of this precedent is included in or is related to the Outer Space Treaty of 1963 , which represented one of the initial major efforts by the United Nations to create legal frameworks for the operation of nations in space. [ 25 ]
The international community has had concerns about space contamination since the 1950s prior to the launch of Sputnik I . [ 26 ] These concerns stemmed from the idea that increasing rates of exploration into further areas of outer space could lead to contamination capable of damaging other planetary bodies, resulting in limitations to human exploration on these bodies and potential harm to the Earth. [ 26 ] Efforts to combat these concerns began in 1956 with the International Astronautical Federation (IAF) and the United Nations Committee on the Peaceful Uses of Outer Space (COPUOUS). These efforts continued to 1957 through the National Academy of Sciences and International Council for Science (ICSU). [ 26 ] Each of these organizations aimed to study space contamination and develop strategies for how to best address its potential consequences. [ 26 ] The ICSU went on to create the Committee on Contamination by Extraterrestrial Exploration (CETEX) that put forward recommendations leading to the establishment of the Committee on Space Research (COSPAR). [ 26 ] COSPAR continues to address outer space research on an international scale today [cite cospar].
Relevant regulations of international space law to sustainability in space can be found in the Outer Space Treaty , which was adopted by the UN General Assembly in 1963. [ 27 ] The Outer Space Treaty contains seventeen articles designed to create a basic framework for how international law can be applied in outer space. [ 25 ] Basic principles of the Outer Space Treaty include the provision in Article IX that parties should "avoid harmful contamination of space and celestial bodies;" [ 25 ] definitions of "harmful contamination" are not provided. [ 28 ] [ 25 ] Other articles of relevance to space sustainability include articles I, II, and III that concern the fair and inclusive international use of space in a manner free from sovereignty, ownership, or occupation by any nation. [ 25 ] In addition, articles VII and VIII protect ownership by their respective countries of any objects launched to space while attributing responsibility for any damages to the property or personnel of other countries by those objects to said countries. [ 25 ] Descriptions or definitions for what these damages may entail are not provided. [ 25 ]
Principles of Article IX provided the basis for the Committee of Space Research (COSPAR) Planetary Protection Policy guidelines, which are generally well-regarded among scientific experts. [ 29 ] Such guidelines, however, are non-binding and often described as "soft-law," as they lack legal mandate. [ 28 ] The Planetary Protection Policy is primarily concerned with providing information regarding best practices to avoid contamination of the space environment during space exploration missions. [ 30 ] COSPAR believes that the prevention of such contamination is in the best interest of humanity as it may impede scientific progress, exploration, and the mission of a search for life. [ 30 ] In addition, the argument is made that cross-contamination of the Earth can be potentially harmful to its environment due to the largely unknown nature of potential space contaminants. [ 30 ]
Regulatory clarifications concerning the Outer Space Treaty of 1963 of relevance to space sustainability were made in subsequent years. The 1967 Return Agreement relates mainly to the return of lost astronauts to their appropriate nations, but also requires Outer Space Treaty signing nations to assist other nations with the return of objects that return to Earth from orbit to their proper owners [ 31 ] The 1972 Liability Convention attributes liability for damages from space objects to the nation that launched the object, regardless of whether that damage occurred in space or on Earth. [ 32 ] Other clarifications include the 1975 registration convention that attempted to create mechanisms for nations to identify space objects, and the 1979 Moon Agreement that established protections for the environments of the Moon and other nearby planetary bodies. [ 33 ] [ 34 ] These agreements and conventions represented attempts to improve the initial Outer Space Treaty as space exploration continued to grow in importance throughout the 20th century. [ 26 ]
Both the state and space agencies are working to improve the laws and regulations that facilitate the long-term sustainability of space. For example, the European Code of Conduct for Space Debris Mitigation signed by France, the UK and other countries in 2016. [ 17 ] China, Brazil, Mexico and others have legal background and methodological measures under long-term space sustainability. [ 35 ] [ 36 ] [ 37 ] However, the main problem is that until the concept of space sustainability is agreed between countries, inter-regional efforts are not working well. [ 17 ]
Currently, the Committee on the Peaceful Uses of Outer Space (COPUOS) encourages states to incorporate the space debris mitigation guidelines developed by bodies such as the Inter-Agency Space Debris Coordination (IADC) into their national legislation, thereby regulating state behavior. [ 38 ] Some countries have responded positively to this, such as Switzerland, the Netherlands and Spain. However, there are still some countries that do not consider debris management approaches in their national legislation, such as Japan and Australia. [ 17 ] Many delegates at the COPUOS meeting expressed their reasons for doing so, arguing that space debris management is closely linked to technology and funding. Technology is dynamic and constantly evolving. Therefore, the incorporation of debris governance guidelines into national law is not an immediate priority at this time. [ 39 ]
A study outlined rationale for governance that regulates the current free externalization of true costs and risks , treating orbital space around the Earth as an "additional ecosystem" or a common "part of the human environment" which should be subject to the same concerns and regulations like oceans on Earth . While scientists may not have the means to make and enforce global laws themselves, the study concluded in 2022 that it needs "new policies, rules and regulations at national and international level". [ 40 ] [ 41 ]
Sustainability mitigation efforts include but are not limited to design specifications, policy change, removal of space debris, and restoration of orbiting semi-functional technologies. [ 17 ] [ 42 ] [ 13 ] [ 43 ] Efforts begin by regulating the debris released during normal operations and post-mission breakups [6]. Due to the increased awareness of high-velocity collisions and orbital debris in the previous decades, missions have adapted design specifications to account for these risks. [ 18 ] For example, the RADARSAT program implemented 17 kilograms of shielding to their spacecraft, which increased the program's predicted success rate to 87% from 50%. [ 18 ] Another effort in mitigation is restoring semi-functional satellites, which allows a spacecraft classified as "debris" to "functional." [ 11 ] Space debris mitigation focuses on limiting debris release during normal operations, collisions and intentional destruction. [ 17 ] Mitigation also includes reducing the possibility for post-mission breakups due to stored energy and/or operations phases, as well as addressing procedure for end of mission disposal for spacecraft. [ 17 ]
One example leading the regulatory sustainability measures is the Space Sustainability Rating (SSR), which is an instigator for industry competitors to incorporate sustainability into spacecraft design. [ 13 ] The Space Sustainability Rating was first conceptualized at the World Economic Forum Global Future Council on Space Technologies designed by international and transdisciplinary consortia. [ 13 ] The four leading organizations are the European Space Agency , Massachusetts Institute of Technology , University of Texas at Austin , and BryceTech with the goal to define the technical and programmatic aspects of the SSR. [ 42 ] The SSR represents an innovative approach to combating orbital debris through incentivizing the industry to prioritize sustainable and responsible operations. [ 13 ] This response entails the consideration of potential harm to the space environment and other spacecraft, all while maintaining mission objectives and high-quality service. [ 42 ] The rating takes inspiration from other standards, like leadership in energy and environmental design (LEED) for the building sector. Several of the factors emphasized in the rating were extracted from LEED design considerations like the incorporation of feedback and public comments, or the rating's advocacy to influence policy, such as orbit fragmentation risks, collision avoidance capabilities, trackability, and adoption of international standards. [ 13 ]
Tracking is one of the main Space Sustainability Rating modules' efforts. The module "Detectability, Identification and Tracking" (DIT) consists of standardizing the comparison of satellite missions to encourage satellite operators to improve their satellite design and operational approaches for the observer to detect, identify, and track the satellites. [ 13 ] Tracking presents challenges when the observer seeks to monitor and predict the spacecraft behavior over time. [ 42 ] While the observer may know the name, owner, and instantaneous location of the satellite, the operator controls the full knowledge of the orbital parameters. [ 42 ] The Space Situational Awareness (SSA) is one the tools geared towards solving the challenges presented when tracking orbiting satellites and debris. [ 17 ] The SSA continuously tracks objects using ground-based radar and optical stations so the orbital paths of debris can be predicted and operations avoid collisions. [ 17 ] It feeds data to 30 different systems like satellites, optical telescopes, radar systems, and supercomputers to predict risk of collision days in advance. [ 17 ] Other efforts in tracking orbital debris are made by the US Space Surveillance Network (SSN). [ 18 ]
Under the "External Services" module of the SSR, the rating offers commitment to use or demonstration of use of end-of-life removal services. [ 13 ] Space debris mitigation measures are found to be inadequate to stabilize debris environments with an actual current compliance of approximately sixty percent. [ 17 ] Moreover, a low compliance rate of approximately thirty percent of the 103 spacecraft that reached end of life between 1997 and 2003 were disposed of in a graveyard orbit. [ 17 ] Since policy has not caught up to ensure the longevity of LEO for future generations, actions like Active Debris Removal (ADR) are being considered to stabilize the future of LEO environment. [ 17 ] Most famous removal concepts are based on directed energy, momentum exchange or electrodynamics, aerodynamic drag augmentation, solar sails, auxiliary propulsion units, retarding surfaces and on-orbit capture. [ 17 ] As ADR consists of an external disposal method to remove obsolete satellites or spacecraft fragments. [ 14 ] Since large-sized debris objects in orbit provide a potential source for tens of thousands of fragments in the future, ADR efforts focus on objects with high mass and large cross-sectional areas, in densely populated regions, and at high altitudes; in this instance, retired satellites and rocket bodies are a priority. [ 17 ] Other practical advancements toward space debris removal include missions like RemoveDEBRIS and End-of-Life Service (ELS-d). [ 17 ]
The previous reduced state of regulation and mitigation on space debris [ 12 ] and rocket fuel emissions [ 43 ] is aggravating the Earth's stratosphere through collisions and ozone depletion, increasing the risk for spacecraft health through its lifetime.
Due to the increase of satellites being launched and the growing amount of orbital debris in LEO, [ 17 ] the risk of LEO becoming inaccessible over time (in accordance with the Kessler syndrome) is increasing in likelihood. The mitigation policies for creating space debris fall under an area of voluntary codes by the states, although it has been disputed whether the Article I Outer Space Treaty or the Article IX Outer Space Treaty protects the space environment from deliberate harm, which has yet to be upheld. [ 12 ] In 2007, an inactive Chinese satellite was purposefully destroyed by the Chinese government as a part of their anti-satellite weapon test (ASAT), spreading nearly 2800 objects of space debris five centimeters or larger into LEO. [ 44 ] An analysis concluded that about eighty percent of the debris will remain in LEO nine years after this destruction. [ 44 ] In addition, the destruction increased the collision likelihood for three Italian satellites that launched the same year as the Fengyun-1C destruction. [ 44 ] The increase in collision ranged between ten and sixty percent. [ 44 ] However, there were no legal consequences against the Chinese government. [ 44 ]
When rockets are launched into space, parts of their fuel enter the stratosphere of the Earth. Rocket fuel emissions are made up of carbon dioxide, water, hydrochloric acid , alumina and soot particles. The most concerning emissions from rocket fuel are chlorine and alumina particles from solid rocket motors (SRMs) and soot from kerosene fueled engines. When the hydrochloric acid from the engine exhaust dissociates, the free chlorine roams freely in the stratosphere. [ 45 ] The chemical reaction between these chlorine and alumina causes ozone depletion. In addition, the soot particles form over a black umbrella over the stratosphere which can cause the temperature of the Earth's surface to lower and further depleting the ozone layer, an unintentional form of geoengineering. [ 43 ] The nature of geoengineering has been disputed as a form of mitigating global warming and has the possibility of being banned and holding rockets accountable for the soot particles they distribute to the stratosphere. New types of engines and fuels are emerging, mainly the liquid oxygen (LOX) and monomethylhydrazine engine, but there is minimal research on their impact on the environment besides their emission of hydroxide and nitrogen oxide compounds, two molecules that have significant impact on the ozone layer. [ 43 ] Currently, rocket fuel emissions have been deemed insignificant when it comes to their consequences to Earth's environment and LEO. [ 43 ] However, emissions will increase in the coming years, making rocket fuel's contribution to global warming much more significant.
Space sustainability concepts and mindsets tend to stay in Low Earth Orbit (LEO). [ 46 ] One reason that cannot be ignored is that it is easier to discuss the problem at hand than to speculate on the unknown. [ 12 ] There are also examples to prove that since Apollo 17 completed its mission and stayed in Low Earth orbit in 1972, human-crewed space missions in Low Earth orbit have ceased to exist. [ 47 ] In this way, it is a reasonable assumption that the closer Moon could be the next object to be explored when the gaze is not limited to LEO. [ 12 ] Both lunar orbit and LEO are part of the space environment. In the context of the presence of space debris in LEO, it is normal to speculate that lunar orbit also possesses the nuisance of debris. Space debris measures similar to those in LEO related to space sustainability would be taken. [ 12 ]
Not only has the Moon been the subject of study, but other bodies have also been taken into account. Elon Musk , the chief executive of SpaceX at the International Astronautical Congress in 2016, explained the ambitious goal of exploring Mars in the 22nd century. [ 48 ] But complicated issues remain, such as the technical aspects of achieving long-distance space flight and the rules and legal aspects associated with the technology, all of which need to be considered. [ 12 ] | https://en.wikipedia.org/wiki/Space_sustainability |
A space telescope (also known as space observatory ) is a telescope in outer space used to observe astronomical objects. Suggested by Lyman Spitzer in 1946, the first operational telescopes were the American Orbiting Astronomical Observatory , OAO-2 launched in 1968, and the Soviet Orion 1 ultraviolet telescope aboard space station Salyut 1 in 1971. Space telescopes avoid several problems caused by the atmosphere, including the absorption or scattering of certain wavelengths of light, obstruction by clouds, and distortions due to atmospheric refraction such as twinkling . Space telescopes can also observe dim objects during the daytime, and they avoid light pollution which ground-based observatories encounter. They are divided into two types: Satellites which map the entire sky ( astronomical survey ), and satellites which focus on selected astronomical objects or parts of the sky and beyond. Space telescopes are distinct from Earth imaging satellites , which point toward Earth for satellite imaging , applied for weather analysis , espionage , and other types of information gathering .
In 1946, American theoretical astrophysicist Lyman Spitzer , "father of Hubble" proposed to put a telescope in space. [ 1 ] [ 2 ] Spitzer's proposal called for a large telescope that would not be hindered by Earth's atmosphere. After lobbying in the 1960s and 70s for such a system to be built, Spitzer's vision ultimately materialized into the Hubble Space Telescope , which was launched on April 24, 1990, by the Space Shuttle Discovery (STS-31). [ 3 ] This was launched due to many efforts by Nancy Grace Roman, "mother of Hubble", who was the first Chief of Astronomy and first female executive at NASA. [ 4 ] She was a program scientist that worked to convince NASA, Congress, and others that Hubble was "very well worth doing". [ 5 ]
The first operational space telescopes were the American Orbiting Astronomical Observatory , OAO-2 launched in 1968, and the Soviet Orion 1 ultraviolet telescope aboard space station Salyut 1 in 1971.
Performing astronomy from ground-based observatories on Earth is limited by the filtering and distortion of electromagnetic radiation ( scintillation or twinkling) due to the atmosphere . A telescope orbiting Earth outside the atmosphere is subject neither to twinkling nor to light pollution from artificial light sources on Earth. As a result, the angular resolution of space telescopes is often much higher than a ground-based telescope with a similar aperture . Many larger terrestrial telescopes, however, reduce atmospheric effects with adaptive optics . [ 6 ]
Space-based astronomy is more important for frequency ranges that are outside the optical window and the radio window , the only two wavelength ranges of the electromagnetic spectrum that are not severely attenuated by the atmosphere. [ 6 ] For example, X-ray astronomy is nearly impossible when done from Earth, and has reached its current importance in astronomy only due to orbiting X-ray telescopes such as the Chandra X-ray Observatory and the XMM-Newton observatory . Infrared and ultraviolet are also largely blocked.
Space telescopes are much more expensive to build than ground-based telescopes. Due to their location, space telescopes are also extremely difficult to maintain. The Hubble Space Telescope was serviced by the Space Shuttle , but most space telescopes cannot be serviced at all.
Satellites have been launched and operated by NASA , ISRO , ESA , CNSA , JAXA and the Soviet space program (later succeeded by Roscosmos of Russia). As of 2022, many space observatories have already completed their missions, while others continue operating on extended time. However, the future availability of space telescopes and observatories depends on timely and sufficient funding. While future space observatories are planned by NASA, JAXA and the CNSA , scientists fear that there would be gaps in coverage that would not be covered immediately by future projects and this would affect research in fundamental science. [ 7 ]
On 16 January 2023, NASA announced preliminary considerations of several future space telescope programs, including the Great Observatory Technology Maturation Program, Habitable Worlds Observatory , and New Great Observatories. [ 8 ] [ 9 ] | https://en.wikipedia.org/wiki/Space_telescope |
The residence time of a fluid parcel is the total time that the parcel has spent inside a control volume (e.g.: a chemical reactor , a lake , a human body ). The residence time of a set of parcels is quantified in terms of the frequency distribution of the residence time in the set, which is known as residence time distribution (RTD) , or in terms of its average, known as mean residence time .
Residence time plays an important role in chemistry and especially in environmental science and pharmacology . Under the name lead time or waiting time it plays a central role respectively in supply chain management and queueing theory , where the material that flows is usually discrete instead of continuous.
The concept of residence time originated in models of chemical reactors. The first such model was an axial dispersion model by Irving Langmuir in 1908. This received little attention for 45 years; other models were developed such as the plug flow reactor model and the continuous stirred-tank reactor , and the concept of a washout function (representing the response to a sudden change in the input) was introduced. Then, in 1953, Peter Danckwerts resurrected the axial dispersion model and formulated the modern concept of residence time. [ 1 ]
The time that a particle of fluid has been in a control volume (e.g. a reservoir) is known as its age . In general, each particle has a different age. The frequency of occurrence of the age τ {\displaystyle \tau } in the set of all the particles that are located inside the control volume at time t {\displaystyle t} is quantified by means of the (internal) age distribution I {\displaystyle I} . [ 2 ]
At the moment a particle leaves the control volume, its age is the total time that the particle has spent inside the control volume, which is known as its residence time . The frequency of occurrence of the age τ {\displaystyle \tau } in the set of all the particles that are leaving the control volume at time t {\displaystyle t} is quantified by means of the residence time distribution , also known as exit age distribution E {\displaystyle E} . [ 2 ]
Both distributions are positive and have by definition unitary integrals along the age: [ 2 ]
In the case of steady flow , the distributions are assumed to be independent of time, that is ∂ t E = ∂ t I = 0 ∀ t {\displaystyle \partial _{t}E=\partial _{t}I=0\;\forall t} , which may allow to redefine the distributions as simple functions of the age only.
If the flow is steady (but a generalization to non-steady flow is possible [ 3 ] ) and is conservative , then the exit age distribution and the internal age distribution can be related one to the other: [ 2 ]
Distributions other than E {\displaystyle E} and I {\displaystyle I} can be usually traced back to them. For example, the fraction of particles leaving the control volume at time t {\displaystyle t} with an age greater or equal than τ {\displaystyle \tau } is quantified by means of the washout function W {\displaystyle W} , that is the complementary to one of the cumulative exit age distribution:
The mean age of all the particles inside the control volume at time t is the first moment of the age distribution: [ 2 ] [ 3 ]
The mean residence time or mean transit time , that is the mean age of all the particles leaving the control volume at time t , is the first moment of the residence time distribution: [ 2 ] [ 3 ]
The mean age and the mean transit time generally have different values, even in stationary conditions: [ 2 ]
If the flow is steady and conservative , the mean residence time equals the ratio between the amount of fluid contained in the control volume and the flow rate through it: [ 2 ]
This ratio is commonly known as the turnover time or flushing time . [ 4 ] When applied to liquids, it is also known as the hydraulic retention time ( HRT ), hydraulic residence time or hydraulic detention time . [ 5 ] In the field of chemical engineering this is also known as space time . [ 6 ]
The residence time of a specific compound in a mixture equals the turnover time (that of the compound, as well as that of the mixture) only if the compound does not take part in any chemical reaction (otherwise its flow is not conservative) and its concentration is uniform . [ 3 ]
Although the equivalence between the residence time and the ratio m / f {\displaystyle m/f} does not hold if the flow is not stationary or it is not conservative, it does hold on average if the flow is steady and conservative on average , and not necessarily at any instant. Under such conditions, which are common in queueing theory and supply chain management , the relation is known as Little's Law .
Design equations are equations relating the space time to the fractional conversion and other properties of the reactor. Different design equations have been derived for different types of the reactor and depending on the reactor the equation more or less resemble that describing the average residence time. Often design equations are used to minimize the reactor volume or volumetric flow rate required to operate a reactor. [ 7 ]
In an ideal plug flow reactor (PFR) the fluid particles leave in the same order they arrived, not mixing with those in front and behind. Therefore, the particles entering at time t will exit at time t + T , all spending a time T inside the reactor. The residence time distribution will be then a Dirac delta function delayed by T :
The mean is T and the variance is zero. [ 1 ]
The RTD of a real reactor deviates from that of an ideal reactor, depending on the hydrodynamics within the vessel. A non-zero variance indicates that there is some dispersion along the path of the fluid, which may be attributed to turbulence, a non-uniform velocity profile, or diffusion. If the mean of the distribution is earlier than the expected time T it indicates that there is stagnant fluid within the vessel. If the RTD curve shows more than one main peak it may indicate channeling, parallel paths to the exit, or strong internal circulation.
In PFRs, reactants enter the reactor at one end and react as they move down the reactor. Consequently, the reaction rate is dependent on the concentrations which vary along the reactor requiring the inverse of the reaction rate to be integrated over the fractional conversion.
Batch reactors are reactors in which the reactants are put in the reactor at time 0 and react until the reaction is stopped. Consequently, the space time is the same as the average residence time in a batch reactor.
In an ideal continuous stirred-tank reactor (CSTR), the flow at the inlet is completely and instantly mixed into the bulk of the reactor. The reactor and the outlet fluid have identical, homogeneous compositions at all times. The residence time distribution is exponential:
Where; the mean is T and the variance is 1. [ 1 ] A notable difference from the plug flow reactor is that material introduced into the system will never completely leave it. [ 4 ]
In reality, it is impossible to obtain such rapid mixing, as there is necessarily a delay between any molecule passing through the inlet and making its way to the outlet, and hence the RTD of a real reactor will deviate from the ideal exponential decay, especially in the case of large reactors. For example, there will be some finite delay before E reaches its maximum value and the length of the delay will reflect the rate of mass transfer within the reactor. Just as was noted for a plug-flow reactor, an early mean will indicate some stagnant fluid within the vessel, while the presence of multiple peaks could indicate channeling, parallel paths to the exit, or strong internal circulation. Short-circuiting fluid within the reactor would appear in an RTD curve as a small pulse of concentrated tracer that reaches the outlet shortly after injection.
Reactants continuously enter and leave a tank where they are mixed. Consequently, the reaction proceeds at a rate dependent on the outlet concentration:
In a laminar flow reactor , the fluid flows through a long tube or parallel plate reactor and the flow is in layers parallel to the walls of the tube. The velocity of the flow is a parabolic function of radius. In the absence of molecular diffusion , the RTD is [ 8 ]
The variance is infinite. In a real reactor, diffusion will eventually mix the layers so that the tail of the RTD becomes exponential and the variance finite; but laminar flow reactors can have variance greater than 1, the maximum for CTSD reactors. [ 1 ]
Recycle reactors are PFRs with a recycle loop. Consequently, they behave like a hybrid between PFRs and CSTRs.
In all of these equations : − r A {\displaystyle -r_{A}} is the consumption rate of A , a reactant. This is equal to the rate expression A is involved in. The rate expression is often related to the fractional conversion both through the consumption of A and through any k changes through temperature changes that are dependent on conversion. [ 7 ]
In some reactions the reactants and the products have significantly different densities. Consequently, as the reaction proceeds the volume of the reaction changes. This variable volume adds terms to the design equations. Taking this volume change into consideration the volume of the reaction becomes:
Plugging this into the design equations results in the following equations:
Generally, when reactions take place in the liquid and solid phases the change in volume due to reaction is not significant enough that it needs to be taken into account. Reactions in the gas phase often have significant changes in volume and in these cases one should use these modified equations. [ 7 ]
Residence time distributions are measured by introducing a non-reactive tracer into the system at the inlet. Its input concentration is changed according to a known function and the output concentration measured. The tracer should not modify the physical characteristics of the fluid (equal density, equal viscosity) or the hydrodynamic conditions and it should be easily detectable. [ 9 ] In general, the change in tracer concentration will either be a pulse or a step . Other functions are possible, but they require more calculations to deconvolute the RTD curve.
This method required the introduction of a very small volume of concentrated tracer at the inlet of the reactor, such that it approaches the Dirac delta function . [ 10 ] [ 8 ] Although an infinitely short injection cannot be produced, it can be made much smaller than the mean residence time of the vessel. If a mass of tracer, M {\displaystyle M} , is introduced into a vessel of volume V {\displaystyle V} and an expected residence
time of τ {\displaystyle \tau } , the resulting curve of C ( t ) {\displaystyle C(t)} can be transformed into a dimensionless residence time distribution curve by the following relation:
The concentration of tracer in a step experiment at the reactor inlet changes abruptly from 0 to C 0 {\displaystyle C_{0}} . The concentration of tracer at the outlet is measured and normalized to the concentration C 0 {\displaystyle C_{0}} to obtain the non-dimensional curve F ( t ) {\displaystyle F(t)} which goes from 0 to 1:
The step- and pulse-responses of a reactor are related by the following:
A step experiment is often easier to perform than a pulse experiment, but it tends to smooth over some of the details that a pulse response could show. It is easy to numerically integrate an experimental pulse response to obtain a very high-quality estimate of the step response, but the reverse is not the case because any noise in the concentration measurement will be amplified by numeric differentiation.
In chemical reactors , the goal is to make components react with a high yield . In a homogeneous, first-order reaction , the probability that an atom or molecule will react depends only on its residence time:
for a rate constant k {\displaystyle k} . Given a RTD, the average probability is equal to the ratio of the concentration a {\displaystyle a} of the component before and after: [ 1 ]
If the reaction is more complicated, then the output is not uniquely determined by the RTD. It also depends on the degree of micromixing , the mixing between molecules that entered at different times. If there is no mixing, the system is said to be completely segregated , and the output can be given in the form
For given RTD, there is an upper limit on the amount of mixing that can occur, called the maximum mixedness , and this determines the achievable yield. A continuous stirred-tank reactor can be anywhere in the spectrum between completely segregated and perfect mixing . [ 1 ]
The RTD of chemical reactors can be obtained by CFD simulations. The very same procedure that is performed in experiments can be followed. A pulse of inert tracer particles (during a very short time) is injected into the reactor. The linear motion of tracer particles is governed by Newton's second law of motion and a one-way coupling is stablished between fluid and tracers. In one-way coupling, fluid affects tracer motion by drag force while tracer does not affect fluid. The size and density of tracers are chosen so small that the time constant of tracers becomes very small. In this way, tracer particles exactly follow the same path as the fluid does. [ 11 ]
Hydraulic residence time (HRT) is an important factor in the transport of environmental toxins or other chemicals through groundwater . The amount of time that a pollutant spends traveling through a delineated subsurface space is related to the saturation and the hydraulic conductivity of the soil or rock. [ 12 ] Porosity is another significant contributing factor to the mobility of water through the ground (e.g. toward the water table ). The intersection between pore density and size determines the degree or magnitude of the flow rate through the media. This idea can be illustrated by a comparison of the ways water moves through clay versus gravel . The retention time through a specified vertical distance in clay will be longer than through the same distance in gravel, even though they are both characterized as high porosity materials. This is because the pore sizes are much larger in gravel media than in clay, and so there is less hydrostatic tension working against the subsurface pressure gradient and gravity.
Groundwater flow is important parameter for consideration in the design of waste rock basins for mining operations. Waste rock is heterogeneous material with particles varying from boulders to clay-sized particles, and it contains sulfidic pollutants which must be controlled such that they do not compromise the quality of the water table and also so the runoff does not create environmental problems in the surrounding areas. [ 12 ] Aquitards are clay zones that can have such a degree of impermeability that they partially or completely retard water flow. [ 5 ] [ 13 ] These clay lenses can slow or stop seepage into the water table, although if an aquitard is fractured and contaminated then it can become a long-term source of groundwater contamination due to its low permeability and high HRT. [ 13 ]
Primary treatment for wastewater or drinking water includes settling in a sedimentation chamber to remove as much of the solid matter as possible before applying additional treatments. [ 5 ] The amount removed is controlled by the hydraulic residence time (HRT). [ 5 ] When water flows through a volume at a slower rate, less energy is available to keep solid particles entrained in the stream and there is more time for them to settle to the bottom. Typical HRTs for sedimentation basins are around two hours, [ 5 ] although some groups recommend longer times to remove micropollutants such as pharmaceuticals and hormones. [ 14 ]
Disinfection is the last step in the tertiary treatment of wastewater or drinking water. The types of pathogens that occur in untreated water include those that are easily killed like bacteria and viruses , and those that are more robust such as protozoa and cysts . [ 5 ] The disinfection chamber must have a long enough HRT to kill or deactivate all of them.
Atoms and molecules of gas or liquid can be trapped on a solid surface in a process called adsorption . This is an exothermic process involving a release of heat , and heating the surface increases the probability that an atom will escape within a given time. At a given temperature T {\displaystyle T} , the residence time of an adsorbed atom is given by
where R {\displaystyle R} is the gas constant , E a {\displaystyle E_{\mathrm {a} }} is an activation energy , and τ 0 {\displaystyle \tau _{0}} is a prefactor that is correlated with the vibration times of the surface atoms (generally of the order of 10 − 12 {\displaystyle 10^{-12}} seconds). [ 15 ] : 27 [ 16 ] : 196
In vacuum technology , the residence time of gases on the surfaces of a vacuum chamber can determine the pressure due to outgassing . If the chamber can be heated, the above equation shows that the gases can be "baked out"; but if not, then surfaces with a low residence time are needed to achieve ultra-high vacuums . [ 16 ] : 195
In environmental terms, the residence time definition is adapted to fit with ground water, the atmosphere, glaciers , lakes, streams, and oceans. More specifically it is the time during which water remains within an aquifer, lake, river, or other water body before continuing around the hydrological cycle . The time involved may vary from days for shallow gravel aquifers to millions of years for deep aquifers with very low values for hydraulic conductivity . Residence times of water in rivers are a few days, while in large lakes residence time ranges up to several decades. Residence times of continental ice sheets is hundreds of thousands of years, of small glaciers a few decades.
Ground water residence time applications are useful for determining the amount of time it will take for a pollutant to reach and contaminate a ground water drinking water source and at what concentration it will arrive. This can also work to the opposite effect to determine how long until a ground water source becomes uncontaminated via inflow, outflow, and volume. The residence time of lakes and streams is important as well to determine the concentration of pollutants in a lake and how this may affect the local population and marine life.
Hydrology, the study of water, discusses the water budget in terms of residence time. The amount of time that water spends in each different stage of life (glacier, atmosphere, ocean, lake, stream, river), is used to show the relation of all of the water on the earth and how it relates in its different forms.
A large class of drugs are enzyme inhibitors that bind to enzymes in the body and inhibit their activity. In this case it is the drug-target residence time (the length of time the drug stays bound to the target) that is of interest. The residence time is defined as the reciprocal value of the koff rate constant (residence time = 1/koff). Drugs with long residence times are desirable because they remain effective for longer and therefore can be used in lower doses. [ 17 ] : 88 This residence time is determined by the kinetics of the interaction, [ 18 ] such as how complementary the shape and charges of the target and drug are and whether outside solvent molecules are kept out of the binding site (thereby preventing them from breaking any bonds formed), [ 19 ] and is proportional to the half-life of the chemical dissociation . [ 18 ] One way to measure the residence time is in a preincubation-dilution experiment where a target enzyme is incubated with the inhibitor, allowed to approach equilibrium, then rapidly diluted. The amount of product is measured and compared to a control in which no inhibitor is added. [ 17 ] : 87–88
Residence time can also refer to the amount of time that a drug spends in the part of the body where it needs to be absorbed. The longer the residence time, the more of it can be absorbed. If the drug is delivered in an oral form and destined for the upper intestines , it usually moves with food and its residence time is roughly that of the food. This generally allows 3 to 8 hours for absorption. [ 20 ] : 196 If the drug is delivered through a mucous membrane in the mouth, the residence time is short because saliva washes it away. Strategies to increase this residence time include bioadhesive polymers , gums, lozenges and dry powders. [ 20 ] : 274
In size-exclusion chromatography , the residence time of a molecule is related to its volume, which is roughly proportional to its molecular weight. Residence times also affect the performance of continuous fermentors . [ 1 ]
Biofuel cells utilize the metabolic processes of anodophiles ( electronegative bacteria) to convert chemical energy from organic matter into electricity. [ 21 ] [ 22 ] [ 23 ] A biofuel cell mechanism consists of an anode and a cathode that are separated by an internal proton exchange membrane (PEM) and connected in an external circuit with an external load. Anodophiles grow on the anode and consume biodegradable organic molecules to produce electrons, protons, and carbon dioxide gas, and as the electrons travel through the circuit they feed the external load. [ 22 ] [ 23 ] The HRT for this application is the rate at which the feed molecules are passed through the anodic chamber. [ 23 ] This can be quantified by dividing the volume of the anodic chamber by the rate at which the feed solution is passed into the chamber. [ 22 ] The hydraulic residence time (HRT) affects the substrate loading rate of the microorganisms that the anodophiles consume, which affects the electrical output. [ 23 ] [ 24 ] Longer HRTs reduce substrate loading in the anodic chamber which can lead to reduced anodophile population and performance when there is a deficiency of nutrients. [ 23 ] Shorter HRTs support the development of non- exoelectrogenous bacteria which can reduce the Coulombic efficiency electrochemical performance of the fuel cell if the anodophiles must compete for resources or if they do not have ample time to effectively degrade nutrients. [ 23 ] | https://en.wikipedia.org/wiki/Space_time_(chemical_engineering) |
Space vector modulation ( SVM ) is an algorithm for the control of pulse-width modulation (PWM), invented by Gerhard Pfaff, Alois Weschta, and Albert Wick in 1982. [ 1 ] [ 2 ] It is used for the creation of alternating current (AC) waveforms ; most commonly to drive 3 phase AC powered motors at varying speeds from DC using multiple class-D amplifiers . There are variations of SVM that result in different quality and computational requirements. One active area of development is in the reduction of total harmonic distortion (THD) created by the rapid switching inherent to these algorithms.
A three-phase inverter as shown to the right converts a DC supply, via a series of switches, to three output legs which could be connected to a three-phase motor.
The switches must be controlled so that at no time are both switches in the same leg turned on or else the DC supply would be shorted. This requirement may be met by the complementary operation of the switches within a leg. i.e. if A + is on then A − is off and vice versa. This leads to eight possible switching vectors for the inverter, V 0 through V 7 with six active switching vectors and two zero vectors.
Note that looking down the columns for the active switching vectors V 1-6 , the output voltages vary as a pulsed sinusoid, with each leg offset by 120 degrees of phase angle .
To implement space vector modulation, a reference signal V ref is sampled with a frequency f s (T s = 1/f s ). The reference signal may be generated from three separate phase references using the αβγ transform . The reference vector is then synthesized using a combination of the two adjacent active switching vectors and one or both of the zero vectors. Various strategies of selecting the order of the vectors and which zero vector(s) to use exist. Strategy selection will affect the harmonic content and the switching losses [ de ] .
More complicated SVM strategies for the unbalanced operation of four-leg three-phase inverters do exist. In these strategies the switching vectors define a 3D shape (a hexagonal prism in α β γ {\displaystyle \alpha \beta \gamma } coordinates [ 3 ] or a dodecahedron in abc coordinates [ 4 ] ) rather than a 2D hexagon . General SVM techniques are also available for converters with any number of legs and levels. [ 5 ] | https://en.wikipedia.org/wiki/Space_vector_modulation |
Space weather is a branch of space physics and aeronomy , or heliophysics , concerned with the varying conditions within the Solar System and its heliosphere . This includes the effects of the solar wind , especially on the Earth's magnetosphere , ionosphere , thermosphere , and exosphere . [ 1 ] Though physically distinct, space weather is analogous to the terrestrial weather of Earth's atmosphere ( troposphere and stratosphere ). The term "space weather" was first used in the 1950s and popularized in the 1990s. [ 2 ] Later, it prompted research into " space climate ", the large-scale and long-term patterns of space weather.
For many centuries, the effects of space weather were noticed, but not understood. Displays of auroral light have long been observed at high latitudes.
In 1724, George Graham reported that the needle of a magnetic compass was regularly deflected from magnetic north over the course of each day. This effect was eventually attributed to overhead electric currents flowing in the ionosphere and magnetosphere by Balfour Stewart in 1882, and confirmed by Arthur Schuster in 1889 from analysis of magnetic observatory data.
In 1852, astronomer and British Major General Edward Sabine showed that the probability of the occurrence of geomagnetic storms on Earth was correlated with the number of sunspots , demonstrating a novel solar-terrestrial interaction. The solar storm of 1859 caused brilliant auroral displays and disrupted global telegraph operations. Richard Carrington correctly connected the storm with a solar flare that he had observed the day before near a large sunspot group, demonstrating that specific solar events could affect the Earth.
Kristian Birkeland explained the physics of aurorae by creating artificial ones in his laboratory, and predicted the solar wind.
The introduction of radio revealed that solar weather could cause extreme static or noise. Radar jamming during a large solar event in 1942 led to the discovery of solar radio bursts, radio waves over a broad frequency range created by a solar flare.
In the 20th century, the interest in space weather expanded as military and commercial systems came to depend on systems affected by space weather. Communications satellites are a vital part of global commerce. Weather satellite systems provide information about terrestrial weather. The signals from satellites of a global positioning system (GPS) are used in a wide variety of applications. Space weather phenomena can interfere with or damage these satellites or interfere with the radio signals with which they operate. Space weather phenomena can cause damaging surges in long-distance transmission lines and expose passengers and crew of aircraft travel to radiation , [ 3 ] [ 4 ] especially on polar routes.
The International Geophysical Year increased research into space weather. Ground-based data obtained during IGY demonstrated that the aurorae occurred in an auroral oval , a permanent region of luminescence 15 to 25° in latitude from the magnetic poles and 5 to 20° wide. [ 5 ] In 1958, the Explorer I satellite discovered the Van Allen belts , [ 6 ] regions of radiation particles trapped by the Earth's magnetic field. In January 1959, the Soviet satellite Luna 1 first directly observed the solar wind and measured its strength. A smaller International Heliophysical Year (IHY) occurred in 2007–2008.
In 1969, INJUN-5 (or Explorer 40 [ 7 ] ) made the first direct observation of the electric field impressed on the Earth's high-latitude ionosphere by the solar wind. [ 8 ] In the early 1970s, Triad data demonstrated that permanent electric currents flowed between the auroral oval and the magnetosphere. [ 9 ]
The term "space weather" came into usage in the late 1950s as the space age began and satellites began to measure the space environment . [ 2 ] The term regained popularity in the 1990s along with the belief that space's impact on human systems demanded a more coordinated research and application framework. [ 10 ]
The purpose of the US National Space Weather Program is to focus research on the needs of the affected commercial and military communities, to connect the research and user communities, to create coordination between operational data centers, and to better define user community needs. NOAA operates the National Weather Service's Space Weather Prediction Center . [ 11 ]
The concept was turned into an action plan in 2000, [ 12 ] an implementation plan in 2002, an assessment in 2006 [ 13 ] and a revised strategic plan in 2010. [ 14 ] A revised action plan was scheduled to be released in 2011 followed by a revised implementation plan in 2012.
International Civil Aviation Organization (ICAO) implemented a Space Weather Advisory program in late 2019. Under this program, ICAO designated four global space weather service providers: [ 15 ]
Within the Solar System , space weather is influenced by the solar wind and the interplanetary magnetic field carried by the solar wind plasma . A variety of physical phenomena is associated with space weather, including geomagnetic storms and substorms , energization of the Van Allen radiation belts , ionospheric disturbances and scintillation of satellite-to-ground radio signals and long-range radar signals, aurorae , and geomagnetically induced currents at Earth's surface. Coronal mass ejections are also important drivers of space weather, as they can compress the magnetosphere and trigger geomagnetic storms. Solar energetic particles (SEP) accelerated by coronal mass ejections or solar flares can trigger solar particle events , a critical driver of human impact space weather, as they can damage electronics onboard spacecraft (e.g. Galaxy 15 failure), and threaten the lives of astronauts , as well as increase radiation hazards to high-altitude, high-latitude aviation.
Some spacecraft failures can be directly attributed to space weather; many more are thought to have a space weather component. For example, 46 of the 70 failures reported in 2003 occurred during the October 2003 geomagnetic storm. The two most common adverse space weather effects on spacecraft are radiation damage and spacecraft charging .
Radiation (high-energy particles) passes through the skin of the spacecraft and into the electronic components. In most cases, the radiation causes an erroneous signal or changes one bit in memory of a spacecraft's electronics ( single event upsets ). In a few cases, the radiation destroys a section of the electronics ( single-event latchup ).
Spacecraft charging is the accumulation of an electrostatic charge on a nonconducting material on the spacecraft's surface by low-energy particles. If enough charge is built up, a discharge (spark) occurs. This can cause an erroneous signal to be detected and acted on by the spacecraft computer. A recent study indicated that spacecraft charging is the predominant space weather effect on spacecraft in geosynchronous orbit . [ 17 ]
The orbits of spacecraft in low Earth orbit (LEO) decay to lower and lower altitudes due to the resistance from the friction between the spacecraft's surface ( i.e. , drag) and the outer layer of the Earth's atmosphere (or the thermosphere and exosphere). Eventually, a LEO spacecraft falls out of orbit and towards the Earth's surface. Many spacecraft launched in the past few decades have the ability to fire a small rocket to manage their orbits. The rocket can increase altitude to extend lifetime, to direct the re-entry towards a particular (marine) site, or route the satellite to avoid collision with other spacecraft. Such maneuvers require precise information about the orbit. A geomagnetic storm can cause an orbit change over a few days that otherwise would occur over a year or more. The geomagnetic storm adds heat to the thermosphere, causing the thermosphere to expand and rise, increasing the drag on spacecraft. The 2009 satellite collision between the Iridium 33 and Cosmos 2251 demonstrated the importance of having precise knowledge of all objects in orbit. Iridium 33 had the capability to maneuver out of the path of Cosmos 2251 and could have evaded the crash, if a credible collision prediction had been available.
The exposure of a human body to ionizing radiation has the same harmful effects whether the source of the radiation is a medical X-ray machine , a nuclear power plant , or radiation in space. The degree of the harmful effect depends on the length of exposure and the radiation's energy density . The ever-present radiation belts extend down to the altitude of crewed spacecraft such as the International Space Station (ISS) and the Space Shuttle , but the amount of exposure is within the acceptable lifetime exposure limit under normal conditions. During a major space weather event that includes an SEP burst, the flux can increase by orders of magnitude. Areas within ISS provide shielding that can keep the total dose within safe limits. [ 18 ] For the Space Shuttle , such an event would have required immediate mission termination.
The ionosphere bends radio waves in the same manner that water in a pool bends visible light. When the medium through which such waves travel is disturbed, the light image or radio information is distorted and can become unrecognizable. The degree of distortion (scintillation) of a radio wave by the ionosphere depends on the signal frequency. Radio signals in the VHF band (30 to 300 MHz) can be distorted beyond recognition by a disturbed ionosphere. Radio signals in the UHF band (300 MHz to 3 GHz) transit a disturbed ionosphere, but a receiver may not be able to keep locked to the carrier frequency. GPS uses signals at 1575.42 MHz (L1) and 1227.6 MHz (L2) that can be distorted by a disturbed ionosphere. Space weather events that corrupt GPS signals can significantly impact society. For example, the Wide Area Augmentation System operated by the US Federal Aviation Administration (FAA) is used as a navigation tool for North American commercial aviation. It is disabled by every major space weather event. Outages can range from minutes to days. Major space weather events can push the disturbed polar ionosphere 10° to 30° of latitude toward the equator and can cause large ionospheric gradients (changes in density over distance of hundreds of km) at mid and low latitude. Both of these factors can distort GPS signals.
Radio waves in the HF band (3 to 30 MHz) (also known as the shortwave band) are reflected by the ionosphere. Since the ground also reflects HF waves, a signal can be transmitted around the curvature of the Earth beyond the line of sight. During the 20th century, HF communications was the only method for a ship or aircraft far from land or a base station to communicate. The advent of systems such as Iridium brought other methods of communications, but HF remains critical for vessels that do not carry the newer equipment and as a critical backup system for others. Space weather events can create irregularities in the ionosphere that scatter HF signals instead of reflecting them, preventing HF communications. At auroral and polar latitudes, small space weather events that occur frequently disrupt HF communications. At mid-latitudes, HF communications are disrupted by solar radio bursts, by X-rays from solar flares (which enhance and disturb the ionospheric D-layer) and by TEC enhancements and irregularities during major geomagnetic storms.
Trans polar airline routes are particularly sensitive to space weather, in part because Federal Aviation Regulations require reliable communication over the entire flight. [ 19 ] Diverting such a flight is estimated to cost about $100,000. [ 20 ]
The magnetosphere guides cosmic ray and solar energetic particles to polar latitudes, while high-energy charged particles enter the mesosphere, stratosphere, and troposphere. These energetic particles at the top of the atmosphere shatter atmospheric atoms and molecules, creating harmful lower-energy particles that penetrate deep into the atmosphere and create measurable radiation. All aircraft flying above 8 km (26,200 feet) altitude are exposed to these particles. The dose exposure is greater in polar regions than at midlatitude and equatorial regions. Many commercial aircraft fly over the polar region. When a space weather event causes radiation exposure to exceed the safe level set by aviation authorities, [ 21 ] the aircraft's flight path is diverted.
Measurements of the radiation environment at commercial aircraft altitudes above 8 km (26,000 ft) have historically been done by instruments that record the data on board where the data are then processed later on the ground. However, a system of real-time radiation measurements on-board aircraft has been developed through the NASA Automated Radiation Measurements for Aerospace Safety (ARMAS) program. [ 22 ] ARMAS has flown hundreds of flights since 2013, mostly on research aircraft, and sent the data to the ground through Iridium satellite links. The eventual goal of these types of measurements is to data assimilate them into physics-based global radiation models, e.g., NASA's Nowcast of Atmospheric Ionizing Radiation System ( NAIRAS ), so as to provide the weather of the radiation environment rather than the climatology.
Magnetic storm activity can induce geoelectric fields in the Earth's conducting lithosphere . [ 23 ] Corresponding voltage differentials can find their way into electric power grids through ground connections , driving uncontrolled electric currents that interfere with grid operation, damage transformers, trip protective relays, and sometimes cause blackouts. [ 24 ] This complicated chain of causes and effects was demonstrated during the magnetic storm of March 1989 , [ 25 ] which caused the complete collapse of the Hydro-Québec electric-power grid in Canada, temporarily leaving nine million people without electricity. The possible occurrence of an even more intense storm [ 26 ] led to operational standards intended to mitigate induction-hazard risks, while reinsurance companies commissioned revised risk assessments . [ 27 ]
Air- and ship-borne magnetic surveys can be affected by rapid magnetic field variations during geomagnetic storms. Such storms cause data-interpretation problems because the space weather-related magnetic field changes are similar in magnitude to those of the subsurface crustal magnetic field in the survey area. Accurate geomagnetic storm warnings, including an assessment of storm magnitude and duration, allows for an economic use of survey equipment.
For economic and other reasons, oil and gas production often involves horizontal drilling of well paths many kilometers from a single wellhead. Accuracy requirements are strict, due to target size – reservoirs may only be a few tens to hundreds of meters across – and safety, because of the proximity of other boreholes. The most accurate gyroscopic method is expensive, since it can stop drilling for hours. An alternative is to use a magnetic survey, which enables measurement while drilling (MWD) . Near real-time magnetic data can be used to correct drilling direction. [ 28 ] [ 29 ] Magnetic data and space weather forecasts can help to clarify unknown sources of drilling error.
The amount of energy entering the troposphere and stratosphere from space weather phenomena is trivial compared to the solar insolation in the visible and infrared portions of the solar electromagnetic spectrum. Although some linkage between the 11-year sunspot cycle and the Earth's climate has been claimed., [ 30 ] this has never been verified. For example, the Maunder minimum , a 70-year period almost devoid of sunspots, has often been suggested to be correlated to a cooler climate, but these correlations have disappeared after deeper studies. The suggested link from changes in cosmic-ray flux causing changes in the amount of cloud formation [ 31 ] did not survive scientific tests. Another suggestion, that variations in the extreme ultraviolet (EUV) flux subtly influence existing drivers of the climate and tip the balance between El Niño / La Niña events [ 32 ] collapsed when new research showed this was not possible. As such, a linkage between space weather and the climate has not been demonstrated.
In addition, a link has been suggested between high energy charged particles (such as SEPs and cosmic rays ) and cloud formation . This is because charged particles interact with the atmosphere to produce volatiles which then condense, creating cloud seeds . [ 33 ] This is a topic of ongoing research at CERN , where experiments test the effect of high-energy charged particles on atmosphere. [ 34 ] If proven, this may suggest a link between space weather (in the form of solar particle events ) and cloud formation. [ 35 ]
Most recently, a statistical connection has been reported between the occurrence of heavy floods and the arrivals of high-speed solar wind streams (HSSs). The enhanced auroral energy deposition during HSSs is suggested as a mechanism for the generation of downward propagating atmospheric gravity waves (AGWs). As AGWs reach lower atmosphere , they may excite the conditional instability in the troposphere , thus leading to excessive rainfall. [ 36 ]
Observation of space weather is done both for scientific research and applications. Scientific observation has evolved with the state of knowledge, while application-related observation expanded with the ability to exploit such data.
Space weather is monitored at ground level by observing changes in the Earth's magnetic field over periods of seconds to days, by observing the surface of the Sun, and by observing radio noise created in the Sun's atmosphere.
The Sunspot Number (SSN) is the number of sunspots on the Sun's photosphere in visible light on the side of the Sun visible to an Earth observer. The number and total area of sunspots are related to the brightness of the Sun in the EUV and X-ray portions of the solar spectrum and to solar activity such as solar flares and coronal mass ejections.
The 10.7 cm radio flux (F10.7) is a measurement of RF emissions from the Sun and is roughly correlated with the solar EUV flux. Since this RF emission is easily obtained from the ground and EUV flux is not, this value has been measured and disseminated continuously since 1947. The world standard measurements are made by the Dominion Radio Astrophysical Observatory at Penticton, BC, Canada and reported once a day at local noon [ 37 ] in solar flux units (10 −22 W·m −2 ·Hz −1 ). F10.7 is archived by the National Geophysical Data Center. [ 38 ]
Fundamental space weather monitoring data are provided by ground-based magnetometers and magnetic observatories. Magnetic storms were first discovered by ground-based measurement of occasional magnetic disturbance. Ground magnetometer data provide real-time situational awareness for postevent analysis. Magnetic observatories have been in continuous operations for decades to centuries, providing data to inform studies of long-term changes in space climatology. [ 39 ] [ 40 ]
Disturbance storm time index (Dst index) is an estimate of the magnetic field change at the Earth's magnetic equator due to a ring of electric current at and just earthward of the geosynchronous orbit . [ 41 ] The index is based on data from four ground-based magnetic observatories between 21° and 33° magnetic latitude during a one-hour period. Stations closer to the magnetic equator are not used due to ionospheric effects. The Dst index is compiled and archived by the World Data Center for Geomagnetism, Kyoto. [ 42 ]
Kp/ap index: 'a' is an index created from the geomagnetic disturbance at one midlatitude (40° to 50° latitude) geomagnetic observatory during a 3-hour period. 'K' is the quasilogarithmic counterpart of the 'a' index. Kp and ap are the average of K and an over 13 geomagnetic observatories to represent planetary-wide geomagnetic disturbances. The Kp/ap index [ 43 ] indicates both geomagnetic storms and substorms (auroral disturbance). Kp/ap data are available from 1932 onward.
AE index is compiled from geomagnetic disturbances at 12 geomagnetic observatories in and near the auroral zones and is recorded at 1-minute intervals. [ 42 ] The public AE index is available with a lag of two to three days that limits its utility for space weather applications. The AE index indicates the intensity of geomagnetic substorms except during a major geomagnetic storm when the auroral zones expand equatorward from the observatories.
Radio noise bursts are reported by the Radio Solar Telescope Network to the U.S. Air Force and to NOAA. The radio bursts are associated with solar flare plasma that interacts with the ambient solar atmosphere.
The Sun's photosphere is observed continuously [ 44 ] for activity that can be the precursors to solar flares and CMEs. The Global Oscillation Network Group (GONG) [ 45 ] project monitors both the surface and the interior of the Sun by using helioseismology , the study of sound waves propagating through the Sun and observed as ripples on the solar surface. GONG can detect sunspot groups on the far side of the Sun. This ability has recently been verified by visual observations from the STEREO spacecraft.
Neutron monitors on the ground indirectly monitor cosmic rays from the Sun and galactic sources. When cosmic rays interact with the atmosphere, atomic interactions occur that cause a shower of lower-energy particles to descend into the atmosphere and to ground level. The presence of cosmic rays in the near-Earth space environment can be detected by monitoring high-energy neutrons at ground level. Small fluxes of cosmic rays are present continuously. Large fluxes are produced by the Sun during events related to energetic solar flares.
Total Electron Content (TEC) is a measure of the ionosphere over a given location. TEC is the number of electrons in a column one meter square from the base of the ionosphere (around 90 km altitude) to the top of the ionosphere (around 1000 km altitude). Many TEC measurements are made by monitoring the two frequencies transmitted by GPS spacecraft. Presently, GPS TEC is monitored and distributed in real time from more than 360 stations maintained by agencies in many countries.
Geoeffectiveness is a measure of how strongly space weather magnetic fields, such as coronal mass ejections, couple with the Earth's magnetic field. This is determined by the direction of the magnetic field held within the plasma that originates from the Sun. New techniques measuring Faraday rotation in radio waves are in development to measure field direction. [ 46 ] [ 47 ]
A host of research spacecraft have explored space weather. [ 48 ] [ 49 ] [ 50 ] [ 51 ] The Orbiting Geophysical Observatory series were among the first spacecraft with the mission of analyzing the space environment. Recent spacecraft include the NASA-ESA Solar-Terrestrial Relations Observatory (STEREO) pair of spacecraft launched in 2006 into solar orbit and the Van Allen Probes , launched in 2012 into a highly elliptical Earth orbit. The two STEREO spacecraft drift away from the Earth by about 22° per year, one leading and the other trailing the Earth in its orbit. Together they compile information about the solar surface and atmosphere in three dimensions. The Van Allen probes record detailed information about the radiation belts, geomagnetic storms, and the relationship between the two.
