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21,600 | (2) Lithium metal plating also results in the loss of lithium inventory (cyclable Ah charge), as well as internal short-circuiting and ignition of a battery. Once Li plating commences during cycling, it results in larger slopes of capacity loss per cycle and resistance increase per cycle. | https://en.wikipedia.org/wiki?curid=201485 |
21,601 | (3) Loss of the (negative or positive) electroactive materials due to dissolution (e.g. of Mn(3+) species), cracking, exfoliation, detachment or even simple regular volume change during cycling. It shows up as both charge and power fade (increased resistance). Both positive and negative electrode materials are subject ... | https://en.wikipedia.org/wiki?curid=201485 |
21,602 | (4) Structural degradation of cathode materials, such as Li+/Ni2+ cation mixing in nickel-rich materials. This manifests as “electrode saturation", loss of cyclable Ah charge and as a "voltage fade". | https://en.wikipedia.org/wiki?curid=201485 |
21,603 | (5) Other material degradations. Negative copper current collector is particularly prone to corrosion/dissolution at low cell voltages. PVDF binder also degrades, causing the detachment of the electroactive materials, and the loss of cyclable Ah charge. | https://en.wikipedia.org/wiki?curid=201485 |
21,604 | These are shown in the figure on the right. A change from one main degradation mechanism to another appears as a knee (slope change) in the capacity vs. cycle number plot. | https://en.wikipedia.org/wiki?curid=201485 |
21,605 | (1) The negative (anode) SEI layer, a passivation coating formed by electrolyte (such as ethylenecarbonate) reduction products, is essential for providing Li+ ion conduction, while preventing electron transfer (and, thus, further solvent reduction). Under typical operating conditions, the negative SEI layer reaches a f... | https://en.wikipedia.org/wiki?curid=201485 |
21,606 | Depending on the electrolyte and additives, common components of the SEI layer that forms on the anode include a mixture of lithium oxide, lithium fluoride and semicarbonates (e.g., lithium alkyl carbonates). At elevated temperatures, alkyl carbonates in the electrolyte decompose into insoluble species such as that in... | https://en.wikipedia.org/wiki?curid=201485 |
21,607 | Electrolyte degradation mechanisms include hydrolysis and thermal decomposition. At concentrations as low as 10 ppm, water begins catalyzing a host of degradation products that can affect the electrolyte, anode and cathode. participates in an equilibrium reaction with LiF and . Under typical conditions, the equilibrium... | https://en.wikipedia.org/wiki?curid=201485 |
21,608 | Batteries generate heat when being charged or discharged, especially at high currents. Large battery packs, such as those used in electric vehicles, are generally equipped with thermal management systems that maintain a temperature between and . Pouch and cylindrical cell temperatures depend linearly on the discharge c... | https://en.wikipedia.org/wiki?curid=201485 |
21,609 | Positive SEI layer in lithium-ion batteries is much less understood than the negative SEI. It is believed to have a low-ionic conductivity and shows up as an increased interfacial resistance of the cathode during cycling and calendar aging./> | https://en.wikipedia.org/wiki?curid=201485 |
21,610 | (2) The randomness of the metallic lithium embedded in the anode during intercalation results in dendrites formation. Over time the dendrites can accumulate and pierce the separator, causing a short circuit leading to heat, fire or explosion. This process is referred to as thermal runaway. Lithium plating is the most s... | https://en.wikipedia.org/wiki?curid=201485 |
21,611 | (3) Certain manganese containing cathodes can degrade by the Hunter degradation mechanism resulting in manganese dissolution and reduction on the anode. By the Hunter mechanism for , hydrofluoric acid catalyzes the loss of manganese through disproportionation of a surface trivalent manganese to form a tetravalent manga... | https://en.wikipedia.org/wiki?curid=201485 |
21,612 | Material loss of the spinel results in capacity fade. Temperatures as low as 50 °C initiate Mndeposition on the anode as metallic manganese with the same effects as lithium and copper plating. Cycling over the theoretical max and min voltage plateaus destroys the crystal lattice via Jahn-Teller distortion, which occurs... | https://en.wikipedia.org/wiki?curid=201485 |
21,613 | (4) Cation mixing is the main reason for the capacity decline of the Ni-rich cathode materials. As the Ni content in the NCM layered material increases the capacity will increase, which is the result of two-electron of Ni2+/Ni4+ redox reaction (please note, that Mn remains electrochemically inactive in the 4+ state) bu... | https://en.wikipedia.org/wiki?curid=201485 |
21,614 | (5) Discharging below 2 V can also result in the dissolution of the copper anode current collector and, thus, in catastrophic internal short-circuiting on recharge. | https://en.wikipedia.org/wiki?curid=201485 |
21,615 | The IEEE standard 1188–1996 recommends replacing Lithium-ion batteries in an electric vehicle, when their charge capacity drops to 80% of the nominal value. In what follows, we shall use the 20% capacity loss as a comparison point between different studies. We shall note, nevertheless, that the linear model of degradat... | https://en.wikipedia.org/wiki?curid=201485 |