Some spacecraft with other primary missions have carried auxiliary instruments for solar observation. Among the earliest such spacecraft were the Applications Technology Satellite [ 52 ] (ATS) series at GEO that were precursors to the modern Geostationary Operational Environmental Satellite (GOES) weather satellite and many communication satellites. The ATS spacecraft carried environmental particle sensors as auxiliary payloads and had their navigational magnetic field sensor used for sensing the environment.
Many of the early instruments were research spacecraft that were re-purposed for space weather applications. One of the first of these was the IMP-8 (Interplanetary Monitoring Platform). [ 53 ] It orbited the Earth at 35 Earth radii and observed the solar wind for two-thirds of its 12-day orbits from 1973 to 2006. Since the solar wind carries disturbances that affect the magnetosphere and ionosphere, IMP-8 demonstrated the utility of continuous solar wind monitoring. IMP-8 was followed by ISEE-3 , which was placed near the L 1 Sun-Earth Lagrangian point , 235 Earth radii above the surface (about 1.5 million km, or 924,000 miles) and continuously monitored the solar wind from 1978 to 1982. The next spacecraft to monitor the solar wind at the L 1 point was WIND from 1994 to 1998. After April 1998, the WIND spacecraft orbit was changed to circle the Earth and occasionally pass the L 1 point. The NASA Advanced Composition Explorer has monitored the solar wind at the L 1 point from 1997 to present.
In addition to monitoring the solar wind, monitoring the Sun is important to space weather. Because the solar EUV cannot be monitored from the ground, the joint NASA - ESA Solar and Heliospheric Observatory (SOHO) spacecraft was launched and has provided solar EUV images beginning in 1995. SOHO is a main source of near-real time solar data for both research and space weather prediction and inspired the STEREO mission. The Yohkoh spacecraft at LEO observed the Sun from 1991 to 2001 in the X-ray portion of the solar spectrum and was useful for both research and space weather prediction. Data from Yohkoh inspired the Solar X-ray Imager on GOES.
Spacecraft with instruments whose primary purpose is to provide data for space weather predictions and applications include the Geostationary Operational Environmental Satellite (GOES) series of spacecraft, the POES series, the DMSP series, and the Meteosat series. The GOES spacecraft have carried an X-ray sensor (XRS) which measures the flux from the whole solar disk in two bands – 0.05 to 0.4 nm and 0.1 to 0.8 nm – since 1974, an X-ray imager (SXI) since 2004, a magnetometer which measures the distortions of the Earth's magnetic field due to space weather, a whole disk EUV sensor since 2004, and particle sensors (EPS/HEPAD) which measure ions and electrons in the energy range of 50 keV to 500 MeV. Starting sometime after 2015, the GOES-R generation of GOES spacecraft will replace the SXI with a solar EUV image (SUVI) similar to the one on SOHO and STEREO and the particle sensor will be augmented with a component to extend the energy range down to 30 eV.
The Deep Space Climate Observatory (DSCOVR) satellite is a NOAA Earth observation and space weather satellite that launched in February 2015. Among its features is advance warning of coronal mass ejections. [ 54 ]
Space weather models are simulations of the space weather environment. Models use sets of mathematical equations to describe physical processes.
These models take a limited data set and attempt to describe all or part of the space weather environment in or to predict how weather evolves over time. Early models were heuristic; i.e ., they did not directly employ physics. These models take less resources than their more sophisticated descendants.
Later models use physics to account for as many phenomena as possible. No model can yet reliably predict the environment from the surface of the Sun to the bottom of the Earth's ionosphere. Space weather models differ from meteorological models in that the amount of input is vastly smaller.
A significant portion of space weather model research and development in the past two decades has been done as part of the Geospace Environmental Model (GEM) program of the National Science Foundation . The two major modeling centers are the Center for Space Environment Modeling (CSEM) [ 55 ] and the Center for Integrated Space weather Modeling (CISM). [ 56 ] The Community Coordinated Modeling Center [ 57 ] (CCMC) at the NASA Goddard Space Flight Center is a facility for coordinating the development and testing of research models, for improving and preparing models for use in space weather prediction and application. [ 58 ]
Modeling techniques include (a) magnetohydrodynamics , in which the environment is treated as a fluid, (b) particle in cell, in which non-fluid interactions are handled within a cell and then cells are connected to describe the environment, (c) first principles, in which physical processes are in balance (or equilibrium) with one another, (d) semi-static modeling, in which a statistical or empirical relationship is described, or a combination of multiple methods.
During the first decade of the 21st Century, a commercial sector emerged that engaged in space weather, serving agency, academia, commercial and consumer sectors. [ 59 ] Space weather providers are typically smaller companies, or small divisions within a larger company, that provide space weather data, models, derivative products and service distribution. [ citation needed ]
The commercial sector includes scientific and engineering researchers as well as users. Activities are primarily directed toward the impacts of space weather upon technology. These include, for example:
Many of these disturbances result in societal impacts that account for a significant part of the national GDP. [ 62 ] [ 63 ]
The concept of incentivizing commercial space weather was first suggested by the idea of a Space Weather Economic Innovation Zone discussed by the American Commercial Space Weather Association (ACSWA) in 2015. The establishment of this economic innovation zone would encourage expanded economic activity developing applications to manage the risks space weather and would encourage broader research activities related to space weather by universities. It could encourage U.S. business investment in space weather services and products. It promoted the support of U.S. business innovation in space weather services and products by requiring U.S. government purchases of U.S. built commercial hardware, software, and associated products and services where no suitable government capability pre-exists. It also promoted U.S. built commercial hardware, software, and associated products and services sales to international partners. designate U.S. built commercial hardware, services, and products as “Space Weather Economic Innovation Zone” activities; Finally, it recommended that U.S. built commercial hardware, services, and products be tracked as Space Weather Economic Innovation Zone contributions within agency reports. In 2015 the U.S. Congress bill HR1561 provided groundwork where social and environmental impacts from a Space Weather Economic Innovation Zone could be far-reaching. In 2016, the Space Weather Research and Forecasting Act (S. 2817) was introduced to build on that legacy. Later, in 2017-2018 the HR3086 Bill took these concepts, included the breadth of material from parallel agency studies as part of the OSTP-sponsored Space Weather Action Program (SWAP), [ 64 ] and with bicameral and bipartisan support the 116th Congress (2019) is considering passage of the Space Weather Coordination Act (S141, 115th Congress). [ citation needed ]
On April 29, 2010, the commercial space weather community created the American Commercial Space Weather Association ( ACSWA ) an industry association. ACSWA promotes space weather risk mitigation for national infrastructure, economic strength and national security. It seeks to: [ 65 ]
A summary of the broad technical capabilities in space weather that are available from the association can be found on their web site http://www.acswa.us . | https://en.wikipedia.org/wiki/Space_weather |
A spacecraft is a vehicle that is designed to fly and operate in outer space . [ 1 ] Spacecraft are used for a variety of purposes, including communications , Earth observation , meteorology , navigation , space colonization , planetary exploration , and transportation of humans and cargo . All spacecraft except single-stage-to-orbit vehicles cannot get into space on their own, and require a launch vehicle (carrier rocket).
On a sub-orbital spaceflight , a space vehicle enters space and then returns to the surface without having gained sufficient energy or velocity to make a full Earth orbit . For orbital spaceflights , spacecraft enter closed orbits around the Earth or around other celestial bodies . Spacecraft used for human spaceflight carry people on board as crew or passengers from start or on orbit ( space stations ) only, whereas those used for robotic space missions operate either autonomously or telerobotically . Robotic spacecraft used to support scientific research are space probes . Robotic spacecraft that remain in orbit around a planetary body are artificial satellites . To date, only a handful of interstellar probes , such as Pioneer 10 and 11 , Voyager 1 and 2 , and New Horizons , are on trajectories that leave the Solar System .
Orbital spacecraft may be recoverable or not. Most are not. Recoverable spacecraft may be subdivided by a method of reentry to Earth into non-winged space capsules and winged spaceplanes . Recoverable spacecraft may be reusable (can be launched again or several times, like the SpaceX Dragon and the Space Shuttle orbiters ) or expendable (like the Soyuz ). In recent years, more space agencies are tending towards reusable spacecraft.
Humanity has achieved space flight, but only a few nations have the technology for orbital launches : Russia ( Roscosmos [ 2 ] ), the United States ( NASA [ 3 ] ), the member states of the European Space Agency , [ 4 ] Japan ( JAXA [ 5 ] ), China ( CNSA [ 6 ] ), India ( ISRO [ 7 ] ), Taiwan ( TSA [ 8 ] [ 9 ] [ 10 ] ), Israel ( ISA ), Iran ( ISA ), and North Korea ( NADA ). In addition, several private companies have developed or are developing the technology for orbital launches independently from government agencies. Two prominent examples of such companies are SpaceX and Blue Origin .
A German V-2 became the first spacecraft when it reached an altitude of 189 km in June 1944 in Peenemünde , Germany. [ 11 ] Sputnik 1 was the first artificial satellite . It was launched into an elliptical low Earth orbit (LEO) by the Soviet Union on 4 October 1957. The launch ushered in new political, military, technological, and scientific developments; while the Sputnik launch was a single event, it marked the start of the Space Age . [ 12 ] [ 13 ] Apart from its value as a technological first, Sputnik 1 also helped to identify the upper atmospheric layer 's density, by measuring the satellite's orbital changes. It also provided data on radio -signal distribution in the ionosphere . Pressurized nitrogen in the satellite's false body provided the first opportunity for meteoroid detection. Sputnik 1 was launched during the International Geophysical Year from Site No.1/5 , at the 5th Tyuratam range, in Kazakh SSR (now at the Baikonur Cosmodrome ). The satellite travelled at 29,000 kilometres per hour (18,000 mph), taking 96.2 minutes to complete an orbit, and emitted radio signals at 20.005 and 40.002 MHz
While Sputnik 1 was the first spacecraft to orbit the Earth, other human-made objects had previously reached an altitude of 100 km, which is the height required by the international organization Fédération Aéronautique Internationale to count as a spaceflight. This altitude is called the Kármán line . In particular, in the 1940s there were several test launches of the V-2 rocket , some of which reached altitudes well over 100 km.
As of 2016, only three nations have flown crewed spacecraft: USSR/Russia, USA, and China.
The first crewed spacecraft was Vostok 1 , which carried Soviet cosmonaut Yuri Gagarin into space in 1961, and completed a full Earth orbit. There were five other crewed missions which used a Vostok spacecraft . [ 14 ] The second crewed spacecraft was named Freedom 7 , and it performed a sub-orbital spaceflight in 1961 carrying American astronaut Alan Shepard to an altitude of just over 187 kilometers (116 mi). There were five other crewed missions using Mercury spacecraft .
Other Soviet crewed spacecraft include the Voskhod , Soyuz , flown uncrewed as Zond/L1 , L3 , TKS , and the Salyut and Mir crewed space stations . Other American crewed spacecraft include the Gemini spacecraft , the Apollo spacecraft including the Apollo Lunar Module , the Skylab space station, the Space Shuttle with undetached European Spacelab and private US Spacehab space stations-modules, and the SpaceX Crew Dragon configuration of their Dragon 2 . US company Boeing also developed and flown a spacecraft of their own, the CST-100 , commonly referred to as Starliner , but a crewed flight is yet to occur. China developed, but did not fly Shuguang , and is currently using Shenzhou (its first crewed mission was in 2003).
Except for the Space Shuttle and the Buran spaceplane of the Soviet Union, the latter of which only ever had one uncrewed test flight, all of the recoverable crewed orbital spacecraft were space capsules .
The International Space Station , crewed since November 2000, is a joint venture between Russia, the United States, Canada and several other countries.
Uncrewed spacecraft are spacecraft without people on board. Uncrewed spacecraft may have varying levels of autonomy from human input; they may be remote controlled , remote guided or even autonomous , meaning they have a pre-programmed list of operations, which they will execute unless otherwise instructed.
Many space missions are more suited to telerobotic rather than crewed operation, due to lower cost and lower risk factors. In addition, some planetary destinations such as Venus or the vicinity of Jupiter are too hostile for human survival. Outer planets such as Saturn , Uranus , and Neptune are too distant to reach with current crewed spaceflight technology, so telerobotic probes are the only way to explore them. Telerobotics also allows exploration of regions that are vulnerable to contamination by Earth micro-organisms since spacecraft can be sterilized. Humans can not be sterilized in the same way as a spaceship, as they coexist with numerous micro-organisms, and these micro-organisms are also hard to contain within a spaceship or spacesuit. Multiple space probes were sent to study Moon, the planets, the Sun, multiple small Solar System bodies (comets and asteroids).
Special class of uncrewed spacecraft is space telescopes , a telescope in outer space used to observe astronomical objects. The first operational telescopes were the American Orbiting Astronomical Observatory , OAO-2 launched in 1968, and the Soviet Orion 1 ultraviolet telescope aboard space station Salyut 1 in 1971. Space telescopes avoid the filtering and distortion ( scintillation ) of electromagnetic radiation which they observe, and avoid light pollution which ground-based observatories encounter. The best-known examples are Hubble Space Telescope and James Webb Space Telescope .
Cargo spacecraft are designed to carry cargo , possibly to support space stations ' operation by transporting food, propellant and other supplies. Automated cargo spacecraft have been used since 1978 and have serviced Salyut 6 , Salyut 7 , Mir , the International Space Station and Tiangong space station.
Some spacecrafts can operate as both a crewed and uncrewed spacecraft. For example, the Buran spaceplane could operate autonomously but also had manual controls, though it never flew with crew onboard. [ 15 ] [ 16 ]
Other dual crewed/uncrewed spacecrafts include: SpaceX Dragon 2 , [ 17 ] [ 18 ] [ 19 ] [ 20 ] Dream Chaser , [ 21 ] [ 22 ] and Tianzhou . [ 23 ] [ 24 ]
A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder ; it creates a communication channel between a source transmitter and a receiver at different locations on Earth . Communications satellites are used for television , telephone , radio , internet , and military applications. [ 25 ] Many communications satellites are in geostationary orbit 22,300 miles (35,900 km) above the equator , so that the satellite appears stationary at the same point in the sky; therefore the satellite dish antennas of ground stations can be aimed permanently at that spot and do not have to move to track the satellite. Others form satellite constellations in low Earth orbit , where antennas on the ground have to follow the position of the satellites and switch between satellites frequently.
The high frequency radio waves used for telecommunications links travel by line of sight and so are obstructed by the curve of the Earth. The purpose of communications satellites is to relay the signal around the curve of the Earth allowing communication between widely separated geographical points. [ 26 ] Communications satellites use a wide range of radio and microwave frequencies . To avoid signal interference, international organizations have regulations for which frequency ranges or "bands" certain organizations are allowed to use. This allocation of bands minimizes the risk of signal interference. [ 27 ]
Cargo or resupply spacecraft are robotic spacecraft that are designed specifically to carry cargo , possibly to support space stations ' operation by transporting food, propellant and other supplies.
Automated cargo spacecraft have been used since 1978 and have serviced Salyut 6 , Salyut 7 , Mir , the International Space Station and Tiangong space station.
As of 2023, three different cargo spacecraft are used to supply the International Space Station : Russian Progress , American SpaceX Dragon 2 and Cygnus . Chinese Tianzhou is used to supply Tiangong space station .
Space probes are robotic spacecraft that are sent to explore deep space, or astronomical bodies other than Earth. They are distinguished from landers by the fact that they work in open space, not on planetary surfaces or in planetary atmospheres. Being robotic eliminates the need for expensive, heavy life support systems (the Apollo crewed Moon landings required the use of the Saturn V rocket that cost over a billion dollars per launch, adjusted for inflation) and so allows for lighter, less expensive rockets. Space probes have visited every planet in the Solar System and Pluto , and the Parker Solar Probe has an orbit that, at its closest point, is in the Sun's chromosphere . There are five space probes that are escaping the Solar System , these are Voyager 1 , Voyager 2 , Pioneer 10 , Pioneer 11 , and New Horizons .
The identical Voyager probes , weighing 721.9 kilograms (1,592 lb), [ 28 ] were launched in 1977 to take advantage of a rare alignment of Jupiter , Saturn , Uranus and Neptune that would allow a spacecraft to visit all four planets in one mission, and get to each destination faster by using gravity assist . In fact, the rocket that launched the probes (the Titan IIIE ) could not even send the probes to the orbit of Saturn , yet Voyager 1 is travelling at roughly 17 km/s (11 mi/s) and Voyager 2 moves at about 15 km/s (9.3 mi/s) kilometres per second as of 2023. In 2012, Voyager 1 exited the heliosphere, followed by Voyager 2 in 2018. Voyager 1 actually launched 16 days after Voyager 2 but it reached Jupiter sooner because Voyager 2 was taking a longer route that allowed it to visit Uranus and Neptune, whereas Voyager 1 did not visit Uranus or Neptune, instead choosing to fly past Saturn’s satellite Titan . As of August 2023, Voyager 1 has passed 160 astronomical units , which means it is over 160 times farther from the Sun than Earth is. This makes it the farthest spacecraft from the Sun. Voyager 2 is 134 AU away from the Sun as of August 2023. NASA provides real time data of their distances and data from the probe’s cosmic ray detectors. [ 29 ] Because of the probe’s declining power output and degradation of the RTGs over time, NASA has had to shut down certain instruments to conserve power. The probes may still have some scientific instruments on until the mid-2020s or perhaps the 2030s. After 2036, they will both be out of range of the Deep Space Network .
A space telescope or space observatory is a telescope in outer space used to observe astronomical objects. Space telescopes avoid the filtering and distortion of electromagnetic radiation which they observe, and avoid light pollution which ground-based observatories encounter. They are divided into two types: satellites which map the entire sky ( astronomical survey ), and satellites which focus on selected astronomical objects or parts of the sky and beyond. Space telescopes are distinct from Earth imaging satellites , which point toward Earth for satellite imaging , applied for weather analysis , espionage , and other types of information gathering .
A lander is a type of spacecraft that makes a soft landing on the surface of an astronomical body other than Earth . Some landers, such as Philae and the Apollo Lunar Module , land entirely by using their fuel supply, however many landers (and landings of spacecraft on Earth ) use aerobraking , especially for more distant destinations. This involves the spacecraft using a fuel burn to change its trajectory so it will pass through a planet (or a moon's) atmosphere. Drag caused by the spacecraft hitting the atmosphere enables it to slow down without using fuel, however this generates very high temperatures and so adds a requirement for a heat shield of some sort.
Space capsules are a type of spacecraft that can return from space at least once. They have a blunt shape, do not usually contain much more fuel than needed, and they do not possess wings unlike spaceplanes . They are the simplest form of recoverable spacecraft, and so the most commonly used. The first such capsule was the Vostok capsule built by the Soviet Union, that carried the first person in space, Yuri Gagarin . Other examples include the Soyuz and Orion capsules, built by the Soviet Union and NASA , respectively.
Spaceplanes are spacecraft that are built in the shape of, and function as, airplanes . The first example of such was the North American X-15 spaceplane, which conducted two crewed flights which reached an altitude of over 100 kilometres (62 mi) in the 1960s. This first reusable spacecraft was air-launched on a suborbital trajectory on July 19, 1963.
The first reusable orbital spaceplane was the Space Shuttle orbiter . The first orbiter to fly in space, the Space Shuttle Columbia , was launched by the USA on the 20th anniversary of Yuri Gagarin 's flight, on April 12, 1981. During the Shuttle era, six orbiters were built, all of which have flown in the atmosphere and five of which have flown in space. Enterprise was used only for approach and landing tests, launching from the back of a Boeing 747 SCA and gliding to deadstick landings at Edwards AFB, California . The first Space Shuttle to fly into space was Columbia , followed by Challenger , Discovery , Atlantis , and Endeavour . Endeavour was built to replace Challenger when it was lost in January 1986. Columbia broke up during reentry in February 2003.
The first autonomous reusable spaceplane was the Buran -class shuttle , launched by the USSR on November 15, 1988, although it made only one flight and this was uncrewed. This spaceplane was designed for a crew and strongly resembled the U.S. Space Shuttle, although its drop-off boosters used liquid propellants and its main engines were located at the base of what would be the external tank in the American Shuttle. Lack of funding, complicated by the dissolution of the USSR , prevented any further flights of Buran. The Space Shuttle was subsequently modified to allow for autonomous re-entry in case of necessity.
Per the Vision for Space Exploration , the Space Shuttle was retired in 2011 mainly due to its old age and high cost of program reaching over a billion dollars per flight. The Shuttle's human transport role is to be replaced by SpaceX 's SpaceX Dragon 2 and Boeing 's CST-100 Starliner . Dragon 2's first crewed flight occurred on May 30, 2020. [ 30 ] The Shuttle's heavy cargo transport role is to be replaced by expendable rockets such as the Space Launch System and ULA 's Vulcan rocket, as well as the commercial launch vehicles.
Scaled Composites ' SpaceShipOne was a reusable suborbital spaceplane that carried pilots Mike Melvill and Brian Binnie on consecutive flights in 2004 to win the Ansari X Prize . The Spaceship Company built a successor SpaceShipTwo . A fleet of SpaceShipTwos operated by Virgin Galactic was planned to begin reusable private spaceflight carrying paying passengers in 2014, but was delayed after the crash of VSS Enterprise .
The Space Shuttle is a retired reusable Low Earth Orbital launch system. It consisted of two reusable Solid Rocket Boosters that landed by parachute, were recovered at sea, and were the most powerful rocket motors ever made until they were superseded by those of NASA’s SLS rocket, with a liftoff thrust of 2,800,000 pounds-force (12 MN), which soon increased to 3,300,000 pounds-force (15 MN) per booster, [ 31 ] and were fueled by a combination of PBAN and APCP , the Space Shuttle Orbiter , with 3 RS-25 engines that used a liquid oxygen / liquid hydrogen propellant combination, and the bright orange throwaway Space Shuttle external tank from which the RS-25 engines sourced their fuel. The orbiter was a spaceplane that was launched at NASA’s Kennedy Space Centre and landed mainly at the Shuttle Landing Facility , which is part of Kennedy Space Centre. A second launch site, Vandenberg Space Launch Complex 6 in California , was revamped so it could be used to launch the shuttles, but it was never used. The launch system could lift about 29 tonnes (64,000 lb) into an eastward Low Earth Orbit . Each orbiter weighed roughly 78 tonnes (172,000 lb), however the different orbiters had differing weights and thus payloads, with Columbia being the heaviest orbiter, Challenger being lighter than Columbia but still heavier than the other three. The orbiter structure was mostly composed of aluminium alloy. The orbiter had seven seats for crew members, though on STS-61-A the launch took place with 8 crew onboard. The orbiters had 4.6 metres (15 ft) wide by 18 metres (59 ft) long payload bays and also were equipped with a 15.2 metres (50 ft) CanadaArm1 , an upgraded version of which is used on the International Space Station . The heat shield (or Thermal Protection System ) of the orbiter, used to protect it from extreme levels of heat during atmospheric reentry and the cold of space, was made up of different materials depending on weight and how much heating a particular area on the shuttle would receive during reentry, which ranged from over 2,900 °F (1,600 °C) to under 700 °F (370 °C). The orbiter was manually operated, though an autonomous landing system was added while the shuttle was still on service. It had an in orbit maneouvreing system known as the Orbital Manoeuvring System, which used the hypergolic propellants monomethylhydrazine (MMH) and dinitrogen tetroxide , which was used for orbital insertion, changes to orbits and the deorbit burn.
Though the shuttle’s goals were to drastically decrease launch costs, it did not do so, ending up being much more expensive than similar expendable launchers. This was due to expensive refurbishment costs and the external tank being expended. Once a landing had occurred, the SRBs and many parts of the orbiter had to be disassembled for inspection, which was long and arduous. Furthermore, the RS-25 engines had to be replaced every few flights. Each of the heat shielding tiles had to go in one specific area on the orbiter, increasing complexity more. Adding to this, the shuttle was a rather dangerous system, with fragile heat shielding tiles, some being so fragile that one could easily scrape it off by hand, often having been damaged in many flights. After 30 years in service from 1981 to 2011 and 135 flights, the shuttle was retired from service due to the cost of maintaining the shuttles, and the 3 remaining orbiters (the other two were destroyed in accidents) were prepared to be displayed in museums.
Some spacecraft do not fit particularly well into any of the general spacecraft categories. This is a list of these spacecraft.
Starship is a spacecraft and second stage [ 32 ] under development by American aerospace company SpaceX . Stacked atop its booster, Super Heavy , it composes the identically named Starship super heavy-lift space vehicle . The spacecraft is designed to transport both crew and cargo to a variety of destinations, including Earth orbit, the Moon, Mars, and potentially beyond. It is intended to enable long duration interplanetary flights for a crew of up to 100 people. [ 32 ] It will also be capable of point-to-point transport on Earth, enabling travel to anywhere in the world in less than an hour. Furthermore, the spacecraft will be used to refuel other Starship vehicles to allow them to reach higher orbits to and other space destinations. Elon Musk , the CEO of SpaceX, estimated in a tweet that 8 launches would be needed to completely refuel a Starship in low Earth orbit , extrapolating this from Starship's payload to orbit and how much fuel a fully fueled Starship contains. [ 33 ] To land on bodies without an atmosphere, such as the Moon, Starship will fire its engines and thrusters to slow down. [ 34 ]
The Mission Extension Vehicle is a robotic spacecraft designed to prolong the life on another spacecraft. It works by docking to its target spacecraft, then correcting its orientation or orbit. This also allows it to rescue a satellite which is in the wrong orbit by using its own fuel to move its target to the correct orbit. The project is currently managed by Northrop Grumman Innovation Systems. As of 2023, 2 have been launched. The first launched on a Proton rocket on 9 October 2019, and did a rendezvous with Intelsat-901 on 25 February 2020. It will remain with the satellite until 2025 before the satellite is moved to a final graveyard orbit and the vehicle does a rendezvous with another satellite. The other one launched on an Ariane 5 rocket on 15 August 2020.
A spacecraft astrionics system comprises different subsystems, depending on the mission profile. Spacecraft subsystems are mounted in the satellite bus and may include attitude determination and control (variously called ADAC, ADC, or ACS), guidance, navigation and control (GNC or GN&C), communications (comms), command and data handling (CDH or C&DH), power (EPS), thermal control (TCS), propulsion, and structures. Attached to the bus are typically payloads . | https://en.wikipedia.org/wiki/Spacecraft |
Spacecraft attitude control is the process of controlling the orientation of a spacecraft (vehicle or satellite) with respect to an inertial frame of reference or another entity such as the celestial sphere , certain fields, and nearby objects, etc.
Controlling vehicle attitude requires actuators to apply the torques needed to orient the vehicle to a desired attitude, and algorithms to command the actuators based on the current attitude and specification of a desired attitude.
Before and during attitude control can be performed, spacecraft attitude determination must be performed, which requires sensors for absolute or relative measurement.
The broader integrated field that studies the combination of sensors, actuators and algorithms is called guidance, navigation and control , which also involves non-attitude concepts, such as position determination and navigation .
A spacecraft's attitude must typically be stabilized and controlled for a variety of reasons. It is often needed so that the spacecraft high-gain antenna may be accurately pointed to Earth for communications, so that onboard experiments may accomplish precise pointing for accurate collection and subsequent interpretation of data, so that the heating and cooling effects of sunlight and shadow may be used intelligently for thermal control, and also for guidance: short propulsive maneuvers must be executed in the right direction.
Many spacecraft have components that require articulation or pointing. Voyager and Galileo , for example, were designed with scan platforms for pointing optical instruments at their targets largely independently of spacecraft orientation. Many spacecraft, such as Mars orbiters, have solar panels that must track the Sun so they can provide electrical power to the spacecraft. Cassini ' s main engine nozzles were steerable. Knowing where to point a solar panel, or scan platform, or a nozzle — that is, how to articulate it — requires knowledge of the spacecraft's attitude. Because a single subsystem keeps track of the spacecraft's attitude, the Sun's location, and Earth's location, it can compute the proper direction to point the appendages. It logically falls to the same subsystem – the Attitude and Articulation Control Subsystem (AACS), then, to manage both attitude and articulation. The name AACS may even be carried over to a spacecraft even if it has no appendages to articulate. [ 1 ]
Attitude is part of the description of how an object is placed in the space it occupies. Attitude and position fully describe how an object is placed in space. (For some applications such as in robotics and computer vision, it is customary to combine position and attitude together into a single description known as Pose .)
Attitude can be described using a variety of methods; however, the most common are Rotation matrices , Quaternions , and Euler angles . While Euler angles are oftentimes the most straightforward representation to visualize, they can cause problems for highly-maneuverable systems because of a phenomenon known as Gimbal lock . A rotation matrix, on the other hand, provides a full description of the attitude at the expense of requiring nine values instead of three. The use of a rotation matrix can lead to increased computational expense and they can be more difficult to work with. Quaternions offer a decent compromise in that they do not suffer from gimbal lock and only require four values to fully describe the attitude.
Attitude control of spacecraft is maintained using one of two principal approaches:
There are advantages and disadvantages to both spin stabilization and three-axis stabilization. Spin-stabilized craft provide a continuous sweeping motion that is desirable for fields and particles instruments, as well as some optical scanning instruments, but they may require complicated systems to de-spin antennas or optical instruments that must be pointed at targets for science observations or communications with Earth. Three-axis controlled craft can point optical instruments and antennas without having to de-spin them, but they may have to carry out special rotating maneuvers to best utilize their fields and particle instruments. If thrusters are used for routine stabilization, optical observations such as imaging must be designed knowing that the spacecraft is always slowly rocking back and forth, and not always exactly predictably. Reaction wheels provide a much steadier spacecraft from which to make observations, but they add mass to the spacecraft, they have a limited mechanical lifetime, and they require frequent momentum desaturation maneuvers, which can perturb navigation solutions because of accelerations imparted by the use of thrusters. [ citation needed ]
Attitude control can be obtained by several mechanisms, including:
Vernier thrusters are the most common actuators, as they may be used for station keeping as well. Thrusters must be organized as a system to provide stabilization about all three axes, and at least two thrusters are generally used in each axis to provide torque as a couple in order to prevent imparting a translation to the vehicle. Their limitations are fuel usage, engine wear, and cycles of the control valves. The fuel efficiency of an attitude control system is determined by its specific impulse (proportional to exhaust velocity) and the smallest torque impulse it can provide (which determines how often the thrusters must fire to provide precise control). Thrusters must be fired in one direction to start rotation, and again in the opposing direction if a new orientation is to be held. Thruster systems have been used on most crewed space vehicles, including Vostok , Mercury , Gemini , Apollo , Soyuz , and the Space Shuttle .
To minimize the fuel limitation on mission duration, auxiliary attitude control systems may be used to reduce vehicle rotation to lower levels, such as small ion thrusters that accelerate ionized gases electrically to extreme velocities, using power from solar cells.
Momentum wheels are electric motor driven rotors made to spin in the direction opposite to that required to re-orient the vehicle. Because momentum wheels make up a small fraction of the spacecraft's mass and are computer controlled, they give precise control. Momentum wheels are generally suspended on magnetic bearings to avoid bearing friction and breakdown problems. [ 5 ] Spacecraft Reaction wheels often use mechanical ball bearings.
To maintain orientation in three dimensional space a minimum of three reaction wheels must be used, [ 6 ] with additional units providing single failure protection. See Euler angles .
These are rotors spun at constant speed, mounted on gimbals to provide attitude control. Although a CMG provides control about the two axes orthogonal to the gyro spin axis, triaxial control still requires two units. A CMG is a bit more expensive in terms of cost and mass, because gimbals and their drive motors must be provided. The maximum torque (but not the maximum angular momentum change) exerted by a CMG is greater than for a momentum wheel, making it better suited to large spacecraft. A major drawback is the additional complexity, which increases the number of failure points. For this reason, the International Space Station uses a set of four CMGs to provide dual failure tolerance.
Small solar sails (devices that produce thrust as a reaction force induced by reflecting incident light) may be used to make small attitude control and velocity adjustments. This application can save large amounts of fuel on a long-duration mission by producing control moments without fuel expenditure. For example, Mariner 10 adjusted its attitude using its solar cells and antennas as small solar sails.
In orbit, a spacecraft with one axis much longer than the other two will spontaneously orient so that its long axis points at the planet's center of mass. This system has the virtue of needing no active control system or expenditure of fuel. The effect is caused by a tidal force . The upper end of the vehicle feels less gravitational pull than the lower end. This provides a restoring torque whenever the long axis is not co-linear with the direction of gravity. Unless some means of damping is provided, the spacecraft will oscillate about the local vertical. Sometimes tethers are used to connect two parts of a satellite, to increase the stabilizing torque. A problem with such tethers is that meteoroids as small as a grain of sand can part them.
Coils or (on very small satellites) permanent magnets exert a moment against the local magnetic field. This method works only where there is a magnetic field against which to react. One classic field "coil" is actually in the form of a conductive tether in a planetary magnetic field. Such a conductive tether can also generate electrical power, at the expense of orbital decay . Conversely, by inducing a counter-current, using solar cell power, the orbit may be raised. Due to massive variability in Earth's magnetic field from an ideal radial field, control laws based on torques coupling to this field will be highly non-linear. Moreover, only two-axis control is available at any given time meaning that a vehicle reorient may be necessary to null all rates.
Three main types of passive attitude control exist for satellites. The first one uses gravity gradient, and it leads to four stable states with the long axis (axis with smallest moment of inertia) pointing towards Earth. As this system has four stable states, if the satellite has a preferred orientation, e.g. a camera pointed at the planet, some way to flip the satellite and its tether end-for-end is needed.
The second passive system orients the satellite along Earth's magnetic field thanks to a magnet. [ 7 ] These purely passive attitude control systems have limited pointing accuracy, because the spacecraft will oscillate around energy minima. This drawback is overcome by adding damper, which can be hysteretic materials or a viscous damper. The viscous damper is a small can or tank of fluid mounted in the spacecraft, possibly with internal baffles to increase internal friction. Friction within the damper will gradually convert oscillation energy into heat dissipated within the viscous damper.
A third form of passive attitude control is aerodynamic stabilization. This is achieved using a drag gradient, as demonstrated on the Get Away Special Passive Attitude Control Satellite (GASPACS) technology demonstration. In low Earth orbit, the force due to drag is many orders of magnitude more dominant than the force imparted due to gravity gradients. [ 8 ] When a satellite is utilizing aerodynamic passive attitude control, air molecules from the Earth's upper atmosphere strike the satellite in such a way that the center of pressure remains behind the center of mass, similar to how the feathers on an arrow stabilize the arrow. GASPACS utilized a 1 m inflatable 'AeroBoom', which extended behind the satellite, creating a stabilizing torque along the satellite's velocity vector. [ 9 ]
Control algorithms are computer programs that receive data from vehicle sensors and derive the appropriate commands to the actuators to rotate the vehicle to the desired attitude. The algorithms range from very simple, e.g. proportional control , to complex nonlinear estimators or many in-between types, depending on mission requirements. Typically, the attitude control algorithms are part of the software running on the computer hardware, which receives commands from the ground and formats vehicle data telemetry for transmission to a ground station.
The attitude control algorithms are written and implemented based on requirement for a particular attitude maneuver. Asides the implementation of passive attitude control such as the gravity-gradient stabilization , most spacecraft make use of active control which exhibits a typical attitude control loop. The design of the control algorithm depends on the actuator to be used for the specific attitude maneuver although using a simple proportional–integral–derivative controller ( PID controller ) satisfies most control needs.
The appropriate commands to the actuators are obtained based on error signals described as the difference between the measured and desired attitude. The error signals are commonly measured as euler angles (Φ, θ, Ψ), however an alternative to this could be described in terms of direction cosine matrix or error quaternions . The PID controller which is most common reacts to an error signal (deviation) based on attitude as follows
where T c {\displaystyle T_{c}} is the control torque, e {\displaystyle e} is the attitude deviation signal, and K p , K i , K d {\displaystyle K_{\text{p}},K_{\text{i}},K_{\text{d}}} are the PID controller parameters.
A simple implementation of this can be the application of the proportional control for nadir pointing making use of either momentum or reaction wheels as actuators. Based on the change in momentum of the wheels, the control law can be defined in 3-axes x, y, z as
This control algorithm also affects momentum dumping.
Another important and common control algorithm involves the concept of detumbling, which is attenuating the angular momentum of the spacecraft. The need to detumble the spacecraft arises from the uncontrollable state after release from the launch vehicle. Most spacecraft in low Earth orbit (LEO) makes use of magnetic detumbling concept which utilizes the effect of the Earth's magnetic field . The control algorithm is called the B-Dot controller and relies on magnetic coils or torque rods as control actuators. The control law is based on the measurement of the rate of change of body-fixed magnetometer signals.
where m {\displaystyle m} is the commanded magnetic dipole moment of the magnetic torquer and K {\displaystyle K} is the proportional gain and B ˙ {\displaystyle {\dot {B}}} is the rate of change of the Earth's magnetic field.
Spacecraft attitude determination is the process of determining the orientation of a spacecraft (vehicle or satellite). It is a pre-requisite for spacecraft attitude control. A variety of sensors are utilized for relative and absolute attitude determination.
Many sensors generate outputs that reflect the rate of change in attitude. These require a known initial attitude, or external information to use them to determine attitude. Many of this class of sensor have some noise, leading to inaccuracies if not corrected by absolute attitude sensors.
Gyroscopes are devices that sense rotation in three-dimensional space without reliance on the observation of external objects. Classically, a gyroscope consists of a spinning mass, but there are also " ring laser gyros " utilizing coherent light reflected around a closed path. Another type of "gyro" is a hemispherical resonator gyro where a crystal cup shaped like a wine glass can be driven into oscillation just as a wine glass "sings" as a finger is rubbed around its rim. The orientation of the oscillation is fixed in inertial space, so measuring the orientation of the oscillation relative to the spacecraft can be used to sense the motion of the spacecraft with respect to inertial space. [ 10 ]
Motion reference units are a kind of inertial measurement unit with single- or multi-axis motion sensors. They utilize MEMS gyroscopes . Some multi-axis MRUs are capable of measuring roll, pitch, yaw and heave . They have applications outside the aeronautical field, such as: [ 11 ]
This class of sensors sense the position or orientation of fields, objects or other phenomena outside the spacecraft.
A horizon sensor is an optical instrument that detects light from the 'limb' of Earth's atmosphere, i.e., at the horizon. Thermal infrared sensing is often used, which senses the comparative warmth of the atmosphere, compared to the much colder cosmic background . This sensor provides orientation with respect to Earth about two orthogonal axes. It tends to be less precise than sensors based on stellar observation. Sometimes referred to as an Earth sensor. [ 12 ]
Similar to the way that a terrestrial gyrocompass uses a pendulum to sense local gravity and force its gyro into alignment with Earth's spin vector, and therefore point north, an orbital gyrocompass uses a horizon sensor to sense the direction to Earth's center, and a gyro to sense rotation about an axis normal to the orbit plane. Thus, the horizon sensor provides pitch and roll measurements, and the gyro provides yaw. [ 13 ] See Tait-Bryan angles .
A Sun sensor is a device that senses the direction to the Sun . This can be as simple as some solar cells and shades, or as complex as a steerable telescope , depending on mission requirements.
An Earth sensor is a device that senses the direction to Earth . It is usually an infrared camera ; nowadays the main method to detect attitude is the star tracker , but Earth sensors are still integrated in satellites for their low cost and reliability. [ 12 ]
A star tracker is an optical device that measures the position(s) of star (s) using photocell (s) or a camera. [ 14 ] It uses magnitude of brightness and spectral type to identify and then calculate the relative position of stars around it.
A magnetometer is a device that senses magnetic field strength and, when used in a three-axis triad, magnetic field direction. As a spacecraft navigational aid, sensed field strength and direction is compared to a map of Earth's magnetic field stored in the memory of an on-board or ground-based guidance computer. If spacecraft position is known then attitude can be inferred. [ 15 ]
Attitude cannot be measured directly by any single measurement, and so must be calculated (or estimated ) from a set of measurements (often using different sensors). This can be done either statically (calculating the attitude using only the measurements currently available), or through the use of a statistical filter (most commonly, the Kalman filter ) that statistically combine previous attitude estimates with current sensor measurements to obtain an optimal estimate of the current attitude.
Static attitude estimation methods are solutions to Wahba's problem . Many solutions have been proposed, notably Davenport's q-method, QUEST, TRIAD, and singular value decomposition . [ 16 ]
Crassidis, John L., and John L. Junkins.. Chapman and Hall/CRC, 2004.
Kalman filtering can be used to sequentially estimate the attitude, as well as the angular rate. Because attitude dynamics (combination of rigid body dynamics and attitude kinematics) are non-linear, a linear Kalman filter is not sufficient. Because attitude dynamics is not very non-linear, the Extended Kalman filter is usually sufficient (however Crassidis and Markely demonstrated that the Unscented Kalman filter could be used, and can provide benefits in cases where the initial estimate is poor). [ 17 ] Multiple methods have been proposed, however the Multiplicative Extended Kalman Filter (MEKF) is by far the most common approach. [ citation needed ] This approach utilizes the multiplicative formulation of the error quaternion, which allows for the unity constraint on the quaternion to be better handled. It is also common to use a technique known as dynamic model replacement, where the angular rate is not estimated directly, but rather the measured angular rate from the gyro is used directly to propagate the rotational dynamics forward in time. This is valid for most applications as gyros are typically far more precise than one's knowledge of disturbance torques acting on the system (which is required for precise estimation of the angular rate).
For some sensors and applications (such as spacecraft using magnetometers) the precise location must also be known. While pose [ clarification needed ] estimation can be employed, for spacecraft it is usually sufficient to estimate the position (via Orbit determination ) separate from the attitude estimation. [ citation needed ] For terrestrial vehicles and spacecraft operating near the Earth, the advent of Satellite navigation systems allows for precise position knowledge to be obtained easily. This problem becomes more complicated for deep space vehicles, or terrestrial vehicles operating in Global Navigation Satellite System (GNSS) denied environments (see Navigation ). | https://en.wikipedia.org/wiki/Spacecraft_attitude_determination_and_control |
A spacecraft is a vehicle that is designed to fly and operate in outer space . [ 1 ] Spacecraft are used for a variety of purposes, including communications , Earth observation , meteorology , navigation , space colonization , planetary exploration , and transportation of humans and cargo . All spacecraft except single-stage-to-orbit vehicles cannot get into space on their own, and require a launch vehicle (carrier rocket).
On a sub-orbital spaceflight , a space vehicle enters space and then returns to the surface without having gained sufficient energy or velocity to make a full Earth orbit . For orbital spaceflights , spacecraft enter closed orbits around the Earth or around other celestial bodies . Spacecraft used for human spaceflight carry people on board as crew or passengers from start or on orbit ( space stations ) only, whereas those used for robotic space missions operate either autonomously or telerobotically . Robotic spacecraft used to support scientific research are space probes . Robotic spacecraft that remain in orbit around a planetary body are artificial satellites . To date, only a handful of interstellar probes , such as Pioneer 10 and 11 , Voyager 1 and 2 , and New Horizons , are on trajectories that leave the Solar System .
Orbital spacecraft may be recoverable or not. Most are not. Recoverable spacecraft may be subdivided by a method of reentry to Earth into non-winged space capsules and winged spaceplanes . Recoverable spacecraft may be reusable (can be launched again or several times, like the SpaceX Dragon and the Space Shuttle orbiters ) or expendable (like the Soyuz ). In recent years, more space agencies are tending towards reusable spacecraft.
Humanity has achieved space flight, but only a few nations have the technology for orbital launches : Russia ( Roscosmos [ 2 ] ), the United States ( NASA [ 3 ] ), the member states of the European Space Agency , [ 4 ] Japan ( JAXA [ 5 ] ), China ( CNSA [ 6 ] ), India ( ISRO [ 7 ] ), Taiwan ( TSA [ 8 ] [ 9 ] [ 10 ] ), Israel ( ISA ), Iran ( ISA ), and North Korea ( NADA ). In addition, several private companies have developed or are developing the technology for orbital launches independently from government agencies. Two prominent examples of such companies are SpaceX and Blue Origin .
A German V-2 became the first spacecraft when it reached an altitude of 189 km in June 1944 in Peenemünde , Germany. [ 11 ] Sputnik 1 was the first artificial satellite . It was launched into an elliptical low Earth orbit (LEO) by the Soviet Union on 4 October 1957. The launch ushered in new political, military, technological, and scientific developments; while the Sputnik launch was a single event, it marked the start of the Space Age . [ 12 ] [ 13 ] Apart from its value as a technological first, Sputnik 1 also helped to identify the upper atmospheric layer 's density, by measuring the satellite's orbital changes. It also provided data on radio -signal distribution in the ionosphere . Pressurized nitrogen in the satellite's false body provided the first opportunity for meteoroid detection. Sputnik 1 was launched during the International Geophysical Year from Site No.1/5 , at the 5th Tyuratam range, in Kazakh SSR (now at the Baikonur Cosmodrome ). The satellite travelled at 29,000 kilometres per hour (18,000 mph), taking 96.2 minutes to complete an orbit, and emitted radio signals at 20.005 and 40.002 MHz
While Sputnik 1 was the first spacecraft to orbit the Earth, other human-made objects had previously reached an altitude of 100 km, which is the height required by the international organization Fédération Aéronautique Internationale to count as a spaceflight. This altitude is called the Kármán line . In particular, in the 1940s there were several test launches of the V-2 rocket , some of which reached altitudes well over 100 km.
As of 2016, only three nations have flown crewed spacecraft: USSR/Russia, USA, and China.
The first crewed spacecraft was Vostok 1 , which carried Soviet cosmonaut Yuri Gagarin into space in 1961, and completed a full Earth orbit. There were five other crewed missions which used a Vostok spacecraft . [ 14 ] The second crewed spacecraft was named Freedom 7 , and it performed a sub-orbital spaceflight in 1961 carrying American astronaut Alan Shepard to an altitude of just over 187 kilometers (116 mi). There were five other crewed missions using Mercury spacecraft .
Other Soviet crewed spacecraft include the Voskhod , Soyuz , flown uncrewed as Zond/L1 , L3 , TKS , and the Salyut and Mir crewed space stations . Other American crewed spacecraft include the Gemini spacecraft , the Apollo spacecraft including the Apollo Lunar Module , the Skylab space station, the Space Shuttle with undetached European Spacelab and private US Spacehab space stations-modules, and the SpaceX Crew Dragon configuration of their Dragon 2 . US company Boeing also developed and flown a spacecraft of their own, the CST-100 , commonly referred to as Starliner , but a crewed flight is yet to occur. China developed, but did not fly Shuguang , and is currently using Shenzhou (its first crewed mission was in 2003).
Except for the Space Shuttle and the Buran spaceplane of the Soviet Union, the latter of which only ever had one uncrewed test flight, all of the recoverable crewed orbital spacecraft were space capsules .
The International Space Station , crewed since November 2000, is a joint venture between Russia, the United States, Canada and several other countries.
Uncrewed spacecraft are spacecraft without people on board. Uncrewed spacecraft may have varying levels of autonomy from human input; they may be remote controlled , remote guided or even autonomous , meaning they have a pre-programmed list of operations, which they will execute unless otherwise instructed.
Many space missions are more suited to telerobotic rather than crewed operation, due to lower cost and lower risk factors. In addition, some planetary destinations such as Venus or the vicinity of Jupiter are too hostile for human survival. Outer planets such as Saturn , Uranus , and Neptune are too distant to reach with current crewed spaceflight technology, so telerobotic probes are the only way to explore them. Telerobotics also allows exploration of regions that are vulnerable to contamination by Earth micro-organisms since spacecraft can be sterilized. Humans can not be sterilized in the same way as a spaceship, as they coexist with numerous micro-organisms, and these micro-organisms are also hard to contain within a spaceship or spacesuit. Multiple space probes were sent to study Moon, the planets, the Sun, multiple small Solar System bodies (comets and asteroids).
Special class of uncrewed spacecraft is space telescopes , a telescope in outer space used to observe astronomical objects. The first operational telescopes were the American Orbiting Astronomical Observatory , OAO-2 launched in 1968, and the Soviet Orion 1 ultraviolet telescope aboard space station Salyut 1 in 1971. Space telescopes avoid the filtering and distortion ( scintillation ) of electromagnetic radiation which they observe, and avoid light pollution which ground-based observatories encounter. The best-known examples are Hubble Space Telescope and James Webb Space Telescope .
Cargo spacecraft are designed to carry cargo , possibly to support space stations ' operation by transporting food, propellant and other supplies. Automated cargo spacecraft have been used since 1978 and have serviced Salyut 6 , Salyut 7 , Mir , the International Space Station and Tiangong space station.
Some spacecrafts can operate as both a crewed and uncrewed spacecraft. For example, the Buran spaceplane could operate autonomously but also had manual controls, though it never flew with crew onboard. [ 15 ] [ 16 ]
Other dual crewed/uncrewed spacecrafts include: SpaceX Dragon 2 , [ 17 ] [ 18 ] [ 19 ] [ 20 ] Dream Chaser , [ 21 ] [ 22 ] and Tianzhou . [ 23 ] [ 24 ]
A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder ; it creates a communication channel between a source transmitter and a receiver at different locations on Earth . Communications satellites are used for television , telephone , radio , internet , and military applications. [ 25 ] Many communications satellites are in geostationary orbit 22,300 miles (35,900 km) above the equator , so that the satellite appears stationary at the same point in the sky; therefore the satellite dish antennas of ground stations can be aimed permanently at that spot and do not have to move to track the satellite. Others form satellite constellations in low Earth orbit , where antennas on the ground have to follow the position of the satellites and switch between satellites frequently.
The high frequency radio waves used for telecommunications links travel by line of sight and so are obstructed by the curve of the Earth. The purpose of communications satellites is to relay the signal around the curve of the Earth allowing communication between widely separated geographical points. [ 26 ] Communications satellites use a wide range of radio and microwave frequencies . To avoid signal interference, international organizations have regulations for which frequency ranges or "bands" certain organizations are allowed to use. This allocation of bands minimizes the risk of signal interference. [ 27 ]
Cargo or resupply spacecraft are robotic spacecraft that are designed specifically to carry cargo , possibly to support space stations ' operation by transporting food, propellant and other supplies.
Automated cargo spacecraft have been used since 1978 and have serviced Salyut 6 , Salyut 7 , Mir , the International Space Station and Tiangong space station.
As of 2023, three different cargo spacecraft are used to supply the International Space Station : Russian Progress , American SpaceX Dragon 2 and Cygnus . Chinese Tianzhou is used to supply Tiangong space station .
Space probes are robotic spacecraft that are sent to explore deep space, or astronomical bodies other than Earth. They are distinguished from landers by the fact that they work in open space, not on planetary surfaces or in planetary atmospheres. Being robotic eliminates the need for expensive, heavy life support systems (the Apollo crewed Moon landings required the use of the Saturn V rocket that cost over a billion dollars per launch, adjusted for inflation) and so allows for lighter, less expensive rockets. Space probes have visited every planet in the Solar System and Pluto , and the Parker Solar Probe has an orbit that, at its closest point, is in the Sun's chromosphere . There are five space probes that are escaping the Solar System , these are Voyager 1 , Voyager 2 , Pioneer 10 , Pioneer 11 , and New Horizons .
The identical Voyager probes , weighing 721.9 kilograms (1,592 lb), [ 28 ] were launched in 1977 to take advantage of a rare alignment of Jupiter , Saturn , Uranus and Neptune that would allow a spacecraft to visit all four planets in one mission, and get to each destination faster by using gravity assist . In fact, the rocket that launched the probes (the Titan IIIE ) could not even send the probes to the orbit of Saturn , yet Voyager 1 is travelling at roughly 17 km/s (11 mi/s) and Voyager 2 moves at about 15 km/s (9.3 mi/s) kilometres per second as of 2023. In 2012, Voyager 1 exited the heliosphere, followed by Voyager 2 in 2018. Voyager 1 actually launched 16 days after Voyager 2 but it reached Jupiter sooner because Voyager 2 was taking a longer route that allowed it to visit Uranus and Neptune, whereas Voyager 1 did not visit Uranus or Neptune, instead choosing to fly past Saturn’s satellite Titan . As of August 2023, Voyager 1 has passed 160 astronomical units , which means it is over 160 times farther from the Sun than Earth is. This makes it the farthest spacecraft from the Sun. Voyager 2 is 134 AU away from the Sun as of August 2023. NASA provides real time data of their distances and data from the probe’s cosmic ray detectors. [ 29 ] Because of the probe’s declining power output and degradation of the RTGs over time, NASA has had to shut down certain instruments to conserve power. The probes may still have some scientific instruments on until the mid-2020s or perhaps the 2030s. After 2036, they will both be out of range of the Deep Space Network .
A space telescope or space observatory is a telescope in outer space used to observe astronomical objects. Space telescopes avoid the filtering and distortion of electromagnetic radiation which they observe, and avoid light pollution which ground-based observatories encounter. They are divided into two types: satellites which map the entire sky ( astronomical survey ), and satellites which focus on selected astronomical objects or parts of the sky and beyond. Space telescopes are distinct from Earth imaging satellites , which point toward Earth for satellite imaging , applied for weather analysis , espionage , and other types of information gathering .
A lander is a type of spacecraft that makes a soft landing on the surface of an astronomical body other than Earth . Some landers, such as Philae and the Apollo Lunar Module , land entirely by using their fuel supply, however many landers (and landings of spacecraft on Earth ) use aerobraking , especially for more distant destinations. This involves the spacecraft using a fuel burn to change its trajectory so it will pass through a planet (or a moon's) atmosphere. Drag caused by the spacecraft hitting the atmosphere enables it to slow down without using fuel, however this generates very high temperatures and so adds a requirement for a heat shield of some sort.
Space capsules are a type of spacecraft that can return from space at least once. They have a blunt shape, do not usually contain much more fuel than needed, and they do not possess wings unlike spaceplanes . They are the simplest form of recoverable spacecraft, and so the most commonly used. The first such capsule was the Vostok capsule built by the Soviet Union, that carried the first person in space, Yuri Gagarin . Other examples include the Soyuz and Orion capsules, built by the Soviet Union and NASA , respectively.