21,616 | Most studies of lithium-ion battery aging have been done at elevated (50-60 °C) temperatures in order to complete the experiments sooner. Under these storage conditions, fully charged nickel-cobalt-aluminum and lithium-iron phosphate cells loose ca. 20% of their cyclable charge in 1-2 year. It is believed, that the afo... | https://en.wikipedia.org/wiki?curid=201485 |
21,617 | Lithium-ion batteries can be a safety hazard since they contain a flammable electrolyte and may become pressurized if they become damaged. A battery cell charged too quickly could cause a short circuit, leading to explosions and fires. A Li-ion battery fire can be started due to (1) thermal abuse, e.g. poor cooling or ... | https://en.wikipedia.org/wiki?curid=201485 |
21,618 | Lithium-ion batteries have a flammable liquid electrolyte. A faulty battery can cause a serious fire. Faulty chargers can affect the safety of the battery because they can destroy the battery's protection circuit. While charging at temperatures below 0 °C, the negative electrode of the cells gets plated with pure lithi... | https://en.wikipedia.org/wiki?curid=201485 |
21,619 | Short-circuiting a battery will cause the cell to overheat and possibly to catch fire. Smoke from thermal runaway in a Li-ion battery is both flammable and toxic. The fire energy content (electrical + chemical) of cobalt-oxide cells is about 100 to 150 kJ/(A·h), most of it chemical. | https://en.wikipedia.org/wiki?curid=201485 |
21,620 | Around 2010, large lithium-ion batteries were introduced in place of other chemistries to power systems on some aircraft; , there had been at least four serious lithium-ion battery fires, or smoke, on the Boeing 787 passenger aircraft, introduced in 2011, which did not cause crashes but had the potential to do so. UPS ... | https://en.wikipedia.org/wiki?curid=201485 |
21,621 | If a lithium-ion battery is damaged, crushed, or is subjected to a higher electrical load without having overcharge protection, then problems may arise. External short circuit can trigger a battery explosion. | https://en.wikipedia.org/wiki?curid=201485 |
21,622 | If overheated or overcharged, Li-ion batteries may suffer thermal runaway and cell rupture. In extreme cases this can lead to leakage, explosion or fire. To reduce these risks, many lithium-ion cells (and battery packs) contain fail-safe circuitry that disconnects the battery when its voltage is outside the safe range ... | https://en.wikipedia.org/wiki?curid=201485 |
21,623 | Lithium-ion cells are susceptible to stress by voltage ranges outside of safe ones between 2.5 and 3.65/4.1/4.2 or 4.35V (depending on the components of the cell). Exceeding this voltage range results in premature aging and in safety risks due to the reactive components in the cells. When stored for long periods the sm... | https://en.wikipedia.org/wiki?curid=201485 |
21,624 | These features are required because the negative electrode produces heat during use, while the positive electrode may produce oxygen. However, these additional devices occupy space inside the cells, add points of failure, and may irreversibly disable the cell when activated. Further, these features increase costs compa... | https://en.wikipedia.org/wiki?curid=201485 |
21,625 | Replacing the lithium cobalt oxide positive electrode material in lithium-ion batteries with a lithium metal phosphate such as lithium iron phosphate (LFP) improves cycle counts, shelf life and safety, but lowers capacity. As of 2006, these safer lithium-ion batteries were mainly used in electric cars and other large-c... | https://en.wikipedia.org/wiki?curid=201485 |
21,626 | IATA estimates that over a billion lithium metal and lithium-ion cells are flown each year. Some kinds of lithium batteries may be prohibited aboard aircraft because of the fire hazard. Some postal administrations restrict air shipping (including EMS) of lithium and lithium-ion batteries, either separately or installed... | https://en.wikipedia.org/wiki?curid=201485 |
21,627 | Extraction of lithium, nickel, and cobalt, manufacture of solvents, and mining byproducts present significant environmental and health hazards. | https://en.wikipedia.org/wiki?curid=201485 |
21,628 | Lithium extraction can be fatal to aquatic life due to water pollution. It is known to cause surface water contamination, drinking water contamination, respiratory problems, ecosystem degradation and landscape damage. It also leads to unsustainable water consumption in arid regions (1.9 million liters per ton of lithiu... | https://en.wikipedia.org/wiki?curid=201485 |
21,629 | Cobalt for Li-ion batteries is largely mined in the Congo (see also Mining industry of the Democratic Republic of the Congo) | https://en.wikipedia.org/wiki?curid=201485 |
21,630 | Manufacturing a kg of Li-ion battery takes about 67 megajoule (MJ) of energy. The global warming potential of lithium-ion batteries manufacturing strongly depends on the energy source used in mining and manufacturing operations, and is difficult to estimate, but one 2019 study estimated 73 kg CO2e/kWh. Effective recycl... | https://en.wikipedia.org/wiki?curid=201485 |
21,631 | Since Li-ion batteries contain less toxic metals than other types of batteries which may contain lead or cadmium, they are generally categorized as non-hazardous waste {Citation needed}. Li-ion battery elements including iron, copper, nickel and cobalt are considered safe for incinerators and landfills. These metals ca... | https://en.wikipedia.org/wiki?curid=201485 |
21,632 | Accumulation of battery waste presents technical challenges and health hazards. Since the environmental impact of electric cars is heavily affected by the production of lithium-ion batteries, the development of efficient ways to repurpose waste is crucial. Recycling is a multi-step process, starting with the storage of... | https://en.wikipedia.org/wiki?curid=201485 |
21,633 | The pyrometallurgical method uses a high-temperature furnace to reduce the components of the metal oxides in the battery to an alloy of Co, Cu, Fe, and Ni. This is the most common and commercially established method of recycling and can be combined with other similar batteries to increase smelting efficiency and improv... | https://en.wikipedia.org/wiki?curid=201485 |
21,634 | This method involves the use of aqueous solutions to remove the desired metals from the cathode. The most common reagent is sulfuric acid. Factors that affect the leaching rate include the concentration of the acid, time, temperature, solid-to-liquid-ratio, and reducing agent. It is experimentally proven that HO acts a... | https://en.wikipedia.org/wiki?curid=201485 |
21,635 | Once leached, the metals can be extracted through precipitation reactions controlled by changing the pH level of the solution. Cobalt, the most expensive metal, can then be recovered in the form of sulfate, oxalate, hydroxide, or carbonate. [75] More recently recycling methods experiment with the direct reproduction of... | https://en.wikipedia.org/wiki?curid=201485 |
21,636 | The main issues with this method, however, is that a large volume of solvent is required and the high cost of neutralization. Although it's easy to shred up the battery, mixing the cathode and anode at the beginning complicates the process, so they will also need to be separated. Unfortunately, the current design of ba... | https://en.wikipedia.org/wiki?curid=201485 |
21,637 | Direct recycling is the removal of the cathode or anode from the electrode, reconditioned, and then reused in a new battery. Mixed metal-oxides can be added to the new electrode with very little change to the crystal morphology. The process generally involves the addition of new lithium to replenish the loss of lithium... | https://en.wikipedia.org/wiki?curid=201485 |
21,638 | This method is extremely cost-effective for noncobalt-based batteries as the raw materials do not make up the bulk of the cost. Direct recycling avoids the time-consuming and expensive purification steps, which is great for low-cost cathodes such as LiMnO and LiFePO. For these cheaper cathodes, most of the cost, embedd... | https://en.wikipedia.org/wiki?curid=201485 |
21,639 | The drawback of the method lies in the condition of the retired battery. In the case where the battery is relatively healthy, direct recycling can cheaply restore its properties. However, for batteries where the state of charge is low, direct recycling may not be worth the investment. The process must also be tailored ... | https://en.wikipedia.org/wiki?curid=201485 |
21,640 | Extraction of raw materials for lithium ion batteries may present dangers to local people, especially land-based indigenous populations. | https://en.wikipedia.org/wiki?curid=201485 |
21,641 | Cobalt sourced from the Democratic Republic of the Congo is often mined by workers using hand tools with few safety precautions, resulting in frequent injuries and deaths. Pollution from these mines has exposed people to toxic chemicals that health officials believe to cause birth defects and breathing difficulties. Hu... | https://en.wikipedia.org/wiki?curid=201485 |
21,642 | A study of relationships between lithium extraction companies and indigenous peoples in Argentina indicated that the state may not have protected indigenous peoples' right to free prior and informed consent, and that extraction companies generally controlled community access to information and set the terms for discuss... | https://en.wikipedia.org/wiki?curid=201485 |
21,643 | Development of the Thacker Pass lithium mine in Nevada, USA has met with protests and lawsuits from several indigenous tribes who have said they were not provided free prior and informed consent and that the project threatens cultural and sacred sites. Links between resource extraction and missing and murdered indigeno... | https://en.wikipedia.org/wiki?curid=201485 |
21,644 | Researchers are actively working to improve the power density, safety, cycle durability (battery life), recharge time, cost, flexibility, and other characteristics, as well as research methods and uses, of these batteries. | https://en.wikipedia.org/wiki?curid=201485 |
21,645 | The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite systems (GNSS) that provides geolocation and time information to a GPS receiver anywh... | https://en.wikipedia.org/wiki?curid=11866 |