Spaceplanes are spacecraft that are built in the shape of, and function as, airplanes . The first example of such was the North American X-15 spaceplane, which conducted two crewed flights which reached an altitude of over 100 kilometres (62 mi) in the 1960s. This first reusable spacecraft was air-launched on a suborbital trajectory on July 19, 1963.
The first reusable orbital spaceplane was the Space Shuttle orbiter . The first orbiter to fly in space, the Space Shuttle Columbia , was launched by the USA on the 20th anniversary of Yuri Gagarin 's flight, on April 12, 1981. During the Shuttle era, six orbiters were built, all of which have flown in the atmosphere and five of which have flown in space. Enterprise was used only for approach and landing tests, launching from the back of a Boeing 747 SCA and gliding to deadstick landings at Edwards AFB, California . The first Space Shuttle to fly into space was Columbia , followed by Challenger , Discovery , Atlantis , and Endeavour . Endeavour was built to replace Challenger when it was lost in January 1986. Columbia broke up during reentry in February 2003.
The first autonomous reusable spaceplane was the Buran -class shuttle , launched by the USSR on November 15, 1988, although it made only one flight and this was uncrewed. This spaceplane was designed for a crew and strongly resembled the U.S. Space Shuttle, although its drop-off boosters used liquid propellants and its main engines were located at the base of what would be the external tank in the American Shuttle. Lack of funding, complicated by the dissolution of the USSR , prevented any further flights of Buran. The Space Shuttle was subsequently modified to allow for autonomous re-entry in case of necessity.
Per the Vision for Space Exploration , the Space Shuttle was retired in 2011 mainly due to its old age and high cost of program reaching over a billion dollars per flight. The Shuttle's human transport role is to be replaced by SpaceX 's SpaceX Dragon 2 and Boeing 's CST-100 Starliner . Dragon 2's first crewed flight occurred on May 30, 2020. [ 30 ] The Shuttle's heavy cargo transport role is to be replaced by expendable rockets such as the Space Launch System and ULA 's Vulcan rocket, as well as the commercial launch vehicles.
Scaled Composites ' SpaceShipOne was a reusable suborbital spaceplane that carried pilots Mike Melvill and Brian Binnie on consecutive flights in 2004 to win the Ansari X Prize . The Spaceship Company built a successor SpaceShipTwo . A fleet of SpaceShipTwos operated by Virgin Galactic was planned to begin reusable private spaceflight carrying paying passengers in 2014, but was delayed after the crash of VSS Enterprise .
The Space Shuttle is a retired reusable Low Earth Orbital launch system. It consisted of two reusable Solid Rocket Boosters that landed by parachute, were recovered at sea, and were the most powerful rocket motors ever made until they were superseded by those of NASA’s SLS rocket, with a liftoff thrust of 2,800,000 pounds-force (12 MN), which soon increased to 3,300,000 pounds-force (15 MN) per booster, [ 31 ] and were fueled by a combination of PBAN and APCP , the Space Shuttle Orbiter , with 3 RS-25 engines that used a liquid oxygen / liquid hydrogen propellant combination, and the bright orange throwaway Space Shuttle external tank from which the RS-25 engines sourced their fuel. The orbiter was a spaceplane that was launched at NASA’s Kennedy Space Centre and landed mainly at the Shuttle Landing Facility , which is part of Kennedy Space Centre. A second launch site, Vandenberg Space Launch Complex 6 in California , was revamped so it could be used to launch the shuttles, but it was never used. The launch system could lift about 29 tonnes (64,000 lb) into an eastward Low Earth Orbit . Each orbiter weighed roughly 78 tonnes (172,000 lb), however the different orbiters had differing weights and thus payloads, with Columbia being the heaviest orbiter, Challenger being lighter than Columbia but still heavier than the other three. The orbiter structure was mostly composed of aluminium alloy. The orbiter had seven seats for crew members, though on STS-61-A the launch took place with 8 crew onboard. The orbiters had 4.6 metres (15 ft) wide by 18 metres (59 ft) long payload bays and also were equipped with a 15.2 metres (50 ft) CanadaArm1 , an upgraded version of which is used on the International Space Station . The heat shield (or Thermal Protection System ) of the orbiter, used to protect it from extreme levels of heat during atmospheric reentry and the cold of space, was made up of different materials depending on weight and how much heating a particular area on the shuttle would receive during reentry, which ranged from over 2,900 °F (1,600 °C) to under 700 °F (370 °C). The orbiter was manually operated, though an autonomous landing system was added while the shuttle was still on service. It had an in orbit maneouvreing system known as the Orbital Manoeuvring System, which used the hypergolic propellants monomethylhydrazine (MMH) and dinitrogen tetroxide , which was used for orbital insertion, changes to orbits and the deorbit burn.
Though the shuttle’s goals were to drastically decrease launch costs, it did not do so, ending up being much more expensive than similar expendable launchers. This was due to expensive refurbishment costs and the external tank being expended. Once a landing had occurred, the SRBs and many parts of the orbiter had to be disassembled for inspection, which was long and arduous. Furthermore, the RS-25 engines had to be replaced every few flights. Each of the heat shielding tiles had to go in one specific area on the orbiter, increasing complexity more. Adding to this, the shuttle was a rather dangerous system, with fragile heat shielding tiles, some being so fragile that one could easily scrape it off by hand, often having been damaged in many flights. After 30 years in service from 1981 to 2011 and 135 flights, the shuttle was retired from service due to the cost of maintaining the shuttles, and the 3 remaining orbiters (the other two were destroyed in accidents) were prepared to be displayed in museums.
Some spacecraft do not fit particularly well into any of the general spacecraft categories. This is a list of these spacecraft.
Starship is a spacecraft and second stage [ 32 ] under development by American aerospace company SpaceX . Stacked atop its booster, Super Heavy , it composes the identically named Starship super heavy-lift space vehicle . The spacecraft is designed to transport both crew and cargo to a variety of destinations, including Earth orbit, the Moon, Mars, and potentially beyond. It is intended to enable long duration interplanetary flights for a crew of up to 100 people. [ 32 ] It will also be capable of point-to-point transport on Earth, enabling travel to anywhere in the world in less than an hour. Furthermore, the spacecraft will be used to refuel other Starship vehicles to allow them to reach higher orbits to and other space destinations. Elon Musk , the CEO of SpaceX, estimated in a tweet that 8 launches would be needed to completely refuel a Starship in low Earth orbit , extrapolating this from Starship's payload to orbit and how much fuel a fully fueled Starship contains. [ 33 ] To land on bodies without an atmosphere, such as the Moon, Starship will fire its engines and thrusters to slow down. [ 34 ]
The Mission Extension Vehicle is a robotic spacecraft designed to prolong the life on another spacecraft. It works by docking to its target spacecraft, then correcting its orientation or orbit. This also allows it to rescue a satellite which is in the wrong orbit by using its own fuel to move its target to the correct orbit. The project is currently managed by Northrop Grumman Innovation Systems. As of 2023, 2 have been launched. The first launched on a Proton rocket on 9 October 2019, and did a rendezvous with Intelsat-901 on 25 February 2020. It will remain with the satellite until 2025 before the satellite is moved to a final graveyard orbit and the vehicle does a rendezvous with another satellite. The other one launched on an Ariane 5 rocket on 15 August 2020.
A spacecraft astrionics system comprises different subsystems, depending on the mission profile. Spacecraft subsystems are mounted in the satellite bus and may include attitude determination and control (variously called ADAC, ADC, or ACS), guidance, navigation and control (GNC or GN&C), communications (comms), command and data handling (CDH or C&DH), power (EPS), thermal control (TCS), propulsion, and structures. Attached to the bus are typically payloads . | https://en.wikipedia.org/wiki/Spacecraft_communication |
Spacecraft design is a process where systems engineering principles are systemically applied in order to construct complex vehicles for missions involving travel , operation or exploration in outer space . This design process produces the detailed design specifications , schematics , and plans for the spacecraft system, including comprehensive documentation outlining the spacecraft's architecture, subsystems, components, interfaces, and operational requirements, and potentially some prototype models or simulations , all of which taken together serve as the blueprint for manufacturing, assembly, integration, and testing of the spacecraft to ensure that it meets mission objectives and performance criteria.
Spacecraft design is conducted in several phases. Initially, a conceptual design is made to determine the feasibility and desirability of a new spacecraft system, showing that a credible design exists to carry out the mission. The conceptual design review ensures that the design meets the mission statement without any technical flaws while being internally consistent. Next, a preliminary design is carried out, where the focus is on functional performance, requirements definition, and interface definition at both subsystem and system levels. The preliminary design review evaluates the adequacy of the preliminary design. In the following phase, detailed design is drawn and coded for the system as a whole and all the subsystems, and a critical design review is performed where it is evaluated whether the design is sufficiently detailed to fabricate, integrate, and test the system. [ 1 ] [ 2 ]
Throughout spacecraft design, potential risks are rigorously identified, assessed, and mitigated, systems components are properly integrated and comprehensively tested. The entire lifecycle (including launch, mission operations and end-of-mission disposal) is taken into account. An iterative process of reviews and testing is continuously employed to refine, optimize and enhance the design's effectiveness and reliability. In particular, the spacecraft's mass, power, thermal control, propulsion, altitude control, telecommunication, command and data, and structural aspects are taken into consideration. Choosing the right launch vehicle and adapting the design to the chosen launch vehicle is also important. [ 1 ] [ 2 ] Regulatory compliance, adherence to International standards, designing for a sustainable, debris-free space environment are some other considerations that have become important in recent times.
Spacecraft design includes the design of both robotic spacecraft ( satellites and planetary probes ), and spacecraft for human spaceflight ( spaceships and space stations ). Human-carrying spacecraft require additional life-support systems, crew accommodation, and safety measures to support human occupants, as well as human factor engineering considerations such as ergonomics, crew comfort, and psychological well-being. Robotic spacecraft require autonomy, reliability, and remote operation capabilities without human presence. The distinctive nature and the unique needs and constraints related to each of them significantly impact spacecraft design considerations.
Recent developments in spacecraft design include electric propulsion systems (e.g. ion thrusters and Hall-effect thrusters ) for high-specific-impulse propulsion, solar sails (using solar radiation pressure ) for continuous thrust without the need for traditional rockets, [ 3 ] additive manufacturing ( 3D printing ) and advanced materials (e.g. advanced composites , nanomaterials and smart materials ) for rapid prototyping and production of lightweight and durable components, artificial intelligence and machine learning -assisted autonomous systems for spacecraft autonomy and improved operational efficiency in long and faraway missions, in situ resource utilization (ISRU) technologies for extraction and utilization of local resources on celestial bodies, and CubeSats and other standardized miniature satellites [ 3 ] for cost-effective space missions around Earth.
Spacecraft design involves experts from various fields such as engineering, physics, mathematics, computer science, etc. who come together to collaborate and participate in interdisciplinary teamwork. Furthermore, international collaboration and partnerships between space agencies, organizations, and countries help share expertise, resources, and capabilities for the mutual benefit of all parties. The challenges of spacecraft design drive technological innovation and engineering breakthroughs in professional and industrial sectors. The complexity of spacecraft design engages students in STEM subjects (science, technology, engineering, and mathematics), fosters scientific literacy and inspire the next generation of scientists, engineers, and innovators.
Spacecraft design was born as a discipline in the 1950s and 60s with the advent of American and Soviet space exploration programs. Since then it has progressed, although typically less than comparable terrestrial technologies. This is for a large part due to the challenging space environment, but also to the lack of basic R&D, and other cultural factors within the design community. On the other hand, another reason for slow space travel application design is the high energy cost, and low efficiency, for achieving orbit. This cost might be seen as too high a "start-up cost." [ citation needed ]
Spacecraft design brings together aspects of various disciplines, namely: [ citation needed ]
The spacecraft bus carries the payload. Its subsystems support the payload and help in pointing the payload correctly. It puts the payload in the right orbit and keeps it there. It provides housekeeping functions. It also provides orbit and attitude maintenance, electric power, command, telemetry, and data handling, structure and rigidity, temperature control, data storage, and communication, if required. The payload and spacecraft bus may be different units or it may be a combined one. The booster adapter provides the load-carrying interface with the vehicle (payload and spacecraft bus together).
The spacecraft may also have a propellant load, which is used to drive or push the vehicle upwards, and a propulsion kick stage. The propellant commonly used is a compressed gas like nitrogen, a quid a such as monopropellant hydrazine or solid fuel, which is used for velocity corrections and attitude control. In a kick stage (also called apogee boost motor, propulsion module, or integral propulsion stage) a separate rocket motor is used to send the spacecraft into its mission orbit.
While designing a spacecraft, the orbit which is going to be used should be considered into thnt as it affects attitude control, thermal design, and the electric power subsystem. But these effects are secondary as compared to the effect caused on the payload due to the orbit. Thus while designing the mission; the designer selects such an orbit which increases the payload performance. The designer even calculates the required spacecraft performance characteristics such as pointing, thermal control, power quantity, and duty cycle. The spacecraft is then made, which satisfies all the requirements. [ citation needed ]
The attitude determination and control subsystem (ADCS) is used to change the attitude (orientation) of the spacecraft. There are some external torques acting on the spacecraft along the axis passing through its center of gravity which can reorient the spacecraft in any direction or can give it a spin. The ADCS nullifies these torques by applying equal and opposite torques using the proion and navigation. Moment of inertia of the body is to be calculated to determine the external torques which also requires determination of vehicle's absolute attitude using sensors. The property called 'gyroscopic stiffness' is used to reduce the spinning effect.
The simplest spacecraft achieve control by spinning or interacting with the Earth's magnetic or gravity fields. Sometimes they are uncontrolled. Spacecraft may have several bodies or they are attached to important parts, such as solar arrays or communication antennas which need individual attitude pointing. For controlling the appendage's attitude, actuators are often used, with separate sensors and controllers.
The various types of control techniques used are: [ citation needed ]
Telemetry, tracking, and command (TT&C) is used for communication between spacecraft and the ground systems. The subsystem functions are:
The process of sending information towards the spacecraft is called uplink or forward link and the opposite process is called downlink or return link. Uplink consists of commands and ranging tones where as downlink consists of status telemetry, ranging tones and even may include payload data. Receiver, transmitter and a wide-angle (hemispheric or omnidirectional) antenna are the main components of a basic communication subsystem. Systems with high data rates may even use a directional antenna, if required. The subsystem can provide us with the coherence between uplink and downlink signals, with the help of which we can measure range-rate Doppler shifts. The communication subsystem is sized by data rate, allowable error rate, communication path length, and RF frequency.
The vast majority of spacecraft communicate using radio antennas -- satellite communication . [ citation needed ] A few spacecraft communicate using lasers —either directly to the ground as with LADEE ; or between satellites as with OICETS , Artemis , Alphabus , and the European Data Relay System .
The electrical power subsystem (EPS) consists of 4 subunits :
Thermal control subsystem (TCS) is used to maintain the temperature of all spacecraft components within certain limits. Both upper and lower limits are defined for each component. There are two limits, namely, operational (in working conditions) and survival (in non-working conditions). Temperature is controlled by using insulators, radiators, heaters, louvers and by giving proper surface finish to components. [ citation needed ]
The main function of the propulsion subsystem is to provide thrust so as to change the spacecraft's translational velocity or to apply torques to change its angular momentum. There is no requirement of thrust and hence even no requirement of propulsion equipment in a simplest spacecraft. But many of them need a controlled thrust in their system, so their design includes some form of metered propulsion (a propulsion system that can be turned on and off in small increments).
Thrusting is used for the following purposes: for changing the orbital parameters, to control attitude during thrusting, correct velocity errors, maneuver, counter disturbance forces (e.g., drag), and control and correct angular momentum. The propulsion subsystem includes a propellant, tankage, distribution system, pressurant, and propellant controls. It also includes thrusters or engines.
Spacecraft design is always informed by the particular mission architecture of the spaceflight under consideration. Typically, a variety of mission architectures can be envisioned that would achieve the overall objective of the flight, whether those objectives be to gather scientific data or merely transport cargo across the space environment to serve any variety of purposes, governmental or economic. [ 4 ]
Spaceflight mission architectures will specify whether a spacecraft is to be autonomous or telerobotic , or even be crewed so as to deal with particular exigencies or goals of the mission. Other considerations include fast or slow trajectories, payload makeup and capacity, length of the mission, or the level of system redundancy so that the flight can achieve various degrees of fault-tolerance . [ 4 ] | https://en.wikipedia.org/wiki/Spacecraft_design |
Spaced learning is a learning method in which highly condensed learning content is repeated three times, with two 10-minute breaks during which distractor activities such as physical activities are performed by the students. It is based on the temporal pattern of stimuli for creating long-term memories reported by R. Douglas Fields in Scientific American in 2005. [ 1 ] This 'temporal code' Fields used in his experiments was developed into a learning method for creating long-term memories by Paul Kelley, who led a team of teachers and scientists as reported in Making Minds [ 2 ] in 2008.
A paper on the method has been published in Frontiers in Human Neuroscience . [ 3 ] This makes a substantial scientific case for this approach to learning based on research over many years in different species. The distinctive features of the approach are made clear: the speed of instruction being minutes (as opposed to hours, days or months), the spaces and their function, and why content is repeated three times. Spaced learning has been reported in other species as being required for long-term memory creation, a finding that gives considerable weight to its use in education.
Spaced Learning had been developed by Kelley and his team over years and rather confusingly was not called 'Spaced Learning' at first. [ 4 ] Earlier descriptions of Spaced Learning often led to its being misunderstood, and the scientific origins of the approach ignored. When the initial reports of outcomes were made public, media seized upon the condensed learning content as the key element in the approach used and the BBC national television news, The Sunday Times, The Independent, and The Economist [ 5 ] reported the approach largely in those terms ('8 minute lessons'). This emphasis was misplaced, since Spaced Learning as a method depends on the length and number of the spaces (Fields' 'temporal code'), not the content presentation (which can vary). However, this misunderstanding was also included in reports in the educational press, notably The Times Educational Supplement . [ 6 ]
The description of the approach as 'Spaced Learning', clarifying the importance of the spaces, only appeared later. Additional research reported in The Times Educational Supplement , The Guardian , The Times , and The Daily Telegraph on 30 January 2009 reported that Spaced Learning successfully prepared students for a national examination in less than two hours with no traditional teaching at all.
The use of the term 'spaced' reflects the distinction in other research between 'spaced training' and 'massed training' where there have been conflicting results reported (for example, see spaced repetition ). Spaced retrieval practice – trying to recover long-term memories quickly and accurately – is the subject of a different line of research but also shows that spaced practice (for example, taking a practice test every month) is more effective than massed practice.
The significance of Spaced Learning may prove important in different ways: | https://en.wikipedia.org/wiki/Spaced_learning |
Spaceflight (or space flight ) is an application of astronautics to fly objects, usually spacecraft , into or through outer space , either with or without humans on board . Most spaceflight is uncrewed and conducted mainly with spacecraft such as satellites in orbit around Earth , but also includes space probes for flights beyond Earth orbit. Such spaceflights operate either by telerobotic or autonomous control. The first spaceflights began in the 1950s with the launches of the Soviet Sputnik satellites and American Explorer and Vanguard missions. Human spaceflight programs include the Soyuz , Shenzhou , the past Apollo Moon landing and the Space Shuttle programs . Other current spaceflight are conducted to the International Space Station and to China's Tiangong Space Station .
Spaceflights include the launches of Earth observation and telecommunications satellites, interplanetary missions , the rendezvouses and dockings with space stations , and crewed spaceflights on scientific or tourist missions.
Spaceflight can be achieved conventionally via multistage rockets , which provide the thrust to overcome the force of gravity and propel spacecraft onto suborbital trajectories . If the mission is orbital , the spacecraft usually separates the first stage and ignites the second stage , which propels the spacecraft to high enough speeds that it reaches orbit. Once in orbit, spacecraft are at high enough speeds that they fall around the Earth rather than fall back to the surface.
Most spacecraft, and all crewed spacecraft, are designed to deorbit themselves or, in the case of uncrewed spacecraft in high-energy orbits, to boost themselves into graveyard orbits . Used upper stages or failed spacecraft, however, often lack the ability to deorbit themselves. This becomes a major issue when large numbers of uncontrollable spacecraft exist in frequently used orbits, increasing the risk of debris colliding with functional satellites. This problem is exacerbated when large objects, often upper stages, break up in orbit or collide with other objects, creating often hundreds of small, hard to find pieces of debris. This problem of continuous collisions is known as Kessler syndrome .
There are several terms that refer to a flight into or through outer space .
A space mission refers to a spaceflight intended to achieve an objective. Objectives for space missions may include space exploration , space research , and national firsts in spaceflight.
Space transport is the use of spacecraft to transport people or cargo into or through outer space. This may include human spaceflight and cargo spacecraft flight.
The first theoretical proposal of space travel using rockets was published by Scottish astronomer and mathematician William Leitch , in an 1861 essay "A Journey Through Space". [ 1 ] More well-known is Konstantin Tsiolkovsky 's work, " Исследование мировых пространств реактивными приборами " ( The Exploration of Cosmic Space by Means of Reaction Devices ), published in 1903. In his work, Tsiolkovsky describes the fundamental rocket equation:
Δ v = v e ln m 0 m f {\displaystyle \Delta v=v_{e}\ln {\frac {m_{0}}{m_{f}}}}
Where:
This equation, known as the Tsiolkovsky rocket equation , can be used to find the total Δ v {\displaystyle \Delta v} , or potential change in velocity. This formula, which is still used by engineers, is a key concept of spaceflight.
Spaceflight became a practical possibility with the work of Robert H. Goddard 's publication in 1919 of his paper A Method of Reaching Extreme Altitudes . His application of the de Laval nozzle to liquid-fuel rockets improved efficiency enough for interplanetary travel to become possible. After further research, Goddard attempted to secure an Army contract for a rocket-propelled weapon in the first World War but his plans were foiled by the November 11, 1918 armistice with Germany . After choosing to work with private financial support, he was the first to launch a liquid-fueled rocket on March 16, 1926.
During World War II , the first guided rocket, the V-2 , was developed and employed as a weapon by Nazi Germany . During a test flight in June 1944, one such rocket reached space at an altitude of 189 kilometers (102 nautical miles), becoming the first human-made object to reach space. [ 2 ] At the end of World War II, most of the V-2 rocket team, including its head, Wernher von Braun , surrendered to the United States, and were expatriated to work on American missiles at what became the Army Ballistic Missile Agency , producing missiles such as Juno I and Atlas . The Soviet Union , in turn, captured several V2 production facilities and built several replicas, with 5 of their 11 rockets successfully reaching their targets. (This was relatively consistent with Nazi Germany's success rate.)
The Soviet Union developed intercontinental ballistic missiles to carry nuclear weapons as a counter measure to United States bomber planes in the 1950s. The Tsiolkovsky-influenced Sergey Korolev became the chief rocket designer, and derivatives of his R-7 Semyorka missiles were used to launch the world's first artificial Earth satellite , Sputnik 1 , on October 4, 1957.
The U.S., after the launch of Sputnik and two embarrassing failures of Vanguard rockets , launched Explorer 1 on February 1, 1958. Three years later, the USSR launched Vostok 1, carrying cosmonaut Yuri Gagarin into orbit. The US responded with the suborbital launch of Alan Shepard on May 5, 1961, and the orbital launch of John Glenn on February 20, 1962. These events were followed by a pledge from U.S. President John F. Kennedy to go to the moon and the creation of the Gemini and Apollo programs. After successfully performing a rendezvous and docking and an EVA , the Gemini program ended just before the Apollo 1 tragedy. Following multiple uncrewed test flights of the Saturn 1B and the Saturn V , the U.S. launched the crewed Apollo 7 mission into low Earth orbit . Shortly after its successful completion, the U.S. launched Apollo 8 (first mission to orbit the Moon), Apollo 9 (first Apollo mission to launch with both the CSM and the LEM ) and Apollo 10 (first mission to nearly land on the Moon). These events culminated with the first crewed Moon landing, Apollo 11 , and six subsequent missions, five of which successfully landed on the Moon.
Spaceflight has been widely employed by numerous government and commercial entities for placing satellites into orbit around Earth for a broad range of purposes. Certain government agencies have also sent uncrewed spacecraft exploring space beyond the Moon and developed continuous crewed human presence in space with a series of space stations , ranging from the Salyut program to the International Space Station .
Rockets are the only means currently capable of reaching orbit or beyond. Other non-rocket spacelaunch technologies have yet to be built, or remain short of orbital speeds. A rocket launch for a spaceflight usually starts from a spaceport (cosmodrome), which may be equipped with launch complexes and launch pads for vertical rocket launches and runways for takeoff and landing of carrier airplanes and winged spacecraft. Spaceports are situated well away from human habitation for noise and safety reasons. ICBMs have various special launching facilities.
A launch is often restricted to certain launch windows . These windows depend upon the position of celestial bodies and orbits relative to the launch site. The biggest influence is often the rotation of the Earth. Once launched, orbits are normally located within relatively constant flat planes at a fixed angle to the axis of the Earth, and the Earth rotates within this orbit.
A launch pad is a fixed structure designed to dispatch airborne vehicles. It generally consists of a launch tower and flame trench. It is surrounded by equipment used to erect, fuel, and maintain launch vehicles. Before launch, the rocket can weigh hundreds of tons. The Space Shuttle Columbia , on STS-1 , weighed 2030 metric tons (4,480,000 lb) at takeoff.
The most commonly used definition of outer space is everything beyond the Kármán line , which is 100 kilometers (62 mi) above the Earth's surface. (The United States defines outer space as everything beyond 50 miles (80 km) in altitude.)
Rocket engines remain the only currently practical means of reaching space, with planes and high-altitude balloons failing due to lack of atmosphere and alternatives such as space elevators not yet being built. Chemical propulsion, or the acceleration of gases at high velocities, is effective mainly because of its ability to sustain thrust even as the atmosphere thins.
Many ways to reach space other than rocket engines have been proposed. Ideas such as the space elevator , and momentum exchange tethers like rotovators or skyhooks require new materials much stronger than any currently known. Electromagnetic launchers such as launch loops might be feasible with current technology. Other ideas include rocket-assisted aircraft/spaceplanes such as Reaction Engines Skylon (currently in early stage development), scramjet powered spaceplanes, and RBCC powered spaceplanes. Gun launch has been proposed for cargo.
On some missions beyond LEO (Low Earth Orbit) , spacecraft are inserted into parking orbits, or lower intermediary orbits. The parking orbit approach greatly simplified Apollo mission planning in several important ways. It acted as a "time buffer" and substantially widened the allowable launch windows . The parking orbit gave the crew and controllers time to thoroughly check out the spacecraft after the stresses of launch before committing it for a long journey to the Moon. [ 3 ]
Robotic missions do not require an abort capability and require radiation minimalization only for delicate electronics, and because modern launchers routinely meet "instantaneous" launch windows, space probes to the Moon and other planets generally use direct injection to maximize performance by limiting the boil off of cryogenic propellants . Although some might coast briefly during the launch sequence, they do not complete one or more full parking orbits before the burn that injects them onto an Earth escape trajectory.
The escape velocity from a celestial body decreases as the distance from the body increases. However, it is more fuel-efficient for a craft to burn its fuel as close as possible to its periapsis (lowest point); see Oberth effect . [ 5 ]
Astrodynamics is the study of spacecraft trajectories, particularly as they relate to gravitational and propulsion effects. Astrodynamics allows for a spacecraft to arrive at its destination at the correct time without excessive propellant use. An orbital maneuvering system may be needed to maintain or change orbits.
Non-rocket orbital propulsion methods include solar sails , magnetic sails , plasma-bubble magnetic systems , and using gravitational slingshot effects.
The term "transfer energy" means the total amount of energy imparted by a rocket stage to its payload. This can be the energy imparted by a first stage of a launch vehicle to an upper stage plus payload, or by an upper stage or spacecraft kick motor to a spacecraft . [ 6 ] [ 7 ]
In order to reach a space station , a spacecraft would have to arrive at the same orbit and approach to a very close distance (e.g. within visual contact). This is done by a set of orbital maneuvers called space rendezvous .
After rendezvousing with the space station, the space vehicle then docks or berths with the station. Docking refers to joining of two separate free-flying space vehicles, [ 8 ] [ 9 ] [ 10 ] [ 11 ] while berthing refers to mating operations where an inactive vehicle is placed into the mating interface of another space vehicle by using a robotic arm . [ 8 ] [ 10 ] [ 11 ]
Vehicles in orbit have large amounts of kinetic energy. This energy must be discarded if the vehicle is to land safely without vaporizing in the atmosphere. Typically this process requires special methods to protect against aerodynamic heating . The theory behind reentry was developed by Harry Julian Allen . Based on this theory, reentry vehicles present blunt shapes to the atmosphere for reentry. Blunt shapes mean that less than 1% of the kinetic energy ends up as heat reaching the vehicle, and the remainder heats the atmosphere.
The Mercury , Gemini , and Apollo capsules splashed down in the sea. These capsules were designed to land at relatively low speeds with the help of a parachute. Soviet/Russian capsules for Soyuz make use of a big parachute and braking rockets to touch down on land. Spaceplanes like the Space Shuttle land like a glider .
After a successful landing, the spacecraft, its occupants, and cargo can be recovered. In some cases, recovery has occurred before landing: while a spacecraft is still descending on its parachute, it can be snagged by a specially designed aircraft. This mid-air retrieval technique was used to recover the film canisters from the Corona spy satellites.
Uncrewed spacecraft or robotic spacecraft are spacecraft without people on board. Uncrewed spacecraft may have varying levels of autonomy from human input, such as remote control , or remote guidance. They may also be autonomous , in which they have a pre-programmed list of operations that will be executed unless otherwise instructed. A robotic spacecraft for scientific measurements is often called a space probe or space observatory .
Many space missions are more suited to telerobotic rather than crewed operation, due to lower cost and risk factors. In addition, some planetary destinations such as Venus or the vicinity of Jupiter are too hostile for human survival, given current technology. Outer planets such as Saturn , Uranus , and Neptune are too distant to reach with current crewed spaceflight technology, so telerobotic probes are the only way to explore them. Telerobotics also allows exploration of regions that are vulnerable to contamination by Earth micro-organisms since spacecraft can be sterilized. Humans can not be sterilized in the same way as a spaceship, as they coexist with numerous micro-organisms, and these micro-organisms are also hard to contain within a spaceship or spacesuit.
The first uncrewed space mission was Sputnik , launched October 4, 1957 to orbit the Earth. Nearly all satellites , landers and rovers are robotic spacecraft. Not every uncrewed spacecraft is a robotic spacecraft; for example, a reflector ball is a non-robotic uncrewed spacecraft. Space missions where other animals but no humans are on-board are called uncrewed missions.
The first human spaceflight was Vostok 1 on April 12, 1961, on which cosmonaut Yuri Gagarin of the USSR made one orbit around the Earth. In official Soviet documents, there is no mention of the fact that Gagarin parachuted the final seven miles. [ 12 ] As of 2020, the only spacecraft regularly used for human spaceflight are Soyuz , Shenzhou , and Crew Dragon . The U.S. Space Shuttle fleet operated from April 1981 until July 2011. SpaceShipOne has conducted three human suborbital space flights.
On a sub-orbital spaceflight the spacecraft reaches space and then returns to the atmosphere after following a (primarily) ballistic trajectory. This is usually because of insufficient specific orbital energy , in which case a suborbital flight will last only a few minutes, but it is also possible for an object with enough energy for an orbit to have a trajectory that intersects the Earth's atmosphere, sometimes after many hours. Pioneer 1 was NASA's first space probe intended to reach the Moon. A partial failure caused it to instead follow a suborbital trajectory to an altitude of 113,854 kilometers (70,746 mi) before reentering the Earth's atmosphere 43 hours after launch.
The most generally recognized boundary of space is the Kármán line 100 km (62 mi) above sea level. (NASA alternatively defines an astronaut as someone who has flown more than 80 km (50 mi) above sea level.) It is not generally recognized by the public that the increase in potential energy required to pass the Kármán line is only about 3% of the orbital energy (potential plus kinetic energy) required by the lowest possible Earth orbit (a circular orbit just above the Kármán line.) In other words, it is far easier to reach space than to stay there. On May 17, 2004, Civilian Space eXploration Team launched the GoFast rocket on a suborbital flight, the first amateur spaceflight. On June 21, 2004, SpaceShipOne was used for the first privately funded human spaceflight .
Point-to-point, or Earth to Earth transportation, is a category of sub-orbital spaceflight in which a spacecraft provides rapid transport between two terrestrial locations. [ 13 ] A conventional airline route between London and Sydney , a flight that normally lasts over twenty hours , could be traversed in less than one hour. [ 14 ] While no company offers this type of transportation today, SpaceX has revealed plans to do so as early as the 2020s using Starship . Suborbital spaceflight over an intercontinental distance requires a vehicle velocity that is only a little lower than the velocity required to reach low Earth orbit. [ 15 ] If rockets are used, the size of the rocket relative to the payload is similar to an Intercontinental Ballistic Missile (ICBM). Any intercontinental spaceflight has to surmount problems of heating during atmospheric re-entry that are nearly as large as those faced by orbital spaceflight.
A minimal orbital spaceflight requires much higher velocities than a minimal sub-orbital flight, and so it is technologically much more challenging to achieve. To achieve orbital spaceflight, the tangential velocity around the Earth is as important as altitude. In order to perform a stable and lasting flight in space, the spacecraft must reach the minimal orbital speed required for a closed orbit .
Interplanetary spaceflight is flight between planets within a single planetary system . In practice, the use of the term is confined to travel between the planets of the Solar System . Plans for future crewed interplanetary spaceflight missions often include final vehicle assembly in Earth orbit, such as NASA's Constellation program and Russia's Kliper / Parom tandem.
New Horizons is the fifth spacecraft put on an escape trajectory leaving the Solar System . Voyager 1 , Voyager 2 , Pioneer 10 , Pioneer 11 are the earlier ones. The one farthest from the Sun is Voyager 1 , which is more than 100 AU distant and is moving at 3.6 AU per year. [ 16 ] In comparison, Proxima Centauri , the closest star other than the Sun, is 267,000 AU distant. It will take Voyager 1 over 74,000 years to reach this distance. Vehicle designs using other techniques, such as nuclear pulse propulsion are likely to be able to reach the nearest star significantly faster. Another possibility that could allow for human interstellar spaceflight is to make use of time dilation , as this would make it possible for passengers in a fast-moving vehicle to travel further into the future while aging very little, in that their great speed slows down the rate of passage of on-board time. However, attaining such high speeds would still require the use of some new, advanced method of propulsion . Dynamic soaring as a way to travel across interstellar space has been proposed as well. [ 17 ] [ 18 ]
Intergalactic travel involves spaceflight between galaxies, and is considered much more technologically demanding than even interstellar travel and, by current engineering terms, is considered science fiction . However, theoretically speaking, there is nothing to conclusively indicate that intergalactic travel is impossible. To date several academics have studied intergalactic travel in a serious manner. [ 19 ] [ 20 ] [ 21 ]
Spacecraft are vehicles designed to operate in space.
The first 'true spacecraft' is sometimes said to be Apollo Lunar Module , [ 22 ] since this was the only crewed vehicle to have been designed for, and operated only in space; and is notable for its non-aerodynamic shape.
Spacecraft today predominantly use rockets for propulsion , but other propulsion techniques such as ion drives are becoming more common, particularly for uncrewed vehicles, and this can significantly reduce the vehicle's mass and increase its delta-v .
Launch systems are used to carry a payload from Earth's surface into outer space.
Most current spaceflight uses multi-stage expendable launch systems to reach space.
The first reusable spacecraft, the X-15 , was air-launched on a suborbital trajectory on 19 July 1963. The first partially reusable orbital spacecraft, the Space Shuttle , was launched by the USA on the 20th anniversary of Yuri Gagarin 's flight, on 12 April 1981. During the Shuttle era, six orbiters were built, all of which flown in the atmosphere and five of which flown in space. The Enterprise was used only for approach and landing tests, launching from the back of a Boeing 747 and gliding to deadstick landings at Edwards AFB, California . The first Space Shuttle to fly into space was the Columbia , followed by the Challenger , Discovery , Atlantis , and Endeavour . The Endeavour was built to replace the Challenger , which was lost in January 1986. The Columbia broke up during reentry in February 2003.
The first automatic partially reusable spacecraft was the Buran ( Snowstorm ), launched by the USSR on 15 November 1988, although it made only one flight. This spaceplane was designed for a crew and strongly resembled the US Space Shuttle, although its drop-off boosters used liquid propellants and its main engines were located at the base of what would be the external tank in the American Shuttle. Lack of funding, complicated by the dissolution of the USSR, prevented any further flights of Buran.
The Space Shuttle was retired in 2011 due mainly to its old age. The Shuttle's human transport role is to be replaced by the SpaceX Dragon 2 and CST-100 in the 2020s. The Shuttle's heavy cargo transport role is now done by commercial launch vehicles.
Scaled Composites SpaceShipOne was a reusable suborbital spaceplane that carried pilots Mike Melvill and Brian Binnie on consecutive flights in 2004 to win the Ansari X Prize . The Spaceship Company has built its successor SpaceShipTwo . A fleet of SpaceShipTwos operated by Virgin Galactic planned to begin reusable private spaceflight carrying paying passengers ( space tourists ) in 2008, but this was delayed due to an accident in the propulsion development. [ 23 ]
SpaceX achieved the first vertical soft landing of a reusable orbital rocket stage on December 21, 2015, after delivering 11 Orbcomm OG-2 commercial satellites into low Earth orbit . [ 24 ]
The first Falcon 9 reflight occurred on 30 March 2017. [ 25 ] SpaceX now routinely recovers and reuses their first stages and fairings . [ 26 ] SpaceX is now developing a fully reusable super heavy lift rocket known as Starship , with the goal of drastically reducing the price of space exploration. [ 27 ] As of April 2025, three Super Heavy boosters, the first stage of Starship, have been recovered. [ 28 ] [ 29 ] [ 30 ]
All launch vehicles contain a huge amount of energy that is needed for some part of it to reach orbit. There is therefore some risk that this energy can be released prematurely and suddenly, with significant effects. When a Delta II rocket exploded 13 seconds after launch on January 17, 1997, there were reports of store windows 10 miles (16 km) away being broken by the blast. [ 31 ]
Space is a fairly predictable environment, but there are still risks of accidental depressurization and the potential failure of equipment, some of which may be very newly developed.
In April 2004 the International Association for the Advancement of Space Safety was established in the Netherlands to further international cooperation and scientific advancement in space systems safety. [ 32 ]
In a microgravity environment such as that provided by a spacecraft in orbit around the Earth, humans experience a sense of "weightlessness." Short-term exposure to microgravity causes space adaptation syndrome , a self-limiting nausea caused by derangement of the vestibular system . Long-term exposure causes multiple health issues. The most significant is bone loss, some of which is permanent, but microgravity also leads to significant deconditioning of muscular and cardiovascular tissues.
Once above the atmosphere, radiation due to the Van Allen belts , solar radiation and cosmic radiation issues occur and increase. Further away from the Earth, solar flares can give a fatal radiation dose in minutes, and the health threat from cosmic radiation significantly increases the chances of cancer over a decade exposure or more. [ 33 ]
In human spaceflight, the life support system is a group of devices that allow a human being to survive in outer space. NASA often uses the phrase Environmental Control and Life Support System or the acronym ECLSS when describing these systems for its human spaceflight missions. [ 34 ] The life support system may supply: air , water and food . It must also maintain the correct body temperature, an acceptable pressure on the body and deal with the body's waste products. Shielding against harmful external influences such as radiation and micro-meteorites may also be necessary. Components of the life support system are life-critical , and are designed and constructed using safety engineering techniques.
Space weather is the concept of changing environmental conditions in outer space . It is distinct from the concept of weather within a planetary atmosphere , and deals with phenomena involving ambient plasma , magnetic fields, radiation and other matter in space (generally close to Earth but also in interplanetary , and occasionally interstellar medium ). "Space weather describes the conditions in space that affect Earth and its technological systems. Our space weather is a consequence of the behavior of the Sun, the nature of Earth's magnetic field, and our location in the Solar System." [ 35 ]
Space weather exerts a profound influence in several areas related to space exploration and development. Changing geomagnetic conditions can induce changes in atmospheric density causing the rapid degradation of spacecraft altitude in Low Earth orbit . Geomagnetic storms due to increased solar activity can potentially blind sensors onboard spacecraft, or interfere with on-board electronics. An understanding of space environmental conditions is also important in designing shielding and life support systems for crewed spacecraft.
Exhaust pollution of rockets depends on the produced exhausts by the propellants reactions and the location of exhaustion. They mostly exhaust greenhouse gases and sometimes toxic components. Particularly at higher levels of the atmosphere the potency of exhausted gases as greenhouse gases increases considerably. [ 36 ] Many solid rockets have chlorine in the form of perchlorate or other chemicals, and this can cause temporary local holes in the ozone layer. Re-entering spacecraft generate nitrates which also can temporarily impact the ozone layer. Most rockets are made of metals that can have an environmental impact during their construction.
While spaceflight altogether pollutes at a fraction of other human activities, it still does pollute heavily if calculated per passenger. [ 36 ]
In addition to the atmospheric effects there are effects on the near-Earth space environment. There is the possibility that orbit could become inaccessible for generations due to exponentially increasing space debris caused by spalling of satellites and vehicles ( Kessler syndrome ). Many launched vehicles today are therefore designed to be re-entered after use.
A wide range of issues such as space traffic management or liability have been issues of spaceflight regulation.
Participation and representation of all humanity in spaceflight is an issue of international space law ever since the first phase of space exploration. [ 37 ] Even though some rights of non-spacefaring countries have been secured, sharing of space for all humanity is still criticized as imperialist and lacking, understanding spaceflight as a resource. [ 37 ]
Inclusion has been a national and international issue, resulting in 1967 in the Outer Space Treaty and its claim of outer space as the " province of all mankind ". Furthermore social inclusion in human spaceflight has been demanded, with women to fly to space being limited, and minorities, like people with disability, only having been selected in European Space Agency 's 2022 astronaut group .
The dominating issue about access in most recent years has been the issue of space debris and space sustainability , since established spacefaring countries endanger access to outer space with their orbital space polluting activity. [ 38 ]
Current and proposed applications for spaceflight include:
Most early spaceflight development was paid for by governments. However, today major launch markets such as communication satellites and satellite television are purely commercial, though many of the launchers were originally funded by governments.
Private spaceflight is a rapidly developing area: space flight that is not only paid for by corporations or even private individuals, but often provided by private spaceflight companies . These companies often assert that much of the previous high cost of access to space was caused by governmental inefficiencies they can avoid. This assertion can be supported by much lower published launch costs for private space launch vehicles such as Falcon 9 developed with private financing. Lower launch costs and excellent safety will be required for the applications such as space tourism and especially space colonization to become feasible for expansion.
To be spacefaring is to be capable of and active in the operation of spacecraft . It involves a knowledge of a variety of topics and development of specialised skills including: aeronautics ; astronautics ; programs to train astronauts ; space weather and forecasting; spacecraft operations; operation of various equipment; spacecraft design and construction; atmospheric takeoff and reentry; orbital mechanics (a.k.a. astrodynamics); communications; engines and rockets; execution of evolutions such as towing, microgravity construction, and space docking ; cargo handling equipment, dangerous cargos and cargo storage; spacewalking ; dealing with emergencies; survival at space and first aid; fire fighting; life support . The degree of knowledge needed within these areas is dependent upon the nature of the work and the type of vessel employed. "Spacefaring" is analogous to seafaring .
There has never been a crewed mission outside the Earth – Moon system. However, the United States, Russia, China, European Space Agency (ESA) countries, and a few corporations and enterprises have plans in various stages to travel to Mars (see Human mission to Mars ).
Spacefaring entities can be sovereign states , supranational entities, and private corporations . Spacefaring nations are those capable of independently building and launching craft into space. [ 39 ] [ 40 ] [ 41 ] A growing number of private entities have become or are becoming spacefaring.
The United Nations Office for Outer Space Affairs (UNOOSA) has been the main multilateral body servicing international contact and exchange on space activity among spacefaring and non-spacefaring states.
Currently Russia , the United States and China are the only crewed spacefaring nations .
Spacefaring nations listed by date of first crewed launch:
The following nations or organizations have developed their own launch vehicles to launch uncrewed spacecraft into orbit either from their own territory or with foreign assistance (date of first launch in parentheses): [ 42 ]
Also several countries, such as Canada, Italy, and Australia, had semi-independent spacefaring capability, launching locally-built satellites on foreign launchers. Canada had designed and built satellites ( Alouette 1 and 2 ) in 1962 and 1965 which were orbited using U.S. launch vehicles. Italy has designed and built several satellites, as well as pressurized modules for the International Space Station . Early Italian satellites were launched using vehicles provided by NASA, first from Wallops Flight Facility in 1964 and then from a spaceport in Kenya ( San Marco Platform ) between 1967 and 1988; [ citation needed ] Italy has led the development of the Vega rocket programme within the European Space Agency since 1998. [ 47 ] The United Kingdom abandoned its independent space launch program in 1972 in favour of co-operating with the European Launcher Development Organisation (ELDO) on launch technologies until 1974. Australia abandoned its launcher program shortly after the successful launch of WRESAT , and became the only non-European member of ELDO.
Considering merely launching an object beyond the Kármán line to be the minimum requirement of spacefaring, Germany , with the V-2 rocket , became the first spacefaring nation in 1944. [ 48 ] The following nations have only achieved suborbital spaceflight capability by launching indigenous rockets or missiles or both into suborbital space:
Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion Arm → Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow ( → ) may be read as "within" or "part of". | https://en.wikipedia.org/wiki/Spaceflight |
In physics , spacetime , also called the space-time continuum , is a mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum . Spacetime diagrams are useful in visualizing and understanding relativistic effects, such as how different observers perceive where and when events occur.
Until the turn of the 20th century, the assumption had been that the three-dimensional geometry of the universe (its description in terms of locations, shapes, distances, and directions) was distinct from time (the measurement of when events occur within the universe). However, space and time took on new meanings with the Lorentz transformation and special theory of relativity .
In 1908, Hermann Minkowski presented a geometric interpretation of special relativity that fused time and the three spatial dimensions into a single four-dimensional continuum now known as Minkowski space . This interpretation proved vital to the general theory of relativity , wherein spacetime is curved by mass and energy .
Non-relativistic classical mechanics treats time as a universal quantity of measurement that is uniform throughout, is separate from space, and is agreed on by all observers. Classical mechanics assumes that time has a constant rate of passage, independent of the observer's state of motion , or anything external. [ 1 ] It assumes that space is Euclidean : it assumes that space follows the geometry of common sense. [ 2 ]
In the context of special relativity , time cannot be separated from the three dimensions of space, because the observed rate at which time passes for an object depends on the object's velocity relative to the observer. [ 3 ] : 214–217 General relativity provides an explanation of how gravitational fields can slow the passage of time for an object as seen by an observer outside the field.
In ordinary space, a position is specified by three numbers, known as dimensions . In the Cartesian coordinate system , these are often called x , y and z . A point in spacetime is called an event , and requires four numbers to be specified: the three-dimensional location in space, plus the position in time (Fig. 1). An event is represented by a set of coordinates x , y , z and t . [ 4 ] Spacetime is thus four-dimensional .
Unlike the analogies used in popular writings to explain events, such as firecrackers or sparks, mathematical events have zero duration and represent a single point in spacetime. [ 5 ] Although it is possible to be in motion relative to the popping of a firecracker or a spark, it is not possible for an observer to be in motion relative to an event.
The path of a particle through spacetime can be considered to be a sequence of events. The series of events can be linked together to form a curve that represents the particle's progress through spacetime. That path is called the particle's world line . [ 6 ] : 105
Mathematically, spacetime is a manifold , which is to say, it appears locally "flat" near each point in the same way that, at small enough scales, the surface of a globe appears to be flat. [ 7 ] A scale factor, c {\displaystyle c} (conventionally called the speed-of-light ) relates distances measured in space to distances measured in time. The magnitude of this scale factor (nearly 300,000 kilometres or 190,000 miles in space being equivalent to one second in time), along with the fact that spacetime is a manifold, implies that at ordinary, non-relativistic speeds and at ordinary, human-scale distances, there is little that humans might observe that is noticeably different from what they might observe if the world were Euclidean. It was only with the advent of sensitive scientific measurements in the mid-1800s, such as the Fizeau experiment and the Michelson–Morley experiment , that puzzling discrepancies began to be noted between observation versus predictions based on the implicit assumption of Euclidean space. [ 8 ]
In special relativity, an observer will, in most cases, mean a frame of reference from which a set of objects or events is being measured. This usage differs significantly from the ordinary English meaning of the term. Reference frames are inherently nonlocal constructs, and according to this usage of the term, it does not make sense to speak of an observer as having a location. [ 9 ]
In Fig. 1-1, imagine that the frame under consideration is equipped with a dense lattice of clocks, synchronized within this reference frame, that extends indefinitely throughout the three dimensions of space. Any specific location within the lattice is not important. The latticework of clocks is used to determine the time and position of events taking place within the whole frame. The term observer refers to the whole ensemble of clocks associated with one inertial frame of reference. [ 9 ] : 17–22
In this idealized case, every point in space has a clock associated with it, and thus the clocks register each event instantly, with no time delay between an event and its recording. A real observer will see a delay between the emission of a signal and its detection due to the speed of light. To synchronize the clocks, in the data reduction following an experiment, the time when a signal is received will be corrected to reflect its actual time were it to have been recorded by an idealized lattice of clocks. [ 9 ] : 17–22
In many books on special relativity, especially older ones, the word "observer" is used in the more ordinary sense of the word. It is usually clear from context which meaning has been adopted.
Physicists distinguish between what one measures or observes , after one has factored out signal propagation delays, versus what one visually sees without such corrections. Failing to understand the difference between what one measures and what one sees is the source of much confusion among students of relativity. [ 10 ]
By the mid-1800s, various experiments such as the observation of the Arago spot and differential measurements of the speed of light in air versus water were considered to have proven the wave nature of light as opposed to a corpuscular theory . [ 11 ] Propagation of waves was then assumed to require the existence of a waving medium; in the case of light waves, this was considered to be a hypothetical luminiferous aether . [ note 1 ] The various attempts to establish the properties of this hypothetical medium yielded contradictory results. For example, the Fizeau experiment of 1851, conducted by French physicist Hippolyte Fizeau , demonstrated that the speed of light in flowing water was less than the sum of the speed of light in air plus the speed of the water by an amount dependent on the water's index of refraction. [ 12 ]
Among other issues, the dependence of the partial aether-dragging implied by this experiment on the index of refraction (which is dependent on wavelength) led to the unpalatable conclusion that aether simultaneously flows at different speeds for different colors of light. [ 13 ] The Michelson–Morley experiment of 1887 (Fig. 1-2) showed no differential influence of Earth's motions through the hypothetical aether on the speed of light, and the most likely explanation, complete aether dragging, was in conflict with the observation of stellar aberration . [ 8 ]
George Francis FitzGerald in 1889, [ 14 ] and Hendrik Lorentz in 1892, independently proposed that material bodies traveling through the fixed aether were physically affected by their passage, contracting in the direction of motion by an amount that was exactly what was necessary to explain the negative results of the Michelson–Morley experiment. No length changes occur in directions transverse to the direction of motion.
By 1904, Lorentz had expanded his theory such that he had arrived at equations formally identical with those that Einstein was to derive later, i.e. the Lorentz transformation . [ 15 ] As a theory of dynamics (the study of forces and torques and their effect on motion), his theory assumed actual physical deformations of the physical constituents of matter. [ 16 ] : 163–174 Lorentz's equations predicted a quantity that he called local time , with which he could explain the aberration of light , the Fizeau experiment and other phenomena.
Henri Poincaré was the first to combine space and time into spacetime. [ 17 ] [ 18 ] : 73–80, 93–95 He argued in 1898 that the simultaneity of two events is a matter of convention. [ 19 ] [ note 2 ] In 1900, he recognized that Lorentz's "local time" is actually what is indicated by moving clocks by applying an explicitly operational definition of clock synchronization assuming constant light speed. [ note 3 ] In 1900 and 1904, he suggested the inherent undetectability of the aether by emphasizing the validity of what he called the principle of relativity . In 1905/1906 [ 20 ] he mathematically perfected Lorentz's theory of electrons in order to bring it into accordance with the postulate of relativity.
While discussing various hypotheses on Lorentz invariant gravitation, he introduced the innovative concept of a 4-dimensional spacetime by defining various four vectors , namely four-position , four-velocity , and four-force . [ 21 ] [ 22 ] He did not pursue the 4-dimensional formalism in subsequent papers, however, stating that this line of research seemed to "entail great pain for limited profit", ultimately concluding "that three-dimensional language seems the best suited to the description of our world". [ 22 ] Even as late as 1909, Poincaré continued to describe the dynamical interpretation of the Lorentz transform. [ 16 ] : 163–174
In 1905, Albert Einstein analyzed special relativity in terms of kinematics (the study of moving bodies without reference to forces) rather than dynamics. His results were mathematically equivalent to those of Lorentz and Poincaré. He obtained them by recognizing that the entire theory can be built upon two postulates: the principle of relativity and the principle of the constancy of light speed. His work was filled with vivid imagery involving the exchange of light signals between clocks in motion, careful measurements of the lengths of moving rods, and other such examples. [ 23 ] [ note 4 ]
Einstein in 1905 superseded previous attempts of an electromagnetic mass –energy relation by introducing the general equivalence of mass and energy , which was instrumental for his subsequent formulation of the equivalence principle in 1907, which declares the equivalence of inertial and gravitational mass. By using the mass–energy equivalence, Einstein showed that the gravitational mass of a body is proportional to its energy content, which was one of the early results in developing general relativity . While it would appear that he did not at first think geometrically about spacetime, [ 3 ] : 219 in the further development of general relativity, Einstein fully incorporated the spacetime formalism.
When Einstein published in 1905, another of his competitors, his former mathematics professor Hermann Minkowski , had also arrived at most of the basic elements of special relativity. Max Born recounted a meeting he had made with Minkowski, seeking to be Minkowski's student/collaborator: [ 25 ]
I went to Cologne, met Minkowski and heard his celebrated lecture 'Space and Time' delivered on 2 September 1908. [...] He told me later that it came to him as a great shock when Einstein published his paper in which the equivalence of the different local times of observers moving relative to each other was pronounced; for he had reached the same conclusions independently but did not publish them because he wished first to work out the mathematical structure in all its splendor. He never made a priority claim and always gave Einstein his full share in the great discovery.
Minkowski had been concerned with the state of electrodynamics after Michelson's disruptive experiments at least since the summer of 1905, when Minkowski and David Hilbert led an advanced seminar attended by notable physicists of the time to study the papers of Lorentz, Poincaré et al. Minkowski saw Einstein's work as an extension of Lorentz's, and was most directly influenced by Poincaré. [ 26 ]
On 5 November 1907 (a little more than a year before his death), Minkowski introduced his geometric interpretation of spacetime in a lecture to the Göttingen Mathematical society with the title, The Relativity Principle ( Das Relativitätsprinzip ). [ note 5 ] On 21 September 1908, Minkowski presented his talk, Space and Time ( Raum und Zeit ), [ 27 ] to the German Society of Scientists and Physicians. The opening words of Space and Time include Minkowski's statement that "Henceforth, space for itself, and time for itself shall completely reduce to a mere shadow, and only some sort of union of the two shall preserve independence." Space and Time included the first public presentation of spacetime diagrams (Fig. 1-4), and included a remarkable demonstration that the concept of the invariant interval ( discussed below ), along with the empirical observation that the speed of light is finite, allows derivation of the entirety of special relativity. [ note 6 ]
The spacetime concept and the Lorentz group are closely connected to certain types of sphere , hyperbolic , or conformal geometries and their transformation groups already developed in the 19th century, in which invariant intervals analogous to the spacetime interval are used. [ note 7 ]
Einstein, for his part, was initially dismissive of Minkowski's geometric interpretation of special relativity, regarding it as überflüssige Gelehrsamkeit (superfluous learnedness). However, in order to complete his search for general relativity that started in 1907, the geometric interpretation of relativity proved to be vital. In 1916, Einstein fully acknowledged his indebtedness to Minkowski, whose interpretation greatly facilitated the transition to general relativity. [ 16 ] : 151–152 Since there are other types of spacetime, such as the curved spacetime of general relativity, the spacetime of special relativity is today known as Minkowski spacetime.
In three dimensions, the distance Δ d {\displaystyle \Delta {d}} between two points can be defined using the Pythagorean theorem :
Although two viewers may measure the x , y , and z position of the two points using different coordinate systems, the distance between the points will be the same for both, assuming that they are measuring using the same units. The distance is "invariant".
In special relativity, however, the distance between two points is no longer the same if measured by two different observers, when one of the observers is moving, because of Lorentz contraction . The situation is even more complicated if the two points are separated in time as well as in space. For example, if one observer sees two events occur at the same place, but at different times, a person moving with respect to the first observer will see the two events occurring at different places, because the moving point of view sees itself as stationary, and the position of the event as receding or approaching. Thus, a different measure must be used to measure the effective "distance" between two events. [ 31 ] : 48–50, 100–102
In four-dimensional spacetime, the analog to distance is the interval. Although time comes in as a fourth dimension, it is treated differently than the spatial dimensions. Minkowski space hence differs in important respects from four-dimensional Euclidean space . The fundamental reason for merging space and time into spacetime is that space and time are separately not invariant, which is to say that, under the proper conditions, different observers will disagree on the length of time between two events (because of time dilation ) or the distance between the two events (because of length contraction ). Special relativity provides a new invariant, called the spacetime interval , which combines distances in space and in time. All observers who measure the time and distance between any two events will end up computing the same spacetime interval. Suppose an observer measures two events as being separated in time by Δ t {\displaystyle \Delta t} and a spatial distance Δ x . {\displaystyle \Delta x.} Then the squared spacetime interval ( Δ s ) 2 {\displaystyle (\Delta {s})^{2}} between the two events that are separated by a distance Δ x {\displaystyle \Delta {x}} in space and by Δ c t = c Δ t {\displaystyle \Delta {ct}=c\Delta t} in the c t {\displaystyle ct} -coordinate is: [ 32 ]
or for three space dimensions,
The constant c , {\displaystyle c,} the speed of light, converts time t {\displaystyle t} units (like seconds) into space units (like meters). The squared interval Δ s 2 {\displaystyle \Delta s^{2}} is a measure of separation between events A and B that are time separated and in addition space separated either because there are two separate objects undergoing events, or because a single object in space is moving inertially between its events. The separation interval is the difference between the square of the spatial distance separating event B from event A and the square of the spatial distance traveled by a light signal in that same time interval Δ t {\displaystyle \Delta t} . If the event separation is due to a light signal, then this difference vanishes and Δ s = 0 {\displaystyle \Delta s=0} .
When the event considered is infinitesimally close to each other, then we may write
In a different inertial frame, say with coordinates ( t ′ , x ′ , y ′ , z ′ ) {\displaystyle (t',x',y',z')} , the spacetime interval d s ′ {\displaystyle ds'} can be written in a same form as above. Because of the constancy of speed of light, the light events in all inertial frames belong to zero interval, d s = d s ′ = 0 {\displaystyle ds=ds'=0} . For any other infinitesimal event where d s ≠ 0 {\displaystyle ds\neq 0} , one can prove that d s 2 = d s ′ 2 {\displaystyle ds^{2}=ds'^{2}} which in turn upon integration leads to s = s ′ {\displaystyle s=s'} . [ 33 ] : 2 The invariance of the spacetime interval between the same events for all inertial frames of reference is one of the fundamental results of special theory of relativity.
Although for brevity, one frequently sees interval expressions expressed without deltas, including in most of the following discussion, it should be understood that in general, x {\displaystyle x} means Δ x {\displaystyle \Delta {x}} , etc. We are always concerned with differences of spatial or temporal coordinate values belonging to two events, and since there is no preferred origin, single coordinate values have no essential meaning.
The equation above is similar to the Pythagorean theorem, except with a minus sign between the ( c t ) 2 {\displaystyle (ct)^{2}} and the x 2 {\displaystyle x^{2}} terms. The spacetime interval is the quantity s 2 , {\displaystyle s^{2},} not s {\displaystyle s} itself. The reason is that unlike distances in Euclidean geometry, intervals in Minkowski spacetime can be negative. Rather than deal with square roots of negative numbers, physicists customarily regard s 2 {\displaystyle s^{2}} as a distinct symbol in itself, rather than the square of something. [ 3 ] : 217
In general s 2 {\displaystyle s^{2}} can assume any real number value. If s 2 {\displaystyle s^{2}} is positive, the spacetime interval is referred to as timelike . Since spatial distance traversed by any massive object is always less than distance traveled by the light for the same time interval, positive intervals are always timelike. If s 2 {\displaystyle s^{2}} is negative, the spacetime interval is said to be spacelike . Spacetime intervals are equal to zero when x = ± c t . {\displaystyle x=\pm ct.} In other words, the spacetime interval between two events on the world line of something moving at the speed of light is zero. Such an interval is termed lightlike or null . A photon arriving in our eye from a distant star will not have aged, despite having (from our perspective) spent years in its passage. [ 31 ] : 48–50
A spacetime diagram is typically drawn with only a single space and a single time coordinate. Fig. 2-1 presents a spacetime diagram illustrating the world lines (i.e. paths in spacetime) of two photons, A and B, originating from the same event and going in opposite directions. In addition, C illustrates the world line of a slower-than-light-speed object. The vertical time coordinate is scaled by c {\displaystyle c} so that it has the same units (meters) as the horizontal space coordinate. Since photons travel at the speed of light, their world lines have a slope of ±1. [ 31 ] : 23–25 In other words, every meter that a photon travels to the left or right requires approximately 3.3 nanoseconds of time.
To gain insight in how spacetime coordinates measured by observers in different reference frames compare with each other, it is useful to work with a simplified setup with frames in a standard configuration. With care, this allows simplification of the math with no loss of generality in the conclusions that are reached. In Fig. 2-2, two Galilean reference frames (i.e. conventional 3-space frames) are displayed in relative motion. Frame S belongs to a first observer O, and frame S′ (pronounced "S prime") belongs to a second observer O′.
Fig. 2-3a redraws Fig. 2-2 in a different orientation. Fig. 2-3b illustrates a relativistic spacetime diagram from the viewpoint of observer O. Since S and S′ are in standard configuration, their origins coincide at times t = 0 in frame S and t ′ = 0 in frame S′. The ct′ axis passes through the events in frame S′ which have x ′ = 0. But the points with x ′ = 0 are moving in the x -direction of frame S with velocity v , so that they are not coincident with the ct axis at any time other than zero. Therefore, the ct′ axis is tilted with respect to the ct axis by an angle θ given by [ 31 ] : 23–31
The x ′ axis is also tilted with respect to the x axis. To determine the angle of this tilt, we recall that the slope of the world line of a light pulse is always ±1. Fig. 2-3c presents a spacetime diagram from the viewpoint of observer O′. Event P represents the emission of a light pulse at x ′ = 0, ct ′ = − a . The pulse is reflected from a mirror situated a distance a from the light source (event Q), and returns to the light source at x ′ = 0, ct ′ = a (event R).
The same events P, Q, R are plotted in Fig. 2-3b in the frame of observer O. The light paths have slopes = 1 and −1, so that △PQR forms a right triangle with PQ and QR both at 45 degrees to the x and ct axes. Since OP = OQ = OR, the angle between x′ and x must also be θ . [ 6 ] : 113–118
While the rest frame has space and time axes that meet at right angles, the moving frame is drawn with axes that meet at an acute angle. The frames are actually equivalent. [ 31 ] : 23–31 The asymmetry is due to unavoidable distortions in how spacetime coordinates can map onto a Cartesian plane , and should be considered no stranger than the manner in which, on a Mercator projection of the Earth, the relative sizes of land masses near the poles (Greenland and Antarctica) are highly exaggerated relative to land masses near the Equator.
In Fig. 2–4, event O is at the origin of a spacetime diagram, and the two diagonal lines represent all events that have zero spacetime interval with respect to the origin event. These two lines form what is called the light cone of the event O, since adding a second spatial dimension (Fig. 2-5) makes the appearance that of two right circular cones meeting with their apices at O. One cone extends into the future (t>0), the other into the past (t<0).
A light (double) cone divides spacetime into separate regions with respect to its apex. The interior of the future light cone consists of all events that are separated from the apex by more time (temporal distance) than necessary to cross their spatial distance at lightspeed; these events comprise the timelike future of the event O. Likewise, the timelike past comprises the interior events of the past light cone. So in timelike intervals Δ ct is greater than Δ x , making timelike intervals positive. [ 3 ] : 220
The region exterior to the light cone consists of events that are separated from the event O by more space than can be crossed at lightspeed in the given time . These events comprise the so-called spacelike region of the event O, denoted "Elsewhere" in Fig. 2-4. Events on the light cone itself are said to be lightlike (or null separated ) from O. Because of the invariance of the spacetime interval, all observers will assign the same light cone to any given event, and thus will agree on this division of spacetime. [ 3 ] : 220
The light cone has an essential role within the concept of causality . It is possible for a not-faster-than-light-speed signal to travel from the position and time of O to the position and time of D (Fig. 2-4). It is hence possible for event O to have a causal influence on event D. The future light cone contains all the events that could be causally influenced by O. Likewise, it is possible for a not-faster-than-light-speed signal to travel from the position and time of A, to the position and time of O. The past light cone contains all the events that could have a causal influence on O. In contrast, assuming that signals cannot travel faster than the speed of light, any event, like e.g. B or C, in the spacelike region (Elsewhere), cannot either affect event O, nor can they be affected by event O employing such signalling. Under this assumption any causal relationship between event O and any events in the spacelike region of a light cone is excluded. [ 35 ]
All observers will agree that for any given event, an event within the given event's future light cone occurs after the given event. Likewise, for any given event, an event within the given event's past light cone occurs before the given event. The before–after relationship observed for timelike-separated events remains unchanged no matter what the reference frame of the observer, i.e. no matter how the observer may be moving. The situation is quite different for spacelike-separated events. Fig. 2-4 was drawn from the reference frame of an observer moving at v = 0. From this reference frame, event C is observed to occur after event O, and event B is observed to occur before event O. [ 36 ]
From a different reference frame, the orderings of these non-causally-related events can be reversed. In particular, one notes that if two events are simultaneous in a particular reference frame, they are necessarily separated by a spacelike interval and thus are noncausally related. The observation that simultaneity is not absolute, but depends on the observer's reference frame, is termed the relativity of simultaneity . [ 36 ]
Fig. 2-6 illustrates the use of spacetime diagrams in the analysis of the relativity of simultaneity. The events in spacetime are invariant, but the coordinate frames transform as discussed above for Fig. 2-3. The three events (A, B, C) are simultaneous from the reference frame of an observer moving at v = 0. From the reference frame of an observer moving at v = 0.3 c , the events appear to occur in the order C, B, A. From the reference frame of an observer moving at v = −0.5 c , the events appear to occur in the order A, B, C . The white line represents a plane of simultaneity being moved from the past of the observer to the future of the observer, highlighting events residing on it. The gray area is the light cone of the observer, which remains invariant.
A spacelike spacetime interval gives the same distance that an observer would measure if the events being measured were simultaneous to the observer. A spacelike spacetime interval hence provides a measure of proper distance , i.e. the true distance = − s 2 . {\displaystyle {\sqrt {-s^{2}}}.} Likewise, a timelike spacetime interval gives the same measure of time as would be presented by the cumulative ticking of a clock that moves along a given world line. A timelike spacetime interval hence provides a measure of the proper time = s 2 . {\displaystyle {\sqrt {s^{2}}}.} [ 3 ] : 220–221
In Euclidean space (having spatial dimensions only), the set of points equidistant (using the Euclidean metric) from some point form a circle (in two dimensions) or a sphere (in three dimensions). In (1+1)-dimensional Minkowski spacetime (having one temporal and one spatial dimension), the points at some constant spacetime interval away from the origin (using the Minkowski metric) form curves given by the two equations
with s 2 {\displaystyle s^{2}} some positive real constant. These equations describe two families of hyperbolae in an x – ct spacetime diagram, which are termed invariant hyperbolae .
In Fig. 2-7a, each magenta hyperbola connects all events having some fixed spacelike separation from the origin, while the green hyperbolae connect events of equal timelike separation.
The magenta hyperbolae, which cross the x axis, are timelike curves, which is to say that these hyperbolae represent actual paths that can be traversed by (constantly accelerating) particles in spacetime: Between any two events on one hyperbola a causality relation is possible, because the inverse of the slope—representing the necessary speed—for all secants is less than c {\displaystyle c} . On the other hand, the green hyperbolae, which cross the ct axis, are spacelike curves because all intervals along these hyperbolae are spacelike intervals: No causality is possible between any two points on one of these hyperbolae, because all secants represent speeds larger than c {\displaystyle c} .
Fig. 2-7b reflects the situation in (1+2)-dimensional Minkowski spacetime (one temporal and two spatial dimensions) with the corresponding hyperboloids. The invariant hyperbolae displaced by spacelike intervals from the origin generate hyperboloids of one sheet, while the invariant hyperbolae displaced by timelike intervals from the origin generate hyperboloids of two sheets.
The (1+2)-dimensional boundary between space- and time-like hyperboloids, established by the events forming a zero spacetime interval to the origin, is made up by degenerating the hyperboloids to the light cone. In (1+1)-dimensions the hyperbolae degenerate to the two grey 45°-lines depicted in Fig. 2-7a.
Fig. 2-8 illustrates the invariant hyperbola for all events that can be reached from the origin in a proper time of 5 meters (approximately 1.67 × 10 −8 s ). Different world lines represent clocks moving at different speeds. A clock that is stationary with respect to the observer has a world line that is vertical, and the elapsed time measured by the observer is the same as the proper time. For a clock traveling at 0.3 c , the elapsed time measured by the observer is 5.24 meters ( 1.75 × 10 −8 s ), while for a clock traveling at 0.7 c , the elapsed time measured by the observer is 7.00 meters ( 2.34 × 10 −8 s ). [ 3 ] : 220–221
This illustrates the phenomenon known as time dilation . Clocks that travel faster take longer (in the observer frame) to tick out the same amount of proper time, and they travel further along the x–axis within that proper time than they would have without time dilation. [ 3 ] : 220–221 The measurement of time dilation by two observers in different inertial reference frames is mutual. If observer O measures the clocks of observer O′ as running slower in his frame, observer O′ in turn will measure the clocks of observer O as running slower.
Length contraction , like time dilation, is a manifestation of the relativity of simultaneity. Measurement of length requires measurement of the spacetime interval between two events that are simultaneous in one's frame of reference. But events that are simultaneous in one frame of reference are, in general, not simultaneous in other frames of reference.
Fig. 2-9 illustrates the motions of a 1 m rod that is traveling at 0.5 c along the x axis. The edges of the blue band represent the world lines of the rod's two endpoints. The invariant hyperbola illustrates events separated from the origin by a spacelike interval of 1 m. The endpoints O and B measured when t ′ = 0 are simultaneous events in the S′ frame. But to an observer in frame S, events O and B are not simultaneous. To measure length, the observer in frame S measures the endpoints of the rod as projected onto the x -axis along their world lines. The projection of the rod's world sheet onto the x axis yields the foreshortened length OC. [ 6 ] : 125
(not illustrated) Drawing a vertical line through A so that it intersects the x ′ axis demonstrates that, even as OB is foreshortened from the point of view of observer O, OA is likewise foreshortened from the point of view of observer O′. In the same way that each observer measures the other's clocks as running slow, each observer measures the other's rulers as being contracted.
In regards to mutual length contraction, Fig. 2-9 illustrates that the primed and unprimed frames are mutually rotated by a hyperbolic angle (analogous to ordinary angles in Euclidean geometry). [ note 8 ] Because of this rotation, the projection of a primed meter-stick onto the unprimed x -axis is foreshortened, while the projection of an unprimed meter-stick onto the primed x′-axis is likewise foreshortened.
Mutual time dilation and length contraction tend to strike beginners as inherently self-contradictory concepts. If an observer in frame S measures a clock, at rest in frame S', as running slower than his', while S' is moving at speed v in S, then the principle of relativity requires that an observer in frame S' likewise measures a clock in frame S, moving at speed − v in S', as running slower than hers. How two clocks can run both slower than the other, is an important question that "goes to the heart of understanding special relativity." [ 3 ] : 198
This apparent contradiction stems from not correctly taking into account the different settings of the necessary, related measurements. These settings allow for a consistent explanation of the only apparent contradiction. It is not about the abstract ticking of two identical clocks, but about how to measure in one frame the temporal distance of two ticks of a moving clock. It turns out that in mutually observing the duration between ticks of clocks, each moving in the respective frame, different sets of clocks must be involved. In order to measure in frame S the tick duration of a moving clock W′ (at rest in S′), one uses two additional, synchronized clocks W 1 and W 2 at rest in two arbitrarily fixed points in S with the spatial distance d .
Conversely, for judging in frame S′ the temporal distance of two events on a moving clock W (at rest in S), one needs two clocks at rest in S′.
The necessary recordings for the two judgements, with "one moving clock" and "two clocks at rest" in respectively S or S′, involves two different sets, each with three clocks. Since there are different sets of clocks involved in the measurements, there is no inherent necessity that the measurements be reciprocally "consistent" such that, if one observer measures the moving clock to be slow, the other observer measures the one's clock to be fast. [ 3 ] : 198–199
Fig. 2-10 illustrates the previous discussion of mutual time dilation with Minkowski diagrams . The upper picture reflects the measurements as seen from frame S "at rest" with unprimed, rectangular axes, and frame S′ "moving with v > 0", coordinatized by primed, oblique axes, slanted to the right; the lower picture shows frame S′ "at rest" with primed, rectangular coordinates, and frame S "moving with − v < 0", with unprimed, oblique axes, slanted to the left.
Each line drawn parallel to a spatial axis ( x , x ′) represents a line of simultaneity. All events on such a line have the same time value ( ct , ct ′). Likewise, each line drawn parallel to a temporal axis ( ct , ct′ ) represents a line of equal spatial coordinate values ( x , x ′).
To show the mutual time dilation immediately in the upper picture, the event D may be constructed as the event at x ′ = 0 (the location of clock W′ in S′), that is simultaneous to C ( OC has equal spacetime interval as OA ) in S′. This shows that the time interval OD is longer than OA , showing that the "moving" clock runs slower. [ 6 ] : 124
In the lower picture the frame S is moving with velocity − v in the frame S′ at rest. The worldline of clock W is the ct -axis (slanted to the left), the worldline of W′ 1 is the vertical ct ′-axis, and the worldline of W′ 2 is the vertical through event C , with ct ′-coordinate D . The invariant hyperbola through event C scales the time interval OC to OA , which is shorter than OD ; also, B is constructed (similar to D in the upper pictures) as simultaneous to A in S, at x = 0. The result OB > OC corresponds again to above.
The word "measure" is important. In classical physics an observer cannot affect an observed object, but the object's state of motion can affect the observer's observations of the object.
Many introductions to special relativity illustrate the differences between Galilean relativity and special relativity by posing a series of "paradoxes". These paradoxes are, in fact, ill-posed problems, resulting from our unfamiliarity with velocities comparable to the speed of light. The remedy is to solve many problems in special relativity and to become familiar with its so-called counter-intuitive predictions. The geometrical approach to studying spacetime is considered one of the best methods for developing a modern intuition. [ 37 ]
The twin paradox is a thought experiment involving identical twins, one of whom makes a journey into space in a high-speed rocket, returning home to find that the twin who remained on Earth has aged more. This result appears puzzling because each twin observes the other twin as moving, and so at first glance, it would appear that each should find the other to have aged less. The twin paradox sidesteps the justification for mutual time dilation presented above by avoiding the requirement for a third clock. [ 3 ] : 207 Nevertheless, the twin paradox is not a true paradox because it is easily understood within the context of special relativity.
The impression that a paradox exists stems from a misunderstanding of what special relativity states. Special relativity does not declare all frames of reference to be equivalent, only inertial frames. The traveling twin's frame is not inertial during periods when she is accelerating. Furthermore, the difference between the twins is observationally detectable: the traveling twin needs to fire her rockets to be able to return home, while the stay-at-home twin does not. [ 38 ] [ note 9 ]
These distinctions should result in a difference in the twins' ages. The spacetime diagram of Fig. 2-11 presents the simple case of a twin going straight out along the x axis and immediately turning back. From the standpoint of the stay-at-home twin, there is nothing puzzling about the twin paradox at all. The proper time measured along the traveling twin's world line from O to C, plus the proper time measured from C to B, is less than the stay-at-home twin's proper time measured from O to A to B. More complex trajectories require integrating the proper time between the respective events along the curve (i.e. the path integral ) to calculate the total amount of proper time experienced by the traveling twin. [ 38 ]
Complications arise if the twin paradox is analyzed from the traveling twin's point of view.
Weiss's nomenclature, designating the stay-at-home twin as Terence and the traveling twin as Stella, is hereafter used. [ 38 ]
Stella is not in an inertial frame. Given this fact, it is sometimes incorrectly stated that full resolution of the twin paradox requires general relativity: [ 38 ]
A pure SR analysis would be as follows: Analyzed in Stella's rest frame, she is motionless for the entire trip. When she fires her rockets for the turnaround, she experiences a pseudo force which resembles a gravitational force. [ 38 ] Figs. 2-6 and 2-11 illustrate the concept of lines (planes) of simultaneity: Lines parallel to the observer's x -axis ( xy -plane) represent sets of events that are simultaneous in the observer frame. In Fig. 2-11, the blue lines connect events on Terence's world line which, from Stella's point of view , are simultaneous with events on her world line. (Terence, in turn, would observe a set of horizontal lines of simultaneity.) Throughout both the outbound and the inbound legs of Stella's journey, she measures Terence's clocks as running slower than her own. But during the turnaround (i.e. between the bold blue lines in the figure), a shift takes place in the angle of her lines of simultaneity, corresponding to a rapid skip-over of the events in Terence's world line that Stella considers to be simultaneous with her own. Therefore, at the end of her trip, Stella finds that Terence has aged more than she has. [ 38 ]
Although general relativity is not required to analyze the twin paradox, application of the Equivalence Principle of general relativity does provide some additional insight into the subject. Stella is not stationary in an inertial frame. Analyzed in Stella's rest frame, she is motionless for the entire trip. When she is coasting her rest frame is inertial, and Terence's clock will appear to run slow. But when she fires her rockets for the turnaround, her rest frame is an accelerated frame and she experiences a force which is pushing her as if she were in a gravitational field. Terence will appear to be high up in that field and because of gravitational time dilation , his clock will appear to run fast, so much so that the net result will be that Terence has aged more than Stella when they are back together. [ 38 ] The theoretical arguments predicting gravitational time dilation are not exclusive to general relativity. Any theory of gravity will predict gravitational time dilation if it respects the principle of equivalence, including Newton's theory. [ 3 ] : 16
This introductory section has focused on the spacetime of special relativity, since it is the easiest to describe. Minkowski spacetime is flat, takes no account of gravity, is uniform throughout, and serves as nothing more than a static background for the events that take place in it. The presence of gravity greatly complicates the description of spacetime. In general relativity, spacetime is no longer a static background, but actively interacts with the physical systems that it contains. Spacetime curves in the presence of matter, can propagate waves, bends light, and exhibits a host of other phenomena. [ 3 ] : 221 A few of these phenomena are described in the later sections of this article.
A basic goal is to be able to compare measurements made by observers in relative motion. If there is an observer O in frame S who has measured the time and space coordinates of an event, assigning this event three Cartesian coordinates and the time as measured on his lattice of synchronized clocks ( x , y , z , t ) (see Fig. 1-1 ). A second observer O′ in a different frame S′ measures the same event in her coordinate system and her lattice of synchronized clocks ( x ′ , y ′ , z ′ , t ′ ) . With inertial frames, neither observer is under acceleration, and a simple set of equations allows us to relate coordinates ( x , y , z , t ) to ( x ′ , y ′ , z ′ , t ′ ) . Given that the two coordinate systems are in standard configuration, meaning that they are aligned with parallel ( x , y , z ) coordinates and that t = 0 when t ′ = 0 , the coordinate transformation is as follows: [ 39 ] [ 40 ]
Fig. 3-1 illustrates that in Newton's theory, time is universal, not the velocity of light. [ 41 ] : 36–37 Consider the following thought experiment: The red arrow illustrates a train that is moving at 0.4 c with respect to the platform. Within the train, a passenger shoots a bullet with a speed of 0.4 c in the frame of the train. The blue arrow illustrates that a person standing on the train tracks measures the bullet as traveling at 0.8 c. This is in accordance with our naive expectations.
More generally, assuming that frame S′ is moving at velocity v with respect to frame S, then within frame S′, observer O′ measures an object moving with velocity u ′ . Velocity u with respect to frame S, since x = ut , x ′ = x − vt , and t = t ′ , can be written as x ′ = ut − vt = ( u − v ) t = ( u − v ) t ′ . This leads to u ′ = x ′ / t ′ and ultimately
which is the common-sense Galilean law for the addition of velocities .
The composition of velocities is quite different in relativistic spacetime. To reduce the complexity of the equations slightly, we introduce a common shorthand for the ratio of the speed of an object relative to light,
Fig. 3-2a illustrates a red train that is moving forward at a speed given by v / c = β = s / a . From the primed frame of the train, a passenger shoots a bullet with a speed given by u ′ / c = β ′ = n / m , where the distance is measured along a line parallel to the red x ′ axis rather than parallel to the black x axis. What is the composite velocity u of the bullet relative to the platform, as represented by the blue arrow? Referring to Fig. 3-2b:
The relativistic formula for addition of velocities presented above exhibits several important features:
It is straightforward to obtain quantitative expressions for time dilation and length contraction. Fig. 3-3 is a composite image containing individual frames taken from two previous animations, simplified and relabeled for the purposes of this section.
To reduce the complexity of the equations slightly, there are a variety of different shorthand notations for ct :
In Fig. 3-3a, segments OA and OK represent equal spacetime intervals. Time dilation is represented by the ratio OB / OK . The invariant hyperbola has the equation w = √ x 2 + k 2 where k = OK , and the red line representing the world line of a particle in motion has the equation w = x / β = xc / v . A bit of algebraic manipulation yields O B = O K / 1 − v 2 / c 2 . {\textstyle OB=OK/{\sqrt {1-v^{2}/c^{2}}}.}
The expression involving the square root symbol appears very frequently in relativity, and one over the expression is called the Lorentz factor, denoted by the Greek letter gamma γ {\displaystyle \gamma } : [ 42 ]
If v is greater than or equal to c , the expression for γ {\displaystyle \gamma } becomes physically meaningless, implying that c is the maximum possible speed in nature. For any v greater than zero, the Lorentz factor will be greater than one, although the shape of the curve is such that for low speeds, the Lorentz factor is extremely close to one.
In Fig. 3-3b, segments OA and OK represent equal spacetime intervals. Length contraction is represented by the ratio OB / OK . The invariant hyperbola has the equation x = √ w 2 + k 2 , where k = OK , and the edges of the blue band representing the world lines of the endpoints of a rod in motion have slope 1/ β = c / v . Event A has coordinates
( x , w ) = ( γk , γβk ). Since the tangent line through A and B has the equation w = ( x − OB )/ β , we have γβk = ( γk − OB )/ β and
The Galilean transformations and their consequent commonsense law of addition of velocities work well in our ordinary low-speed world of planes, cars and balls. Beginning in the mid-1800s, however, sensitive scientific instrumentation began finding anomalies that did not fit well with the ordinary addition of velocities.
Lorentz transformations are used to transform the coordinates of an event from one frame to another in special relativity.
The Lorentz factor appears in the Lorentz transformations:
The inverse Lorentz transformations are:
When v ≪ c and x is small enough, the v 2 / c 2 and vx / c 2 terms approach zero, and the Lorentz transformations approximate to the Galilean transformations.
t ′ = γ ( t − v x / c 2 ) , {\displaystyle t'=\gamma (t-vx/c^{2}),} x ′ = γ ( x − v t ) {\displaystyle x'=\gamma (x-vt)} etc., most often really mean Δ t ′ = γ ( Δ t − v Δ x / c 2 ) , {\displaystyle \Delta t'=\gamma (\Delta t-v\Delta x/c^{2}),} Δ x ′ = γ ( Δ x − v Δ t ) {\displaystyle \Delta x'=\gamma (\Delta x-v\Delta t)} etc. Although for brevity the Lorentz transformation equations are written without deltas, x means Δ x , etc. We are, in general, always concerned with the space and time differences between events.
Calling one set of transformations the normal Lorentz transformations and the other the inverse transformations is misleading, since there is no intrinsic difference between the frames. Different authors call one or the other set of transformations the "inverse" set. The forwards and inverse transformations are trivially related to each other, since the S frame can only be moving forwards or reverse with respect to S ′ . So inverting the equations simply entails switching the primed and unprimed variables and replacing v with − v . [ 43 ] : 71–79
Example: Terence and Stella are at an Earth-to-Mars space race. Terence is an official at the starting line, while Stella is a participant. At time t = t ′ = 0 , Stella's spaceship accelerates instantaneously to a speed of 0.5 c . The distance from Earth to Mars is 300 light-seconds (about 90.0 × 10 6 km ). Terence observes Stella crossing the finish-line clock at t = 600.00 s . But Stella observes the time on her ship chronometer to be t ′ = γ ( t − v x / c 2 ) = 519.62 s {\displaystyle t^{\prime }=\gamma \left(t-vx/c^{2}\right)=519.62\ {\text{s}}} as she passes the finish line, and she calculates the distance between the starting and finish lines, as measured in her frame, to be 259.81 light-seconds (about 77.9 × 10 6 km ). 1).
There have been many dozens of derivations of the Lorentz transformations since Einstein's original work in 1905, each with its particular focus. Although Einstein's derivation was based on the invariance of the speed of light, there are other physical principles that may serve as starting points. Ultimately, these alternative starting points can be considered different expressions of the underlying principle of locality , which states that the influence that one particle exerts on another can not be transmitted instantaneously. [ 44 ]
The derivation given here and illustrated in Fig. 3-5 is based on one presented by Bais [ 41 ] : 64–66 and makes use of previous results from the Relativistic Composition of Velocities, Time Dilation, and Length Contraction sections. Event P has coordinates ( w , x ) in the black "rest system" and coordinates ( w ′ , x ′ ) in the red frame that is moving with velocity parameter β = v / c . To determine w ′ and x ′ in terms of w and x (or the other way around) it is easier at first to derive the inverse Lorentz transformation.
The above equations are alternate expressions for the t and x equations of the inverse Lorentz transformation, as can be seen by substituting ct for w , ct ′ for w ′ , and v / c for β . From the inverse transformation, the equations of the forwards transformation can be derived by solving for t ′ and x ′ .
The Lorentz transformations have a mathematical property called linearity, since x ′ and t ′ are obtained as linear combinations of x and t , with no higher powers involved. The linearity of the transformation reflects a fundamental property of spacetime that was tacitly assumed in the derivation, namely, that the properties of inertial frames of reference are independent of location and time. In the absence of gravity, spacetime looks the same everywhere. [ 41 ] : 67 All inertial observers will agree on what constitutes accelerating and non-accelerating motion. [ 43 ] : 72–73 Any one observer can use her own measurements of space and time, but there is nothing absolute about them. Another observer's conventions will do just as well. [ 3 ] : 190
A result of linearity is that if two Lorentz transformations are applied sequentially, the result is also a Lorentz transformation.
Example: Terence observes Stella speeding away from him at 0.500 c , and he can use the Lorentz transformations with β = 0.500 to relate Stella's measurements to his own. Stella, in her frame, observes Ursula traveling away from her at 0.250 c , and she can use the Lorentz transformations with β = 0.250 to relate Ursula's measurements with her own. Because of the linearity of the transformations and the relativistic composition of velocities, Terence can use the Lorentz transformations with β = 0.666 to relate Ursula's measurements with his own.
The Doppler effect is the change in frequency or wavelength of a wave for a receiver and source in relative motion. For simplicity, we consider here two basic scenarios: (1) The motions of the source and/or receiver are exactly along the line connecting them (longitudinal Doppler effect), and (2) the motions are at right angles to the said line ( transverse Doppler effect ). We are ignoring scenarios where they move along intermediate angles.
The classical Doppler analysis deals with waves that are propagating in a medium, such as sound waves or water ripples, and which are transmitted between sources and receivers that are moving towards or away from each other. The analysis of such waves depends on whether the source, the receiver, or both are moving relative to the medium. Given the scenario where the receiver is stationary with respect to the medium, and the source is moving directly away from the receiver at a speed of v s for a velocity parameter of β s , the wavelength is increased, and the observed frequency f is given by
On the other hand, given the scenario where source is stationary, and the receiver is moving directly away from the source at a speed of v r for a velocity parameter of β r , the wavelength is not changed, but the transmission velocity of the waves relative to the receiver is decreased, and the observed frequency f is given by
Light, unlike sound or water ripples, does not propagate through a medium, and there is no distinction between a source moving away from the receiver or a receiver moving away from the source. Fig. 3-6 illustrates a relativistic spacetime diagram showing a source separating from the receiver with a velocity parameter β , {\displaystyle \beta ,} so that the separation between source and receiver at time w {\displaystyle w} is β w {\displaystyle \beta w} . Because of time dilation, w = γ w ′ . {\displaystyle w=\gamma w'.} Since the slope of the green light ray is −1, T = w + β w = γ w ′ ( 1 + β ) . {\displaystyle T=w+\beta w=\gamma w'(1+\beta ).} Hence, the relativistic Doppler effect is given by [ 41 ] : 58–59
Suppose that a source and a receiver, both approaching each other in uniform inertial motion along non-intersecting lines, are at their closest approach to each other. It would appear that the classical analysis predicts that the receiver detects no Doppler shift. Due to subtleties in the analysis, that expectation is not necessarily true. Nevertheless, when appropriately defined, transverse Doppler shift is a relativistic effect that has no classical analog. The subtleties are these: [ 45 ] : 541–543
Two other scenarios are commonly examined in discussions of transverse Doppler shift:
<!—end plainlist—>
In scenario (a), the point of closest approach is frame-independent and represents the moment where there is no change in distance versus time (i.e. dr/dt = 0 where r is the distance between receiver and source) and hence no longitudinal Doppler shift. The source observes the receiver as being illuminated by light of frequency f ′ , but also observes the receiver as having a time-dilated clock. In frame S, the receiver is therefore illuminated by blueshifted light of frequency
In scenario (b) the illustration shows the receiver being illuminated by light from when the source was closest to the receiver, even though the source has moved on. Because the source's clocks are time dilated as measured in frame S, and since dr/dt was equal to zero at this point, the light from the source, emitted from this closest point, is redshifted with frequency
Scenarios (c) and (d) can be analyzed by simple time dilation arguments. In (c), the receiver observes light from the source as being blueshifted by a factor of γ {\displaystyle \gamma } , and in (d), the light is redshifted. The only seeming complication is that the orbiting objects are in accelerated motion. However, if an inertial observer looks at an accelerating clock, only the clock's instantaneous speed is important when computing time dilation. (The converse, however, is not true.) [ 45 ] : 541–543 Most reports of transverse Doppler shift refer to the effect as a redshift and analyze the effect in terms of scenarios (b) or (d). [ note 11 ]
In classical mechanics, the state of motion of a particle is characterized by its mass and its velocity. Linear momentum , the product of a particle's mass and velocity, is a vector quantity, possessing the same direction as the velocity: p = m v . It is a conserved quantity, meaning that if a closed system is not affected by external forces, its total linear momentum cannot change.
In relativistic mechanics, the momentum vector is extended to four dimensions. Added to the momentum vector is a time component that allows the spacetime momentum vector to transform like the spacetime position vector ( x , t ) {\displaystyle (x,t)} . In exploring the properties of the spacetime momentum, we start, in Fig. 3-8a, by examining what a particle looks like at rest. In the rest frame, the spatial component of the momentum is zero, i.e. p = 0 , but the time component equals mc .
We can obtain the transformed components of this vector in the moving frame by using the Lorentz transformations, or we can read it directly from the figure because we know that ( m c ) ′ = γ m c {\displaystyle (mc)^{\prime }=\gamma mc} and p ′ = − β γ m c {\displaystyle p^{\prime }=-\beta \gamma mc} , since the red axes are rescaled by gamma. Fig. 3-8b illustrates the situation as it appears in the moving frame. It is apparent that the space and time components of the four-momentum go to infinity as the velocity of the moving frame approaches c . [ 41 ] : 84–87
We will use this information shortly to obtain an expression for the four-momentum .
Light particles, or photons, travel at the speed of c , the constant that is conventionally known as the speed of light . This statement is not a tautology, since many modern formulations of relativity do not start with constant speed of light as a postulate. Photons therefore propagate along a lightlike world line and, in appropriate units, have equal space and time components for every observer.
A consequence of Maxwell's theory of electromagnetism is that light carries energy and momentum, and that their ratio is a constant: E / p = c {\displaystyle E/p=c} . Rearranging, E / c = p {\displaystyle E/c=p} , and since for photons, the space and time components are equal, E / c must therefore be equated with the time component of the spacetime momentum vector.
Photons travel at the speed of light, yet have finite momentum and energy. For this to be so, the mass term in γmc must be zero, meaning that photons are massless particles . Infinity times zero is an ill-defined quantity, but E / c is well-defined.
By this analysis, if the energy of a photon equals E in the rest frame, it equals E ′ = ( 1 − β ) γ E {\displaystyle E^{\prime }=(1-\beta )\gamma E} in a moving frame. This result can be derived by inspection of Fig. 3-9 or by application of the Lorentz transformations, and is consistent with the analysis of Doppler effect given previously. [ 41 ] : 88
Consideration of the interrelationships between the various components of the relativistic momentum vector led Einstein to several important conclusions.
Another way of looking at the relationship between mass and energy is to consider a series expansion of γmc 2 at low velocity:
The second term is just an expression for the kinetic energy of the particle. Mass indeed appears to be another form of energy. [ 41 ] : 90–92 [ 43 ] : 129–130, 180
The concept of relativistic mass that Einstein introduced in 1905, m rel , although amply validated every day in particle accelerators around the globe (or indeed in any instrumentation whose use depends on high velocity particles, such as electron microscopes, [ 46 ] old-fashioned color television sets, etc.), has nevertheless not proven to be a fruitful concept in physics in the sense that it is not a concept that has served as a basis for other theoretical development. Relativistic mass, for instance, plays no role in general relativity.
For this reason, as well as for pedagogical concerns, most physicists currently prefer a different terminology when referring to the relationship between mass and energy. [ 47 ] "Relativistic mass" is a deprecated term. The term "mass" by itself refers to the rest mass or invariant mass , and is equal to the invariant length of the relativistic momentum vector. Expressed as a formula,
This formula applies to all particles, massless as well as massive. For photons where m rest equals zero, it yields, E = ± p c {\displaystyle E=\pm pc} . [ 41 ] : 90–92
Because of the close relationship between mass and energy, the four-momentum (also called 4-momentum) is also called the energy–momentum 4-vector. Using an uppercase P to represent the four-momentum and a lowercase p to denote the spatial momentum, the four-momentum may be written as
In physics, conservation laws state that certain particular measurable properties of an isolated physical system do not change as the system evolves over time. In 1915, Emmy Noether discovered that underlying each conservation law is a fundamental symmetry of nature. [ 48 ] The fact that physical processes do not care where in space they take place ( space translation symmetry ) yields conservation of momentum , the fact that such processes do not care when they take place ( time translation symmetry ) yields conservation of energy , and so on. In this section, we examine the Newtonian views of conservation of mass, momentum and energy from a relativistic perspective.
To understand how the Newtonian view of conservation of momentum needs to be modified in a relativistic context, we examine the problem of two colliding bodies limited to a single dimension.
In Newtonian mechanics, two extreme cases of this problem may be distinguished yielding mathematics of minimum complexity:
For both cases (1) and (2), momentum, mass, and total energy are conserved. However, kinetic energy is not conserved in cases of inelastic collision. A certain fraction of the initial kinetic energy is converted to heat.
In case (2), two masses with momentums p 1 = m 1 v 1 {\displaystyle {\boldsymbol {p}}_{\boldsymbol {1}}=m_{1}{\boldsymbol {v}}_{\boldsymbol {1}}} and p 2 = m 2 v 2 {\displaystyle {\boldsymbol {p}}_{\boldsymbol {2}}=m_{2}{\boldsymbol {v}}_{\boldsymbol {2}}} collide to produce a single particle of conserved mass m = m 1 + m 2 {\displaystyle m=m_{1}+m_{2}} traveling at the center of mass velocity of the original system, v c m = ( m 1 v 1 + m 2 v 2 ) / ( m 1 + m 2 ) {\displaystyle {\boldsymbol {v_{cm}}}=\left(m_{1}{\boldsymbol {v_{1}}}+m_{2}{\boldsymbol {v_{2}}}\right)/\left(m_{1}+m_{2}\right)} . The total momentum p = p 1 + p 2 {\displaystyle {\boldsymbol {p=p_{1}+p_{2}}}} is conserved.
Fig. 3-10 illustrates the inelastic collision of two particles from a relativistic perspective. The time components E 1 / c {\displaystyle E_{1}/c} and E 2 / c {\displaystyle E_{2}/c} add up to total E/c of the resultant vector, meaning that energy is conserved. Likewise, the space components p 1 {\displaystyle {\boldsymbol {p_{1}}}} and p 2 {\displaystyle {\boldsymbol {p_{2}}}} add up to form p of the resultant vector. The four-momentum is, as expected, a conserved quantity. However, the invariant mass of the fused particle, given by the point where the invariant hyperbola of the total momentum intersects the energy axis, is not equal to the sum of the invariant masses of the individual particles that collided. Indeed, it is larger than the sum of the individual masses: m > m 1 + m 2 {\displaystyle m>m_{1}+m_{2}} . [ 41 ] : 94–97
Looking at the events of this scenario in reverse sequence, we see that non-conservation of mass is a common occurrence: when an unstable elementary particle spontaneously decays into two lighter particles, total energy is conserved, but the mass is not. Part of the mass is converted into kinetic energy. [ 43 ] : 134–138
The freedom to choose any frame in which to perform an analysis allows us to pick one which may be particularly convenient. For analysis of momentum and energy problems, the most convenient frame is usually the " center-of-momentum frame " (also called the zero-momentum frame, or COM frame). This is the frame in which the space component of the system's total momentum is zero. Fig. 3-11 illustrates the breakup of a high speed particle into two daughter particles. In the lab frame, the daughter particles are preferentially emitted in a direction oriented along the original particle's trajectory. In the COM frame, however, the two daughter particles are emitted in opposite directions, although their masses and the magnitude of their velocities are generally not the same. [ 49 ]
In a Newtonian analysis of interacting particles, transformation between frames is simple because all that is necessary is to apply the Galilean transformation to all velocities. Since v ′ = v − u {\displaystyle v'=v-u} , the momentum p ′ = p − m u {\displaystyle p'=p-mu} . If the total momentum of an interacting system of particles is observed to be conserved in one frame, it will likewise be observed to be conserved in any other frame. [ 43 ] : 241–245
Conservation of momentum in the COM frame amounts to the requirement that p = 0 both before and after collision. In the Newtonian analysis, conservation of mass dictates that m = m 1 + m 2 {\displaystyle m=m_{1}+m_{2}} . In the simplified, one-dimensional scenarios that we have been considering, only one additional constraint is necessary before the outgoing momenta of the particles can be determined—an energy condition. In the one-dimensional case of a completely elastic collision with no loss of kinetic energy, the outgoing velocities of the rebounding particles in the COM frame will be precisely equal and opposite to their incoming velocities. In the case of a completely inelastic collision with total loss of kinetic energy, the outgoing velocities of the rebounding particles will be zero. [ 43 ] : 241–245
Newtonian momenta, calculated as p = m v {\displaystyle p=mv} , fail to behave properly under Lorentzian transformation. The linear transformation of velocities v ′ = v − u {\displaystyle v'=v-u} is replaced by the highly nonlinear v ′ = ( v − u ) / ( 1 − v u / c 2 ) {\displaystyle v^{\prime }=(v-u)/(1-{vu}/{c^{2}})} so that a calculation demonstrating conservation of momentum in one frame will be invalid in other frames. Einstein was faced with either having to give up conservation of momentum, or to change the definition of momentum. This second option was what he chose. [ 41 ] : 104
The relativistic conservation law for energy and momentum replaces the three classical conservation laws for energy, momentum and mass. Mass is no longer conserved independently, because it has been subsumed into the total relativistic energy. This makes the relativistic conservation of energy a simpler concept than in nonrelativistic mechanics, because the total energy is conserved without any qualifications. Kinetic energy converted into heat or internal potential energy shows up as an increase in mass. [ 43 ] : 127
Fig. 3-12a illustrates the energy–momentum diagram for this decay reaction in the rest frame of the pion. Because of its negligible mass, a neutrino travels at very nearly the speed of light. The relativistic expression for its energy, like that of the photon, is E v = p c , {\displaystyle E_{v}=pc,} which is also the value of the space component of its momentum. To conserve momentum, the muon has the same value of the space component of the neutrino's momentum, but in the opposite direction.
Newton's theories assumed that motion takes place against the backdrop of a rigid Euclidean reference frame that extends throughout all space and all time. Gravity is mediated by a mysterious force, acting instantaneously across a distance, whose actions are independent of the intervening space. [ note 12 ] In contrast, Einstein denied that there is any background Euclidean reference frame that extends throughout space. Nor is there any such thing as a force of gravitation, only the structure of spacetime itself. [ 51 ] : 175–190
In spacetime terms, the path of a satellite orbiting the Earth is not dictated by the distant influences of the Earth, Moon and Sun. Instead, the satellite moves through space only in response to local conditions. Since spacetime is everywhere locally flat when considered on a sufficiently small scale, the satellite is always following a straight line in its local inertial frame. We say that the satellite always follows along the path of a geodesic . No evidence of gravitation can be discovered following alongside the motions of a single particle. [ 51 ] : 175–190
In any analysis of spacetime, evidence of gravitation requires that one observe the relative accelerations of two bodies or two separated particles. In Fig. 5-1, two separated particles, free-falling in the gravitational field of the Earth, exhibit tidal accelerations due to local inhomogeneities in the gravitational field such that each particle follows a different path through spacetime. The tidal accelerations that these particles exhibit with respect to each other do not require forces for their explanation. Rather, Einstein described them in terms of the geometry of spacetime, i.e. the curvature of spacetime. These tidal accelerations are strictly local. It is the cumulative total effect of many local manifestations of curvature that result in the appearance of a gravitational force acting at a long range from Earth. [ 51 ] : 175–190
Two central propositions underlie general relativity.
In Poincaré's conventionalist views, the essential criteria according to which one should select a Euclidean versus non-Euclidean geometry would be economy and simplicity. A realist would say that Einstein discovered spacetime to be non-Euclidean. A conventionalist would say that Einstein merely found it more convenient to use non-Euclidean geometry. The conventionalist would maintain that Einstein's analysis said nothing about what the geometry of spacetime really is. [ 54 ]
Such being said,
In response to the first question, a number of authors including Deser, Grishchuk, Rosen, Weinberg, etc. have provided various formulations of gravitation as a field in a flat manifold. Those theories are variously called " bimetric gravity ", the "field-theoretical approach to general relativity", and so forth. [ 55 ] [ 56 ] [ 57 ] [ 58 ] Kip Thorne has provided a popular review of these theories. [ 59 ] : 397–403
The flat spacetime paradigm posits that matter creates a gravitational field that causes rulers to shrink when they are turned from circumferential orientation to radial, and that causes the ticking rates of clocks to dilate. The flat spacetime paradigm is fully equivalent to the curved spacetime paradigm in that they both represent the same physical phenomena. However, their mathematical formulations are entirely different. Working physicists routinely switch between using curved and flat spacetime techniques depending on the requirements of the problem. The flat spacetime paradigm is convenient when performing approximate calculations in weak fields. Hence, flat spacetime techniques tend be used when solving gravitational wave problems, while curved spacetime techniques tend be used in the analysis of black holes. [ 59 ] : 397–403
The spacetime symmetry group for Special Relativity is the Poincaré group , which is a ten-dimensional group of three Lorentz boosts, three rotations, and four spacetime translations. It is logical to ask what symmetries if any might apply in General Relativity . A tractable case might be to consider the symmetries of spacetime as seen by observers located far away from all sources of the gravitational field. The naive expectation for asymptotically flat spacetime symmetries might be simply to extend and reproduce the symmetries of flat spacetime of special relativity, viz. , the Poincaré group.
In 1962 Hermann Bondi , M. G. van der Burg, A. W. Metzner [ 60 ] and Rainer K. Sachs [ 61 ] addressed this asymptotic symmetry problem in order to investigate the flow of energy at infinity due to propagating gravitational waves . Their first step was to decide on some physically sensible boundary conditions to place on the gravitational field at lightlike infinity to characterize what it means to say a metric is asymptotically flat, making no a priori assumptions about the nature of the asymptotic symmetry group—not even the assumption that such a group exists. Then after designing what they considered to be the most sensible boundary conditions, they investigated the nature of the resulting asymptotic symmetry transformations that leave invariant the form of the boundary conditions appropriate for asymptotically flat gravitational fields. [ 62 ] : 35
What they found was that the asymptotic symmetry transformations actually do form a group and the structure of this group does not depend on the particular gravitational field that happens to be present. This means that, as expected, one can separate the kinematics of spacetime from the dynamics of the gravitational field at least at spatial infinity. The puzzling surprise in 1962 was their discovery of a rich infinite-dimensional group (the so-called BMS group) as the asymptotic symmetry group, instead of the finite-dimensional Poincaré group, which is a subgroup of the BMS group. Not only are the Lorentz transformations asymptotic symmetry transformations, there are also additional transformations that are not Lorentz transformations but are asymptotic symmetry transformations. In fact, they found an additional infinity of transformation generators known as supertranslations . This implies the conclusion that General Relativity (GR) does not reduce to special relativity in the case of weak fields at long distances. [ 62 ] : 35
Riemannian geometry is the branch of differential geometry that studies Riemannian manifolds , defined as smooth manifolds with a Riemannian metric (an inner product on the tangent space at each point that varies smoothly from point to point). This gives, in particular, local notions of angle , length of curves , surface area and volume . From those, some other global quantities can be derived by integrating local contributions.
For physical reasons, a spacetime continuum is mathematically defined as a four-dimensional, smooth, connected Lorentzian manifold ( M , g ) {\displaystyle (M,g)} . This means the smooth Lorentz metric g {\displaystyle g} has signature ( 3 , 1 ) {\displaystyle (3,1)} . The metric determines the geometry of spacetime , as well as determining the geodesics of particles and light beams. About each point (event) on this manifold, coordinate charts are used to represent observers in reference frames. Usually, Cartesian coordinates ( x , y , z , t ) {\displaystyle (x,y,z,t)} are used. Moreover, for simplicity's sake, units of measurement are usually chosen such that the speed of light c {\displaystyle c} is equal to 1. [ 64 ]
A reference frame (observer) can be identified with one of these coordinate charts; any such observer can describe any event p {\displaystyle p} . Another reference frame may be identified by a second coordinate chart about p {\displaystyle p} . Two observers (one in each reference frame) may describe the same event p {\displaystyle p} but obtain different descriptions. [ 64 ]
Usually, many overlapping coordinate charts are needed to cover a manifold. Given two coordinate charts, one containing p {\displaystyle p} (representing an observer) and another containing q {\displaystyle q} (representing another observer), the intersection of the charts represents the region of spacetime in which both observers can measure physical quantities and hence compare results. The relation between the two sets of measurements is given by a non-singular coordinate transformation on this intersection. The idea of coordinate charts as local observers who can perform measurements in their vicinity also makes good physical sense, as this is how one actually collects physical data—locally. [ 64 ]
For example, two observers, one of whom is on Earth, but the other one who is on a fast rocket to Jupiter, may observe a comet crashing into Jupiter (this is the event p {\displaystyle p} ). In general, they will disagree about the exact location and timing of this impact, i.e., they will have different 4-tuples ( x , y , z , t ) {\displaystyle (x,y,z,t)} (as they are using different coordinate systems). Although their kinematic descriptions will differ, dynamical (physical) laws, such as momentum conservation and the first law of thermodynamics, will still hold. In fact, relativity theory requires more than this in the sense that it stipulates these (and all other physical) laws must take the same form in all coordinate systems. This introduces tensors into relativity, by which all physical quantities are represented.
Geodesics are said to be timelike, null, or spacelike if the tangent vector to one point of the geodesic is of this nature. Paths of particles and light beams in spacetime are represented by timelike and null (lightlike) geodesics, respectively. [ 64 ]
There are two kinds of dimensions: spatial (bidirectional) and temporal (unidirectional). [ 66 ] Let the number of spatial dimensions be N and the number of temporal dimensions be T . That N = 3 and T = 1 , setting aside the compactified dimensions invoked by string theory and undetectable to date, can be explained by appealing to the physical consequences of letting N differ from 3 and T differ from 1. The argument is often of an anthropic character and possibly the first of its kind, albeit before the complete concept came into vogue.
The implicit notion that the dimensionality of the universe is special is first attributed to Gottfried Wilhelm Leibniz , who in the Discourse on Metaphysics suggested that the world is " the one which is at the same time the simplest in hypothesis and the richest in phenomena ". [ 67 ] Immanuel Kant argued that 3-dimensional space was a consequence of the inverse square law of universal gravitation . While Kant's argument is historically important, John D. Barrow said that it "gets the punch-line back to front: it is the three-dimensionality of space that explains why we see inverse-square force laws in Nature, not vice-versa" (Barrow 2002:204). [ note 13 ]
In 1920, Paul Ehrenfest showed that if there is only a single time dimension and more than three spatial dimensions, the orbit of a planet about its Sun cannot remain stable. The same is true of a star's orbit around the center of its galaxy . [ 68 ] Ehrenfest also showed that if there are an even number of spatial dimensions, then the different parts of a wave impulse will travel at different speeds. If there are 5 + 2 k {\displaystyle 5+2k} spatial dimensions, where k is a positive whole number, then wave impulses become distorted. In 1922, Hermann Weyl claimed that Maxwell 's theory of electromagnetism can be expressed in terms of an action only for a four-dimensional manifold. [ 69 ] Finally, Tangherlini showed in 1963 that when there are more than three spatial dimensions, electron orbitals around nuclei cannot be stable; electrons would either fall into the nucleus or disperse. [ 70 ]
Max Tegmark expands on the preceding argument in the following anthropic manner. [ 71 ] If T differs from 1, the behavior of physical systems could not be predicted reliably from knowledge of the relevant partial differential equations . In such a universe, intelligent life capable of manipulating technology could not emerge. Moreover, if T > 1 , Tegmark maintains that protons and electrons would be unstable and could decay into particles having greater mass than themselves. (This is not a problem if the particles have a sufficiently low temperature.) [ 71 ] Lastly, if N < 3 , gravitation of any kind becomes problematic, and the universe would probably be too simple to contain observers. For example, when N < 3 , nerves cannot cross without intersecting. [ 71 ] Hence anthropic and other arguments rule out all cases except N = 3 and T = 1 , which describes the world around us.
On the other hand, in view of creating black holes from an ideal monatomic gas under its self-gravity, Wei-Xiang Feng showed that (3 + 1) -dimensional spacetime is the marginal dimensionality. Moreover, it is the unique dimensionality that can afford a "stable" gas sphere with a "positive" cosmological constant . However, a self-gravitating gas cannot be stably bound if the mass sphere is larger than ~10 21 solar masses, due to the small positivity of the cosmological constant observed. [ 72 ] | https://en.wikipedia.org/wiki/Spacetime |
In physics, curved spacetime is the mathematical model in which, with Einstein 's theory of general relativity , gravity naturally arises, as opposed to being described as a fundamental force in Newton's static Euclidean reference frame . Objects move along geodesics —curved paths determined by the local geometry of spacetime—rather than being influenced directly by distant bodies. This framework led to two fundamental principles: coordinate independence, which asserts that the laws of physics are the same regardless of the coordinate system used, and the equivalence principle, which states that the effects of gravity are indistinguishable from those of acceleration in sufficiently small regions of space. These principles laid the groundwork for a deeper understanding of gravity through the geometry of spacetime, as formalized in Einstein's field equations.
Newton's theories assumed that motion takes place against the backdrop of a rigid Euclidean reference frame that extends throughout all space and all time. Gravity is mediated by a mysterious force, acting instantaneously across a distance, whose actions are independent of the intervening space. [ note 1 ] In contrast, Einstein denied that there is any background Euclidean reference frame that extends throughout space. Nor is there any such thing as a force of gravitation, only the structure of spacetime itself. [ 1 ] : 175–190
In spacetime terms, the path of a satellite orbiting the Earth is not dictated by the distant influences of the Earth, Moon and Sun. Instead, the satellite moves through space only in response to local conditions. Since spacetime is everywhere locally flat when considered on a sufficiently small scale, the satellite is always following a straight line in its local inertial frame. We say that the satellite always follows along the path of a geodesic . No evidence of gravitation can be discovered following alongside the motions of a single particle. [ 1 ] : 175–190
In any analysis of spacetime, evidence of gravitation requires that one observe the relative accelerations of two bodies or two separated particles. In Fig. 5-1, two separated particles, free-falling in the gravitational field of the Earth, exhibit tidal accelerations due to local inhomogeneities in the gravitational field such that each particle follows a different path through spacetime. The tidal accelerations that these particles exhibit with respect to each other do not require forces for their explanation. Rather, Einstein described them in terms of the geometry of spacetime, i.e. the curvature of spacetime. These tidal accelerations are strictly local. It is the cumulative total effect of many local manifestations of curvature that result in the appearance of a gravitational force acting at a long range from Earth. [ 1 ] : 175–190
Two central propositions underlie general relativity.
To go from the elementary description above of curved spacetime to a complete description of gravitation requires tensor calculus and differential geometry, topics both requiring considerable study. Without these mathematical tools, it is possible to write about general relativity, but it is not possible to demonstrate any non-trivial derivations.
In the discussion of special relativity, forces played no more than a background role. Special relativity assumes the ability to define inertial frames that fill all of spacetime, all of whose clocks run at the same rate as the clock at the origin. Is this really possible? In a nonuniform gravitational field, experiment dictates that the answer is no. Gravitational fields make it impossible to construct a global inertial frame. In small enough regions of spacetime, local inertial frames are still possible. General relativity involves the systematic stitching together of these local frames into a more general picture of spacetime. [ 4 ] : 118–126
Years before publication of the general theory in 1916, Einstein used the equivalence principle to predict the existence of gravitational redshift in the following thought experiment : (i) Assume that a tower of height h (Fig. 5-3) has been constructed. (ii) Drop a particle of rest mass m from the top of the tower. It falls freely with acceleration g , reaching the ground with velocity v = (2 gh ) 1/2 , so that its total energy E , as measured by an observer on the ground, is m + 1 2 m v 2 / c 2 = m + m g h / c 2 {\displaystyle m+{{\tfrac {1}{2}}mv^{2}}/{c^{2}}=m+{mgh}/{c^{2}}} (iii) A mass-energy converter transforms the total energy of the particle into a single high energy photon, which it directs upward. (iv) At the top of the tower, an energy-mass converter transforms the energy of the photon E ' back into a particle of rest mass m ' . [ 4 ] : 118–126
It must be that m = m ' , since otherwise one would be able to construct a perpetual motion device. We therefore predict that E ' = m , so that
A photon climbing in Earth's gravitational field loses energy and is redshifted. Early attempts to measure this redshift through astronomical observations were somewhat inconclusive, but definitive laboratory observations were performed by Pound & Rebka (1959) and later by Pound & Snider (1964). [ 5 ]
Light has an associated frequency, and this frequency may be used to drive the workings of a clock. The gravitational redshift leads to an important conclusion about time itself: Gravity makes time run slower. Suppose we build two identical clocks whose rates are controlled by some stable atomic transition. Place one clock on top of the tower, while the other clock remains on the ground. An experimenter on top of the tower observes that signals from the ground clock are lower in frequency than those of the clock next to her on the tower. Light going up the tower is just a wave, and it is impossible for wave crests to disappear on the way up. Exactly as many oscillations of light arrive at the top of the tower as were emitted at the bottom. The experimenter concludes that the ground clock is running slow, and can confirm this by bringing the tower clock down to compare side by side with the ground clock. [ 6 ] : 16–18 For a 1 km tower, the discrepancy would amount to about 9.4 nanoseconds per day, easily measurable with modern instrumentation.
Clocks in a gravitational field do not all run at the same rate. Experiments such as the Pound–Rebka experiment have firmly established curvature of the time component of spacetime. The Pound–Rebka experiment says nothing about curvature of the space component of spacetime. But the theoretical arguments predicting gravitational time dilation do not depend on the details of general relativity at all. Any theory of gravity will predict gravitational time dilation if it respects the principle of equivalence. [ 6 ] : 16 This includes Newtonian gravitation. A standard demonstration in general relativity is to show how, in the " Newtonian limit " (i.e. the particles are moving slowly, the gravitational field is weak, and the field is static), curvature of time alone is sufficient to derive Newton's law of gravity. [ 7 ] : 101–106
Newtonian gravitation is a theory of curved time. General relativity is a theory of curved time and curved space. Given G as the gravitational constant, M as the mass of a Newtonian star, and orbiting bodies of insignificant mass at distance r from the star, the spacetime interval for Newtonian gravitation is one for which only the time coefficient is variable: [ 6 ] : 229–232
The ( 1 − 2 G M / ( c 2 r ) ) {\displaystyle (1-2GM/(c^{2}r))} coefficient in front of ( c Δ t ) 2 {\displaystyle (c\Delta t)^{2}} describes the curvature of time in Newtonian gravitation, and this curvature completely accounts for all Newtonian gravitational effects. As expected, this correction factor is directly proportional to G {\displaystyle G} and M {\displaystyle M} , and because of the r {\displaystyle r} in the denominator, the correction factor increases as one approaches the gravitating body, meaning that time is curved.
But general relativity is a theory of curved space and curved time, so if there are terms modifying the spatial components of the spacetime interval presented above, should not their effects be seen on, say, planetary and satellite orbits due to curvature correction factors applied to the spatial terms?
The answer is that they are seen, but the effects are tiny. The reason is that planetary velocities are extremely small compared to the speed of light, so that for planets and satellites of the Solar System , the ( c Δ t ) 2 {\displaystyle (c\Delta t)^{2}} term dwarfs the spatial terms. [ 6 ] : 234–238
Despite the minuteness of the spatial terms, the first indications that something was wrong with Newtonian gravitation were discovered over a century-and-a-half ago. In 1859, Urbain Le Verrier , in an analysis of available timed observations of transits of Mercury over the Sun's disk from 1697 to 1848, reported that known physics could not explain the orbit of Mercury, unless there possibly existed a planet or asteroid belt within the orbit of Mercury. The perihelion of Mercury's orbit exhibited an excess rate of precession over that which could be explained by the tugs of the other planets. [ 8 ] The ability to detect and accurately measure the minute value of this anomalous precession (only 43 arc seconds per tropical century ) is testimony to the sophistication of 19th century astrometry .
As the astronomer who had earlier discovered the existence of Neptune "at the tip of his pen" by analyzing irregularities in the orbit of Uranus, Le Verrier's announcement triggered a two-decades long period of "Vulcan-mania", as professional and amateur astronomers alike hunted for the hypothetical new planet. This search included several false sightings of Vulcan. It was ultimately established that no such planet or asteroid belt existed. [ 9 ]
In 1916, Einstein was to show that this anomalous precession of Mercury is explained by the spatial terms in the curvature of spacetime. Curvature in the temporal term, being simply an expression of Newtonian gravitation, has no part in explaining this anomalous precession. The success of his calculation was a powerful indication to Einstein's peers that the general theory of relativity could be correct.
The most spectacular of Einstein's predictions was his calculation that the curvature terms in the spatial components of the spacetime interval could be measured in the bending of light around a massive body. Light has a slope of ±1 on a spacetime diagram. Its movement in space is equal to its movement in time. For the weak field expression of the invariant interval, Einstein calculated an exactly equal but opposite sign curvature in its spatial components. [ 6 ] : 234–238
In Newton's gravitation, the ( 1 − 2 G M / ( c 2 r ) ) {\displaystyle (1-2GM/(c^{2}r))} coefficient in front of ( c Δ t ) 2 {\displaystyle (c\Delta t)^{2}} predicts bending of light around a star. In general relativity, the ( 1 + 2 G M / ( c 2 r ) ) {\displaystyle (1+2GM/(c^{2}r))} coefficient in front of [ ( Δ x ) 2 + ( Δ y ) 2 + ( Δ z ) 2 ] {\displaystyle \left[(\Delta x)^{2}+(\Delta y)^{2}+(\Delta z)^{2}\right]} predicts a doubling of the total bending. [ 6 ] : 234–238
The story of the 1919 Eddington eclipse expedition and Einstein's rise to fame is well told elsewhere. [ 10 ]
In Newton's theory of gravitation , the only source of gravitational force is mass .
In contrast, general relativity identifies several sources of spacetime curvature in addition to mass. In the Einstein field equations ,
the sources of gravity are presented on the right-hand side in T μ ν , {\displaystyle T_{\mu \nu },} the stress–energy tensor . [ 11 ]
Fig. 5-5 classifies the various sources of gravity in the stress–energy tensor:
One important conclusion to be derived from the equations is that, colloquially speaking, gravity itself creates gravity . [ note 2 ] Energy has mass. Even in Newtonian gravity, the gravitational field is associated with an energy, E = m g h , {\displaystyle E=mgh,} called the gravitational potential energy . In general relativity, the energy of the gravitational field feeds back into creation of the gravitational field. This makes the equations nonlinear and hard to solve in anything other than weak field cases. [ 6 ] : 240 Numerical relativity is a branch of general relativity using numerical methods to solve and analyze problems, often employing supercomputers to study black holes , gravitational waves , neutron stars and other phenomena in the strong field regime.
In special relativity, mass-energy is closely connected to momentum . Just as space and time are different aspects of a more comprehensive entity called spacetime, mass–energy and momentum are merely different aspects of a unified, four-dimensional quantity called four-momentum . In consequence, if mass–energy is a source of gravity, momentum must also be a source. The inclusion of momentum as a source of gravity leads to the prediction that moving or rotating masses can generate fields analogous to the magnetic fields generated by moving charges, a phenomenon known as gravitomagnetism . [ 12 ]
It is well known that the force of magnetism can be deduced by applying the rules of special relativity to moving charges. (An eloquent demonstration of this was presented by Feynman in volume II, chapter 13–6 of his Lectures on Physics , available online.) [ 13 ] Analogous logic can be used to demonstrate the origin of gravitomagnetism. [ 6 ] : 245–253
In Fig. 5-7a, two parallel, infinitely long streams of massive particles have equal and opposite velocities − v and + v relative to a test particle at rest and centered between the two. Because of the symmetry of the setup, the net force on the central particle is zero. Assume v ≪ c {\displaystyle v\ll c} so that velocities are simply additive. Fig. 5-7b shows exactly the same setup, but in the frame of the upper stream. The test particle has a velocity of + v , and the bottom stream has a velocity of +2 v . Since the physical situation has not changed, only the frame in which things are observed, the test particle should not be attracted towards either stream. [ 6 ] : 245–253
It is not at all clear that the forces exerted on the test particle are equal. (1) Since the bottom stream is moving faster than the top, each particle in the bottom stream has a larger mass energy than a particle in the top. (2) Because of Lorentz contraction, there are more particles per unit length in the bottom stream than in the top stream. (3) Another contribution to the active gravitational mass of the bottom stream comes from an additional pressure term which, at this point, we do not have sufficient background to discuss. All of these effects together would seemingly demand that the test particle be drawn towards the bottom stream. [ 6 ] : 245–253
The test particle is not drawn to the bottom stream because of a velocity-dependent force that serves to repel a particle that is moving in the same direction as the bottom stream. This velocity-dependent gravitational effect is gravitomagnetism. [ 6 ] : 245–253
Matter in motion through a gravitomagnetic field is hence subject to so-called frame-dragging effects analogous to electromagnetic induction . It has been proposed that such gravitomagnetic forces underlie the generation of the relativistic jets (Fig. 5-8) ejected by some rotating supermassive black holes . [ 14 ] [ 15 ]
Quantities that are directly related to energy and momentum should be sources of gravity as well, namely internal pressure and stress . Taken together, mass-energy , momentum, pressure and stress all serve as sources of gravity: Collectively, they are what tells spacetime how to curve.
General relativity predicts that pressure acts as a gravitational source with exactly the same strength as mass–energy density. The inclusion of pressure as a source of gravity leads to dramatic differences between the predictions of general relativity versus those of Newtonian gravitation. For example, the pressure term sets a maximum limit to the mass of a neutron star . The more massive a neutron star, the more pressure is required to support its weight against gravity. The increased pressure, however, adds to the gravity acting on the star's mass. Above a certain mass determined by the Tolman–Oppenheimer–Volkoff limit , the process becomes runaway and the neutron star collapses to a black hole . [ 6 ] : 243, 280
The stress terms become highly significant when performing calculations such as hydrodynamic simulations of core-collapse supernovae. [ 16 ]
These predictions for the roles of pressure, momentum and stress as sources of spacetime curvature are elegant and play an important role in theory. In regards to pressure, the early universe was radiation dominated, [ 17 ] and it is highly unlikely that any of the relevant cosmological data (e.g. nucleosynthesis abundances, etc.) could be reproduced if pressure did not contribute to gravity, or if it did not have the same strength as a source of gravity as mass–energy. Likewise, the mathematical consistency of the Einstein field equations would be broken if the stress terms did not contribute as a source of gravity.
Bondi distinguishes between different possible types of mass: (1) active mass ( m a {\displaystyle m_{a}} ) is the mass which acts as the source of a gravitational field; (2) passive mass ( m p {\displaystyle m_{p}} ) is the mass which reacts to a gravitational field; (3) inertial mass ( m i {\displaystyle m_{i}} ) is the mass which reacts to acceleration. [ 18 ]
In Newtonian theory,
In general relativity,
The classic experiment to measure the strength of a gravitational source (i.e. its active mass) was first conducted in 1797 by Henry Cavendish (Fig. 5-9a). Two small but dense balls are suspended on a fine wire, making a torsion balance . Bringing two large test masses close to the balls introduces a detectable torque. Given the dimensions of the apparatus and the measurable spring constant of the torsion wire, the gravitational constant G can be determined.
To study pressure effects by compressing the test masses is hopeless, because attainable laboratory pressures are insignificant in comparison with the mass-energy of a metal ball.
However, the repulsive electromagnetic pressures resulting from protons being tightly squeezed inside atomic nuclei are typically on the order of 10 28 atm ≈ 10 33 Pa ≈ 10 33 kg·s −2 m −1 . This amounts to about 1% of the nuclear mass density of approximately 10 18 kg/m 3 (after factoring in c 2 ≈ 9×10 16 m 2 s −2 ). [ 19 ]
If pressure does not act as a gravitational source, then the ratio m a / m p {\displaystyle m_{a}/m_{p}} should be lower for nuclei with higher atomic number Z , in which the electrostatic pressures are higher. L. B. Kreuzer (1968) did a Cavendish experiment using a Teflon mass suspended in a mixture of the liquids trichloroethylene and dibromoethane having the same buoyant density as the Teflon (Fig. 5-9b). Fluorine has atomic number Z = 9 , while bromine has Z = 35 . Kreuzer found that repositioning the Teflon mass caused no differential deflection of the torsion bar, hence establishing active mass and passive mass to be equivalent to a precision of 5×10 −5 . [ 20 ]
Although Kreuzer originally considered this experiment merely to be a test of the ratio of active mass to passive mass, Clifford Will (1976) reinterpreted the experiment as a fundamental test of the coupling of sources to gravitational fields. [ 21 ]
In 1986, Bartlett and Van Buren noted that lunar laser ranging had detected a 2 km offset between the moon's center of figure and its center of mass. This indicates an asymmetry in the distribution of Fe (abundant in the Moon's core) and Al (abundant in its crust and mantle). If pressure did not contribute equally to spacetime curvature as does mass–energy, the moon would not be in the orbit predicted by classical mechanics. They used their measurements to tighten the limits on any discrepancies between active and passive mass to about 10 −12 . [ 22 ] With decades of additional lunar laser ranging data, Singh et al. (2023) reported improvement on these limits by a factor of about 100. [ 23 ]
The existence of gravitomagnetism was proven by Gravity Probe B (GP-B) , a satellite-based mission which launched on 20 April 2004. [ 24 ] The spaceflight phase lasted until 2005 . The mission aim was to measure spacetime curvature near Earth, with particular emphasis on gravitomagnetism .
Initial results confirmed the relatively large geodetic effect (which is due to simple spacetime curvature, and is also known as de Sitter precession) to an accuracy of about 1%. The much smaller frame-dragging effect (which is due to gravitomagnetism, and is also known as Lense–Thirring precession ) was difficult to measure because of unexpected charge effects causing variable drift in the gyroscopes. Nevertheless, by August 2008 , the frame-dragging effect had been confirmed to within 15% of the expected result, [ 25 ] while the geodetic effect was confirmed to better than 0.5%. [ 26 ] [ 27 ]
Subsequent measurements of frame dragging by laser-ranging observations of the LARES , LAGEOS -1 and LAGEOS-2 satellites has improved on the GP-B measurement, with results (as of 2016) demonstrating the effect to within 5% of its theoretical value, [ 28 ] although there has been some disagreement on the accuracy of this result. [ 29 ]
Another effort, the Gyroscopes in General Relativity (GINGER) experiment, seeks to use three 6 m ring lasers mounted at right angles to each other 1400 m below the Earth's surface to measure this effect. [ 30 ] [ 31 ] The first ten years of experience with a prototype ring laser gyroscope array, GINGERINO, established that the full scale experiment should be able to measure gravitomagnetism due to the Earth's rotation to within a 0.1% level or even better. [ 32 ] | https://en.wikipedia.org/wiki/Spacetime_curvature |
A spacetime diagram is a graphical illustration of locations in space at various times, especially in the special theory of relativity . Spacetime diagrams can show the geometry underlying phenomena like time dilation and length contraction without mathematical equations.
The history of an object's location through time traces out a line or curve on a spacetime diagram, referred to as the object's world line . Each point in a spacetime diagram represents a unique position in space and time and is referred to as an event .
The most well-known class of spacetime diagrams are known as Minkowski diagrams , developed by Hermann Minkowski in 1908. Minkowski diagrams are two-dimensional graphs that depict events as happening in a universe consisting of one space dimension and one time dimension. Unlike a regular distance-time graph, the distance is displayed on the horizontal axis and time on the vertical axis. Additionally, the time and space units of measurement are chosen in such a way that an object moving at the speed of light is depicted as following a 45° angle to the diagram's axes.
In the study of 1-dimensional kinematics , position vs. time graphs (called x-t graphs for short) provide a useful means to describe motion. Kinematic features besides the object's position are visible by the slope and shape of the lines. [ 1 ] In Fig 1-1, the plotted object moves away from the origin at a positive constant velocity (1.66 m/s) for 6 seconds, halts for 5 seconds, then returns to the origin over a period of 7 seconds at a non-constant speed (but negative velocity).
At its most basic level, a spacetime diagram is merely a time vs position graph, with the directions of the axes in a usual p-t graph exchanged; that is, the vertical axis refers to temporal and the horizontal axis to spatial coordinate values. Especially when used in special relativity (SR), the temporal axes of a spacetime diagram are often scaled with the speed of light c , and thus are often labeled by ct. This changes the dimension of the addressed physical quantity from < Time > to < Length >, in accordance with the dimension associated with the spatial axis, which is frequently labeled x.
To ease insight into how spacetime coordinates, measured by observers in different reference frames , compare with each other, it is useful to standardize and simplify the setup. Two Galilean reference frames (i.e., conventional 3-space frames), S and S′ (pronounced "S prime"), each with observers O and O′ at rest in their respective frames, but measuring the other as moving with speeds ± v are said to be in standard configuration , when:
This spatial setting is displayed in the Fig 1-2, in which the temporal coordinates are separately annotated as quantities t and t' .
In a further step of simplification it is often sufficient to consider just the direction of the observed motion and ignore the other two spatial components, allowing x and ct to be plotted in 2-dimensional spacetime diagrams, as introduced above.
The black axes labelled x and ct on Fig 1-3 are the coordinate system of an observer, referred to as at rest , and who is positioned at x = 0 . This observer's world line is identical with the ct time axis. Each parallel line to this axis would correspond also to an object at rest but at another position. The blue line describes an object moving with constant speed v to the right, such as a moving observer.
This blue line labelled ct ′ may be interpreted as the time axis for the second observer. Together with the x axis, which is identical for both observers, it represents their coordinate system. Since the reference frames are in standard configuration, both observers agree on the location of the origin of their coordinate systems. The axes for the moving observer are not perpendicular to each other and the scale on their time axis is stretched. To determine the coordinates of a certain event, two lines, each parallel to one of the two axes, must be constructed passing through the event, and their intersections with the axes read off.
Determining position and time of the event A as an example in the diagram leads to the same time for both observers, as expected. Only for the position different values result, because the moving observer has approached the position of the event A since t = 0 . Generally stated, all events on a line parallel to the x axis happen simultaneously for both observers. There is only one universal time t = t ′ , modelling the existence of one common position axis. On the other hand, due to two different time axes the observers usually measure different coordinates for the same event. This graphical translation from x and t to x ′ and t ′ and vice versa is described mathematically by the so-called Galilean transformation .
The term Minkowski diagram refers to a specific form of spacetime diagram frequently used in special relativity. A Minkowski diagram is a two-dimensional graphical depiction of a portion of Minkowski space , usually where space has been curtailed to a single dimension. The units of measurement in these diagrams are taken such that the light cone at an event consists of the lines of slope plus or minus one through that event. [ 3 ] The horizontal lines correspond to the usual notion of simultaneous events for a stationary observer at the origin.
A particular Minkowski diagram illustrates the result of a Lorentz transformation . The Lorentz transformation relates two inertial frames of reference , where an observer stationary at the event (0, 0) makes a change of velocity along the x -axis. As shown in Fig 2-1, the new time axis of the observer forms an angle α with the previous time axis, with α < π / 4 . In the new frame of reference the simultaneous events lie parallel to a line inclined by α to the previous lines of simultaneity. This is the new x -axis. Both the original set of axes and the primed set of axes have the property that they are orthogonal with respect to the Minkowski inner product or relativistic dot product .
The original position on your time line (ct) is perpendicular to position A, the original position on your mutual timeline (x) where (t) is zero. This timeline where timelines come together are positioned then on the same timeline even when there are 2 different positions. The 2 positions are on the 45 degree Event line on the original position of A. Hence position A and position A’ on the Event line and (t)=0, relocate A’ back to position A.
Whatever the magnitude of α , the line ct = x forms the universal bisector , as shown in Fig 2-2.
One frequently encounters Minkowski diagrams where the time units of measurement are scaled by a factor of c such that one unit of x equals one unit of t . Such a diagram may have units of
With that, light paths are represented by lines parallel to the bisector between the axes.
The angle α between the x and x ′ axes will be identical with that between the time axes ct and ct ′ . This follows from the second postulate of special relativity, which says that the speed of light is the same for all observers, regardless of their relative motion (see below). The angle α is given by [ 4 ]
tan α = v c = β . {\displaystyle \tan \alpha ={\frac {v}{c}}=\beta .}
The corresponding boost from x and t to x ′ and t ′ and vice versa is described mathematically by the Lorentz transformation , which can be written
c t ′ = γ ( c t − β x ) , x ′ = γ ( x − β c t ) {\displaystyle {\begin{aligned}ct'&=\gamma (ct-\beta x),\\x'&=\gamma (x-\beta ct)\\\end{aligned}}}
where γ = ( 1 − β 2 ) − 1 2 {\textstyle \gamma =\left(1-\beta ^{2}\right)^{-{\frac {1}{2}}}} is the Lorentz factor . By applying the Lorentz transformation, the spacetime axes obtained for a boosted frame will always correspond to conjugate diameters of a pair of hyperbolas .
As illustrated in Fig 2-3, the boosted and unboosted spacetime axes will in general have unequal unit lengths. If U is the unit length on the axes of ct and x respectively, the unit length on the axes of ct ′ and x ′ is: [ 5 ]
U ′ = U 1 + β 2 1 − β 2 . {\displaystyle U'=U{\sqrt {\frac {1+\beta ^{2}}{1-\beta ^{2}}}}\,.}
The ct -axis represents the worldline of a clock resting in S , with U representing the duration between two events happening on this worldline, also called the proper time between these events. Length U upon the x -axis represents the rest length or proper length of a rod resting in S . The same interpretation can also be applied to distance U ′ upon the ct ′ - and x ′ -axes for clocks and rods resting in S ′ .
Albert Einstein announced his theory of special relativity in 1905, [ 6 ] with Hermann Minkowski providing his graphical representation in 1908. [ 7 ]
In Minkowski's 1908 paper there were three diagrams, first to illustrate the Lorentz transformation, then the partition of the plane by the light-cone, and finally illustration of worldlines. [ 7 ] The first diagram used a branch of the unit hyperbola t 2 − x 2 = 1 {\textstyle t^{2}-x^{2}=1} to show the locus of a unit of proper time depending on velocity, thus illustrating time dilation. The second diagram showed the conjugate hyperbola to calibrate space, where a similar stretching leaves the impression of FitzGerald contraction . In 1914 Ludwik Silberstein [ 8 ] included a diagram of "Minkowski's representation of the Lorentz transformation". This diagram included the unit hyperbola, its conjugate , and a pair of conjugate diameters . Since the 1960s a version of this more complete configuration has been referred to as The Minkowski Diagram, and used as a standard illustration of the transformation geometry of special relativity. E. T. Whittaker has pointed out that the principle of relativity is tantamount to the arbitrariness of what hyperbola radius is selected for time in the Minkowski diagram. In 1912 Gilbert N. Lewis and Edwin B. Wilson applied the methods of synthetic geometry to develop the properties of the non-Euclidean plane that has Minkowski diagrams. [ 9 ] [ 10 ] [ self-published source? ]
When Taylor and Wheeler composed Spacetime Physics (1966), they did not use the term Minkowski diagram for their spacetime geometry. Instead they included an acknowledgement of Minkowski's contribution to philosophy by the totality of his innovation of 1908. [ 11 ]
While a frame at rest in a Minkowski diagram has orthogonal spacetime axes, a frame moving relative to the rest frame in a Minkowski diagram has spacetime axes which form an acute angle. This asymmetry of Minkowski diagrams can be misleading, since special relativity postulates that any two inertial reference frames must be physically equivalent. The Loedel diagram is an alternative spacetime diagram that makes the symmetry of inertial references frames much more manifest.
Several authors showed that there is a frame of reference between the resting and moving ones where their symmetry would be apparent ("median frame"). [ 12 ] In this frame, the two other frames are moving in opposite directions with equal speed. Using such coordinates makes the units of length and time the same for both axes. If β = v / c and γ = ( 1 − β 2 ) − 1 2 {\textstyle \gamma =\left(1-\beta ^{2}\right)^{-{\frac {1}{2}}}} are given between S {\displaystyle S} and S ′ {\displaystyle S^{\prime }} , then these expressions are connected with the values in their median frame S 0 as follows: [ 12 ] [ 13 ]
( 1 ) β = 2 β 0 1 + β 0 2 , ( 2 ) β 0 = γ − 1 β γ . {\displaystyle {\begin{aligned}&(1)&\beta &={\frac {2\beta _{0}}{1+{\beta _{0}}^{2}}},\\[3pt]&(2)&\beta _{0}&={\frac {\gamma -1}{\beta \gamma }}.\end{aligned}}}
For instance, if β = 0.5 between S {\textstyle S} and S ′ {\textstyle S^{\prime }} , then by (2) they are moving in their median frame S 0 with approximately ±0.268 c each in opposite directions. On the other hand, if β 0 = 0.5 in S 0 , then by (1) the relative velocity between S {\displaystyle S} and S ′ {\displaystyle S^{\prime }} in their own rest frames is 0.8 c . The construction of the axes of S {\textstyle S} and S ′ {\textstyle S^{\prime }} is done in accordance with the ordinary method using tan α = β 0 with respect to the orthogonal axes of the median frame (Fig. 3–1).
However, it turns out that when drawing such a symmetric diagram, it is possible to derive the diagram's relations even without mentioning the median frame and β 0 at all. Instead, the relative velocity β = v / c between S {\textstyle S} and S ′ {\textstyle S^{\prime }} can directly be used in the following construction, providing the same result: [ 14 ]
If φ is the angle between the axes of ct ′ and ct (or between x and x ′ ), and θ between the axes of x ′ and ct ′ , it is given: [ 14 ] [ 15 ] [ 16 ] [ 17 ]
sin φ = cos θ = β , cos φ = sin θ = 1 γ , tan φ = cot θ = β γ . {\displaystyle {\begin{aligned}\sin \varphi =\cos \theta &=\beta ,\\\cos \varphi =\sin \theta &={\frac {1}{\gamma }},\\\tan \varphi =\cot \theta &=\beta \gamma .\end{aligned}}}
Two methods of construction are obvious from Fig. 3-2: the x -axis is drawn perpendicular to the ct ′ -axis, the x ′ and ct -axes are added at angle φ ; and the x ′-axis is drawn at angle θ with respect to the ct ′ -axis, the x -axis is added perpendicular to the ct ′ -axis and the ct -axis perpendicular to the x ′ -axis.
In a Minkowski diagram, lengths on the page cannot be directly compared to each other, due to warping factor between the axes' unit lengths in a Minkowski diagram. In particular, if U {\textstyle U} and U ′ {\textstyle U^{\prime }} are the unit lengths of the rest frame axes and moving frame axes, respectively, in a Minkowski diagram, then the two unit lengths are warped relative to each other via the formula:
U ′ = U 1 + β 2 1 − β 2 {\displaystyle U^{\prime }=U{\sqrt {\frac {1+\beta ^{2}}{1-\beta ^{2}}}}}
By contrast, in a symmetric Loedel diagram, both the S {\textstyle S} and S ′ {\textstyle S^{\prime }} frame axes are warped by the same factor relative to the median frame and hence have identical unit lengths. This implies that, for a Loedel spacetime diagram, we can directly compare spacetime lengths between different frames as they appear on the page; no unit length scaling/conversion between frames is necessary due to the symmetric nature of the Loedel diagram.
Relativistic time dilation refers to the fact that a clock (indicating its proper time in its rest frame) that moves relative to an observer is observed to run slower. The situation is depicted in the symmetric Loedel diagrams of Fig 4-1. Note that we can compare spacetime lengths on page directly with each other, due to the symmetric nature of the Loedel diagram.
In Fig 4-2, the observer whose reference frame is given by the black axes is assumed to move from the origin O towards A. The moving clock has the reference frame given by the blue axes and moves from O to B. For the black observer, all events happening simultaneously with the event at A are located on a straight line parallel to its space axis. This line passes through A and B, so A and B are simultaneous from the reference frame of the observer with black axes. However, the clock that is moving relative to the black observer marks off time along the blue time axis. This is represented by the distance from O to B. Therefore, the observer at A with the black axes notices their clock as reading the distance from O to A while they observe the clock moving relative him or her to read the distance from O to B. Due to the distance from O to B being smaller than the distance from O to A, they conclude that the time passed on the clock moving relative to them is smaller than that passed on their own clock.
A second observer, having moved together with the clock from O to B, will argue that the black axis clock has only reached C and therefore runs slower. The reason for these apparently paradoxical statements is the different determination of the events happening synchronously at different locations. Due to the principle of relativity, the question of who is right has no answer and does not make sense.
Relativistic length contraction refers to the fact that a ruler (indicating its proper length in its rest frame) that moves relative to an observer is observed to contract/shorten. The situation is depicted in symmetric Loedel diagrams in Fig 4-3. Note that we can compare spacetime lengths on page directly with each other, due to the symmetric nature of the Loedel diagram.
In Fig 4-4, the observer is assumed again to move along the ct -axis. The world lines of the endpoints of an object moving relative to him are assumed to move along the ct ′ -axis and the parallel line passing through A and B. For this observer the endpoints of the object at t = 0 are O and A. For a second observer moving together with the object, so that for him the object is at rest, it has the proper length OB at t ′ = 0 . Due to OA < OB . the object is contracted for the first observer.
The second observer will argue that the first observer has evaluated the endpoints of the object at O and A respectively and therefore at different times, leading to a wrong result due to his motion in the meantime. If the second observer investigates the length of another object with endpoints moving along the ct -axis and a parallel line passing through C and D he concludes the same way this object to be contracted from OD to OC. Each observer estimates objects moving with the other observer to be contracted. This apparently paradoxical situation is again a consequence of the relativity of simultaneity as demonstrated by the analysis via Minkowski diagram.
For all these considerations it was assumed, that both observers take into account the speed of light and their distance to all events they see in order to determine the actual times at which these events happen from their point of view.
Another postulate of special relativity is the constancy of the speed of light. It says that any observer in an inertial reference frame measuring the vacuum speed of light relative to themself obtains the same value regardless of his own motion and that of the light source. This statement seems to be paradoxical, but it follows immediately from the differential equation yielding this, and the Minkowski diagram agrees. It explains also the result of the Michelson–Morley experiment which was considered to be a mystery before the theory of relativity was discovered, when photons were thought to be waves through an undetectable medium.
For world lines of photons passing the origin in different directions x = ct and x = − ct holds. That means any position on such a world line corresponds with steps on x - and ct -axes of equal absolute value. From the rule for reading off coordinates in coordinate system with tilted axes follows that the two world lines are the angle bisectors of the x - and ct -axes. As shown in Fig 4-5, the Minkowski diagram illustrates them as being angle bisectors of the x′ - and ct ′ -axes as well. That means both observers measure the same speed c for both photons.
Further coordinate systems corresponding to observers with arbitrary velocities can be added to this Minkowski diagram. For all these systems both photon world lines represent the angle bisectors of the axes. The more the relative speed approaches the speed of light the more the axes approach the corresponding angle bisector. The x {\textstyle x} axis is always more flat and the time axis more steep than the photon world lines. The scales on both axes are always identical, but usually different from those of the other coordinate systems.
Straight lines passing the origin which are steeper than both photon world lines correspond with objects moving more slowly than the speed of light. If this applies to an object, then it applies from the viewpoint of all observers, because the world lines of these photons are the angle bisectors for any inertial reference frame. Therefore, any point above the origin and between the world lines of both photons can be reached with a speed smaller than that of the light and can have a cause-and-effect relationship with the origin. This area is the absolute future, because any event there happens later compared to the event represented by the origin regardless of the observer, which is obvious graphically from the Minkowski diagram in Fig 4-6.
Following the same argument the range below the origin and between the photon world lines is the absolute past relative to the origin. Any event there belongs definitely to the past and can be the cause of an effect at the origin.
The relationship between any such pairs of event is called timelike , because they have a time distance greater than zero for all observers. A straight line connecting these two events is always the time axis of a possible observer for whom they happen at the same place. Two events which can be connected just with the speed of light are called lightlike .
In principle a further dimension of space can be added to the Minkowski diagram leading to a three-dimensional representation. In this case the ranges of future and past become cones with apexes touching each other at the origin. They are called light cones .
Following the same argument, all straight lines passing through the origin and which are more nearly horizontal than the photon world lines, would correspond to objects or signals moving faster than light regardless of the speed of the observer. Therefore, no event outside the light cones can be reached from the origin, even by a light-signal, nor by any object or signal moving with less than the speed of light. Such pairs of events are called spacelike because they have a finite spatial distance different from zero for all observers. On the other hand, a straight line connecting such events is always the space coordinate axis of a possible observer for whom they happen at the same time. By a slight variation of the velocity of this coordinate system in both directions it is always possible to find two inertial reference frames whose observers estimate the chronological order of these events to be different.
Given an object moving faster than light, say from O to A in Fig 4-7, then for any observer watching the object moving from O to A, another observer can be found (moving at less than the speed of light with respect to the first) for whom the object moves from A to O. The question of which observer is right has no unique answer, and therefore makes no physical sense. Any such moving object or signal would violate the principle of causality.
Also, any general technical means of sending signals faster than light would permit information to be sent into the originator's own past. In the diagram, an observer at O in the x - ct system sends a message moving faster than light to A. At A, it is received by another observer, moving so as to be in the x ′- ct ′ system, who sends it back, again faster than light, arriving at B. But B is in the past relative to O. The absurdity of this process becomes obvious when both observers subsequently confirm that they received no message at all, but all messages were directed towards the other observer as can be seen graphically in the Minkowski diagram. Furthermore, if it were possible to accelerate an observer to the speed of light, their space and time axes would coincide with their angle bisector. The coordinate system would collapse, in concordance with the fact that due to time dilation , time would effectively stop passing for them.
These considerations show that the speed of light as a limit is a consequence of the properties of spacetime, and not of the properties of objects such as technologically imperfect space ships. The prohibition of faster-than-light motion, therefore, has nothing in particular to do with electromagnetic waves or light, but comes as a consequence of the structure of spacetime.
It is often, incorrectly, asserted that special relativity cannot handle accelerating particles or accelerating reference frames. In reality, accelerating particles present no difficulty at all in special relativity. On the other hand, accelerating frames do require some special treatment, However, as long as one is dealing with flat, Minkowskian spacetime, special relativity can handle the situation. It is only in the presence of gravitation that general relativity is required. [ 29 ]
An accelerating particle's 4-vector acceleration is the derivative with respect to proper time of its 4-velocity. This is not a difficult situation to handle. Accelerating frames require that one understand the concept of a momentarily comoving reference frame (MCRF), which is to say, a frame traveling at the same instantaneous velocity of a particle at any given instant.
Consider the animation in Fig 5–1. The curved line represents the world line of a particle that undergoes continuous acceleration, including complete changes of direction in the positive and negative x -directions. The red axes are the axes of the MCRF for each point along the particle's trajectory. The coordinates of events in the unprimed (stationary) frame can be related to their coordinates in any momentarily co-moving primed frame using the Lorentz transformations.
Fig 5-2 illustrates the changing views of spacetime along the world line of a rapidly accelerating particle. The c t ′ {\textstyle ct'} axis (not drawn) is vertical, while the x ′ {\textstyle x'} axis (not drawn) is horizontal. The dashed line is the spacetime trajectory ("world line") of the particle. The balls are placed at regular intervals of proper time along the world line. The solid diagonal lines are the light cones for the observer's current event, and they intersect at that event. The small dots are other arbitrary events in the spacetime.
The slope of the world line (deviation from being vertical) is the velocity of the particle on that section of the world line. Bends in the world line represent particle acceleration. As the particle accelerates, its view of spacetime changes. These changes in view are governed by the Lorentz transformations. Also note that:
If one imagines each event to be the flashing of a light, then the events that are within the past light cone of the observer are the events visible to the observer. The slope of the world line (deviation from being vertical) gives the velocity relative to the observer.
The photon world lines are determined using the metric with d τ = 0 {\textstyle d\tau =0} . [ 30 ] The light cones are deformed according to the position. In an inertial reference frame a free particle has a straight world line. In a non-inertial reference frame the world line of a free particle is curved.
Take the example of the fall of an object dropped without initial velocity from a rocket. The rocket has a uniformly accelerated motion with respect to an inertial reference frame. As can be seen from Fig 6-2 of a Minkowski diagram in a non-inertial reference frame, the object once dropped, gains speed, reaches a maximum, and then sees its speed decrease and asymptotically cancel on the horizon where its proper time freezes at t H {\textstyle t_{\text{H}}} . The velocity is measured by an observer at rest in the accelerated rocket.
Media related to Minkowski diagrams at Wikimedia Commons | https://en.wikipedia.org/wiki/Spacetime_diagram |
Spacetime symmetries are features of spacetime that can be described as exhibiting some form of symmetry . The role of symmetry in physics is important in simplifying solutions to many problems. Spacetime symmetries are used in the study of exact solutions of Einstein's field equations of general relativity . Spacetime symmetries are distinguished from internal symmetries .
Physical problems are often investigated and solved by noticing features which have some form of symmetry. For example, in the Schwarzschild solution , the role of spherical symmetry is important in deriving the Schwarzschild solution and deducing the physical consequences of this symmetry (such as the nonexistence of gravitational radiation in a spherically pulsating star). In cosmological problems, symmetry plays a role in the cosmological principle , which restricts the type of universes that are consistent with large-scale observations (e.g. the Friedmann–Lemaître–Robertson–Walker (FLRW) metric ). Symmetries usually require some form of preserving property, the most important of which in general relativity include the following:
These and other symmetries will be discussed below in more detail. This preservation property which symmetries usually possess (alluded to above) can be used to motivate a useful definition of these symmetries themselves.
A rigorous definition of symmetries in general relativity has been given by Hall (2004). In this approach, the idea is to use (smooth) vector fields whose local flow diffeomorphisms preserve some property of the spacetime . (Note that one should emphasize in one's thinking this is a diffeomorphism—a transformation on a differential element. The implication is that the behavior of objects with extent may not be as manifestly symmetric.) This preserving property of the diffeomorphisms is made precise as follows. A smooth vector field X on a spacetime M is said to preserve a smooth tensor T on M (or T is invariant under X ) if, for each smooth local flow diffeomorphism ϕ t associated with X , the tensors T and ϕ ∗ t ( T ) are equal on the domain of ϕ t . This statement is equivalent to the more usable condition that the Lie derivative of the tensor under the vector field vanishes: L X T = 0 {\displaystyle {\mathcal {L}}_{X}T=0} on M . This has the consequence that, given any two points p and q on M , the coordinates of T in a coordinate system around p are equal to the coordinates of T in a coordinate system around q . A symmetry on the spacetime is a smooth vector field whose local flow diffeomorphisms preserve some (usually geometrical) feature of the spacetime. The (geometrical) feature may refer to specific tensors (such as the metric, or the energy–momentum tensor) or to other aspects of the spacetime such as its geodesic structure. The vector fields are sometimes referred to as collineations , symmetry vector fields or just symmetries . The set of all symmetry vector fields on M forms a Lie algebra under the Lie bracket operation as can be seen from the identity: L [ X , Y ] T = L X ( L Y T ) − L Y ( L X T ) {\displaystyle {\mathcal {L}}_{[X,Y]}T={\mathcal {L}}_{X}({\mathcal {L}}_{Y}T)-{\mathcal {L}}_{Y}({\mathcal {L}}_{X}T)} the term on the right usually being written, with an abuse of notation , as [ L X , L Y ] T . {\displaystyle [{\mathcal {L}}_{X},{\mathcal {L}}_{Y}]T.}
A Killing vector field is one of the most important types of symmetries and is defined to be a smooth vector field X that preserves the metric tensor g : L X g = 0. {\displaystyle {\mathcal {L}}_{X}g=0.}
This is usually written in the expanded form as: X a ; b + X b ; a = 0. {\displaystyle X_{a;b}+X_{b;a}=0.}
Killing vector fields find extensive applications (including in classical mechanics ) and are related to conservation laws .
A homothetic vector field is one which satisfies: L X g = 2 c g . {\displaystyle {\mathcal {L}}_{X}g=2cg.} where c is a real constant. Homothetic vector fields find application in the study of singularities in general relativity.
An affine vector field is one that satisfies: ( L X g ) a b ; c = 0 {\displaystyle ({\mathcal {L}}_{X}g)_{ab;c}=0}
An affine vector field preserves geodesics and preserves the affine parameter.
The above three vector field types are special cases of projective vector fields which preserve geodesics without necessarily preserving the affine parameter.
A conformal vector field is one which satisfies: L X g = ϕ g {\displaystyle {\mathcal {L}}_{X}g=\phi g} where ϕ is a smooth real-valued function on M .
A curvature collineation is a vector field which preserves the Riemann tensor : L X R a b c d = 0 {\displaystyle {\mathcal {L}}_{X}{R^{a}}_{bcd}=0}
where R a bcd are the components of the Riemann tensor. The set of all smooth curvature collineations forms a Lie algebra under the Lie bracket operation (if the smoothness condition is dropped, the set of all curvature collineations need not form a Lie algebra). The Lie algebra is denoted by CC ( M ) and may be infinite - dimensional . Every affine vector field is a curvature collineation.
A less well-known form of symmetry concerns vector fields that preserve the energy–momentum tensor. These are variously referred to as matter collineations or matter symmetries and are defined by: L X T = 0 {\displaystyle {\mathcal {L}}_{X}T=0} where T is the covariant energy–momentum tensor. The intimate relation between geometry and physics may be highlighted here, as the vector field X is regarded as preserving certain physical quantities along the flow lines of X , this being true for any two observers. In connection with this, it may be shown that every Killing vector field is a matter collineation (by the Einstein field equations, with or without cosmological constant ). Thus, given a solution of the EFE, a vector field that preserves the metric necessarily preserves the corresponding energy–momentum tensor . When the energy–momentum tensor represents a perfect fluid, every Killing vector field preserves the energy density, pressure and the fluid flow vector field. When the energy–momentum tensor represents an electromagnetic field, a Killing vector field does not necessarily preserve the electric and magnetic fields.
As mentioned at the start of this article, the main application of these symmetries occur in general relativity, where solutions of Einstein's equations may be classified by imposing some certain symmetries on the spacetime.
Classifying solutions of the EFE constitutes a large part of general relativity research. Various approaches to classifying spacetimes, including using the Segre classification of the energy–momentum tensor or the Petrov classification of the Weyl tensor have been studied extensively by many researchers, most notably Stephani et al. (2003). They also classify spacetimes using symmetry vector fields (especially Killing and homothetic symmetries). For example, Killing vector fields may be used to classify spacetimes, as there is a limit to the number of global, smooth Killing vector fields that a spacetime may possess (the maximum being ten for four-dimensional spacetimes). Generally speaking, the higher the dimension of the algebra of symmetry vector fields on a spacetime, the more symmetry the spacetime admits. For example, the Schwarzschild solution has a Killing algebra of dimension four (three spatial rotational vector fields and a time translation), whereas the Friedmann–Lemaître–Robertson–Walker metric (excluding the Einstein static subcase) has a Killing algebra of dimension six (three translations and three rotations). The Einstein static metric has a Killing algebra of dimension seven (the previous six plus a time translation).
The assumption of a spacetime admitting a certain symmetry vector field can place restrictions on the spacetime.
The following spacetimes have their own distinct articles in Wikipedia: | https://en.wikipedia.org/wiki/Spacetime_symmetries |
Spaceworthiness , [ 1 ] [ 2 ] or aerospaceworthiness , [ 3 ] is a property , or ability of a spacecraft to perform to its design objectives and navigate successfully through both the space environment and the atmosphere as a part of a journey to or from space. The concept may less commonly be extended to other devices, such as spacesuits , which are designed to spend some amount of time exposed to space.
As in airworthiness , the spaceworthiness of a spacecraft depends on at least three basic components: [ 4 ] [ 5 ]
Spaceworthiness is typically maintained through a maintenance program and / or a system of analysis , diagnosis and management of health and reliability of the spacecraft. [ 8 ] [ 9 ] [ 10 ] [ 11 ] [ 12 ]
Spaceworthiness of launch vehicles and spacecraft is an extension of the concepts of roadworthiness for cars , railworthiness for trains , seaworthiness for boats and ships , and airworthiness for aircraft . | https://en.wikipedia.org/wiki/Spaceworthiness |
A spaghetti bridge is an architectural model of a bridge , made of uncooked spaghetti or other hard, dry, straight noodles. Bridges are constructed for both educational experiments and competitions. The aim is usually to construct a bridge with a specific quantity of materials over a specific span, that can sustain a load. In competitions, the bridge that can hold the greatest load for a short period of time wins the contest. [ 1 ] [ better source needed ] There are many contests around the world, usually held by schools and colleges.
The original Spaghetti Bridge competition has run at Okanagan College in British Columbia since 1983, [ 2 ] and is open to international entrants [ 3 ] who are full-time secondary or post-secondary students.
The winners of the 2009 competition were Norbert Pozsonyi and Aliz Totivan of the Szechenyi Istvan University of Győr in Hungary . They won $1,500 with a bridge that weighed 982 grams and held 443.58 kg. Second place went to Brendon Syryda and Tyler Pearson of Okanagan College with a bridge that weighed 982 grams and held 98.71 kg. [ 4 ]
Spaghetti bridge building contests around the world include:
Winston Science http://www.winston-school.org/?PageName=LatestNews&Section=Highlights&ItemID=106650&ISrc=School&Itype=Highlights&SchoolID=4831
- Estimating the weight and the failure load of a spaghetti bridge: a deep learning approach DOI:10.1080/0952813X.2019.1694590 | https://en.wikipedia.org/wiki/Spaghetti_bridge |
Spaghetti code is a pejorative phrase for difficult-to- maintain and unstructured computer source code . Code being developed with poor structure can be due to any of several factors, such as volatile project requirements, lack of programming style rules, and software engineers with insufficient ability or experience. [ 1 ]
Code that overuses GOTO statements rather than structured programming constructs, resulting in convoluted and unmaintainable programs, is often called spaghetti code. [ 2 ] Such code has a complex and tangled control structure , resulting in a program flow that is conceptually like a bowl of spaghetti , twisted and tangled. [ 3 ]
In a 1980 publication by the United States National Bureau of Standards , the phrase spaghetti program was used to describe older programs having "fragmented and scattered files". [ 4 ]
Spaghetti code can also describe an anti-pattern in which object-oriented code is written in a procedural style, such as by creating classes whose methods are overly long and messy, or forsaking object-oriented concepts like polymorphism . [ 5 ] The presence of this form of spaghetti code can significantly reduce the comprehensibility of a system. [ 6 ]
It is not clear when the phrase spaghetti code came into common usage; however, a references appeared in 1972 including The principal motivation behind eliminating the goto statement is the hope that the resulting programs will not look like a bowl of spaghetti. by Martin Hopkins . [ 7 ] In the 1978 book A primer on disciplined programming using PL/I, PL/CS, and PL/CT , Richard Conway described programs that "have the same clean logical structure as a plate of spaghetti", [ 8 ] a phrase repeated in the 1979 book An Introduction to Programming he co-authored with David Gries . [ 9 ] In the 1988 paper A spiral model of software development and enhancement , the term is used to describe the older practice of the code and fix model , which lacked planning and eventually led to the development of the waterfall model . [ 10 ] In the 1979 book Structured programming for the COBOL programmer , author Paul Noll uses the phrases spaghetti code and rat's nest as synonyms to describe poorly structured source code. [ 11 ]
In the Ada – Europe '93 conference, Ada was described as forcing the programmer to "produce understandable, instead of spaghetti code", because of its restrictive exception propagation mechanism. [ 12 ]
In a 1981 computer languages spoof in The Michigan Technic titled "BASICally speaking...FORTRAN bytes!!", the author described FORTRAN stating that "it consists entirely of spaghetti code". [ 13 ]
Richard Hamming described in his lectures [ 14 ] the etymology of the term in the context of early programming in binary codes:
If, in fixing up an error, you wanted to insert some omitted instructions then you took the immediately preceding instruction and replaced it by a transfer to some empty space. There you put in the instruction you just wrote over, added the instructions you wanted to insert, and then followed by a transfer back to the main program. Thus the program soon became a sequence of jumps of the control to strange places. When, as almost always happens, there were errors in the corrections you then used the same trick again, using some other available space. As a result the control path of the program through storage soon took on the appearance of a can of spaghetti. Why not simply insert them in the run of instructions? Because then you would have to go over the entire program and change all the addresses which referred to any of the moved instructions! Anything but that!
Ravioli code is a term specific to object-oriented programming . It describes code that comprises well-structured classes that are easy to understand in isolation, but difficult to understand as a whole. [ 15 ]
Lasagna code refers to code whose layers are so complicated and intertwined that making a change in one layer would necessitate changes in all other layers. [ 16 ]
Here follows what would be considered a trivial example of spaghetti code in BASIC . The program prints each of the numbers 1 to 100 to the screen along with its square. Indentation is not used to differentiate the various actions performed by the code, and the program's GOTO statements create a reliance on line numbers . The flow of execution from one area to another is harder to predict. Real-world occurrences of spaghetti code are more complex and can add greatly to a program's maintenance costs.
Here is the same code written in a structured programming style:
The program jumps from one area to another, but this jumping is formal and more easily predictable, because for loops and functions provide flow control whereas the goto statement encourages arbitrary flow control. Though this example is small, real world programs are composed of many lines of code and are difficult to maintain when written in a spaghetti code fashion.
Here is another example of spaghetti code with embedded GOTO statements. | https://en.wikipedia.org/wiki/Spaghetti_code |
Paracelsianism (also Paracelsism ; German: Paracelsismus ) was an early modern medical movement based on the theories and therapies of Paracelsus .
It developed in the second half of the 16th century, during the decades following Paracelsus's death in 1541, and it flourished during the first half of the 17th century, representing one of the most comprehensive alternatives to learned medicine , the traditional system of therapeutics derived from Galenic physiology .
Based on the by then antiquated principle of maintaining harmony between the microcosm and macrocosm , Paracelsianism fell rapidly into decline in the later 17th century with the rise of the scientific movement, [ 1 ] but left its mark on medical practices. It was responsible for the widespread introduction of mineral therapies and several other iatrochemical techniques.
Spagyric , or spagyria , is a method developed by Paracelsus and his followers which was thought to improve the efficacy of existing medicines by separating them into their primordial elements (the tria prima : sulphur, mercury, and salt) and then again recombining them. Paracelsian physicians held that through this method the medically beneficial ingredients of a compound (the purified tria prima ) were separated from the harmful and toxic ones, turning even some poisons into medicines. [ 2 ]
This procedure involved fermentation , distillation , and extraction of mineral components from the ash of the plant . These processes were in use in medieval alchemy generally for the separation and purification of metals from ores (see Calcination ), and salts from brines and other aqueous solutions . [ citation needed ]
Originally coined by Paracelsus, the word comes from the Ancient Greek σπάω spao ('to separate, to draw out') and ἀγείρω ageiro ('to combine', 'to recombine', 'to gather'). [ 3 ] In its original use, the word spagyric was commonly used synonymously with the word alchemy , however, in more recent times it has often been adopted by alternative medicine theorists and various techniques of holistic medicine . [ citation needed ] | https://en.wikipedia.org/wiki/Spagyric |
Spall are fragments of a material that are broken off a larger solid body . It can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion , weathering , cavitation , or excessive rolling pressure (as in a ball bearing ). Spalling and spallation both describe the process of surface failure in which spall is shed.
The terms spall , spalling , and spallation have been adopted by particle physicists ; in neutron scattering instruments, neutrons are generated by bombarding a uranium (or other) target with a stream of atoms . The neutrons that are ejected from the target are known as "spall".
Mechanical spalling occurs at high-stress contact points, for example, in a ball bearing . Spalling occurs in preference to brinelling , where the maximal shear stress occurs not at the surface, but just below, shearing the spall off.
One of the simplest forms of mechanical spalling is plate impact, in which two waves of compression are reflected on the free-surfaces of the plates and then interact to generate a region of high tensile stress inside one of the plates.
Spalling can also occur as an effect of cavitation , where fluids are subjected to localized low pressures that cause vapour bubbles to form, typically in pumps, water turbines, vessel propellers, and even piping under some conditions. When such bubbles collapse, a localized high pressure can cause spalling on adjacent surfaces.
In anti-tank warfare , spalling through mechanical stress is an intended effect of high-explosive squash head (HESH) anti-tank shells and many other munitions, which may not be powerful enough to pierce the armour of a target. The relatively soft warhead, containing or made of plastic explosive, flattens against the armour plating on tanks and other armoured fighting vehicles (AFVs) and explodes, creating a shock wave that travels through the armour as a compression wave and is reflected at the free surface as a tensile wave breaking (tensile stress/strain fracture) the metal on the inside. The resulting spall is dangerous to crew and equipment, and may result in a partial or complete disablement of a vehicle and/or its crew. Many AFVs are equipped with spall liners inside their armour for protection.
A kinetic energy penetrator , if it can defeat the armour, generally causes spalling within the target as well, which helps to destroy or disable the vehicle and its crew. [ 1 ]
An early example of anti-tank weapon intentionally designed to cause spallation instead of penetration is the wz. 35 anti-tank rifle .
Spalling is a common mechanism of rock weathering, and occurs at the surface of a rock when there are large shear stresses under the surface. This form of mechanical weathering can be caused by freezing and thawing, unloading, thermal expansion and contraction, or salt deposition.
Unloading is the release of pressure due to the removal of an overburden. When the pressure is reduced rapidly, the rapid expansion of the rock causes high surface stress and spalling.
Freeze–thaw weathering is caused by moisture freezing inside cracks in rock. Upon freezing its volume expands, causing large forces which cracks spall off the outer surface. As this cycle repeats the outer surface repeatedly undergoes spalling, resulting in weathering.
Some stone and masonry surfaces used as building surfaces will absorb moisture at their surface. If exposed to severe freezing conditions, the surface may flake off due to the expansion of the water. This effect can also be seen in terracotta surfaces (even if glazed) if there is an entrance for water at the edges.
Exfoliation (or onion skin weathering) is the gradual removing of spall due to the cyclic increase and decrease in the temperature of the surface layers of the rock. Rocks do not conduct heat well, so when they are exposed to extreme heat, the outermost layer becomes much hotter than the rock underneath causing differential thermal expansion . This differential expansion causes sub-surface shear stress, in turn causing spalling. Extreme temperature change, such as forest fires, can also cause spalling of rock. This mechanism of weathering causes the outer surface of the rock to fall off in thin fragments, sheets or flakes, hence the name exfoliation or onion skin weathering.
Salt spalling is a specific type of weathering which occurs in porous building materials , such as brick, natural stone, tiles and concrete. Dissolved salt is carried through the material in water and crystallizes inside the material near the surface as the water evaporates. As the salt crystals expand this builds up shear stresses which break away spall from the surface.
In corrosion, spalling occurs when a substance ( metal or concrete ) sheds tiny particles of corrosion products as the corrosion reaction progresses. Although they are not soluble or permeable, these corrosion products do not adhere to the parent material's surface to form a barrier to further corrosion, as happens in passivation . Spallation happens as the result of a large volume change during the reaction.
In the case of actinide metals (most notably the depleted uranium used in some types of ammunition ), the material expands so strongly upon exposure to air that a fine layer of oxide is forcibly expelled from the surface. A slowly oxidised plug of metallic uranium can sometimes resemble an onion subjected to desquamation . The main hazard however arises from the pyrophoric character of actinide metals which can spontaneously ignite when their specific area is high. This property, along with the inherent toxicity and (for some to a lesser extent) radioactivity of these elements, make them dangerous to handle in metallic form under air. Therefore, they are often handled under an inert atmosphere ( nitrogen or argon ) inside an anaerobic glovebox .
There are two drivers for spalling of concrete: thermal strain caused by rapid heating and internal pressures due to the removal of water. Being able to predict the outcome of different heating rates on thermal stresses and internal pressure during water removal is particularly important to industry and other concrete structures.
Explosive spalling events of refractory concrete can result in serious problems. If an explosive spalling occurs, projectiles of reasonable mass (1–10 kg) can be thrust violently over many metres, which will have safety implications and render the refractory structure unfit for service. Repairs will then be required resulting in significant costs to industry. [ 2 ] [ failed verification ]
Blast-wave overpressure from explosions can cause spalling in the human body where the wave travels across the interface between denser to less-dense areas of anatomy. This is notable at the boundary between liquid and air, for example from the bowel wall to a gas-filled bowel, or from lung tissue to cavity. Spallation, implosion, and shearing are the three primary mechanisms known to cause blast injuries . [ 3 ] [ 4 ] | https://en.wikipedia.org/wiki/Spall |
Spalting is any form of wood coloration caused by fungi . Although primarily found in dead trees , spalting can also occur in living trees under stress . Although spalting can cause weight loss and strength loss in the wood, the unique coloration and patterns of spalted wood are sought by woodworkers . [ 1 ]
Spalting is divided into three main types: pigmentation , white rot, and zone lines. Spalted wood may exhibit one or all of these types in varying degrees. Both hardwoods ( deciduous ) and softwoods ( coniferous ) can spalt, but zone lines and white rot are more commonly found on hardwoods due to enzymatic differences in white rotting fungi. Brown rots are more common to conifers, although one brown rot, Fistulina hepatica (beefsteak fungus), is known to cause spalting among deciduous trees. [ 2 ]
Pigmentation is caused when fungi produce extracellular pigments inside wood. Bluestain is also a form of pigmentation; however, bluestain pigments are generally bound within the hyphae cell walls. [ 3 ] [ 4 ] A visible color change can be seen if enough hyphae are concentrated in an area. [ 5 ] Pigmenting fungi classified as spalting fungi do decay wood, they simply do so at a slower rate (soft rotting) than white rotting fungi. [ 6 ] [ 7 ] The most common groups of pigmentation fungi are the imperfect fungi and the ascomycetes . [ 8 ] Mold fungi, such as Trichoderma spp., are not considered to be spalting fungi, as their hyphae do not colonize the wood internally and they do not produce the enzymes necessary to digest the wood cell wall components.
The mottled white pockets and bleaching effect seen in spalted wood is due to white rot fungi. Primarily found on hardwoods, these fungi "bleach" by consuming lignin , which is the slightly pigmented area of a wood cell wall. [ 9 ] Some white rotting can also be caused by an effect similar to pigmentation, in which the white hyphae of a fungus, such as Trametes versicolor (Fr.) Pil., is so concentrated in an area that a visual effect is created. [ 10 ]
Both strength and weight loss occur with white rot decay, causing the "punky" area often referred to by woodworkers. Brown rots, the "unpleasing" type of spalting, do not degrade lignin, thus creating a crumbly, cracked surface which cannot be stabilized. [ 5 ] Both types of rot, if uncontrolled, will render wood useless.
Dark dotting, winding lines and thin streaks of red, brown and black are known as zone lines . This type of spalting does not occur due to any specific type of fungus, but is instead an interaction zone in which different fungi have erected barriers to protect their resources. [ 8 ] They can also be caused by a single fungus delineating itself. The lines are often clumps of hard, dark mycelium , referred to as pseudosclerotial plate formation. [ 11 ]
Zone lines themselves do not damage the wood. However, the fungi responsible for creating them often do. Spalted wood is also sometimes known as web wood.
Conditions required for spalting are the same as the conditions required for fungal growth: fixed nitrogen, micronutrients , water, warm temperatures and oxygen. [ 5 ] [ 12 ]
Water: Wood must be saturated to a 20% moisture content or higher for fungal colonization to occur. Wood placed underwater lacks sufficient oxygen, and colonization cannot occur. [ 13 ]
Temperature: The majority of fungi prefer warm temperatures between 10 and 40 °C, [ 13 ] with rapid growth occurring between 20 and 32 °C. [ 14 ]
Oxygen: Fungi do not require much oxygen, but conditions such as waterlogging will inhibit growth. [ 15 ] [ 16 ]
Time: Different fungi require different amounts of time to colonize wood. Research conducted on some common spalting fungi found that Trametes versicolor , when paired with Bjerkandera adusta , took eight weeks to spalt 1.5 inch (38 mm) cubes of Acer saccharum . [ 1 ] Colonization continued to progress after this time period, but the structural integrity of the wood was compromised. The same study also found that Polyporus brumalis , when paired with Trametes versicolor , required 10 weeks to spalt the same size cubes.
The Ohio Department of Natural Resources found that pale hardwoods had the best ability to spalt. [ 17 ] Some common trees in this category include maple ( Acer spp.), birch ( Betula spp.) and beech ( Fagus spp.). However, recent research suggests that sugar maple ( Acer saccharum ) and aspen ( Populus sp.) are preferred by both white rot and pigment fungi. [ 18 ] [ 19 ]
One of the trickier aspects to spalting is that some fungi cannot colonize wood alone; they require other fungi to have preceded them to create favorable conditions. Fungi progress in waves of primary and secondary colonizers, [ 4 ] where primary colonizers initially capture and control resources, change the pH of the wood and its structure, and then must defend against secondary colonizers that then have the ability to colonize the substrate. [ 4 ] [ 20 ]
Ceratocystis spp. (Ascomycetes) contains the most common blue stain fungi . [ 21 ] Other pigmenting fungi include Chlorociboria aeruginascens , Chlorociboria aeruginosa , Scytalidium cuboideum , and Scytalidium ganodermophthorum . [ 22 ] Trametes versicolor , (Basidiomycetes) is found all over the world and is a quick and efficient white rot of hardwoods. [ 4 ] Xylaria polymorpha (Pers. ex Mer.) Grev. (Ascomycetes) has been known to bleach wood, but is unique in that it is one of the few fungi that will erect zone lines without any antagonism from other fungi. [ 23 ]
Initial lab work was conducted on spalting in the 1980s at Brigham Young University . A method for improving machinability in spalted wood using methyl methacrylate was developed in 1982, [ 24 ] and several white rot fungi responsible for zone line formation were identified in 1987. [ 25 ] Current research at Michigan Technological University has identified specific time periods at which certain spalting fungi will interact, and how long it takes for said fungi to render the wood useless. [ 1 ] Researchers from this university also developed a test for evaluating the machinability of spalted wood using a universal test machine. [ 26 ] | https://en.wikipedia.org/wiki/Spalting |
In engineering , span is the distance between two adjacent structural supports (e.g., two piers ) of a structural member (e.g., a beam ). Span is measured in the horizontal direction either between the faces of the supports ( clear span ) or between the centers of the bearing surfaces ( effective span ): [ 1 ]
A span can be closed by a solid beam or by a rope. The first kind is used for bridges, the second one for power lines , overhead telecommunication lines, some type of antennas or for aerial tramways . [ citation needed ]
Span is a significant factor in finding the strength and size of a beam as it determines the maximum bending moment and deflection . The maximum bending moment M m a x {\displaystyle M_{max}} and deflection δ m a x {\displaystyle \delta _{max}} in the pictured beam is found using: [ 2 ]
where
The maximum bending moment and deflection occur midway between the two supports. From this it follows that if the span is doubled, the maximum moment (and with it the stress ) will quadruple, and deflection will increase by a factor of sixteen.
This engineering-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Span_(engineering) |
In evolutionary biology , a spandrel is a phenotypic trait that is a byproduct of the evolution of some other characteristic, rather than a direct product of adaptive selection . Stephen Jay Gould and Richard Lewontin brought the term into biology in their 1979 paper " The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme ". [ 1 ] Adaptationism is a point of view that sees most organismal traits as adaptive products of natural selection. Gould and Lewontin sought to temper what they saw as adaptationist bias by promoting a more structuralist view of evolution.
The term " spandrel " originates from architecture, where it refers to the roughly triangular spaces between the top of an arch and the ceiling. [ 2 ]
The term was coined by paleontologist Stephen Jay Gould and population geneticist Richard Lewontin in their paper "The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme" (1979). [ 1 ] Evolutionary biologist Günter P. Wagner called the paper "the most influential structuralist manifesto". [ 3 ]
In their paper, Gould and Lewontin employed the analogy of spandrels in Renaissance architecture , such as the curved areas of masonry between arches supporting a dome that arise as a consequence of decisions about the shape of the arches and the base of the dome, rather than being designed for the artistic purposes for which they were often employed. The authors singled out properties like the necessary number of four spandrels and their specific three-dimensional shape. At the time, it was widely thought in the scientific community that everything an animal has developed that has a positive effect on that animal's fitness was due to natural selection or some adaptation . Gould and Lewontin proposed an alternative hypothesis: that due to adaptation and natural selection, byproducts are also formed. Because these byproducts of adaptations that had no real relative advantage to survival, they were termed spandrels. In the biological sense, a "spandrel" might result from a requirement inherent in the body plan of an organism, or as a byproduct of some other constraint on adaptive evolution.
In response to the position that spandrels are just small, unimportant byproducts, Gould and Lewontin argue that "we must not recognize that small means unimportant. Spandrels can be as prominent as primary adaptations". A main example used by Gould and Lewontin is the human brain. Many secondary processes and actions come in addition to the main functions of the human brain. These secondary processes and thoughts can eventually turn into an adaptation or provide a fitness advantage to humans. Just because something is a secondary trait or byproduct of an adaptation does not mean it has no use.
In 1982, Gould and Vrba introduced the term " exaptation " for characteristics that enhance fitness in their present role but were not built for that role by natural selection. [ 4 ] Exaptations may be divided into two subcategories: pre-adaptations and spandrels. Spandrels are characteristics that did not originate by the direct action of natural selection and that were later co-opted for a current use. Gould saw the term to be optimally suited for evolutionary biology for "the concept of a nonadaptive architectural by-product of definite and necessary form – a structure of particular size and shape that then becomes available for later and secondary utility". [ 5 ]
Gould and Lewontin's proposal generated a large literature of critique, which Gould characterised as being grounded in two ways. [ 5 ] First, a terminological claim was offered that the "spandrels" of Basilica di San Marco were not spandrels at all, but rather were pendentives . Gould responded, "The term spandrel may be extended from its particular architectural use for two-dimensional byproducts to the generality of 'spaces left over', a definition that properly includes the San Marco pendentives." [ 5 ]
Other critics, such as Daniel Dennett , further claimed (in Darwin's Dangerous Idea and elsewhere) that these pendentives are not merely architectural by-products as Gould and Lewontin supposed. Dennett argues that alternatives to pendentives, such as corbels or squinches , would have served equally well from an architectural standpoint, but pendentives were deliberately selected due to their aesthetic value. [ 2 ] [ 6 ] Critics such as H. Allen Orr argued that Lewontin and Gould's oversight in this regard illustrates their underestimation of the pervasiveness of adaptations found in nature. [ 6 ] [ 7 ]
Gould responded that critics ignore that later selective value is a separate issue from origination as necessary consequences of structure; he summarised his use of the term 'spandrel' in 1997: "Evolutionary biology needs such an explicit term for features arising as byproducts, rather than adaptations, whatever their subsequent exaptive utility ... Causes of historical origin must always be separated from current utilities; their conflation has seriously hampered the evolutionary analysis of form in the history of life." Gould cites the masculinized genitalia of female hyenas [ 8 ] and the brooding chamber of some snails as examples of evolutionary spandrels. [ 9 ]
Gould (1991) outlines some considerations for grounds for assigning or denying a structure the status of spandrel, pointing first to the fact that a structure originating as a spandrel through primary exaptation may have been further crafted for its current utility by a suite of secondary adaptations, thus the grounds of how well crafted a structure is for a function cannot be used as grounds for assigning or denying spandrel status. The nature of the current utility of a structure also does not provide a basis for assigning or denying spandrel status, nor does he see the origin of a structure as having any relationship to the extent or vitality of a later co-opted role, but places importance on the later evolutionary meaning of a structure. This seems to imply that the design and secondary utilization of spandrels may feed back into the evolutionary process and thus determine major features of the entire structure. The grounds Gould does accept to have validity in assigning or denying a structure the status of spandrel are historical order and comparative anatomy . [ 10 ] Historical order involves the use of historical evidence to determine which feature arose as a primary adaptation and which one appeared subsequently as a co-opted by-product. In the absence of historical evidence, inferences are drawn about the evolution of a structure through comparative anatomy. Evidence is obtained by comparing current examples of the structure in a cladistic context and by subsequently trying to determine a historical order from the distribution yielded by tabulation. [ 11 ]
The human chin has been proposed as an example of a spandrel, since modern humans ( Homo sapiens ) are the only species with a chin, an anatomical feature with no known function. [ 12 ] Alternatively however, it has been suggested that chins may be the result of selection, based on an analysis of the rate of chin evolution in the fossil record. [ 13 ]
A commonly cited example of a spandrel is the navel : it is a necessary but fitness-neutral by-product of umbilical cords in placental mammals. [ 14 ] [ 15 ]
There is disagreement among experts as to whether language is a spandrel.
Linguist Noam Chomsky and Gould himself have both argued that human language may have originated as a spandrel. [ 16 ] [ 17 ] Chomsky writes that the language faculty , and the property of discrete infinity or recursion that plays a central role in his theory of universal grammar (UG), may have evolved as a spandrel. [ 16 ] In this view, Chomsky initially pointed to language being a result of increased brain size and increasing complexity, though he provides no definitive answers as to what factors may have led to the brain attaining the size and complexity of which discrete infinity is a consequence. Steven Pinker and Ray Jackendoff say Chomsky's case is unconvincing. [ 18 ] Pinker contends that the language faculty is not a spandrel, but rather a result of natural selection. [ 19 ]
Newmeyer (1998) instead views the lack of symmetry, irregularity and idiosyncrasy that universal grammar tolerates and the widely different principles of organization of its various sub-components and consequent wide variety of linking rules relating them as evidence that such design features do not qualify as an exaptation. He suggests that universal grammar cannot be derivative and autonomous at the same time, and that Chomsky wants language to be an epiphenomenon and an "organ" simultaneously, where an organ is defined as a product of a dedicated genetic blueprint. [ 20 ] Rudolph Botha counters that Chomsky has offered his conception of the feature of recursion but not a theory of the evolution of the language faculty as a whole. [ 21 ]
There is disagreement among experts as to whether music is a spandrel.
Pinker has written that "As far as biological cause and effect are concerned, music is useless. It shows no signs of design for attaining a goal such as long life, grandchildren, or accurate perception and prediction of the world", and "I suspect that music is auditory cheesecake, an exquisite confection crafted to tickle the sensitive spots of at least six of our mental faculties." [ 22 ] Dunbar found this conclusion odd, and stated that "it falls foul of what we might refer to as the Spandrel Fallacy: 'I haven't really had time to determine empirically whether or not something has a function, so I'll conclude that it can't possibly have one.'" [ 23 ] Dunbar states that there are at least two potential roles of music in evolution: "One is its role in mating and mate choice, the other is its role in social bonding." [ 23 ] [ 24 ] | https://en.wikipedia.org/wiki/Spandrel_(biology) |
In mathematics , Spanier–Whitehead duality is a duality theory in homotopy theory , based on a geometrical idea that a topological space X may be considered as dual to its complement in the n - sphere , where n is large enough. Its origins lie in Alexander duality theory, in homology theory , concerning complements in manifolds . The theory is also referred to as S-duality , but this can now cause possible confusion with the S-duality of string theory . It is named for Edwin Spanier and J. H. C. Whitehead , who developed it in papers from 1955.
The basic point is that sphere complements determine the homology, but not the homotopy type , in general. What is determined, however, is the stable homotopy type , which was conceived as a first approximation to homotopy type. Thus Spanier–Whitehead duality fits into stable homotopy theory .
Let X be a compact neighborhood retract in R n {\displaystyle \mathbb {R} ^{n}} . Then X + {\displaystyle X^{+}} and Σ − n Σ ′ ( R n ∖ X ) {\displaystyle \Sigma ^{-n}\Sigma '(\mathbb {R} ^{n}\setminus X)} are dual objects in the category of pointed spectra with the smash product as a monoidal structure. Here X + {\displaystyle X^{+}} is the union of X {\displaystyle X} and a point, Σ {\displaystyle \Sigma } and Σ ′ {\displaystyle \Sigma '} are reduced and unreduced suspensions respectively.
Taking homology and cohomology with respect to an Eilenberg–MacLane spectrum recovers Alexander duality formally. | https://en.wikipedia.org/wiki/Spanier–Whitehead_duality |
Spanish Astrobiology Center (Spanish: Centro de Astrobiología ( CAB )) is a state-run institute in Spain dedicated to astrobiology research, and it is part of the National Institute of Aerospace Technology (INTA) as well as the Spanish National Research Council (CSIC). [ 1 ] It was created in 1999 and it is affiliated with NASA Astrobiology Institute .
Its main objective is "understanding life as a consequence of the evolution of the matter and energy in the Universe." [ 2 ]
The foundation of Spain's Astrobiology Center (CAB) had its beginnings in 1998 when a group of Spanish scientists led by Juan Pérez-Mercader , presented a proposal of affiliation to the newly created NASA Astrobiology Institute (NAI). [ 3 ] The affiliation was accepted and the center was officially created on 19 November 1999. It operated from offices at the National Institute of Aerospace Technology (INTA) until it moved to its own building inaugurated in January 2003.
The Astrobiology Center is based in Madrid, Spain , its director is Víctor Parro García , and the Vicedirector is Francisco Najarro . The center is organized into several research and support units, and some of these are associated to Spanish universities, including the University of Valladolid and the Autonomous University of Madrid . The center is part of the National Institute of Aerospace Technology (INTA) as well as the Spanish National Research Council (CSIC). [ 1 ]
The center is structured in several departments: [ 4 ] [ 5 ] Astrophysics Department, Molecular Evolution Department, Planetary Science and Habitability Department, Advanced Instrumentations Department, as well as several support units.
CAB has contributed to NASA in its mission to better characterize and find conditions for life in the Universe, and has prioritized Martian weather research and endurance of some extremophile microorganisms. [ 3 ] CAB has developed instruments for multiple missions:
This article about an organisation based in Spain is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Spanish_Astrobiology_Center |
The Spanish Royal Society of Chemistry (RSEQ) is a Spanish scientific society dedicated to the development and dissemination of chemistry , in its aspect of pure science and in its applications. It originated in 1980 after the split of the Spanish Royal Society of Physics and Chemistry which itself was founded in 1903. [ citation needed ]
The purpose of the RSEQ is "to facilitate the advancement and improvement of scientific activity, teaching, research and professional in the field of Chemistry and Chemical Engineering." [ 1 ]
The RSEQ is a member of EuCheMS (European Association for Chemical and Molecular Sciences) , a non-profit organization founded in 1970 that promotes cooperation between scientific societies and European techniques in the field of chemistry. [ 2 ]
Although the Spanish Royal Society of Chemistry (RSEQ) emerged in 1980, its history dates back to 1903, the year of the founding of the Spanish Society of Physics and Chemistry (SEFQ) and soon began publishing the journal Annals of the Spanish Society Physics and Chemistry. The number of members was 263 in the first year, professionals experimental sciences, primarily engaged in the field of chemistry. [ citation needed ]
In the 1920s, after major development and internationalization, the company incorporated at the IUPAC . In 1928, to mark the 25th anniversary of its founding, the company was honored by King Alfonso XIII with the name Royal Spanish Society of Physics and Chemistry. From this date forward, it created local branches ( Sevilla , Barcelona , Madrid , Valencia ) [ 3 ] and hold biennial meetings of the Society.
In 1934, the Royal Society organized the IX International Congress of Chemistry in Madrid, attended by 1,500 chemists in all countries. [ 4 ] At that time, the Society already had about 1400 members. After the interruption of the Spanish Civil War and its disastrous consequences, the society began to reach new heights, especially from the 60s onward, as a result of the developing policies of the time.
In the 70 territorial sections are consolidated specialized groups, such as Organic Chemistry and Biochemistry [ 5 ] (created in 1967), and Adsorption (created in 1978). At the end of the decade it was decided to divide the society into two independent branches, the Royal Society of Chemistry (RSEQ) and Physics (RSEF). Successors of the work of the parent company held their biennial meeting in Burgos, 29 September to 3 October 1980.
In the following years the focus groups were widespread within the RSEQ, and biennial meetings continued. The publication Annals of Chemistry was divided into three series between 1980 and 1989:
From 1990 to 1995, subseries A, B and C are joined to form again Annals of Chemistry, ( ISSN 1130-2283 , CODEN ANQUEX). Between 1996 and 1998 the magazine changed its name to Annals of Chemistry, International Edition, ( ISSN 1130-2283 , CODEN AQIEFZ) and published in English during this period. [ 6 ]
In 1998 it merged with other European publications, to edit together several magazines in English, but the tradition of publishing in Spanish with the founding in 1999 of continuing Annals of the Spanish Royal Society of Chemistry (Annals RSEQ), ISSN 1575-3417 , quarterly.
Since 1999, Annals of the Spanish Royal Society of Chemistry , ISSN 1575-3417 , is published quarterly. This journal is a continuation of classical Annals of Chemistry , which was integrated into a consortium of European magazines along with Acta Chimica Hungarica , Models in Chemistry , Bulletin des Sociétés Chimiques Belges , Bulletin of Société Chimique de France , Chemische Berichte , Chimika Chronika , Gazzetta Chimica Italiana , Liebigs Annalen , Polish Journal of Chemistry , Recueil des Travaux des Pays-Bas Chimiques and Revista Portuguesa de Química .
The Association of European Journals in partnership with Wiley-VCH publishes several magazines: Chemistry - A European Journal , European Journal of Inorganic Chemistry , European Journal of Organic Chemistry , ChemBioChem , ChemMedChem and ChemSusChem .
The RSEQ is also co-editor of the journal Analytical and Bioanalytical Chemistry (published by Springer ) and Physical Chemistry Chemical Physics (PCCP), published by the Royal Society of Chemistry.
The society also periodically publishes a newsletter and other publications without fixed periodicity.
Anales de Química | https://en.wikipedia.org/wiki/Spanish_Royal_Society_of_Chemistry |
During the Third Rif War in Spanish Morocco between 1921 and 1927, the Spanish Army of Africa deployed chemical weapons in an attempt to put down the Berber rebellion against colonial rule in the region of the Rif led by the guerrilla Abd el-Krim . [ 1 ] In 1921, following the Rifian victory in the Battle of Annual , which was considered the worst Spanish defeat of the 20th-century, the Spanish army pursued a campaign of retribution involving the indiscriminate and routine dropping of toxic gas bombs targeting civilian populations, markets and rivers. [ 2 ]
These attacks in 1924 marked the first widespread employment of chemical warfare in the post-WWI era [ 2 ] and the second confirmed case of mustard gas being dropped from airplanes. While Spain signed the Geneva Protocol a year later, which prohibited the use of chemical and biological weapons, such use was not illegal in non-international armed conflicts. [ 3 ] [ 4 ] [ 2 ]
While Spain pursued its chemical campaign in secrecy from the public, French intelligence provided Spain with weapon systems including tear gas and smaller gas agents, and a German company helped Spain obtain more effective chemical agents. [ 2 ] The gas used in these attacks was produced by the "Fábrica Nacional de Productos Químicos" (National factory of chemical products) at La Marañosa near Madrid ; a plant founded with significant assistance from Hugo Stoltzenberg , a chemist associated with clandestine chemical warfare activities in the early 1920s [ 5 ] who was later given Spanish citizenship. [ 6 ]
The Spanish bombings were covered up but some observers of military aviation , like Pedro Tonda Bueno in his autobiography La vida y yo ( Life and I ), published in 1974, talked about dropping toxic gases from airplanes and the consequent poisoning of the Rif fields. Likewise, Spanish Army air arm pilot Ignacio Hidalgo de Cisneros , in his autobiographical work Cambio de rumbo ( Course change ), reveals how he witnessed several chemical attacks. Years later, in 1990, two German journalists and investigators, Rudibert Kunz and Rolf-Dieter Müller , in their work Giftgas gegen Abd El Krim: Deutschland, Spanien und der Gaskrieg in Spanisch-Marokko, 1922-1927 ( Poison Gas against Abd El Krim: Germany, Spain and the Gas War in Spanish Morocco, 1922-1927 ), proved with scientific tests that chemical attacks had indeed occurred. The British historian Sebastian Balfour , of the London School of Economics , in his book Deadly Embrace , confirmed massive use of chemical arms after having studied numerous Spanish, French and British archives. According to his research, the strategy of the Spanish military was to choose highly populated zones as targets. Additional evidence is found in a telegram from a British official, H. Pughe Lloyd, sent to the British Minister of War. [ 7 ]
According to Sebastian Balfour , the motivation for the chemical attacks was based primarily on revenge for the defeat of the Spanish Army of Africa and their Moroccan recruits the Regulares [ 8 ] at the Battle of Annual on July 22, 1921. [ 9 ]
The Spanish defeat at Annual left 13,000 Spanish and Moroccan colonial soldiers dead according to the official count, many of them killed after surrendering to the Rif armies, and led to a major political crisis and a redefinition of Spanish colonial policy toward the Rif region. The political crisis led Indalecio Prieto to say in the Congress of Deputies : "We are at the most acute period of Spanish decadence. The campaign in Africa is a total failure, absolute, without extenuation, of the Spanish Army."
The Minister of War ordered the creation of an investigative commission, directed by the respected general Juan Picasso González , which eventually developed the Expediente Picasso report. Despite identifying numerous military mistakes, it did not, owing to obstructions raised by various ministers and judges, go so far as to lay political responsibility for the defeat. Popular opinion widely blamed King Alfonso XIII who, according to several sources, encouraged General Manuel Fernández Silvestre 's irresponsible penetration of positions far from Melilla without having adequate defenses in his rear.
Spain was one of the first powers to use chemical weapons against civilians [ 10 ] in their use against the Rif rebellion. Between 1921 and 1927, the Spanish army indiscriminately used phosgene , diphosgene , chloropicrin and mustard gas (known as Iperita [ 11 ] ). [ 12 ] [ 13 ] Common targets were civilian populations, markets, and rivers. [ 13 ]
Spanish leaders justified their usage of gas by dehumanising the natives as uncivilised beings. The Spanish king reportedly called them "malicious beasts". In a secret letter to the king, a general described the Rif Moor as "completely irreducible and uncivilized... They despise all the advantages of civilization. They are hermetic to benevolence and fear only punishment". [ 2 ] In a telegram sent by the High Commissioner of Spanish Morocco Dámaso Berenguer on August 12, 1921 to the Spanish minister of War, Berenguer stated: [ 14 ]
I have been obstinately resistant to the use of suffocating gases against these indigenous peoples but after what they have done, and of their treacherous and deceptive conduct, I have to use them with true joy.
Spain used mustard gas as a force multiplier against native tribes who used rough terrain to their advantage. [ 2 ]
On August 20, 1921, Spain asked Germany to deliver mustard gas via Hugo Stoltzenberg , although Germany was prohibited from manufacturing such weapons by the Treaty of Versailles of 1919. The first delivery occurred in 1923. [ 14 ] The use of chemical weapons against the Rif was first described in an article of a (now defunct) Francophone daily newspaper published in Tangier called La Dépêche marocaine dated on November 27, 1921. [ 15 ] [ 16 ] Historian Juan Pando has been the only Spanish historian to have confirmed the usage of mustard gas starting in 1923. [ 14 ] Spanish newspaper La Correspondencia de España published an article called Cartas de un soldado ( Letters of a soldier ) on August 16, 1923 which backed the usage of mustard gas. [ 15 ]
According to military aviation general Hidalgo de Cisneros in his autobiographical book Cambio de rumbo , [ 17 ] he was the first warfighter to drop a 100-kilogram mustard gas bomb from his Farman F60 Goliath aircraft in the summer of 1924. [ 18 ] About 127 fighters and bombers flew in the campaign, dropping around 1,680 bombs each day. Thirteen of these planes were stationed in the military air base of Seville. [ 19 ] The mustard gas bombs were brought from the stockpiles of Germany and delivered to Melilla before being carried on Farman F60 Goliath airplanes. [ 20 ]
Chemical weapons used in the region are alleged to be the main reason for the high occurrence of cancer among the population. [ 21 ] [ 22 ]
The Association for the Defence of Victims of the Rif War considers that the toxic effects of chemical warfare during the war are still being felt in the Rif region. [ 23 ] Head of the Association of Toxic Gas Victims (ATGV) in the Rif said 50% of cancer cases in Morocco are concentrated in the Rif region and added that, “Research has shown there are strong indicators that the cancer is caused by the gases that were used against the resistance in the north.” [ 24 ]
However, no independent scientific study has proven a relationship between the usage of chemical weapons and the high rate of cancer in the area. [ 25 ]
On February 14, 2007, the Catalan party of the Republican Left ( Esquerra Republicana de Catalunya ) passed a bill to the Spanish Congress of Deputies requesting Spain to acknowledge the "systematic" use of chemical weapons against the population of the Rif mountains. [ 26 ] The bill was rejected by 33 votes from the governing Socialist Labor Party and the opposition right-wing Popular Party who form the majority in the Spanish parliament. [ 27 ] | https://en.wikipedia.org/wiki/Spanish_use_of_chemical_weapons_in_the_Rif_War |
A spar is a marine structure, used for floating oil/gas platforms . Named after navigation channel Spar buoys , spar platforms were developed as an extreme deepwater alternative to conventional platforms. [ 1 ] The deep draft design of spars makes them less affected by wind, wave, and currents and allows for both dry tree and subsea production.
A spar platform consists of a large-diameter, vertical buoyant cylinder (s) supporting a deck. Spars are permanently anchored to the seabed by a spread mooring system composed of either a chain-wire-chain or chain-polyester-chain configuration. [ 2 ] The cylinder comprises a number of tanks; the lowest contains ballast, mid-water and/or extracted oil, the upper, air for buoyancy. [ 3 ] Helical strakes are fitted to larger & more recent designs to mitigate the effects of vortex-induced motion.
There are three primary types of spars; classic, truss, and cell:
Cylinders are either buoyancy only, or subdivided into buoyancy and ballast.
The first spar platform was the Brent Spar . Designed for storage and offloading of crude oil products, it was installed on the UK 's Brent Field in June 1976. Shell's attempted deep sea disposal of the platform in the 1990s created a massive environmental backlash by Greenpeace . The spar was eventually dismantled, with ballast used as a foundation for a quay in Norway . [ 4 ]
The first spar platform designed for production was the Neptune spar, located in the Gulf of Mexico , and was installed in September 1996 by Kerr McGee . [ 5 ]
The first, and thus far unique, cell-spar platform was Kerr-McGee's Red Hawk spar (7 ea. 8 m (26 ft) diameter cells). [ 6 ] Field-depletion occurred 4 years after production started, so Red Hawk was decommissioned in 2014 under the Bureau of Safety and Environmental Enforcement 's " Rigs-to-Reefs " program, at which time it was the deepest floating platform to be decommissioned. [ 7 ]
The world's deepest production platform is Perdido , a truss spar in the Gulf of Mexico, with a mean water depth of 2,438 m (7,999 ft). It is operated by Royal Dutch Shell and was built at a cost of $3 billion. [ 8 ] | https://en.wikipedia.org/wiki/Spar_(platform) |
A spare part , spare , service part , repair part , or replacement part , is an interchangeable part that is kept in an inventory and used for the repair or refurbishment of defective equipment/units. Spare parts are an important feature of logistics engineering and supply chain management , often comprising dedicated spare parts management systems.
Spare parts are an outgrowth of the industrial development of interchangeable parts and mass production .
In an industrial environment, spare parts are described in several manner to distinguish key features of various spare parts. The following describes spare part types and their typically functionality.
1. Capital parts are spare parts which, although acknowledged to have a long life or a small chance of failure , would cause a long shutdown of equipment because it would take a long time to get a replacement for them. Capital parts are typically repaired or replaced during planned overhauls/scheduled inspections. As description implies, these Capital Parts are typically expensive and are depreciated over time.
Examples of capital parts include pumps and motor sets used in industrial plants, or impeller or a rotor required for a pump or motor. This “spare” requirement would be determined by redundancy of equipment used in the industrial processes.
2. Consumables can be divided into two groups:
3. Inspection spares or outage spares typically refer to those spare parts used in conjunction with Capital Parts during planned overhauls/scheduled inspections and maybe reused but typically are not repairable and are discarded after removal from use if Inspection Spares are damaged. These Inspection Spares are sometimes mis-characterized as Capital spares (vs Capital Parts) and are also confounded with Inspection Consumables, which must be replaced at every inspection/outage. (an example of inspection spares would be bearings and mechanical seals, large bolts and nuts.)
4. Operational spares typically refer to those spare parts that are used during operation of equipment and would not require planned overhauls/scheduled inspections to replace. In an industrial setting, operational spares would be gages, valves (solenoid, MOVs that are in redundancy), transmitters, I/O boards, small AC/DC power supplies, etc.) (for a car, it would windshield wiper)
In logistics , spare parts can be broadly classified into two groups, repairables and consumables .
Economically, there is a tradeoff between the cost of ordering a replacement part and the cost of repairing a failed part. When the cost of repair becomes a significant percentage of the cost of replacement, it becomes economically favorable to simply order a replacement part. In such cases, the part is said to be "beyond economic repair" (BER), and the percentage associated with this threshold is known as the BER rate. Analysis of economic tradeoffs is formally evaluated using Level of Repair Analysis (LORA).
Repairable parts are parts that are deemed worthy of repair, usually by virtue of economic consideration of their repair cost. Rather than bear the cost of completely replacing a finished product, repairables typically are designed to enable more affordable maintenance by being more modular. That allows components to be more easily removed, repaired, and replaced, enabling cheaper replacement. Spare parts that are needed to support condemnation of repairable parts are known as replenishment spares .
A rotable pool is a pool of repairable spare parts inventory set aside to allow for multiple repairs to be accomplished simultaneously, which can be used to minimize stockout conditions for repairable items.
Parts that are not repairable are considered consumable parts. Consumable parts are usually scrapped , or "condemned", when they are found to have failed. Since no attempt at repair is made, for a fixed mean time between failures (MTBF), replacement rates for consumption of consumables are higher than an equivalent item treated as a repairable part. Therefore, consumables tend to be lower-cost items. One Example is in heavy machinery such as brake oils, hydraulic fluids, and belts. [ 1 ]
Because consumables are lower cost and higher volume, economies of scale can be found by ordering in large lot sizes, a so-called economic order quantity .
From a commercial perspective, spare parts can be classified into three main types:
OEM (Original Equipment Manufacturer) Parts: These parts are produced by the same manufacturer that made the original equipment.
Aftermarket Parts : These are replacement parts made by companies other than the original manufacturer. They can serve as cost-effective substitutes for OEM parts.
Used or Second - Hand Parts: These can be either OEM or aftermarket parts that have been refurbished and resold at a lower price. [ 2 ]
There is no UK or EU legislation which states that spare parts have to be available for any set period of time, [ 3 ] but some trade associations require their members to ensure products are not rendered useless because spare parts are not available. [ 4 ] The 'six year rule' in the UK Sale of Goods Act 1979 relates to the time period for enforcing claims that goods were defective when sold, not to whether spare parts are available to repair them, and section 23(3) of the Consumer Rights Act 2015 states that a consumer cannot require a trader to repair or replace goods if "the repair or replacement is impossible", implying that if spare parts are no longer available the consumer's Right to Repair (or to have a spare part supplied) would be lost. [ 5 ]
From the perspective of logistics , a model of the life cycle of parts in a supply chain can be developed. This model, called the repair cycle, consists of functioning parts in use by equipment operators, and the entire sequence of suppliers or repair providers that replenish functional part inventories, either by production or repair, when they have failed. Ultimately, this sequence ends with the manufacturer . This type of model allows demands on a supply system to ultimately be traced to their operational reliability , allowing for analysis of the dynamics of the supply system, in particular, spare parts.
When stockout conditions occur, cannibalization can result. This is the practice of removing parts or subsystems necessary for repair from another similar device, rather than from inventory . The source system is usually crippled as a result, if only temporarily, in order to allow the recipient device to function properly again. As a result, operational availability is impaired.
Industrialization has seen the widespread growth of commercial manufacturing enterprises, such as the automotive industry , and later, the computer industry . The resulting complex systems have evolved modular support infrastructures, with the reliance on auto parts in the automotive industry, and replaceable computer modules known as field-replaceable units (FRUs).
Military operations are significantly affected by logistics operations. The system availability, also known as mission capable rate , of weapon systems and the ability to effect the repair of damaged equipment are significant contributors to the success of military operations. Systems that are in a mission-incapable (MICAP) status due lack of spare parts are said to be "awaiting parts" (AWP), also known as not mission capable due to supply (NMCS).
Because of this sensitivity to logistics, militaries have sought to make their logistics operations as effective as possible, focusing effort on operations research and optimal maintenance . Maintenance has been simplified by the introduction of interchangeable modules known as line-replaceable units (LRUs). LRUs make it possible to quickly replace an unserviceable (failed) part with a serviceable (working) replacement. This makes it relatively straightforward to repair complex military hardware, at the expense of having a ready supply of spare parts.
The cost of having serviceable parts available in inventory can be tremendous, as items that are prone to failure may be demanded frequently from inventory, requiring significant inventory levels to avoid depletion. For military programs, the cost of spare inventory can be a significant portion of acquisition cost .
In recent years, the United States Department of Defense (DoD) has advocated the use of performance-based logistics (PBL) contracts to manage costs for support of weapon systems. [ citation needed ] | https://en.wikipedia.org/wiki/Spare_part |
In chemistry , sparging , also known as gas flushing in metallurgy , is a technique in which a gas is bubbled through a liquid in order to remove other dissolved gas(es) and/or dissolved volatile liquid(s) from that liquid. It is a method of degassing . According to Henry's law , the concentration of each gas in a liquid is proportional to the partial pressure of that gas (in the gaseous state) in contact with the liquid. Sparging introduces a gas that has little or no partial pressure of the gas(es) to be removed, and increases the area of the gas-liquid interface , which encourages some of the dissolved gas(es) to diffuse into the sparging gas before the sparging gas escapes from the liquid. Many sparging processes, such as solvent removal, use air as the sparging gas. To remove oxygen, or for sensitive solutions or reactive molten metals, a chemically inert gas such as nitrogen , argon , or helium is used.
Solvents used in high-performance liquid chromatography (HPLC) are often sparged with helium. [ 1 ]
In biochemical engineering , sparging can remove low-boiling liquids from a solution. The low-boiling components evaporate more rapidly, so the gas bubbles remove more of them from the bulk solution containing higher-boiling components. It is an alternative to distillation , and it does not require heat.
In environmental chemistry , air sparging is an in situ remediation technique that removes volatile pollutants from contaminated groundwater and soil.
In metallurgy , gas flushing removes dissolved gases from the molten metal prior to the material being processed. [ 2 ] [ 3 ] For example, before casting aluminium alloys , argon bubbles are injected into liquid aluminium using a rotary degasser . The argon bubbles rise to the surface, bringing with them some of the dissolved hydrogen. The degassing step reduces the occurrence of hydrogen gas porosity . In the steel making process, this method is used very commonly for duplex steel and some high reactivity metals. | https://en.wikipedia.org/wiki/Sparging_(chemistry) |
A spark-gap transmitter is an obsolete type of radio transmitter which generates radio waves by means of an electric spark . [ 1 ] [ 2 ] Spark-gap transmitters were the first type of radio transmitter, and were the main type used during the wireless telegraphy or "spark" era, the first three decades of radio , from 1887 to the end of World War I. [ 3 ] [ 4 ] German physicist Heinrich Hertz built the first experimental spark-gap transmitters in 1887, with which he proved the existence of radio waves and studied their properties.
A fundamental limitation of spark-gap transmitters is that they generate a series of brief transient pulses of radio waves called damped waves ; they are unable to produce the continuous waves used to carry audio (sound) in modern AM or FM radio transmission. So spark-gap transmitters could not transmit audio, and instead transmitted information by radiotelegraphy ; the operator switched the transmitter on and off with a telegraph key , creating pulses of radio waves to spell out text messages in Morse code .
The first practical spark gap transmitters and receivers for radiotelegraphy communication were developed by Guglielmo Marconi around 1896. One of the first uses for spark-gap transmitters was on ships, to communicate with shore and broadcast a distress call if the ship was sinking. They played a crucial role in maritime rescues such as the 1912 RMS Titanic disaster. After World War I, vacuum tube transmitters were developed, which were less expensive and produced continuous waves which had a greater range, produced less interference, and could also carry audio, making spark transmitters obsolete by 1920. The radio signals produced by spark-gap transmitters are electrically "noisy"; they have a wide bandwidth , creating radio frequency interference (RFI) that can disrupt other radio transmissions. This type of radio emission has been prohibited by international law since 1934. [ 5 ] [ 6 ]
Electromagnetic waves are radiated by electric charges when they are accelerated . [ 7 ] [ 8 ] Radio waves , electromagnetic waves of radio frequency , can be generated by time-varying electric currents , consisting of electrons flowing through a conductor which suddenly change their velocity, thus accelerating. [ 8 ] [ 9 ]
An electrically charged capacitance discharged through an electric spark across a spark gap between two conductors was the first device known which could generate radio waves. [ 10 ] : p.3 The spark itself doesn't produce the radio waves, it merely serves as a fast acting switch to excite resonant radio frequency oscillating electric currents in the conductors of the attached circuit. The conductors radiate the energy in this oscillating current as radio waves.
Due to the inherent inductance of circuit conductors, the discharge of a capacitor through a low enough resistance (such as a spark) is oscillatory ; the charge flows rapidly back and forth through the spark gap for a brief period, charging the conductors on each side alternately positive and negative, until the oscillations die away. [ 11 ] [ 12 ]
A practical spark gap transmitter consists of these parts: [ 11 ] [ 13 ] [ 14 ] [ 15 ]
The transmitter works in a rapid repeating cycle in which the capacitor is charged to a high voltage by the transformer and discharged through the coil by a spark across the spark gap. [ 11 ] [ 16 ] The impulsive spark excites the resonant circuit to "ring" like a bell, producing a brief oscillating current which is radiated as electromagnetic waves by the antenna. [ 11 ] The transmitter repeats this cycle at a rapid rate, so the spark appeared continuous, and the radio signal sounded like a whine or buzz in a radio receiver .
The cycle is very rapid, taking less than a millisecond. With each spark, this cycle produces a radio signal consisting of an oscillating sinusoidal wave that increases rapidly to a high amplitude and decreases exponentially to zero, called a damped wave . [ 11 ] The frequency f {\displaystyle f} of the oscillations, which is the frequency of the emitted radio waves, is equal to the resonant frequency of the resonant circuit, determined by the capacitance C {\displaystyle C} of the capacitor and the inductance L {\displaystyle L} of the coil:
The transmitter repeats this cycle rapidly, so the output is a repeating string of damped waves. This is equivalent to a radio signal amplitude modulated with a steady frequency, so it could be demodulated in a radio receiver by a rectifying AM detector , such as the crystal detector or Fleming valve used during the wireless telegraphy era. The frequency of repetition (spark rate) is in the audio range, typically 50 to 1000 sparks per second, so in a receiver's earphones the signal sounds like a steady tone, whine, or buzz. [ 13 ]
In order to transmit information with this signal, the operator turns the transmitter on and off rapidly by tapping on a switch called a telegraph key in the primary circuit of the transformer, producing sequences of short (dot) and long (dash) strings of damped waves, to spell out messages in Morse code . As long as the key is pressed the spark gap fires repetitively, creating a string of pulses of radio waves, so in a receiver the keypress sounds like a buzz; the entire Morse code message sounds like a sequence of buzzes separated by pauses. In low-power transmitters the key directly breaks the primary circuit of the supply transformer, while in high-power transmitters the key operates a heavy duty relay that breaks the primary circuit.
The circuit which charges the capacitors, along with the spark gap itself, determines the spark rate of the transmitter, the number of sparks and resulting damped wave pulses it produces per second, which determines the tone of the signal heard in the receiver. The spark rate should not be confused with the frequency of the transmitter, which is the number of sinusoidal oscillations per second in each damped wave. Since the transmitter produces one pulse of radio waves per spark, the output power of the transmitter was proportional to the spark rate, so higher rates were favored. Spark transmitters generally used one of three types of power circuits: [ 11 ] [ 13 ] [ 17 ] : p.359–362
An induction coil (Ruhmkorff coil) was used in low-power transmitters, usually less than 500 watts, often battery-powered. An induction coil is a type of transformer powered by DC, in which a vibrating arm switch contact on the coil called an interrupter repeatedly breaks the circuit that provides current to the primary winding, causing the coil to generate pulses of high voltage. When the primary current to the coil is turned on, the primary winding creates a magnetic field in the iron core which pulls the springy interrupter arm away from its contact, opening the switch and cutting off the primary current. Then the magnetic field collapses, creating a pulse of high voltage in the secondary winding, and the interrupter arm springs back to close the contact again, and the cycle repeats. Each pulse of high voltage charged up the capacitor until the spark gap fired, resulting in one spark per pulse. Interrupters were limited to low spark rates of 20–100 Hz, sounding like a low buzz in the receiver. In powerful induction coil transmitters, instead of a vibrating interrupter, a mercury turbine interrupter was used. This could break the current at rates up to several thousand hertz, and the rate could be adjusted to produce the best tone.
In higher power transmitters powered by AC, a transformer steps the input voltage up to the high voltage needed. The sinusoidal voltage from the transformer is applied directly to the capacitor, so the voltage on the capacitor varies from a high positive voltage, to zero, to a high negative voltage. The spark gap is adjusted so sparks only occur near the maximum voltage, at peaks of the AC sine wave , when the capacitor was fully charged. Since the AC sine wave has two peaks per cycle, ideally two sparks occurred during each cycle, so the spark rate was equal to twice the frequency of the AC power [ 15 ] (often multiple sparks occurred during the peak of each half cycle). The spark rate of transmitters powered by 50 or 60 Hz mains power was thus 100 or 120 Hz. However higher audio frequencies cut through interference better, so in many transmitters the transformer was powered by a motor–alternator set, an electric motor with its shaft turning an alternator , that produced AC at a higher frequency, usually 500 Hz, resulting in a spark rate of 1000 Hz. [ 15 ]
The speed at which signals may be transmitted is naturally limited by the time taken for the spark to be extinguished. If, as described above, the conductive plasma does not, during the zero points of the alternating current, cool enough to extinguish the spark, a 'persistent spark' is maintained until the stored energy is dissipated, permitting practical operation only up to around 60 signals per second. [ citation needed ] If active measures are taken to break the arc (either by blowing air through the spark or by lengthening the spark gap), a much shorter "quenched spark" may be obtained. [ citation needed ] A simple quenched spark system still permits several oscillations of the capacitor circuit in the time taken for the spark to be quenched. With the spark circuit broken, the transmission frequency is solely determined by the antenna resonant circuit, which permits simpler tuning.
In a transmitter with a "rotary" spark gap (below) , the capacitor was charged by AC from a high-voltage transformer as above, and discharged by a spark gap consisting of electrodes spaced around a wheel which was spun by an electric motor, which produced sparks as they passed by a stationary electrode. [ 11 ] [ 15 ] The spark rate was equal to the rotations per second times the number of spark electrodes on the wheel. It could produce spark rates up to several thousand hertz, and the rate could be adjusted by changing the speed of the motor. The rotation of the wheel was usually synchronized to the AC sine wave so the moving electrode passed by the stationary one at the peak of the sine wave, initiating the spark when the capacitor was fully charged, which produced a musical tone in the receiver. When tuned correctly in this manner, the need for external cooling or quenching airflow was eliminated, as was the loss of power directly from the charging circuit (parallel to the capacitor) through the spark.
The invention of the radio transmitter resulted from the convergence of two lines of research.
One was efforts by inventors to devise a system to transmit telegraph signals without wires. Experiments by a number of inventors had shown that electrical disturbances could be transmitted short distances through the air. However most of these systems worked not by radio waves but by electrostatic induction or electromagnetic induction , which had too short a range to be practical. [ 18 ] In 1866 Mahlon Loomis claimed to have transmitted an electrical signal through the atmosphere between two 600 foot wires held aloft by kites on mountaintops 14 miles apart. [ 18 ] Thomas Edison had come close to discovering radio in 1875; he had generated and detected radio waves which he called "etheric currents" experimenting with high-voltage spark circuits, but due to lack of time did not pursue the matter. [ 17 ] : p.259–261 David Edward Hughes in 1879 had also stumbled on radio wave transmission which he received with his carbon microphone detector, however he was persuaded that what he observed was induction . [ 17 ] : p.259–261 Neither of these individuals are usually credited with the discovery of radio, because they did not understand the significance of their observations and did not publish their work before Hertz.
The other was research by physicists to confirm the theory of electromagnetism proposed in 1864 by Scottish physicist James Clerk Maxwell , now called Maxwell's equations . Maxwell's theory predicted that a combination of oscillating electric and magnetic fields could travel through space as an " electromagnetic wave ". Maxwell proposed that light consisted of electromagnetic waves of short wavelength, but no one knew how to confirm this, or generate or detect electromagnetic waves of other wavelengths. By 1883 it was theorized that accelerated electric charges could produce electromagnetic waves, and George Fitzgerald had calculated the output power of a loop antenna . [ 19 ] Fitzgerald in a brief note published in 1883 suggested that electromagnetic waves could be generated practically by discharging a capacitor rapidly; the method used in spark transmitters, [ 20 ] [ 21 ] however there is no indication that this inspired other inventors.
The division of the history of spark transmitters into the different types below follows the organization of the subject used in many wireless textbooks. [ 22 ]
German physicist Heinrich Hertz in 1887 built the first experimental spark gap transmitters during his historic experiments to demonstrate the existence of electromagnetic waves predicted by James Clerk Maxwell in 1864, in which he discovered radio waves , [ 23 ] [ 24 ] : p.3-4 [ 25 ] [ 17 ] : p.19, 260, 331–332 which were called "Hertzian waves" until about 1910. Hertz was inspired to try spark excited circuits by experiments with "Reiss spirals", a pair of flat spiral inductors with their conductors ending in spark gaps. A Leyden jar capacitor discharged through one spiral, would cause sparks in the gap of the other spiral.
See circuit diagram. Hertz's transmitters consisted of a dipole antenna made of a pair of collinear metal rods of various lengths with a spark gap (S) between their inner ends and metal balls or plates for capacitance (C) attached to the outer ends. [ 23 ] [ 17 ] : p.19, 260, 331–332 [ 25 ] The two sides of the antenna were connected to an induction coil (Ruhmkorff coil) (T) a common lab power source which produced pulses of high voltage, 5 to 30 kV. In addition to radiating the waves, the antenna also acted as a harmonic oscillator ( resonator ) which generated the oscillating currents. High-voltage pulses from the induction coil (T) were applied between the two sides of the antenna. Each pulse stored electric charge in the capacitance of the antenna, which was immediately discharged by a spark across the spark gap. The spark excited brief oscillating standing waves of current between the sides of the antenna. The antenna radiated the energy as a momentary pulse of radio waves; a damped wave . The frequency of the waves was equal to the resonant frequency of the antenna, which was determined by its length; it acted as a half-wave dipole , which radiated waves roughly twice the length of the antenna (for example a dipole 1 meter long would generate 150 MHz radio waves). Hertz detected the waves by observing tiny sparks in micrometer spark gaps (M) in loops of wire which functioned as resonant receiving antennas. Oliver Lodge was also experimenting with spark oscillators at this time and came close to discovering radio waves before Hertz, but his focus was on waves on wires, not in free space. [ 26 ] [ 17 ] : p.226
Hertz and the first generation of physicists who built these "Hertzian oscillators", such as Jagadish Chandra Bose , Lord Rayleigh , George Fitzgerald , Frederick Trouton , Augusto Righi and Oliver Lodge , were mainly interested in radio waves as a scientific phenomenon , and largely failed to foresee its possibilities as a communication technology. [ 27 ] : p.54, 98 [ 24 ] : p.5-9, 22 [ 17 ] : p.260, 263–265 [ 28 ] Due to the influence of Maxwell's theory, their thinking was dominated by the similarity between radio waves and light waves; they thought of radio waves as an invisible form of light. [ 24 ] : p.5-9, 22 [ 17 ] : p.260, 263–265 By analogy with light, they assumed that radio waves only traveled in straight lines, so they thought radio transmission was limited by the visual horizon like existing optical signalling methods such as semaphore , and therefore was not capable of longer distance communication. [ 26 ] [ 29 ] [ 30 ] As late as 1894 Oliver Lodge speculated that the maximum distance Hertzian waves could be transmitted was a half mile. [ 24 ] : p.5-9, 22
To investigate the similarity between radio waves and light waves , these researchers concentrated on producing short wavelength high-frequency waves with which they could duplicate classic optics experiments with radio waves, using quasioptical components such as prisms and lenses made of paraffin wax , sulfur , and pitch and wire diffraction gratings . [ 17 ] : p.476-484 Their short antennas generated radio waves in the VHF , UHF , or microwave bands. In his various experiments, Hertz produced waves with frequencies from 50 to 450 MHz, roughly the frequencies used today by broadcast television transmitters . Hertz used them to perform historic experiments demonstrating standing waves , refraction , diffraction , polarization and interference of radio waves. [ 31 ] [ 17 ] : p.19, 260, 331–332 He also measured the speed of radio waves, showing they traveled at the same speed as light. These experiments established that light and radio waves were both forms of Maxwell's electromagnetic waves , differing only in frequency. Augusto Righi and Jagadish Chandra Bose around 1894 generated microwaves of 12 and 60 GHz respectively, using small metal balls as resonator-antennas. [ 32 ] [ 17 ] : p.291-308
The high frequencies produced by Hertzian oscillators could not travel beyond the horizon. The dipole resonators also had low capacitance and couldn't store much charge , limiting their power output. [ 24 ] : p.5-9, 22 Therefore, these devices were not capable of long distance transmission; their reception range with the primitive receivers employed was typically limited to roughly 100 yards (100 meters). [ 24 ] : p.5-9, 22
I could scarcely conceive it possible that [radio's] application to useful purposes could have escaped the notice of such eminent scientists.
Italian radio pioneer Guglielmo Marconi was one of the first people to believe that radio waves could be used for long distance communication, and singlehandedly developed the first practical radiotelegraphy transmitters and receivers , [ 28 ] [ 34 ] [ 24 ] : ch.1&2 mainly by combining and tinkering with the inventions of others. Starting at age 21 on his family's estate in Italy, between 1894 and 1901 he conducted a long series of experiments to increase the transmission range of Hertz's spark oscillators and receivers. [ 33 ]
He was unable to communicate beyond a half-mile until 1895, when he discovered that the range of transmission could be increased greatly by replacing one side of the Hertzian dipole antenna in his transmitter and receiver with a connection to Earth and the other side with a long wire antenna suspended high above the ground. [ 24 ] : p.20-21 [ 28 ] [ 36 ] : 195–218 [ 37 ] These antennas functioned as quarter-wave monopole antennas . [ 38 ] The length of the antenna determined the wavelength of the waves produced and thus their frequency. Longer, lower frequency waves have less attenuation with distance. [ 38 ] As Marconi tried longer antennas, which radiated lower frequency waves, probably in the MF band around 2 MHz, [ 37 ] he found that he could transmit further. [ 33 ] Another advantage was that these vertical antennas radiated vertically polarized waves, instead of the horizontally polarized waves produced by Hertz's horizontal antennas. [ 39 ] These longer vertically polarized waves could travel beyond the horizon, because they propagated as a ground wave that followed the contour of the Earth. Under certain conditions they could also reach beyond the horizon by reflecting off layers of charged particles ( ions ) in the upper atmosphere, later called skywave propagation. [ 30 ] Marconi did not understand any of this at the time; he simply found empirically that the higher his vertical antenna was suspended, the further it would transmit.
After failing to interest the Italian government, in 1896 Marconi moved to England, where William Preece of the British General Post Office funded his experiments. [ 38 ] [ 37 ] [ 33 ] Marconi applied for a patent on his radio system 2 June 1896, [ 35 ] often considered the first wireless patent. [ 17 ] : p.352-353, 355–358 [ 40 ] In May 1897 he transmitted 14 km (8.7 miles), [ 38 ] on 27 March 1899 he transmitted across the English Channel , 46 km (28 miles), [ 33 ] in fall 1899 he extended the range to 136 km (85 miles), [ 24 ] : p.60-61 and by January 1901 he had reached 315 km (196 miles). These demonstrations of wireless Morse code communication at increasingly long distances convinced the world that radio, or "wireless telegraphy" as it was called, was not just a scientific curiosity but a commercially useful communication technology.
In 1897 Marconi started a company to produce his radio systems, which became the Marconi Wireless Telegraph Company . [ 38 ] [ 33 ] and radio communication began to be used commercially around 1900. His first large contract in 1901 was with the insurance firm Lloyd's of London to equip their ships with wireless stations. Marconi's company dominated marine radio throughout the spark era. Inspired by Marconi, in the late 1890s other researchers also began developing competing spark radio communication systems; Alexander Popov in Russia, Eugène Ducretet in France, Reginald Fessenden and Lee de Forest in America, [ 1 ] and Karl Ferdinand Braun , Adolf Slaby , and Georg von Arco in Germany who in 1903 formed the Telefunken Co., Marconi's chief rival. [ 41 ] [ 42 ]
The primitive transmitters prior to 1897 had no resonant circuits (also called LC circuits, tank circuits, or tuned circuits), the spark gap was in the antenna, which functioned as the resonator to determine the frequency of the radio waves. [ 33 ] [ 43 ] [ 17 ] : p.352-353, 355–358 [ 44 ] These were called "unsyntonized" or "plain antenna" transmitters. [ 17 ] : p.352-353, 355–358 [ 45 ]
The average power output of these transmitters was low, because due to its low capacitance the antenna was a highly damped oscillator (in modern terminology, it had very low Q factor ). [ 10 ] : p.4–7, 32–33 During each spark the energy stored in the antenna was quickly radiated away as radio waves, so the oscillations decayed to zero quickly. [ 46 ] The radio signal consisted of brief pulses of radio waves, repeating tens or at most a few hundreds of times per second, separated by comparatively long intervals of no output. [ 17 ] : p.352-353, 355–358 The power radiated was dependent on how much electric charge could be stored in the antenna before each spark, which was proportional to the capacitance of the antenna. To increase their capacitance to ground, antennas were made with multiple parallel wires, often with capacitive toploads, in the "harp", "cage", " umbrella ", "inverted-L", and " T " antennas characteristic of the "spark" era. [ 47 ] The only other way to increase the energy stored in the antenna was to charge it up to very high voltages. [ 48 ] [ 17 ] : p.352-353, 355–358 However the voltage that could be used was limited to about 100 kV by corona discharge which caused charge to leak off the antenna, particularly in wet weather, and also energy lost as heat in the longer spark.
A more significant drawback of the large damping was that the radio transmissions were electrically "noisy"; they had a very large bandwidth . [ 11 ] [ 24 ] : p.90-93 [ 33 ] [ 36 ] : 72–75 These transmitters did not produce waves of a single frequency , but a continuous band of frequencies. [ 36 ] : 72–75 [ 24 ] : p.90-93 They were essentially radio noise sources radiating energy over a large part of the radio spectrum , which made it impossible for other transmitters to be heard. [ 13 ] When multiple transmitters attempted to operate in the same area, their broad signals overlapped in frequency and interfered with each other. [ 33 ] [ 44 ] The radio receivers used also had no resonant circuits, so they had no way of selecting one signal from others besides the broad resonance of the antenna, and responded to the transmissions of all transmitters in the vicinity. [ 44 ] An example of this interference problem was an embarrassing public debacle in August 1901 when Marconi, Lee de Forest , and G. W. Pickard attempted to report the New York Yacht Race to newspapers from ships with their untuned spark transmitters. [ 49 ] [ 50 ] [ 51 ] The Morse code transmissions interfered, and the reporters on shore failed to receive any information from the garbled signals.
It became clear that for multiple transmitters to operate, some system of "selective signaling" [ 53 ] [ 54 ] had to be devised to allow a receiver to select which transmitter's signal to receive, and reject the others. In 1892 William Crookes had given an influential [ 55 ] lecture [ 56 ] on radio in which he suggested using resonance (then called syntony ) to reduce the bandwidth of transmitters and receivers. [ 17 ] : p.352-353, 355–358 Using a resonant circuit (also called tuned circuit or tank circuit) in transmitters would narrow the bandwidth of the radiated signal, it would occupy a smaller range of frequencies around its center frequency, so that the signals of transmitters "tuned" to transmit on different frequencies would no longer overlap. A receiver which had its own resonant circuit could receive a particular transmitter by "tuning" its resonant frequency to the frequency of the desired transmitter, analogously to the way one musical instrument could be tuned to resonance with another. [ 53 ] This is the system used in all modern radio.
During the period 1897 to 1900 wireless researchers realized the advantages of "syntonic" or "tuned" systems, and added capacitors ( Leyden jars ) and inductors (coils of wire) to transmitters and receivers, to make resonant circuits (tuned circuits, or tank circuits). [ 36 ] : p. 125-136, 254–255, 259 Oliver Lodge , who had been researching electrical resonance for years, [ 36 ] : p.108-109 [ 44 ] patented the first "syntonic" transmitter and receiver in May 1897 [ 52 ] [ 57 ] [ 26 ] [ 36 ] : p.130–143 [ 24 ] : p.90-93 Lodge added an inductor (coil) between the sides of his dipole antennas, which resonated with the capacitance of the antenna to make a tuned circuit. [ 44 ] [ 36 ] : p. 125-136, 254–255, 259 Although his complicated circuit did not see much practical use, Lodge's "syntonic" patent was important because it was the first to propose a radio transmitter and receiver containing resonant circuits which were tuned to resonance with each other. [ 44 ] [ 36 ] : p. 125-136, 254–255, 259 In 1911 when the patent was renewed the Marconi Company was forced to buy it to protect its own syntonic system against infringement suits. [ 36 ] : p. 125-136, 254–255, 259
The resonant circuit functioned analogously to a tuning fork , storing oscillating electrical energy, increasing the Q factor of the circuit so the oscillations were less damped. [ 36 ] : p. 125-136, 254–255, 259 Another advantage was the frequency of the transmitter was no longer determined by the length of the antenna but by the resonant circuit, so it could easily be changed by adjustable taps on the coil. The antenna was brought into resonance with the tuned circuit using loading coils . The energy in each spark, and thus the power output, was no longer limited by the capacitance of the antenna but by the size of the capacitor in the resonant circuit. [ 17 ] : p.352-353, 355–358 In order to increase the power very large capacitor banks were used. The form that the resonant circuit took in practical transmitters was the inductively-coupled circuit described in the next section.
In developing these syntonic transmitters, researchers found it impossible to achieve low damping with a single resonant circuit. A resonant circuit can only have low damping (high Q, narrow bandwidth) if it is a "closed" circuit, with no energy dissipating components. [ 58 ] [ 24 ] : p.90-93 [ 36 ] : p.108-109 But such a circuit does not produce radio waves. A resonant circuit with an antenna radiating radio waves (an "open" tuned circuit) loses energy quickly, giving it high damping (low Q, wide bandwidth). There was a fundamental tradeoff between a circuit which produced persistent oscillations which had narrow bandwidth, and one which radiated high power. [ 11 ]
The solution found by a number of researchers was to use two resonant circuits in the transmitter, with their coils inductively (magnetically) coupled , making a resonant transformer (called an oscillation transformer ); [ 11 ] [ 46 ] [ 17 ] : p.352-353, 355–358 this was called an " inductively coupled ", " coupled circuit " [ 45 ] or " two circuit " transmitter. [ 33 ] [ 48 ] [ 24 ] : p.98-100 See circuit diagram. The primary winding of the oscillation transformer ( L1 ) with the capacitor ( C1 ) and spark gap ( S ) formed a "closed" resonant circuit which generated the oscillations, while the secondary winding ( L2 ) was connected to the wire antenna ( A ) and ground, forming an "open" resonant circuit with the capacitance of the antenna ( C2 ). [ 17 ] : p.352-353, 355–358 Both circuits were tuned to the same resonant frequency . [ 17 ] : p.352-353, 355–358 The advantage of the inductively coupled circuit was that the "loosely coupled" transformer transferred the oscillating energy of the tank circuit to the radiating antenna circuit gradually, creating long "ringing" waves. [ 46 ] [ 11 ] A second advantage was that it allowed a large primary capacitance (C1) to be used which could store a lot of energy, increasing the power output enormously. [ 46 ] [ 17 ] : p.352-353, 355–358 Powerful transoceanic transmitters often had huge Leyden jar capacitor banks filling rooms (see pictures above) . The receiver in most systems also used two inductively coupled circuits, with the antenna an "open" resonant circuit coupled through an oscillation transformer to a "closed" resonant circuit containing the detector . A radio system with a "two circuit" (inductively coupled) transmitter and receiver was called a "four circuit" system.
The first person to use resonant circuits in a radio application was Nikola Tesla , who invented the resonant transformer in 1891. [ 59 ] At a March 1893 St. Louis lecture [ 60 ] he had demonstrated a wireless system that, although it was intended for wireless power transmission , had many of the elements of later radio communication systems. [ 61 ] [ 62 ] [ 17 ] : p.352-353, 355–358 [ 36 ] : p. 125-136, 254–255, 259 [ 63 ] A grounded capacitance-loaded spark-excited resonant transformer (his Tesla coil ) attached to an elevated wire monopole antenna transmitted radio waves, which were received across the room by a similar wire antenna attached to a receiver consisting of a second grounded resonant transformer tuned to the transmitter's frequency, which lighted a Geissler tube . [ 64 ] [ 63 ] [ 65 ] This system, patented by Tesla 2 September 1897, [ 66 ] 4 months after Lodge's "syntonic" patent, was in effect an inductively coupled radio transmitter and receiver, the first use of the "four circuit" system claimed by Marconi in his 1900 patent (below) . [ 67 ] [ 17 ] : p.352-353, 355–358 [ 63 ] [ 61 ] However, Tesla was mainly interested in wireless power and never developed a practical radio communication system. [ 68 ] [ 69 ] [ 64 ] [ 17 ] : p.352-353, 355–358
In addition to Tesla's system, inductively coupled radio systems were patented by Oliver Lodge in February 1898, [ 70 ] [ 71 ] Karl Ferdinand Braun , [ 24 ] : p.98-100 [ 17 ] : p.352-353, 355–358 [ 43 ] [ 72 ] in November 1899, and John Stone Stone in February 1900. [ 73 ] [ 71 ] Braun made the crucial discovery that low damping required "loose coupling" (reduced mutual inductance ) between the primary and secondary coils. [ 74 ] [ 17 ] : p.352-353, 355–358
Marconi at first paid little attention to syntony, but by 1900 developed a radio system incorporating features from these systems, [ 74 ] [ 43 ] with a two circuit transmitter and two circuit receiver, with all four circuits tuned to the same frequency, using a resonant transformer he called the "jigger". [ 58 ] [ 33 ] [ 24 ] : p.98-100 In spite of the above prior patents, Marconi in his 26 April 1900 "four circuit" or "master tuning" patent [ 75 ] on his system claimed rights to the inductively coupled transmitter and receiver. [ 17 ] : p.352-353, 355–358 [ 71 ] [ 63 ] This was granted a British patent, but the US patent office twice rejected his patent as lacking originality. Then in a 1904 appeal a new patent commissioner reversed the decision and granted the patent, [ 76 ] [ 63 ] on the narrow grounds that Marconi's patent by including an antenna loading coil (J in circuit above) provided the means for tuning the four circuits to the same frequency, whereas in the Tesla and Stone patents this was done by adjusting the length of the antenna. [ 71 ] [ 63 ] This patent gave Marconi a near monopoly of syntonic wireless telegraphy in England and America. [ 77 ] [ 33 ] Tesla sued Marconi's company for patent infringement but didn't have the resources to pursue the action. In 1943 the US Supreme Court invalidated the inductive coupling claims of Marconi's patent [ 78 ] due to the prior patents of Lodge, Tesla, and Stone, but this came long after spark transmitters had become obsolete. [ 71 ] [ 63 ]
The inductively coupled or "syntonic" spark transmitter was the first type that could communicate at intercontinental distances, and also the first that had sufficiently narrow bandwidth that interference between transmitters was reduced to a tolerable level. It became the dominant type used during the "spark" era. [ 33 ] A drawback of the plain inductively coupled transmitter was that unless the primary and secondary coils were very loosely coupled it radiated on two frequencies. [ 17 ] : p.352-353, 355–358 [ 79 ] This was remedied by the quenched-spark and rotary gap transmitters (below) .
In recognition of their achievements in radio, Marconi and Braun shared the 1909 Nobel Prize in physics . [ 17 ] : p.352-353, 355–358
Marconi decided in 1900 to attempt transatlantic communication, which would allow him to dominate Atlantic shipping and compete with submarine telegraph cables . [ 24 ] : p.60-61 [ 17 ] : p.387-392 This would require a major scale-up in power, a risky gamble for his company. Up to that time his small induction coil transmitters had an input power of 100 - 200 watts, and the maximum range achieved was around 150 miles. [ 24 ] : p.60-61 [ 80 ] To build the first high power transmitter, Marconi hired an expert in electric power engineering, Prof. John Ambrose Fleming of University College, London, who applied power engineering principles. Fleming designed a complicated inductively-coupled transmitter (see circuit) with two cascaded spark gaps (S1, S2) firing at different rates, and three resonant circuits, powered by a 25 kW alternator (D) turned by a combustion engine. [ 80 ] [ 24 ] : p.60-61 [ 81 ] The first spark gap and resonant circuit (S1, C1, T2) generated the high voltage to charge the capacitor (C2) powering the second spark gap and resonant circuit (S2, C2, T3) , which generated the output. [ 81 ] The spark rate was low, perhaps as low as 2 - 3 sparks per second. [ 81 ] Fleming estimated the radiated power was around 10 - 12 kW. [ 80 ]
The transmitter was built in secrecy on the coast at Poldhu , Cornwall , UK. [ 80 ] [ 24 ] : p.60-61 Marconi was pressed for time because Nikola Tesla was building his own transatlantic radiotelegraphy transmitter on Long Island, New York , in a bid to be first [ 24 ] : p.286-288 (this was the Wardenclyffe Tower , which lost funding and was abandoned unfinished after Marconi's success). Marconi's original round 400-wire transmitting antenna collapsed in a storm 17 September 1901 and he hastily erected a temporary antenna consisting of 50 wires suspended in a fan shape from a cable between two 160 foot poles. [ 80 ] [ 81 ] [ 24 ] : p.286-288 The frequency used is not known precisely, as Marconi did not measure wavelength or frequency, but it was between 166 and 984 kHz, probably around 500 kHz. [ 17 ] : p.387-392 He received the signal on the coast of St. John's, Newfoundland using an untuned coherer receiver with a 400 ft. wire antenna suspended from a kite . [ 17 ] : p.387-392 [ 80 ] [ 24 ] : p.286-288 Marconi announced the first transatlantic radio transmission took place on 12 December 1901, from Poldhu , Cornwall to Signal Hill, Newfoundland , a distance of 2100 miles (3400 km). [ 17 ] : p.387-392 [ 24 ] : p.286-288
Marconi's achievement received worldwide publicity, and was the final proof that radio was a practical communication technology. The scientific community at first doubted Marconi's report. Virtually all wireless experts besides Marconi believed that radio waves traveled in straight lines, so no one (including Marconi) understood how the waves had managed to propagate around the 300 mile high curve of the Earth between Britain and Newfoundland. [ 30 ] In 1902 Arthur Kennelly and Oliver Heaviside independently theorized that radio waves were reflected by a layer of ionized atoms in the upper atmosphere, enabling them to return to Earth beyond the horizon. [ 30 ] In 1924 Edward V. Appleton demonstrated the existence of this layer, now called the " Kennelly–Heaviside layer " or "E-layer", for which he received the 1947 Nobel Prize in Physics .
Knowledgeable sources today doubt whether Marconi actually received this transmission. [ 82 ] [ 81 ] [ 17 ] : p.387-392 Ionospheric conditions should not have allowed the signal to be received during the daytime at that range. Marconi knew the Morse code signal to be transmitted was the letter 'S' (three dots). [ 17 ] : p.387-392 He and his assistant could have mistaken atmospheric radio noise ("static") in their earphones for the clicks of the transmitter. [ 81 ] [ 17 ] : p.387-392 Marconi made many subsequent transatlantic transmissions which clearly establish his priority, but reliable transatlantic communication was not achieved until 1907 with more powerful transmitters. [ 81 ]
The inductively-coupled transmitter had a more complicated output waveform than the non-syntonic transmitter, due to the interaction of the two resonant circuits. The two magnetically coupled tuned circuits acted as a coupled oscillator , producing beats (see top graphs) . The oscillating radio frequency energy was passed rapidly back and forth between the primary and secondary resonant circuits as long as the spark continued. [ 84 ] [ 79 ] [ 85 ] Each time the energy returned to the primary, some was lost as heat in the spark. [ 85 ] [ 79 ] In addition, unless the coupling was very loose the oscillations caused the transmitter to transmit on two separate frequencies. [ 79 ] [ 86 ] Since the narrow passband of the receiver's resonant circuit could only be tuned to one of these frequencies, the power radiated at the other frequency was wasted.
This troublesome backflow of energy to the primary circuit could be prevented by extinguishing (quenching) the spark at the right instant, after all the energy from the capacitors was transferred to the antenna circuit. [ 83 ] [ 86 ] Inventors tried various methods to accomplish this, such as air blasts and Elihu Thomson 's magnetic blowout . [ 79 ] [ 86 ]
In 1906, a new type of spark gap was developed by German physicist Max Wien , [ 87 ] called the series or quenched gap. [ 88 ] [ 89 ] [ 90 ] [ 85 ] A quenched gap consisted of a stack of wide cylindrical electrodes separated by thin insulating spacer rings to create many narrow spark gaps in series, [ 89 ] of around 0.1–0.3 mm (0.004–0.01 in). [ 88 ] The wide surface area of the electrodes terminated the ionization in the gap quickly by cooling it after the current stopped. In the inductively coupled transmitter, the narrow gaps extinguished ("quenched") the spark at the first nodal point ( Q ) when the primary current momentarily went to zero after all the energy had been transferred to the secondary winding (see lower graph) . [ 83 ] Since without the spark no current could flow in the primary circuit, this effectively uncoupled the secondary from the primary circuit, allowing the secondary resonant circuit and antenna to oscillate completely free of the primary circuit after that (until the next spark). This produced output power centered on a single frequency instead of two frequencies. It also eliminated most of the energy loss in the spark, producing very lightly damped, long "ringing" waves, with decrements of only 0.08 to 0.25 [ 91 ] (a Q of 12-38) and consequently a very "pure", narrow bandwidth radio signal. Another advantage was the rapid quenching allowed the time between sparks to be reduced, allowing higher spark rates of around 1000 Hz to be used, which had a musical tone in the receiver which penetrated radio static better. The quenched gap transmitter was called the "singing spark" system. [ 91 ] [ 88 ]
The German wireless giant Telefunken Co., Marconi's rival, acquired the patent rights and used the quenched spark gap in their transmitters. [ 90 ] [ 88 ] [ 85 ]
A second type of spark gap that had a similar quenching effect [ 15 ] was the "rotary gap", invented by Tesla in 1896 [ 92 ] [ 93 ] and applied to radio transmitters by Reginald Fessenden and others. [ 17 ] : p.359–362 [ 79 ] It consisted of multiple electrodes equally spaced around a disk rotor spun at high speed by a motor, which created sparks as they passed by a stationary electrode. [ 11 ] [ 48 ] By using the correct motor speed, the rapidly separating electrodes extinguished the spark after the energy had been transferred to the secondary. [ 15 ] [ 11 ] [ 17 ] : p.359–362 [ 79 ] The rotating wheel also kept the electrodes cooler, important in high-power transmitters.
There were two types of rotary spark transmitter: [ 15 ] [ 17 ] : p.359–362 [ 11 ] [ 79 ] [ 81 ]
To reduce interference caused by the "noisy" signals of the burgeoning numbers of spark transmitters, the 1912 US Congress "Act to Regulate Radio Communication" required that " the logarithmic decrement per oscillation in the wave trains emitted by the transmitter shall not exceed two tenths " [ 48 ] [ 11 ] [ 94 ] (this is equivalent to a Q factor of 15 or greater). Virtually the only spark transmitters which could satisfy this condition were the quenched-spark and rotary gap types above, [ 48 ] and they dominated wireless telegraphy for the rest of the spark era.
In 1912 in his high-power stations Marconi developed a refinement of the rotary discharger called the "timed spark" system, which generated what was probably the nearest to a continuous wave that sparks could produce. [ 95 ] [ 96 ] [ 17 ] : p.399 He used several identical resonant circuits in parallel, with the capacitors charged by a DC dynamo . [ 97 ] These were discharged sequentially by multiple rotary discharger wheels on the same shaft to create overlapping damped waves shifted progressively in time, which were added together in the oscillation transformer so the output was a superposition of damped waves. The speed of the discharger wheel was controlled so that the time between sparks was equal to an integer multiple of the wave period. Therefore, oscillations of the successive wave trains were in phase and reinforced each other. The result was essentially a continuous sinusoidal wave, whose amplitude varied with a ripple at the spark rate. This system was necessary to give Marconi's transoceanic stations a narrow enough bandwidth that they didn't interfere with other transmitters on the narrow VLF band. Timed spark transmitters achieved the longest transmission range of any spark transmitters, but these behemoths represented the end of spark technology. [ 17 ] : p.399
The first application of radio was on ships, to keep in touch with shore, and send out a distress call if the ship were sinking. [ 100 ] The Marconi Company built a string of shore stations and in 1904 established the first Morse code distress call, the letters CQD , used until the Second International Radiotelegraphic Convention in 1906 at which SOS was agreed on. The first significant marine rescue due to radiotelegraphy was the 23 January 1909 sinking of the luxury liner RMS Republic , in which 1500 people were saved.
Spark transmitters and the crystal receivers used to receive them were simple enough that they were widely built by hobbyists. [ 15 ] During the first decades of the 20th century this exciting new high tech hobby attracted a growing community of " radio amateurs ", many of them teenage boys, who used their homebuilt sets recreationally to contact distant amateurs and chat with them by Morse code, and relay messages. [ 102 ] [ 103 ] Low-power amateur transmitters ("squeak boxes") were often built with " trembler " ignition coils from early automobiles such as the Ford Model T . [ 102 ] In the US prior to 1912 there was no government regulation of radio, and a chaotic "wild west" atmosphere prevailed, with stations transmitting without regard to other stations on their frequency, and deliberately interfering with each other. [ 103 ] [ 104 ] [ 105 ] The expanding numbers of non-syntonic broadband spark transmitters created uncontrolled congestion in the airwaves, interfering with commercial and military wireless stations. [ 105 ]
The RMS Titanic sinking 14 April 1912 increased public appreciation for the role of radio, but the loss of life brought attention to the disorganized state of the new radio industry, [ 106 ] and prompted regulation which corrected some abuses. [ 103 ] Although the Titanic radio operator's CQD distress calls summoned the RMS Carpathia which rescued 705 survivors, the rescue operation was delayed four hours because the nearest ship, the SS Californian , only a few miles away, did not hear the Titanic ' s call as its radio operator had gone to bed. This was held responsible for most of the 1500 deaths. Existing international regulations required all ships with more than 50 passengers to carry wireless equipment, but after the disaster subsequent regulations mandated ships have enough radio officers so that a round-the-clock radio watch could be kept. US President Taft and the public heard reports of chaos on the air the night of the disaster, with amateur stations interfering with official naval messages and passing false information. [ 106 ] [ 107 ] In response Congress passed the 1912 Radio Act, in which licenses were required for all radio transmitters, maximum damping of transmitters was limited to a decrement of 0.2 to get old noisy non-syntonic transmitters off the air, and amateurs were mainly restricted to the unused frequencies above 1.5 MHz and output power of 1 kilowatt. [ 94 ] [ 105 ] [ 15 ]
The largest spark transmitters were powerful transoceanic radiotelegraphy stations with input power of 100 - 300 kW. [ 108 ] [ 109 ] Beginning about 1910, industrial countries built global networks of these stations to exchange commercial and diplomatic telegram traffic with other countries and communicate with their overseas colonies. [ 110 ] [ 111 ] [ 112 ] During World War I , radio became a strategic defensive technology, as it was realized a nation without long distance radiotelegraph stations could be isolated by an enemy cutting its submarine telegraph cables . [ 111 ] Most of these networks were built by the two giant wireless corporations of the age: the British Marconi Company , which constructed the Imperial Wireless Chain to link the possessions of the British Empire , and the German Telefunken Co. which was dominant outside the British Empire. [ 110 ] Marconi transmitters used the timed spark rotary discharger, while Telefunken transmitters used its quenched spark gap technology. Paper tape machines were used to transmit Morse code text at high speed. To achieve a maximum range of around 3000 – 6000 miles, transoceanic stations transmitted mainly in the very low frequency (VLF) band, from 50 kHz to as low as 15 – 20 kHz. At these wavelengths even the largest antennas were electrically short , a tiny fraction of a wavelength tall, and so had low radiation resistance (often below 1 ohm), so these transmitters required enormous wire umbrella and flattop antennas up to several miles long with large capacitive toploads, to achieve adequate efficiency. The antenna required a large loading coil at the base, 6 – 10 feet tall, to make it resonant with the transmitter.
Although their damping had been reduced as much as possible, spark transmitters still produced damped waves , which due to their large bandwidth caused interference between transmitters. [ 4 ] [ 36 ] : p.72-79 The spark also made a very loud noise when operating, produced corrosive ozone gas, eroded the spark electrodes, and could be a fire hazard. [ 15 ] Despite its drawbacks, most wireless experts believed along with Marconi that the impulsive "whipcrack" of a spark was necessary to produce radio waves that would communicate long distances. [ 17 ] : p.374 [ 27 ] : p.78
From the beginning, physicists knew that another type of waveform, continuous sinusoidal waves (CW), had theoretical advantages over damped waves for radio transmission. [ 113 ] [ 10 ] : p.4–7, 32–33 Because their energy is essentially concentrated at a single frequency, in addition to causing almost no interference to other transmitters on adjacent frequencies, continuous wave transmitters could transmit longer distances with a given output power. [ 36 ] : p.72-79 They could also be modulated with an audio signal to carry sound. [ 36 ] : p.72-79 The problem was no techniques were known for generating them. The efforts described above to reduce the damping of spark transmitters can be seen as attempts to make their output approach closer to the ideal of a continuous wave, but spark transmitters could not produce true continuous waves. [ 10 ] : p.4–7, 32–33
Beginning about 1904, continuous wave transmitters were developed using new principles, which competed with spark transmitters. Continuous waves were first generated by two short-lived technologies: [ 36 ] : p.72-79
These transmitters, which could produce power outputs of up to one megawatt , slowly replaced the spark transmitter in high-power radiotelegraphy stations. However spark transmitters remained popular in two way communication stations because most continuous wave transmitters were not capable of a mode called "break in" or "listen in" operation. [ 114 ] With a spark transmitter, when the telegraph key was up between Morse symbols the carrier wave was turned off and the receiver was turned on, so the operator could listen for an incoming message. This allowed the receiving station, or a third station, to interrupt or "break in" to an ongoing transmission. In contrast, these early CW transmitters had to operate continuously; the carrier wave was not turned off between Morse code symbols, words, or sentences but just detuned, so a local receiver could not operate as long as the transmitter was powered up. Therefore, these stations could not receive messages until the transmitter was turned off.
All these early technologies were superseded by the vacuum tube feedback electronic oscillator , invented in 1912 by Edwin Armstrong and Alexander Meissner , which used the triode vacuum tube invented in 1906 by Lee de Forest . [ 1 ] Vacuum tube oscillators were a far cheaper source of continuous waves, and could be easily modulated to carry sound. Due to the development of the first high-power transmitting tubes by the end of World War I, in the 1920s tube transmitters replaced the arc converter and alternator transmitters, as well as the last of the old noisy spark transmitters.
The 1927 International Radiotelegraph Convention in Washington, D.C. saw a political battle to finally eliminate spark radio. [ 6 ] Spark transmitters were obsolete at this point, and broadcast radio audiences and aviation authorities were complaining of the disruption to radio reception that noisy legacy marine spark transmitters were causing. But shipping interests vigorously fought a blanket prohibition on damped waves, due to the capital expenditure that would be required to replace spark equipment that was still being used on older ships. The Convention prohibited licensing of new land spark transmitters after 1929. [ 115 ] Damped wave radio emission, called Class B, was banned after 1934 except for emergency use on ships. [ 5 ] [ 115 ] This loophole allowed shipowners to avoid replacing spark transmitters, which were kept as emergency backup transmitters on ships through World War II.
One legacy of spark-gap transmitters is that radio operators were regularly nicknamed "Sparky" long after the devices ceased to be used. Even today, the German verb funken , literally, "to spark", also means "to send a radio message".
The spark gap oscillator was also used in nonradio applications, continuing long after it became obsolete in radio. In the form of the Tesla coil and Oudin coil it was used until the 1940s in the medical field of diathermy for deep body heating. [ 116 ] [ 117 ] High oscillating voltages of hundreds of thousands of volts at frequencies of 0.1 - 1 MHz from a Tesla coil were applied directly to the patient's body. The treatment was not painful, because currents in the radio frequency range do not cause the physiological reaction of electric shock . In 1926 William T. Bovie discovered that RF currents applied to a scalpel could cut and cauterize tissue in medical operations, and spark oscillators were used as electrosurgery generators or "Bovies" as late as the 1980s. [ 118 ]
In the 1950s a Japanese toy company, Matsudaya, produced a line of cheap remote control toy trucks, boats and robots called Radicon, which used a low-power spark transmitter in the controller as an inexpensive way to produce the radio control signals. [ 119 ] [ 120 ] The signals were received in the toy by a coherer receiver.
Spark gap oscillators are still used to generate high-frequency high voltage needed to initiate welding arcs in gas tungsten arc welding . [ 121 ] Powerful spark gap pulse generators are still used to simulate EMPs . | https://en.wikipedia.org/wiki/Spark-gap_transmitter |
Spark is an open-source instant messaging program (based on the XMPP protocol) that allows users to communicate in real time. [ 4 ]
It can be integrated with the Openfire server to provide additional features [ 5 ] such as controlling the various Spark functionalities from a central management console or integrating with a proprietary customer support service known as Fastpath which allows its users to interact with the platform using the Spark client.
Being a cross-platform application, Spark can run on various systems. Installers for Windows , macOS and Linux [ 6 ] are available on the official website. The server is JRE -based, where the client is not. The Spark xmpp -client supports neither Jingle nor Omemo encryption.
Previously known as Jive Communicator, Spark was designed by Jive Software with a lightweight graphical design and simplistic user interface for business usage. [ citation needed ] Later, it was open-sourced and donated to the Ignite Realtime community, along with Openfire , for further improvement and development. [ citation needed ]
Spark is based on the open-source Smack API library, [ 7 ] also developed by Ignite Realtime. It has a tabbed interface for managing conversations, a quick and full history, and a search feature inside the contacts window which is designed for organizations with many units and employees. Other features include shortcuts to access recent and favorite contacts.
Spark supports ad hoc and regular group chats. It also supports SSL/TLS encryption, and additionally provides an option to use Off-the-Record Messaging for end-to-end encryption. Though it is designed to work with XMPP servers, it can also integrate with Kraken IM Gateway plugin for Openfire , and provides an option to connect with many other IM networks.
The software’s user interface is intended to be lightweight with skins, tabbed conversations and plugin support. It contains single sign-on and file transfer capability, as well as privacy list. | https://en.wikipedia.org/wiki/Spark_(XMPP_client) |
SparrowIQ is a packet-based traffic analysis and network performance monitoring solution that provides network managers with near real-time traffic visibility into network usage based on conversations, applications, users and class of service. [ 1 ] [ 2 ]
The product was developed by Solana Networks ( Ottawa, Ontario , Canada ) to allow smaller businesses to gain access to flow-based network traffic monitoring solutions - normally too complex or unaffordable. [ 3 ] [ 4 ] [ 5 ]
SparrowIQ was awarded the "Best New Product" by the ASCII Group in June 2015 [ 6 ] and "Strong Value" award by Enterprise Management Associates in 2013. [ 7 ]
SparrowIQ key features [ 8 ] [ 9 ] | https://en.wikipedia.org/wiki/Sparrowiq |
A Sparse graph code is a code which is represented by a sparse graph .
Any linear code can be represented as a graph, where there are two sets of nodes - a set representing the transmitted bits and another set representing the constraints that the transmitted bits have to satisfy. The state of the art classical error-correcting codes are based on sparse graphs, achieving close to the Shannon limit . The archetypal sparse-graph codes are Gallager's low-density parity-check codes .
This article about matrices is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sparse_graph_code |
In mathematics, a sparse polynomial (also lacunary polynomial [ 1 ] or fewnomial [ 2 ] ) is a polynomial that has far fewer terms than its degree and number of variables would suggest. For example, x 10 + 3 x 3 + 1 {\displaystyle x^{10}+3x^{3}+1} is a sparse polynomial, as it is a trinomial with a degree of 10 {\displaystyle 10} .
The motivation for studying sparse polynomials is to concentrate on the structure of a polynomial's monomials instead of its degree, as one can see, for instance, by comparing Bernstein–Kushnirenko theorem with Bezout's theorem . Research on sparse polynomials has also included work on algorithms whose running time grows as a function of the number of terms rather than on the degree, [ 3 ] for problems including polynomial multiplication [ 4 ] [ 5 ] , division , [ 6 ] root-finding algorithms , [ 7 ] and polynomial greatest common divisors . [ 8 ] Sparse polynomials have also been used in pure mathematics, especially in the study of Galois groups , because it has been easier to determine the Galois groups of certain families of sparse polynomials than it is for other polynomials. [ 9 ]
The algebraic varieties determined by sparse polynomials have a simple structure, which is also reflected in the structure of the solutions of certain related differential equations . [ 2 ] Additionally, a sparse positivstellensatz exists for univariate sparse polynomials. It states that the non-negativity of a polynomial can be certified by SOS polynomials whose degree only depends on the number of monomials of the polynomial. [ 10 ]
Sparse polynomials often come up in sum or difference of powers equations. The sum of two cubes states that ( x + y ) ( x 2 − x y + y 2 ) = x 3 + y 3 {\displaystyle (x+y)(x^{2}-xy+y^{2})=x^{3}+y^{3}} . Here x 3 + y 3 {\displaystyle x^{3}+y^{3}} is a sparse polynomial, since out of the 16 {\displaystyle 16} possible terms, only 2 {\displaystyle 2} appear.
Other examples include the identities ( x − y ) ∑ k = 0 N − 1 x k y N − 1 − k = x N − y N {\displaystyle (x-y)\sum _{k=0}^{N-1}x^{k}y^{N-1-k}=x^{N}-y^{N}} and also ( x + y ) ∑ k = 0 2 n ( − 1 ) k x k y 2 n − k = x 2 n + 1 + y 2 n + 1 , {\displaystyle (x+y)\sum _{k=0}^{2n}(-1)^{k}x^{k}y^{2n-k}=x^{2n+1}+y^{2n+1},} where the product of two polynomials give a spearse polynomial. The Bring–Jerrard normal form of a quintic, x 5 + p x + q , {\displaystyle x^{5}+px+q,} is also a sparse polynomial.
This polynomial -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sparse_polynomial |
A sparse ruler is a ruler in which some of the distance marks may be missing. More abstractly, a sparse ruler of length L {\displaystyle L} with m {\displaystyle m} marks is a sequence of integers a 1 , a 2 , . . . , a m {\displaystyle a_{1},a_{2},...,a_{m}} where 0 = a 1 < a 2 < . . . < a m = L {\displaystyle 0=a_{1}<a_{2}<...<a_{m}=L} . The marks a 1 {\displaystyle a_{1}} and a m {\displaystyle a_{m}} correspond to the ends of the ruler. In order to measure the distance K {\displaystyle K} , with 0 ≤ K ≤ L {\displaystyle 0\leq K\leq L} there must be marks a i {\displaystyle a_{i}} and a j {\displaystyle a_{j}} such that a j − a i = K {\displaystyle a_{j}-a_{i}=K} .
A complete sparse ruler allows one to measure any integer distance up to its full length. A complete sparse ruler is called minimal if there is no complete sparse ruler of length L {\displaystyle L} with m − 1 {\displaystyle m-1} marks. In other words, if any of the marks is removed one can no longer measure all of the distances, even if the marks could be rearranged. A complete sparse ruler is called maximal if there is no complete sparse ruler of greater length with m {\displaystyle m} marks. Complete minimal rulers of length 135 and 136 require one more mark than those of lengths 124-134, 137 and 138. A sparse ruler is called optimal if it is both minimal and maximal.
Since the number of distinct pairs of marks is m ( m − 1 ) / 2 {\displaystyle m(m-1)/2} , this is an upper bound on the length L {\displaystyle L} of any maximal sparse ruler with m {\displaystyle m} marks. This upper bound can be achieved only for 2, 3 or 4 marks. For larger numbers of marks, the difference between the optimal length and the bound grows gradually, and unevenly.
For example, for 6 marks the upper bound is 15, but the maximal length is 13. There are 3 different configurations of sparse rulers of length 13 with 6 marks. One is {0, 1, 2, 6, 10, 13}. To measure a length of 7, say, with this ruler one would take the distance between the marks at 6 and 13.
A Golomb ruler is a sparse ruler that requires all of the differences a j − a i {\displaystyle a_{j}-a_{i}} be distinct. In general, a Golomb ruler with m {\displaystyle m} marks will be considerably longer than an optimal sparse ruler with m {\displaystyle m} marks, since m ( m − 1 ) / 2 {\displaystyle m(m-1)/2} is a lower bound for the length of a Golomb ruler. A long Golomb ruler will have gaps, that is, it will have distances which it cannot measure. For example, the optimal Golomb ruler {0, 1, 4, 10, 12, 17} has length 17, but cannot measure lengths of 14 or 15.
As found by Brian Wichmann, many optimal rulers [ 1 ] are of the form W ( r , s ) = 1 r , r + 1 , ( 2 r + 1 ) r , ( 4 r + 3 ) s , ( 2 r + 2 ) ( r + 1 ) , 1 r , {\displaystyle W(r,s)=1^{r},r+1,(2r+1)^{r},(4r+3)^{s},(2r+2)^{(r+1)},1^{r},} where a b {\displaystyle a^{b}} represents b {\displaystyle b} segments of length a {\displaystyle a} . Thus, if r = 1 {\displaystyle r=1} and s = 2 {\displaystyle s=2} , then W ( 1 , 2 ) {\displaystyle W(1,2)} has (in order): 1 segment of length 1, 1 segment of length 2, 1 segment of length 3, 2 segments of length 7, 2 segments of length 4, 1 segment of length 1.
A minor variant is w ( r , s ) = 1 r , r + 1 , ( 2 r + 1 ) ( r + 1 ) , ( 4 r + 3 ) s , ( 2 r + 2 ) r , 1 r , {\displaystyle w(r,s)=1^{r},r+1,(2r+1)^{(r+1)},(4r+3)^{s},(2r+2)^{r},1^{r},} , with a length one less than W ( r , s ) {\displaystyle W(r,s)} .
W ( 1 , 2 ) {\displaystyle W(1,2)} gives the ruler {0, 1, 3, 6, 13, 20, 24, 28, 29}, while w ( 1 , 2 ) {\displaystyle w(1,2)} gives {0, 1, 3, 6, 9, 16, 23, 27, 28}. The length of a Wichmann ruler is 4 r ( r + s + 2 ) + 3 ( s + 1 ) {\displaystyle 4r(r+s+2)+3(s+1)} and the number of marks is 4 r + s + 3 {\displaystyle 4r+s+3} . Note that not all Wichmann rulers are optimal and not all optimal rulers can be generated this way. None of the optimal rulers of length 1, 13, 17, 23 and 58 follow this pattern. That sequence ends with 58 if the Optimal Ruler Conjecture of Peter Luschny is correct. The conjecture is known to be true to length 213. [ 2 ]
For every n {\displaystyle n} let l ( n ) {\displaystyle l(n)} be the smallest number of marks for a ruler of length n {\displaystyle n} . For example, l ( 6 ) = 4 {\displaystyle l(6)=4} . The asymptotic of the function l ( n ) {\displaystyle l(n)} was studied by Erdos, Gal [ 3 ] (1948) and continued by Leech [ 4 ] (1956) who proved that the limit lim n → ∞ l ( n ) 2 / n {\displaystyle \lim _{n\to \infty }{l(n)^{2}}/n} exists and is lower and upper bounded by 2 + 4 3 π = 2.424... < 2.434... = max 0 < θ < 2 π 2 ( 1 − sin ( θ ) θ ) ≤ lim n → ∞ l ( n ) 2 n ≤ 375 112 = 3.348... {\displaystyle 2+{\tfrac {4}{3\pi }}=2.424...<2.434...=\max _{0<\theta <2\pi }2(1-{\tfrac {\sin(\theta )}{\theta }})\leq \lim _{n\to \infty }{\frac {l(n)^{2}}{n}}\leq {\frac {375}{112}}=3.348...}
Much better upper bounds exist for n {\displaystyle n} -perfect rulers. Those are subsets A {\displaystyle A} of N {\displaystyle \mathbb {N} } such that each positive number k ≤ n {\displaystyle k\leq n} can be written as a difference k = a − b {\displaystyle k=a-b} for some a , b ∈ A {\displaystyle a,b\in A} . For every number n {\displaystyle n} let k ( n ) {\displaystyle k(n)} be the smallest cardinality of an n {\displaystyle n} -perfect ruler. It is clear that k ( n ) ≤ l ( n ) {\displaystyle k(n)\leq l(n)} . The asymptotics of the sequence k ( n ) {\displaystyle k(n)} was studied by Redei, Renyi [ 5 ] (1949) and then by Leech (1956) and Golay [ 6 ] (1972). Due to their efforts the following upper and lower bounds were obtained: max 0 < θ < 2 π 2 ( 1 − sin ( θ ) θ ) ≤ lim n → ∞ k ( n ) 2 n = inf n ∈ N k ( n ) 2 n ≤ 128 2 6166 = 2.6571... < 8 3 . {\displaystyle \max _{0<\theta <2\pi }2(1-{\tfrac {\sin(\theta )}{\theta }})\leq \lim _{n\to \infty }{\frac {k(n)^{2}}{n}}=\inf _{n\in \mathbb {N} }{\frac {k(n)^{2}}{n}}\leq {\frac {128^{2}}{6166}}=2.6571...<{\frac {8}{3}}.}
Define the excess as E ( n ) = l ( n ) − ⌈ 3 n + 9 4 ⌋ {\displaystyle E(n)=l(n)-\lceil {\sqrt {3n+{\tfrac {9}{4}}}}\rfloor } . In 2020, Pegg proved by construction that E ( n ) {\displaystyle E(n)} ≤ 1 for all lengths n {\displaystyle n} . [ 7 ] If the Optimal Ruler Conjecture is true, then E ( n ) = 0 | 1 {\displaystyle E(n)=0|1} for all n {\displaystyle n} , leading to the ″dark mills″ pattern when arranged in columns, OEIS A326499. [ 8 ] All of the windows in the dark mills pattern are Wichmann rulers. None of the best known sparse rulers n > 213 {\displaystyle n>213} are proven minimal as of Sep 2020. Many of the current best known E = 1 {\displaystyle E=1} constructions for n > 213 {\displaystyle n>213} are believed to non-minimal, especially the "cloud" values.
The following are examples of minimal sparse rulers. Optimal rulers are highlighted. When there are too many to list, not all are included. Mirror images are not shown.
III..I....I....I..........I..........I..........I..........I..........I..........I..........I..........I.....I.....I.....III
A few incomplete rulers can fully measure up to a longer distance than an optimal sparse ruler with the same number of marks. { 0 , 2 , 7 , 14 , 15 , 18 , 24 } {\displaystyle \{0,2,7,14,15,18,24\}} , { 0 , 2 , 7 , 13 , 16 , 17 , 25 } {\displaystyle \{0,2,7,13,16,17,25\}} , { 0 , 5 , 7 , 13 , 16 , 17 , 31 } {\displaystyle \{0,5,7,13,16,17,31\}} , and { 0 , 6 , 10 , 15 , 17 , 18 , 31 } {\displaystyle \{0,6,10,15,17,18,31\}} can each measure up to 18, while an optimal sparse ruler with 7 marks can measure only up to 17. The table below lists these rulers, up to rulers with 13 marks. Mirror images are not shown. Rulers that can fully measure up to a longer distance than any shorter ruler with the same number of marks are highlighted. | https://en.wikipedia.org/wiki/Sparse_ruler |
A sparse voxel octree ( SVO ) is a 3D computer graphics rendering technique using a raycasting or sometimes a ray tracing approach into an octree data representation.
The technique generally relies on generating and processing the hull of points (sparse voxels ) which are visible, or may be visible, given the resolution and size of the screen. [ 1 ] There are two main advantages to the technique. The first is that only pixels that will be displayed are computed, with the screen resolution limiting the level of detail required; this limits computational cost during rendering. The second is that interior voxels (those fully enclosed by other voxels) need not be included in the 3D data set; this limits the amount of 3D voxel data (and thus storage space) required for realistic, high-resolution digital models and/or environments.
The basic advantage of octrees is that, as a hierarchical data structure , they need not be explored to their full depth. This means that a system can extract a small subset of voxels as they are needed. In addition, octrees permit smoothing of the underlying data, to help with antialiasing .
It is, however, a generally less well developed technique than standard polygon-based rasterisation schemes.
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sparse_voxel_octree |
Spartan is a molecular modelling and computational chemistry application from Wavefunction. [ 2 ] It contains code for molecular mechanics , semi-empirical methods , ab initio models , [ 3 ] density functional models , [ 4 ] post-Hartree–Fock models, [ 5 ] thermochemical recipes including G3(MP2) [ 6 ] and T1, [ 7 ] and machine learning models like corrected MMFF [ 8 ] and Est. Density Functional. [ 9 ] Quantum chemistry calculations in Spartan are powered by Q-Chem . [ 10 ]
Primary functions are to supply information about structures, relative stabilities and other properties of isolated molecules. Molecular mechanics calculations on complex molecules are common in the chemical community. Quantum chemical calculations, including Hartree–Fock method molecular orbital calculations, but especially calculations that include electronic correlation , are more time-consuming in comparison.
Quantum chemical calculations are also called upon to furnish information about mechanisms and product distributions of chemical reactions, either directly by calculations on transition states , or based on Hammond's postulate , [ 11 ] by modeling the steric and electronic demands of the reactants. Quantitative calculations, leading directly to information about the geometries of transition states , and about reaction mechanisms in general, are increasingly common, while qualitative models are still needed for systems that are too large to be subjected to more rigorous treatments. Quantum chemical calculations can supply information to complement existing experimental data or replace it altogether, for example, atomic charges for quantitative structure-activity relationship (QSAR) [ 12 ] analyses, and intermolecular potentials for molecular mechanics and molecular dynamics calculations.
Spartan applies computational chemistry methods (theoretical models) to many standard tasks that provide calculated data applicable to the determination of molecular shape conformation , structure (equilibrium and transition state geometry), NMR , IR , Raman , and UV-visible spectra , molecular (and atomic) properties, reactivity, and selectivity.
This software provides the molecular mechanics , Merck Molecular Force Field (MMFF), [ 13 ] (for validation test suite), MMFF with extensions, and SYBYL, [ 14 ] force fields calculation, Semi-empirical calculations , MNDO /MNDO(D), [ 15 ] Austin Model 1 (AM1), [ 16 ] PM3 , [ 17 ] [ 18 ] [ 19 ] [ 20 ] Recife Model 1 (RM1) [ 21 ] PM6. [ 22 ]
Available computational models provide molecular, thermodynamic, QSAR, atomic, graphical, and spectral properties. A calculation dialogue provides access to the following computational tasks:
The software contains an integrated graphical user interface . Touch screen operations are supported for Windows 7 and 8 devices. Construction of molecules in 3D is facilitated with molecule builders (included are organic, inorganic, peptide, nucleotide, and substituent builders). 2D construction is supported for organic molecules with a 2D sketch palette. The Windows version interface can access ChemDraw ; which versions 9.0 or later may also be used for molecule building in 2D. A calculations dialogue is used for specification of task and computational method. Data from calculations are displayed in dialogues, or as text output. Additional data analysis, including linear regression , is possible from an internal spreadsheet. [ 73 ]
Graphical models, especially molecular orbitals, electron density, and electrostatic potential maps, are a routine means of molecular visualization in chemistry education. [ 75 ] [ 76 ] [ 77 ] [ 78 ] [ 79 ]
Available spectra data and plots for:
Experimental spectra may be imported for comparison with calculated spectra: IR and UV/vis spectra in Joint Committee on Atomic and Molecular Physical Data (JCAMP) [ 88 ] (.dx) format and NMR spectra in Chemical Markup Language (.cml) format. Access to public domain spectral databases is available for IR, NMR, and UV/vis spectra.
Spartan accesses several external databases. | https://en.wikipedia.org/wiki/Spartan_(chemistry_software) |
The Spartan Packet Radio Experiment ( SPRE ) was an amateur radio communications experiment that flew on the Space Shuttle Endeavour ' s STS-72 mission as part of NASA 's Spartan/OAST-Flyer spacecraft in January 1996. [ 1 ] The experiment was intended to test the tracking of satellites via amateur packet radio ( Automatic Packet Reporting System ), and was designed and built by the Amateur Radio Association at the University of Maryland (W3EAX). [ 2 ] [ 3 ] Required GPS data for the experiment was provided by another portion of the Spartan payload. [ 2 ] The operating mode was FM , AFSK 1200 baud packet radio, transmitted at 145.550 MHz. [ 4 ]
This article related to amateur radio is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Spartan_Packet_Radio_Experiment |
A spaser or plasmonic laser is a type of laser which aims to confine light at a subwavelength scale far below Rayleigh's diffraction limit of light , by storing some of the light energy in electron oscillations called surface plasmon polaritons . [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] The phenomenon was first described by David J. Bergman and Mark Stockman in 2003. [ 6 ] The word spaser is an acronym for " surface plasmon amplification by stimulated emission of radiation". [ 6 ] The first such devices were announced in 2009 by three groups: a 44- nanometer -diameter nanoparticle with a gold core surrounded by a dyed silica gain medium created by researchers from Purdue, Norfolk State and Cornell universities, [ 7 ] a nanowire on a silver screen by a Berkeley group, [ 1 ] and a semiconductor layer of 90 nm surrounded by silver pumped electrically by groups at the Eindhoven University of Technology and at Arizona State University. [ 4 ] While the Purdue-Norfolk State-Cornell team demonstrated the confined plasmonic mode, the Berkeley team and the Eindhoven-Arizona State team demonstrated lasing in the so-called plasmonic gap mode. In 2018, a team from Northwestern University demonstrated a tunable nanolaser that can preserve its high mode quality by exploiting hybrid quadrupole plasmons as an optical feedback mechanism. [ 8 ]
The spaser is a proposed nanoscale source of optical fields that is being investigated in a number of leading laboratories around the world. Spasers could find a wide range of applications, including nanoscale lithography , fabrication of ultra-fast photonic nano circuits, single-molecule biochemical sensing, and microscopy. [ 5 ]
From Nature Photonics : [ 9 ]
A spaser is the nanoplasmonic counterpart of a laser , but it (ideally) does not emit photons . It is analogous to the conventional laser, but in a spaser photons are replaced by surface plasmons and the resonant cavity is replaced by a nanoparticle, which supports the plasmonic modes. Similarly to a laser, the energy source for the spasing mechanism is an active (gain) medium that is excited externally. This excitation field may be optical and unrelated to the spaser’s operating frequency; for instance, a spaser can operate in the near- infrared but the excitation of the gain medium can be achieved using an ultraviolet pulse.
The reason that surface plasmons in a spaser can work analogously to photons in a laser is that their relevant physical properties are the same. First, surface plasmons are bosons : they are vector excitations and have spin 1, just as photons do. Second, surface plasmons are electrically neutral excitations. And third, surface plasmons are the most collective material oscillations known in nature, which implies they are the most harmonic (that is, they interact very weakly with one another). As such, surface plasmons can undergo stimulated emission, accumulating in a single mode in large numbers, which is the physical foundation of both the laser and the spaser.
Study of the quantum mechanical model of the spaser suggests that it should be possible to manufacture a spasing device analogous in function to the MOSFET transistor, [ 10 ] but this has not yet been experimentally verified. | https://en.wikipedia.org/wiki/Spaser |
Spathulenol is a tricyclic sesquiterpene alcohol which has a basic skeleton similar to the azulenes . It occurs in oregano among other plants.
A volatile oil was extracted from mugwort distillery ( Artemisia vulgaris ) and tarragon ( Artemisia dracunculus ), from which the sesquiterpene alcohol spathulenol was isolated for the first time in 1975 as a colorless, viscous compound with an earth-aromatic odor and bitter-spicy taste. [ 1 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Spathulenol |
The spatial-numerical association of response codes (SNARC) is an example of the spatial organisation of magnitude information. Put simply, when presented with smaller numbers (0 to 4), people tend to respond faster if those stimuli are associated with the left extrapersonal hemiside of their perceived surroundings; when presented with larger numbers (6 to 9), people respond faster if those stimuli are instead associated with the right extrapersonal hemiside of their perceived surroundings. The SNARC effect is this automatic association that occurs between the location of the response hand and the semantic magnitude of a modality-independent number. [ 1 ]
Even for tasks in which magnitude is irrelevant, like parity judgement or phoneme detection, larger numbers are faster responded to with the right response key while smaller numbers are faster responded to with the left. This also occurs when the hands are crossed, with the right hand activating the left response key and vice versa. The explanation given by Dehaene and colleagues is that the magnitude of a number on an oriented mental number line is automatically activated. The mental number line is assumed to be oriented from left to right in populations with a left-to-right writing system (e.g. English), and oriented from right to left in populations with a right-to-left writing system (e.g. Iranian) [ 2 ]
The SNARC has been observed primarily in two scenarios: attentional and oculomotor . The first of these involves people being faster to detect left probes after smaller numbers are shown and right probes after large numbers, [ 3 ] whereas the oculomotor effects are seen when participants look at greater speeds towards the left after detecting small numbers and to the right after detecting large ones. [ 4 ]
Newer research shows a motor bias to also be associated with the SNARC effect. In an experiment conducted into random number generation , participants tended to generate numbers of a larger magnitude when turning their heads to the right, and numbers of a smaller magnitude when turning their heads to the left. [ 5 ] This has been replicated using hand sizes: smaller distances between the index finger and thumb when generating a random number evoked smaller numbers, and larger spaces evoked larger numbers. [ 6 ] | https://en.wikipedia.org/wiki/Spatial-numerical_association_of_response_codes |
Spatial anxiety (sometimes also referred to as spatial orientation discomfort [ 1 ] ) is a sense of anxiety an individual experiences while processing environmental information contained in one's geographical space (in the sense of Montello's classification of space), [ 2 ] with the purpose of navigation and orientation through that space (usually unfamiliar, or very little known). [ 3 ] Spatial anxiety is also linked to the feeling of stress regarding the anticipation of a spatial-content related performance task [ 4 ] [ 5 ] (such as mental rotation , spatial perception, spatial visualisation , object location memory, dynamic spatial ability). [ 6 ] Particular cases of spatial anxiety can result in a more severe form of distress, as in agoraphobia . [ 7 ]
It is still investigated [ when? ] whether spatial anxiety would be considered as one solid, concrete ("unitary") construct (including the experiences of anxiety due to any spatial task), or whether it could be considered to be a "multifactorial construct" (including various subcomponents), attributing the experience of anxiety to several aspects. Evidence has shown that [ weasel words ] spatial anxiety seems to be a "multifactorial construct" that entails two components; that of anxiety regarding navigation and that of anxiety regarding the demand of rotation and visualization skills. [ 5 ]
Gender differences appear to be one of the most prominent differences in spatial anxiety as well as in navigational strategies. Evidence show higher levels of spatial anxiety in women, who tend to choose route strategies, as opposed to men, who tend to choose orientation strategies (a fact which, in turn, has been found to be negatively related to spatial anxiety). [ 3 ]
Spatial anxiety levels also seem to vary across different age groups. Evidence has shown spatial anxiety to appear also, early on, during the elementary school years, [ 4 ] with anxiety varying in level and tending to be stable; with minimum fluctuations, across life span. [ 8 ]
There are two primary ways of measuring spatial anxiety. One of them is Lawton's Spatial Anxiety Scale, [ 3 ] which was dominant during its era of creation. The other is the Child Spatial Anxiety Questionnaire, which was first one to assess spatial anxiety levels related to other spatial abilities other than navigation and map reading. [ 4 ]
The scale measures the degree of anxiety regarding the individual's experience and performance, in tasks assessing one's information processing related to the environment; such as way-finding and navigation. [ 3 ]
In total there are eight statements. Some examples are "leaving a store that you have been to for the first time and deciding which way to turn to get to a destination" and "finding your way around in an unfamiliar mall". The rating takes place on a 5-point scale, expressing the degree of anxiety with a continuum from "not at all" to "very much". [ 3 ]
The Child Spatial Anxiety Questionnaire was designed for young children and attempts to assess anxiety related to a wider (than usually) range of spatial abilities. Children are asked to report the level of anxiety they feel while in particular spatial abilities-demanding situations. In total it includes eight situations. Some examples are: "how do you feel being asked to say which direction is right or left?", "how do you feel when you are asked to point to a certain place on a map, like this one?", "how do you feel when you have to solve a maze like this in one minute?". [ 4 ]
In the original version, the rating takes place on a 3-point scale which includes three different faces; each facial expression , representing a different emotional state (getting from "calm", to "somewhat nervous", to "very nervous"). The revised version assessment takes place on a 5-point scale, with two more facial expressions added. [ 4 ]
Self-reported spatial anxiety is negatively correlated with performance in spatial tasks, both small-scale – as assessing mental rotation , spatial visualization; and large scale – as environment learning, with participants scoring higher in spatial anxiety scale showing lowered performance. [ 9 ] [ 10 ] Spatial anxiety is also negatively correlated navigation proficiency ratings on the self-reported sense of direction measures, [ 11 ] [ 12 ] as well as orientation (map based) and route ( egocentric ) strategies. Additionally, as anxiety has been shown to influence performance on tasks that utilize working memory resources, working memory is bound to be affected by spatial anxiety, especially visuo-spatial working memory. [ 13 ] [ 14 ] [ 15 ]
There has been evidence demonstrating the negative relationship between spatial anxiety and environmental learning ability. For example, spatial anxiety is found to induce more errors in directional pointing tasks. [ 10 ] In an experiment where participants were required to use directional instructions to move a toy car in a virtual three-dimensional environment, those with higher reported spatial anxiety performed with less accuracy. As spatial anxiety increases, pointing accuracy decreases, and navigation errors increase significantly. [ 16 ] This effect has been also shown in patients with cognitive impairment . [ 1 ] Early detection might therefore allow for timely therapeutical intervention, e.g., in Alzheimer's disease [ 17 ]
Moreover, spatial anxiety has been shown to relate to gender differences in spatial abilities. Generally, women report higher levels of spatial anxiety than men. The use of orientation (based on map view) strategies in indoor or/and outdoor environment can be associated with lower levels of spatial anxiety. [ 16 ] Women tend to report using route strategies more than orientation strategies, whereas men report the opposite. [ 9 ] Spatial anxiety also contributes to gender differences in environment learning. Recent findings in university students indicate that men rely more than women upon distal gradient cues that provide information on both orientation and direction (i.e., hill lines) whereas women depend upon proximal pinpoint (i.e., landmark) cues more than other cue types when identifying a visual scene. The addition of an exogenous stressor would differentially alter the impact of spatial anxiety on performance in men and women by producing a higher perception of stress in women than males, which results in decreasing performance in females. The findings suggest that gender differences in distal gradient and new cue perception varied based on stress condition. [ 15 ]
Some studies have discovered that acute stress can reduce memory for spatial locations, and people reporting difficulties in memorizing landmarks and directions when they are displaced also report higher levels of spatial anxiety. [ 9 ] [ 15 ] In addition, it has been demonstrated that people with Agoraphobia Disorder have reduced visuo-spatial working memory when they are required to process multiple spatial elements simultaneously. Specifically, in tasks where they were required to navigate using the landmarks independent of themselves ( allocentric coordinates), visuo-spatial working memory deficits were shown to hinder their performance. [ 15 ]
Bilateral vestibulopathy can cause higher levels of spatial anxiety, potentially related to hippocampal atrophy. [ 18 ] Overall, the role of the vestibular system on spatial anxiety is not yet fully understood, but vestibular function plays a relevant role in emotion processing [ 19 ] and the development of ( vertigo -related) anxiety, [ 20 ] as well as in spatial perception. [ 21 ] [ 22 ]
Possible explanations for the negative correlation between spatial anxiety and the ability to form cognitive map include: individuals lacking sense of their own position with respect to the external environment are more likely to get anxious when faced with unplanned navigation, and the anxiety about becoming lost itself may reduce the ability to attend to cues necessary for way-finding strategizing. [ 9 ] [ 23 ]
The influence of spatial anxiety can be counteracted by positive beliefs, such as spatial self-efficacy and confidence (i.e. as the belief that one will do well in cognitive tasks). For example, it has been demonstrated that confidence was a predictive factor for accuracy in mental rotation tasks, with participants being more accurate when they were more confident. When this factor was manipulated, the performance was significantly affected. [ 24 ] Furthermore, having more self-perception of spatial self-efficacy has a positive role in supporting environment learning beyond the role of gender. [ 25 ] | https://en.wikipedia.org/wiki/Spatial_anxiety |
Spatial capacity is an indicator of " data intensity" in a transmission medium. It is usually used in conjunction with wireless transport mechanisms. This is analogous to the way that lumens per square meter determine illumination intensity. [ 1 ]
Spatial capacity focuses not only on bit rates for data transfer but on bit rates available in confined spaces defined by short transmission ranges. It is measured in bits per second per square meter.
Among those leading research in spatial capacity are Jan Rabaey at the University of California, Berkeley . Some have suggested the term "spatial efficiency" as more descriptive. Marc Weiser, former chief technologist of Xerox PARC , was another contributor to the field who commented on the importance of spatial capacity. [ 2 ]
The System spectral efficiency is the spatial capacity divided by the bandwidth in hertz of the available frequency band.
Engineers at Intel and elsewhere have reported the relative spatial capacities of various wireless technologies as follows: | https://en.wikipedia.org/wiki/Spatial_capacity |
A spatial data infrastructure ( SDI ), also called geospatial data infrastructure , [ 1 ] is a data infrastructure implementing a framework of geographic data , metadata , users and tools that are interactively connected in order to use spatial data in an efficient and flexible way. Another definition is "the technology, policies, standards, human resources , and related activities necessary to acquire, process, distribute, use, maintain, and preserve spatial data". [ 2 ] Most commonly, institutions with large repositories of geographic data (especially government agencies) create SDIs to facilitate the sharing of their data with a broader audience.
A further definition is given in Kuhn (2005): [ 3 ] "An SDI is a coordinated series of agreements on technology standards, institutional arrangements, and policies that enable the discovery and use of geospatial information by users and for purposes other than those it was created for."
Some of the main principles are that data and metadata should not be managed centrally, but by the data originator and/or owner, and that tools and services connect via computer networks to the various sources. [ 4 ] A GIS is often the platform for deploying an individual node within an SDI. To achieve these objectives, good coordination between all the actors is necessary and the definition of standards is very important.
The original example of an SDI is the United States National Spatial Data Infrastructure ( NSDI ) , first mandated in the OMB Circular A-16 in 1996. In Europe since 2007, INSPIRE is a European Commission initiative to build a European SDI beyond national boundaries; the United Nations Spatial Data Infrastructure ( UNSDI ) plans to do the same for over 30 UN Funds, Programs, Specialized Agencies and member countries.
An SDI should enable the discovery and delivery of spatial data from a data repository, via a spatial service provider, to a user. As mentioned earlier it is often wished that the data provider is able to update spatial data stored in a repository. Hence, the basic software components of an SDI are: [ 4 ]
Besides these software components, a range of (international) technical standards are necessary that allow interaction between the different software components. [ 4 ] [ 5 ] Among those are geospatial standards defined by the Open Geospatial Consortium (e.g., OGC WMS, WFS, GML, etc.) and ISO (e.g., ISO 19115) for the delivery of maps, vector and raster data , but also data format and internet transfer standards by W3C consortium.
List by country or administrative zone. It is not complete, is a sample of National Spatial Data Infrastructure (NSDI) official websites. | https://en.wikipedia.org/wiki/Spatial_data_infrastructure |
A spatial decision support system ( SDSS ) is an interactive, computer-based system designed to assist in decision making while solving a semi-structured spatial problem. [ 1 ] It is designed to assist the spatial planner with guidance in making land use decisions. A system which models decisions could be used to help identify the most effective decision path.
An SDSS is sometimes referred to as a policy support system, and comprises a decision support system (DSS) and a geographic information system (GIS). This entails use of a database management system (DBMS), which holds and handles the geographical data; a library of potential models that can be used to forecast the possible outcomes of decisions; and an interface to aid the users interaction with the computer system and to assist in analysis of outcomes.
An SDSS usually exists in the form of a computer model or collection of interlinked computer models, including a land use model. Although various techniques are available to simulate land use dynamics, two types are particularly suitable for SDSS. These are cellular automata (CA) based models [ 2 ] and Agent based models (ABM). [ 3 ]
An SDSS typically uses a variety of spatial and nonspatial information, like data on land use, transportation, water management , demographics , agriculture, climate, epidemiology , resource management or employment. By using two or more known points in history the models can be calibrated and then projections into the future can be made to analyze different spatial policy options. Using these techniques spatial planners can investigate the effects of different scenarios, and provide information to make informed decisions. To allow the user to easily adapt the system to deal with possible intervention possibilities an interface allows for simple modification to be made. | https://en.wikipedia.org/wiki/Spatial_decision_support_system |
In the physics of continuous media , spatial dispersion is a phenomenon where material parameters such as the permittivity or conductivity have dependence on wavevector . Normally such a dependence is assumed to be absent for simplicity, however spatial dispersion exists to varying degrees in all materials.
The underlying physical reason for the wavevector dependence is often that the material has some spatial structure smaller than the wavelength of any signals (such as light or sound) being considered. Since these small spatial structures cannot be resolved by the waves, only indirect effects (e.g. wavevector dependence) remain detectable. In such a case, although the light cannot resolve the individual atoms, they nevertheless can as an aggregate affect how the light propagates. Another common mechanism is that the (e.g.) light is coupled to an excitation of the material, such as a plasmon .
Spatial dispersion can be compared to temporal dispersion, the latter often just called dispersion . Temporal dispersion represents memory effects in systems, commonly seen in optics and electronics. Spatial dispersion on the other hand represents spreading effects and is usually significant only at microscopic length scales. Spatial dispersion contributes relatively small perturbations to optics, providing weak effects such as optical activity . Spatial dispersion and temporal dispersion may occur in the same system.
Spatial dispersion is also distinct from anisotropic effects like birefringence . In such phenomena, the effective material parameters felt by a wave depend on direction of the wavevector, but that can be entirely captured as a tensorial material parameter where the tensor components are independent of wavevector. By contrast, spatial dispersion means that the tensor parameter itself has wavevector dependence.
The origin of spatial dispersion can be modelled as a nonlocal response, where response to a force field appears at many locations, and can appear even in locations where the force is zero. This usually arises due to a spreading of effects by the hidden microscopic degrees of freedom. [ 1 ]
As an example, consider the current J ( x , t ) {\displaystyle J(x,t)} that is driven in response to an electric field E ( x , t ) {\displaystyle E(x,t)} , which is varying in space (x) and time (t). Simplified laws such as Ohm's law would say that these are directly proportional to each other, J = σ E {\displaystyle J=\sigma E} , but this breaks down if the system has memory (temporal dispersion) or spreading (spatial dispersion). The most general linear response is given by:
where σ ( x , x ′ , t , t ′ ) d x ′ d t ′ {\displaystyle \sigma (x,x',t,t')dx'\,dt'} is the nonlocal conductivity function.
If the system is invariant in time ( time translation symmetry ) and invariant in space (space translation symmetry), then we can simplify because σ ( x , x ′ , t , t ′ ) = σ s y m ( x − x ′ , t − t ′ ) {\displaystyle \sigma (x,x',t,t')=\sigma _{\rm {sym}}(x-x',t-t')} for some convolution kernel σ s y m {\displaystyle \sigma _{\rm {sym}}} . We can also consider plane wave solutions for E {\displaystyle E} and J {\displaystyle J} like so:
which yields a remarkably simple relationship between the two plane waves' complex amplitudes:
where the function σ ~ ( k , ω ) {\displaystyle {\tilde {\sigma }}(k,\omega )} is given by a Fourier transform of the space-time response function:
The conductivity function σ ~ ( k , ω ) {\displaystyle {\tilde {\sigma }}(k,\omega )} has spatial dispersion if it is dependent on the wavevector k . This occurs if the spatial function σ s y m ( x − x ′ , t − t ′ ) {\displaystyle \sigma _{\rm {sym}}(x-x',t-t')} is not pointlike ( delta function ) response in x-x' .
In electromagnetism , spatial dispersion plays a role in a few material effects such as optical activity and doppler broadening . Spatial dispersion also plays an important role in the understanding of electromagnetic metamaterials . Most commonly, the spatial dispersion in permittivity ε is of interest.
Inside crystals there may be a combination of spatial dispersion, temporal dispersion, and anisotropy. [ 2 ] The constitutive relation for the polarization vector can be written as:
i.e., the permittivity is a wavevector- and frequency-dependent tensor .
Considering Maxwell's equations , one can find the plane wave normal modes inside such crystals. These occur when the following relationship is satisfied for a nonzero electric field vector E → {\displaystyle {\vec {E}}} : [ 2 ]
Spatial dispersion in ϵ ( k → , ω ) {\displaystyle \epsilon ({\vec {k}},\omega )} can lead to strange phenomena, such as the existence of multiple modes at the same frequency and wavevector direction, but with different wavevector magnitudes.
Nearby crystal surfaces and boundaries, it is no longer valid to describe system response in terms of wavevectors. For a full description it is necessary to return to a full nonlocal response function (without translational symmetry ), however the end effect can sometimes be described by "additional boundary conditions" (ABC's).
In materials that have no relevant crystalline structure, spatial dispersion can be important.
Although symmetry demands that the permittivity is isotropic for zero wavevector, this restriction does not apply for nonzero wavevector. The non-isotropic permittivity for nonzero wavevector leads to effects such as optical activity in solutions of chiral molecules. In isotropic materials without optical activity, the permittivity tensor can be broken down to transverse and longitudinal components, referring to the response to electric fields either perpendicular or parallel to the wavevector. [ 1 ]
For frequencies nearby an absorption line (e.g., an exciton ), spatial dispersion can play an important role. [ 1 ]
In plasma physics, a wave can be collisionlessly damped by particles in the plasma whose velocity matches the wave's phase velocity. This is typically represented as a spatially dispersive loss in the plasma's permittivity.
At nonzero frequencies, it is possible to represent all magnetizations as time-varying polarizations . Moreover, since the electric and magnetic fields are directly related by ∇ × E = − ∂ B / ∂ t {\displaystyle \nabla \times E=-\partial B/\partial t} , the magnetization induced by a magnetic field can be represented instead as a polarization induced by the electric field, though with a highly dispersive relationship.
What this means is that at nonzero frequency, any contribution to permeability μ can instead be alternatively represented by a spatially dispersive contribution to permittivity ε . The values of the permeability and permittivity are different in this alternative representation, however this leads to no observable differences in real quantities such as electric field, magnetic flux density, magnetic moments, and current.
As a result, it is most common at optical frequencies to set μ to the vacuum permeability μ 0 and only consider a dispersive permittivity ε . [ 1 ] There is some discussion over whether this is appropriate in metamaterials where effective medium approximations for μ are used, and debate over the reality of "negative permeability" seen in negative index metamaterials . [ 3 ]
Even at zero frequency, a charge disturbance in one location will cause a delocalized cloud that screens its effect. This delocalization can be described as spatial dispersion in the static permittivity. [ 4 ] In a metal this takes the form of Friedel oscillations , wherein in the permittivity function ϵ ( k ) {\displaystyle \epsilon (k)} can be understood as a hard cutoff for wavevectors exceeding twice the Fermi wavevector, and this hard cutoff causing a form of ringing artifact .
In acoustics , especially in solids, spatial dispersion can be significant for wavelengths comparable to the lattice spacing, which typically occurs at very high frequencies ( gigahertz and above).
In solids, the difference in propagation for transverse acoustic modes and longitudinal acoustic modes of sound is due to a spatial dispersion in the elasticity tensor which relates stress and strain. For polar vibrations ( optical phonons ), the distinction between longitudinal and transverse modes can be seen as a spatial dispersion in the restoring forces, from the "hidden" non-mechanical degree of freedom that is the electromagnetic field.
Many electromagnetic wave effects from spatial dispersion find an analogue in acoustic waves . For example, there is acoustical activity — the rotation of the polarization plane of transverse sound waves — in chiral materials , [ 5 ] analogous to optical activity. | https://en.wikipedia.org/wiki/Spatial_dispersion |
Spatial ecology studies the ultimate distributional or spatial unit occupied by a species . In a particular habitat shared by several species, each of the species is usually confined to its own microhabitat or spatial niche because two species in the same general territory cannot usually occupy the same ecological niche for any significant length of time.
In nature, organisms are neither distributed uniformly nor at random , forming instead some sort of spatial pattern . [ 1 ] This is due to various energy inputs, disturbances , and species interactions that result in spatially patchy structures or gradients . This spatial variance in the environment creates diversity in communities of organisms, as well as in the variety of the observed biological and ecological events. [ 1 ] The type of spatial arrangement present may suggest certain interactions within and between species, such as competition , predation , and reproduction . [ 2 ] On the other hand, certain spatial patterns may also rule out specific ecological theories previously thought to be true. [ 3 ]
Although spatial ecology deals with spatial patterns, it is usually based on observational data rather than on an existing model . [ 2 ] This is because nature rarely follows set expected order. To properly research a spatial pattern or population, the spatial extent to which it occurs must be detected. Ideally, this would be accomplished beforehand via a benchmark spatial survey, which would determine whether the pattern or process is on a local, regional, or global scale. This is rare in actual field research, however, due to the lack of time and funding, as well as the ever-changing nature of such widely-studied organisms such as insects and wildlife . [ 4 ] With detailed information about a species' life-stages, dynamics, demography , movement, behavior, etc., models of spatial pattern may be developed to estimate and predict events in unsampled locations. [ 2 ]
Most mathematical studies in ecology in the nineteenth century assumed a uniform distribution of living organisms in their habitat. [ 1 ] In the past quarter century, ecologists have begun to recognize the degree to which organisms respond to spatial patterns in their environment. Due to the rapid advances in computer technology in the same time period, more advanced methods of statistical data analysis have come into use. [ 3 ] Also, the repeated use of remotely sensed imagery and geographic information systems in a particular area has led to increased analysis and identification of spatial patterns over time. [ 4 ] These technologies have also increased the ability to determine how human activities have impacted animal habitat and climate change . [ 5 ] The natural world has become increasingly fragmented due to human activities; anthropogenic landscape change has had a ripple-effect impacts on wildlife populations, which are now more likely to be small, restricted in distribution, and increasingly isolated from one another. In part as a reaction to this knowledge, and partially due to increasingly sophisticated theoretical developments, ecologists began stressing the importance of spatial context in research. Spatial ecology emerged from this movement toward spatial accountability; "the progressive introduction of spatial variation and complexity into ecological analysis, including changes in spatial patterns over time". [ 6 ]
In spatial ecology, scale refers to the spatial extent of ecological processes and the spatial interpretation of the data. [ 7 ] The response of an organism or a species to the environment is particular to a specific scale, and may respond differently at a larger or smaller scale. [ 8 ] Choosing a scale that is appropriate to the ecological process in question is very important in accurately hypothesizing and determining the underlying cause. [ 9 ] [ 10 ] Most often, ecological patterns are a result of multiple ecological processes, which often operate at more than one spatial scale. [ 11 ] Through the use of such spatial statistical methods such as geostatistics and principal coordinate analysis of neighbor matrices (PCNM), one can identify spatial relationships between organisms and environmental variables at multiple scales. [ 8 ]
Spatial autocorrelation refers to the value of samples taken close to each other are more likely to have similar magnitude than by chance alone. [ 7 ] When a pair of values located at a certain distance apart are more similar than expected by chance, the spatial autocorrelation is said to be positive. When a pair of values are less similar, the spatial autocorrelation is said to be negative. It is common for values to be positively autocorrelated at shorter distances and negative autocorrelated at longer distances. [ 1 ] This is commonly known as Tobler's first law of geography , summarized as "everything is related to everything else, but nearby objects are more related than distant objects".
In ecology, there are two important sources of spatial autocorrelation, which both arise from spatial-temporal processes, such as dispersal or migration : [ 11 ]
Most ecological data exhibit some degree of spatial autocorrelation, depending on the ecological scale (spatial resolution) of interest. As the spatial arrangement of most ecological data is not random, traditional random population samples tend to overestimate the true value of a variable, or infer significant correlation where there is none. [ 1 ] This bias can be corrected through the use of geostatistics and other more statistically advanced models. Regardless of method, the sample size must be appropriate to the scale and the spatial statistical method used in order to be valid. [ 4 ]
Spatial patterns, such as the distribution of a species, are the result of either true or induced spatial autocorrelation. [ 7 ] In nature, organisms are distributed neither uniformly nor at random. The environment is spatially structured by various ecological processes, [ 1 ] which in combination with the behavioral response of species generally results in:
Theoretically, any of these structures may occur at any given scale. Due to the presence of spatial autocorrelation, in nature gradients are generally found at the global level, whereas patches represent intermediate (regional) scales, and noise at local scales. [ 11 ]
The analysis of spatial ecological patterns comprises two families of methods: [ 12 ]
Analysis of spatial trends has been used to research wildlife management , fire ecology , population ecology , disease ecology , invasive species , marine ecology , and carbon sequestration modeling using the spatial relationships and patterns to determine ecological processes and their effects on the environment.
Spatial patterns have different ecosystem functioning in ecology for examples enhanced productive. [ 14 ]
The concepts of spatial ecology are fundamental to understanding the spatial dynamics of population and community ecology . The spatial heterogeneity of populations and communities plays a central role in such ecological theories as succession , adaptation , community stability, competition , predator-prey interactions , parasitism , and epidemics . [ 1 ] The rapidly expanding field of landscape ecology utilizes the basic aspects of spatial ecology in its research. [ citation needed ]
The practical use of spatial ecology concepts is essential to understanding the consequences of fragmentation and habitat loss for wildlife. Understanding the response of a species to a spatial structure provides useful information in regards to biodiversity conservation and habitat restoration. [ 15 ]
Spatial ecology modeling uses components of remote sensing and geographical information systems (GIS). [ citation needed ]
A number of statistical tests have been developed to study such relations.
Clark and Evans in 1954 [ 16 ] proposed a test based on the density and distance between organisms. Under the null hypothesis the expected distance ( r e ) between the organisms (measured as the nearest neighbor's distance) with a known constant density ( ρ ) is
The difference between the observed ( r o ) and the expected ( r e ) can be tested with a Z test
where N is the number of nearest neighbor measurements. For large samples Z is distributed normally. The results are usually reported in the form of a ratio: R = ( r o ) / ( r e )
Pielou in 1959 devised a different statistic. [ 17 ] She considered instead of the nearest neighbors the distance between an organism and a set of pre-chosen random points within the sampling area, again assuming a constant density. If the population is randomly dispersed in the area these distances will equal the nearest neighbor distances. Let ω be the ratio between the distances from the random points and the distances calculated from the nearest neighbor calculations. The α is [ citation needed ]
where d is the constant common density and π has its usual numerical value. Values of α less than, equal to or greater than 1 indicate uniformity, randomness (a Poisson distribution ) or aggregation respectively. Alpha may be tested for a significant deviation from 1 by computing the test statistic
where χ 2 is distributed with 2 n degrees of freedom. n here is the number of organisms sampled.
Montford in 1961 showed that when the density is estimated rather than a known constant, this version of alpha tended to overestimate the actual degree of aggregation. He provided a revised formulation which corrects this error.
There is a wide range of mathematical problems related to spatial ecological models, relating to spatial patterns and processes associated with chaotic phenomena, bifurcations and instability. [ 18 ] | https://en.wikipedia.org/wiki/Spatial_ecology |
In mathematics , physics , and engineering , spatial frequency is a characteristic of any structure that is periodic across position in space . The spatial frequency is a measure of how often sinusoidal components (as determined by the Fourier transform ) of the structure repeat per unit of distance.
The SI unit of spatial frequency is the reciprocal metre (m −1 ), [ 1 ] although cycles per meter (c/m) is also common. In image-processing applications, spatial frequency is often expressed in units of cycles per millimeter (c/mm) or also line pairs per millimeter (LP/mm).
In wave propagation , the spatial frequency is also known as wavenumber . Ordinary wavenumber is defined as the reciprocal of wavelength λ {\displaystyle \lambda } and is commonly denoted by ξ {\displaystyle \xi } [ 2 ] or sometimes ν {\displaystyle \nu } : [ 3 ] ξ = 1 λ . {\displaystyle \xi ={\frac {1}{\lambda }}.} Angular wavenumber k {\displaystyle k} , expressed in radian per metre (rad/m), is related to ordinary wavenumber and wavelength by k = 2 π ξ = 2 π λ . {\displaystyle k=2\pi \xi ={\frac {2\pi }{\lambda }}.}
In the study of visual perception , sinusoidal gratings are frequently used to probe the capabilities of the visual system , such as contrast sensitivity . In these stimuli , spatial frequency is expressed as the number of cycles per degree of visual angle . Sine-wave gratings also differ from one another in amplitude (the magnitude of difference in intensity between light and dark stripes), orientation , and phase .
The spatial-frequency theory refers to the theory that the visual cortex operates on a code of spatial frequency, not on the code of straight edges and lines hypothesised by Hubel and Wiesel on the basis of early experiments on V1 neurons in the cat. [ 4 ] [ 5 ] In support of this theory is the experimental observation that the visual cortex neurons respond even more robustly to sine-wave gratings that are placed at specific angles in their receptive fields than they do to edges or bars. Most neurons in the primary visual cortex respond best when a sine-wave grating of a particular frequency is presented at a particular angle in a particular location in the visual field. [ 6 ] (However, as noted by Teller (1984), [ 7 ] it is probably not wise to treat the highest firing rate of a particular neuron as having a special significance with respect to its role in the perception of a particular stimulus, given that the neural code is known to be linked to relative firing rates. For example, in color coding by the three cones in the human retina, there is no special significance to the cone that is firing most strongly – what matters is the relative rate of firing of all three simultaneously. Teller (1984) similarly noted that a strong firing rate in response to a particular stimulus should not be interpreted as indicating that the neuron is somehow specialized for that stimulus, since there is an unlimited equivalence class of stimuli capable of producing similar firing rates.)
The spatial-frequency theory of vision is based on two physical principles:
The theory (for which empirical support has yet to be developed) states that in each functional module of the visual cortex, Fourier analysis (or its piecewise form [ 8 ] ) is performed on the receptive field and the neurons in each module are thought to respond selectively to various orientations and frequencies of sine wave gratings. [ 9 ] When all of the visual cortex neurons that are influenced by a specific scene respond together, the perception of the scene is created by the summation of the various sine-wave gratings. (This procedure, however, does not address the problem of the organization of the products of the summation into figures, grounds, and so on. It effectively recovers the original (pre-Fourier analysis) distribution of photon intensity and wavelengths across the retinal projection, but does not add information to this original distribution. So the functional value of such a hypothesized procedure is unclear. Some other objections to the "Fourier theory" are discussed by Westheimer (2001) [ 10 ] ). One is generally not aware of the individual spatial frequency components since all of the elements are essentially blended together into one smooth representation. However, computer-based filtering procedures can be used to deconstruct an image into its individual spatial frequency components. [ 11 ] Research on spatial frequency detection by visual neurons complements and extends previous research using straight edges rather than refuting it. [ 12 ]
Further research shows that different spatial frequencies convey different information about the appearance of a stimulus. High spatial frequencies represent abrupt spatial changes in the image, such as edges, and generally correspond to featural information and fine detail. M. Bar (2004) has proposed that low spatial frequencies represent global information about the shape, such as general orientation and proportions. [ 13 ] Rapid and specialised perception of faces is known to rely more on low spatial frequency information. [ 14 ] In the general population of adults, the threshold for spatial frequency discrimination is about 7%. It is often poorer in dyslexic individuals. [ 15 ]
When spatial frequency is used as a variable in a mathematical function, the function is said to be in k-space . Two dimensional k-space has been introduced into MRI as a raw data storage space. The value of each data point in k-space is measured in the unit of 1/meter, i.e. the unit of spatial frequency.
It is very common that the raw data in k-space shows features of periodic functions. The periodicity is not spatial frequency, but is temporal frequency. An MRI raw data matrix is composed of a series of phase-variable spin-echo signals. Each of the spin-echo signal is a sinc function of time, which can be described by Spin-Echo = M 0 sin ω r t ω r t {\displaystyle {\text{Spin-Echo}}={\frac {M_{\mathrm {0} }\sin \omega _{\mathrm {r} }t}{\omega _{\mathrm {r} }t}}} Where ω r = ω 0 + γ ¯ r G {\displaystyle \omega _{\mathrm {r} }=\omega _{\mathrm {0} }+{\bar {\gamma }}rG} Here γ ¯ {\displaystyle {\bar {\gamma }}} is the gyromagnetic ratio constant, and ω 0 {\displaystyle \omega _{\mathrm {0} }} is the basic resonance frequency of the spin. Due to the presence of the gradient G , the spatial information r is encoded onto the frequency ω {\displaystyle \omega } . The periodicity seen in the MRI raw data is just this frequency ω r {\displaystyle \omega _{\mathrm {r} }} , which is basically the temporal frequency in nature.
In a rotating frame, ω 0 = 0 {\displaystyle \omega _{\mathrm {0} }=0} , and ω r {\displaystyle \omega _{\mathrm {r} }} is simplified to γ ¯ r G {\displaystyle {\bar {\gamma }}rG} . Just by letting k = γ ¯ G t {\displaystyle k={\bar {\gamma }}Gt} , the spin-echo signal is expressed in an alternative form Spin-Echo = M 0 sin r k r k {\displaystyle {\text{Spin-Echo}}={\frac {M_{\mathrm {0} }\sin rk}{rk}}}
Now, the spin-echo signal is in the k-space. It becomes a periodic function of k with r as the k-space frequency but not as the "spatial frequency", since "spatial frequency" is reserved for the name of the periodicity seen in the real space r.
The k-space domain and the space domain form a Fourier pair. Two pieces of information are found in each domain, the spatial information and the spatial frequency information. The spatial information, which is of great interest to all medical doctors, is seen as periodic functions in the k-space domain and is seen as the image in the space domain. The spatial frequency information, which might be of interest to some MRI engineers, is not easily seen in the space domain but is readily seen as the data points in the k-space domain. | https://en.wikipedia.org/wiki/Spatial_frequency |
Spatial heterogeneity is a property generally ascribed to a landscape or to a population . It refers to the uneven distribution of various concentrations of each species within an area. A landscape with spatial heterogeneity has a mix of concentrations of multiple species of plants or animals (biological), or of terrain formations (geological), or environmental characteristics (e.g. rainfall, temperature, wind) filling its area. A population showing spatial heterogeneity is one where various concentrations of individuals of this species are unevenly distributed across an area; nearly synonymous with "patchily distributed."
Spatial heterogeneity can be re-phrased as scaling hierarchy of far more small things than large ones. It has been formulated as a scaling law. [ 1 ]
Spatial heterogeneity or scaling hierarchy can be measured or quantified by ht-index : a head/tail breaks induced number. [ 2 ] [ 3 ]
Environments with a wide variety of habitats such as different topographies , soil types , and climates are able to accommodate a greater amount of species . The leading scientific explanation for this is that when organisms can finely subdivide a landscape into unique suitable habitats, more species can coexist in a landscape without competition, a phenomenon termed "niche partitioning." Spatial heterogeneity is a concept parallel to ecosystem productivity, the species richness of animals is directly related to the species richness of plants in a certain habitat. Vegetation serves as food sources, habitats , and so on. Therefore, if vegetation is scarce, the animal populations will be as well. The more plant species there are in an ecosystem, the greater variety of microhabitats there are. Plant species richness directly reflects spatial heterogeneity in an ecosystem.
There exist two main types of spatial heterogeneity. The spatial local heterogeneity categorises the geographic phenomena whose attributes' values are significantly similar within a directly local neighbourhood, but which significantly differ in the nearby surrounding-areas beyond this directly local neighbourhood (e.g. hot spots, cold spots). The spatial stratified heterogeneity categorises the geographic phenomena where the within- strata variance of its attributes' values is significantly lower than its between-strata variance, such as collections of ecological zones or land-use classes within a given geographic area depict. [ 4 ]
Spatial local heterogeneity can be tested by LISA, Gi and SatScan, while spatial stratified heterogeneity of an attribute can be measured by geographical detector q -statistic: [ 4 ]
where a population is partitioned into h = 1, ..., L strata; N stands for the size of the population, σ 2 stands for variance of the attribute. The value of q is within [0, 1], 0 indicates no spatial stratified heterogeneity, 1 indicates perfect spatial stratified heterogeneity. The value of q indicates the percent of the variance of an attribute explained by the stratification. The q follows a noncentral F probability density function.
Spatial heterogeneity for multivariate data and 3D data can also be statistically assessed using the "HTA index (HeTerogeneity Average index)" . : [ 5 ]
Optimal Parameters-based Geographical Detector (OPGD) characterizes spatial heterogeneity with the optimized parameters of spatial data discretization for identifying geographical factors and interactive impacts of factors, and estimating risks. [ 6 ] [ 7 ]
Interactive Detector for Spatial Associations (IDSA) estimates power of interactive determinants (PID) on the basis of spatial stratified heterogeneity, spatial autocorrelation, and spatial fuzzy overlay of explanatory variables. [ 8 ]
Geographically Optimal Zones-based Heterogeneity (GOZH) explores individual and interactive determinants of geographical attributes (e.g., global soil moisture) across a large study area based on the identification of explainable geographically optimal zones. [ 9 ]
Robust Geographical Detector (RGD) overcomes the limitation of the sensitivity in spatial data discretization and estimates robust power of determinants of explanatory variables. [ 10 ]
The model-agnostic Spatial Transformation And modeRation (meta-STAR) is a framework for integrating the spatial heterogeneity into spatial statistical models (e.g. spatial ensemble methods, spatial neural networks), so to improve their accuracy. It involves the use of spatial networks/transformations and spatial moderators , plus handles the geo-spatial datasets representing geographic phenomena at multiple scales. [ 11 ]
In a 2004 publication titled "The Validity and Usefulness of Laws in Geographic Information Science and Geography," Michael Frank Goodchild proposed Spatial heterogeneity could be a candidate for a law of geography similar to Tobler's first law of geography . [ 12 ] The literature cites this paper and states this law as "geographic variables exhibit uncontrolled variance." [ 12 ] [ 13 ] [ 14 ] Often referred to as the second law of geography, or Michael Goodchild's second law of geography, it is one of many concepts competing for that term, including Tobler's second law of geography , and Arbia's law of geography . [ 13 ] [ 14 ] [ 15 ] | https://en.wikipedia.org/wiki/Spatial_heterogeneity |
Spatial multiplexing or space-division multiplexing ( SM , SDM or SMX ) is a multiplexing technique in MIMO wireless communication , fiber-optic communication and other communications technologies used to transmit independent channels separated in space.
In fiber-optic communication SDM refers to the usage of the transverse dimension of the fiber to separate the channels.
Multi-core fibers are designed with more than a single core. Different types of MCFs exist, of which “Uncoupled MCF” is the most common, in which each core is treated as an independent optical path. The main limitation of these systems is the presence of inter-core crosstalk. In recent times, different splicing techniques, and coupling methods have been proposed and demonstrated, and despite many of the component technologies still being in the development stage, MCF systems already present the capability for huge transmission capacity. [ citation needed ]
Recently, some developed component technologies for multicore optical fiber have been demonstrated, such as three-dimensional Y-splitters between different multicore fibers, [ 1 ] a universal interconnection among the same fiber cores, [ 2 ] and a device for fast swapping and interchange of wavelength-division multiplexed data among cores of multicore optical fiber. [ 3 ]
Multi-mode fibers have a larger core that allows the propagation of multiple cylindrical transverse modes (Also referred as linearly polarized modes), in contrast to a single mode fiber (SMF) that only supports the fundamental mode. Each transverse mode is spatially orthogonal, and allows for the propagation in both orthogonal polarization.
Typical MMF are currently not viable for SDM, as the high mode count results in unmanageable levels of modal coupling and dispersion. The utilization of few-mode fibers, which are MMFs with a core size designed specially to allow a low count of spatial modes, is currently under consideration.
Due to physical imperfections, the modes exchange power and are experience different effective refractive indexes as they propagate through the fiber. [ 4 ] The power exchange results in modal coupling, and this effect is known to reduce the achievable capacity of the fiber, [ 5 ] if the modes experience unequal gain or attenuation. Therefore, if not compensated, the capacity increase is not linear to the mode count. The effective refractive index difference results in inter-symbolic interference, resulting from delay spread. [ 6 ]
Mode multiplexers consist of photonic lanterns, multi-plane light conversion, and others.
Bundled fibers are also considered a form of SDM.
If the transmitter is equipped with N t {\displaystyle N_{t}} antennas and the receiver has N r {\displaystyle N_{r}} antennas, the maximum spatial multiplexing order (the number of streams) is,
if a linear receiver is used. This means that N s {\displaystyle N_{s}} streams can be transmitted in parallel, ideally leading to an N s {\displaystyle N_{s}} increase of the spectral efficiency (the number of bits per second per Hz that can be transmitted over the wireless channel). The practical multiplexing gain can be limited by spatial correlation , which means that some of the parallel streams may have very weak channel gains.
In an open-loop MIMO system with N t {\displaystyle N_{t}} transmitter antennas and N r {\displaystyle N_{r}} receiver antennas, the input-output relationship can be described as
where x = [ x 1 , x 2 , … , x N t ] T {\displaystyle \mathbf {x} =[x_{1},x_{2},\ldots ,x_{N_{t}}]^{T}} is the N t × 1 {\displaystyle N_{t}\times 1} vector of transmitted symbols, y , n {\displaystyle \mathbf {y,n} } are the N r × 1 {\displaystyle N_{r}\times 1} vectors of received symbols and noise respectively and H {\displaystyle \mathbf {H} } is the N r × N t {\displaystyle N_{r}\times N_{t}} matrix of channel coefficients. An often encountered problem in open loop spatial multiplexing is to guard against instance of high channel correlation and strong power imbalances between the multiple streams. One such extension which is being considered for DVB-NGH systems is the so-called enhanced Spatial Multiplexing (eSM) scheme.
A closed-loop MIMO system utilizes Channel State Information (CSI) at the transmitter. In most cases, only partial CSI is available at the transmitter because of the limitations of the feedback channel. In a closed-loop MIMO system the input-output relationship with a closed-loop approach can be described as
where s = [ s 1 , s 2 , … , s N s ] T {\displaystyle \mathbf {s} =[s_{1},s_{2},\ldots ,s_{N_{s}}]^{T}} is the N s × 1 {\displaystyle N_{s}\times 1} vector of transmitted symbols, y , n {\displaystyle \mathbf {y,n} } are the N r × 1 {\displaystyle N_{r}\times 1} vectors of received symbols and noise respectively, H {\displaystyle \mathbf {H} } is the N r × N t {\displaystyle N_{r}\times N_{t}} matrix of channel coefficients and W {\displaystyle \mathbf {W} } is the N t × N s {\displaystyle N_{t}\times N_{s}} linear precoding matrix.
A precoding matrix W {\displaystyle \mathbf {W} } is used to precode the symbols in the vector to enhance the performance. The column dimension N s {\displaystyle N_{s}} of W {\displaystyle \mathbf {W} } can be selected smaller than N t {\displaystyle N_{t}} which is useful if the system requires N s ( ≠ N t ) {\displaystyle N_{s}(\neq N_{t})} streams because of several reasons. Examples of the reasons are as follows: either the rank of the MIMO channel or the number of receiver antennas is smaller than the number of transmit antennas. | https://en.wikipedia.org/wiki/Spatial_multiplexing |
A spatial relation [ 1 ] [ 2 ] specifies how some object is located in space in relation to some reference object. When the reference object is much bigger than the object to locate, the latter is often represented by a point. The reference object is often represented by a bounding box .
In Anatomy it might be the case that a spatial relation is not fully applicable. Thus, the degree of applicability is defined which specifies from 0 till 100% how strongly a spatial relation holds. Often researchers concentrate on defining the applicability function for various spatial relations.
In spatial databases and geospatial topology the spatial relations are used for spatial analysis and constraint specifications.
In cognitive development for walk and for catch objects, or for understand objects-behaviour ; in robotic Natural Features Navigation ; and many other areas, spatial relations plays a central role.
Commonly used types of spatial relations are: topological , directional and distance relations.
The DE-9IM model expresses important space relations which are invariant to rotation , translation and scaling transformations.
For any two spatial objects a and b , that can be points, lines and/or polygonal areas, there are 9 relations derived from DE-9IM :
Directional relations can again be differentiated into external directional relations and internal directional relations. An internal directional relation specifies where an object is located inside the reference object while an external relations specifies where the object is located outside of the reference objects.
Distance relations specify how far is the object away from the reference object.
Reference objects represented by a bounding box or another kind of "spatial envelope" that encloses its borders, can be denoted with the maximum number of dimensions of this envelope: '0' for punctual objects , '1' for linear objects , '2' for planar objects , '3' for volumetric objects . So, any object, in a 2D modeling , can by classified as point , line or area according to its delimitation. Then, a type of spatial relation can be expressed by the class of the objects that participate in the relation:
More complex modeling schemas can represent an object as a composition of simple sub-objects . Examples: represent in an astronomical map a star by a point and a binary star by two points ; represent in geographical map a river with a line , for its source stream , and with an strip- area , for the rest of the river. These schemas can use the above classes, uniform composition classes ( multi-point , multi-line and multi-area ) and heterogeneous composition ( points + lines as "object of dimension 1", points + lines + areas as "object of dimension 2").
Two internal components of a complex object can express (the above) binary relations between them, and ternary relations , using the whole object as a frame of reference . Some relations can be expressed by an abstract component, such the center of mass of the binary star, or a center line of the river.
For human thinking, spatial relations include qualities like size, distance, volume, order, and, also, time:
Time is spatial: it requires understanding ordered sequences such as days of the week, months of the year, and seasons. A person with spatial difficulties may have problems understanding “yesterday,” “last week,” and “next month”.
Time expressed digitally is just as spatial as time expressed by moving clock hands, but digital clocks remove the need to translate the hand position into numbers.
Stockdale and Possin [ 3 ] discusses the many ways in which people with difficulty establishing spatial and temporal relationships can face problems in ordinary situations. | https://en.wikipedia.org/wiki/Spatial_relation |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.