21,646 | The GPS project was started by the U.S. Department of Defense in 1973. The first prototype spacecraft was launched in 1978 and the full constellation of 24 satellites became operational in 1993. Originally limited to use by the United States military, civilian use was allowed from the 1980s following an executive order... | https://en.wikipedia.org/wiki?curid=11866 |
21,647 | From the early 1990s, GPS positional accuracy was degraded by the United States government by a program called Selective Availability, which could selectively degrade or deny access to the system at any time, as happened to the Indian military in 1999 during the Kargil War. However, this practice was discontinued on Ma... | https://en.wikipedia.org/wiki?curid=11866 |
21,648 | The Russian Global Navigation Satellite System (GLONASS) was developed contemporaneously with GPS, but suffered from incomplete coverage of the globe until the mid-2000s. GLONASS reception in addition to GPS can be combined in a receiver thereby allowing for additional satellites available to enable faster position fix... | https://en.wikipedia.org/wiki?curid=11866 |
21,649 | China's BeiDou Navigation Satellite System began global services in 2018, and finished its full deployment in 2020. | https://en.wikipedia.org/wiki?curid=11866 |
21,650 | There are also the European Union Galileo navigation satellite system, and India's NavIC. Japan's Quasi-Zenith Satellite System (QZSS) is a GPS satellite-based augmentation system to enhance GPS's accuracy in Asia-Oceania, with satellite navigation independent of GPS scheduled for 2023. | https://en.wikipedia.org/wiki?curid=11866 |
21,651 | When selective availability was lifted in 2000, GPS had about a accuracy. GPS receivers that use the L5 band have much higher accuracy, pinpointing to within , while high-end users (typically engineering and land surveying applications) are able to have accuracy on several of the bandwidth signals to within two centime... | https://en.wikipedia.org/wiki?curid=11866 |
21,652 | The GPS project was launched in the United States in 1973 to overcome the limitations of previous navigation systems, combining ideas from several predecessors, including classified engineering design studies from the 1960s. The U.S. Department of Defense developed the system, which originally used 24 satellites, for u... | https://en.wikipedia.org/wiki?curid=11866 |
21,653 | The design of GPS is based partly on similar ground-based radio-navigation systems, such as LORAN and the Decca Navigator, developed in the early 1940s. | https://en.wikipedia.org/wiki?curid=11866 |
21,654 | In 1955, Friedwardt Winterberg proposed a test of general relativity—detecting time slowing in a strong gravitational field using accurate atomic clocks placed in orbit inside artificial satellites. Special and general relativity predicted that the clocks on GPS satellites, as observed by those on Earth, run 38 microse... | https://en.wikipedia.org/wiki?curid=11866 |
21,655 | In 1955, Dutch Naval officer Wijnand Langeraar submitted a patent application for a radio-based Long-Range Navigation System, with the US Patent office on February 16, 1955, and was granted Patent US2980907A on April 18, 1961. | https://en.wikipedia.org/wiki?curid=11866 |
21,656 | When the Soviet Union launched the first artificial satellite (Sputnik 1) in 1957, two American physicists, William Guier and George Weiffenbach, at Johns Hopkins University's Applied Physics Laboratory (APL) decided to monitor its radio transmissions. Within hours they realized that, because of the Doppler effect, the... | https://en.wikipedia.org/wiki?curid=11866 |
21,657 | Early the next year, Frank McClure, the deputy director of the APL, asked Guier and Weiffenbach to investigate the inverse problem: pinpointing the user's location, given the satellite's. (At the time, the Navy was developing the submarine-launched Polaris missile, which required them to know the submarine's location.)... | https://en.wikipedia.org/wiki?curid=11866 |
21,658 | TRANSIT was first successfully tested in 1960. It used a constellation of five satellites and could provide a navigational fix approximately once per hour. | https://en.wikipedia.org/wiki?curid=11866 |
21,659 | In 1967, the U.S. Navy developed the Timation satellite, which proved the feasibility of placing accurate clocks in space, a technology required for GPS. | https://en.wikipedia.org/wiki?curid=11866 |
21,660 | In the 1970s, the ground-based OMEGA navigation system, based on phase comparison of signal transmission from pairs of stations, became the first worldwide radio navigation system. Limitations of these systems drove the need for a more universal navigation solution with greater accuracy. | https://en.wikipedia.org/wiki?curid=11866 |
21,661 | Although there were wide needs for accurate navigation in military and civilian sectors, almost none of those was seen as justification for the billions of dollars it would cost in research, development, deployment, and operation of a constellation of navigation satellites. During the Cold War arms race, the nuclear th... | https://en.wikipedia.org/wiki?curid=11866 |
21,662 | Precise navigation would enable United States ballistic missile submarines to get an accurate fix of their positions before they launched their SLBMs. The USAF, with two thirds of the nuclear triad, also had requirements for a more accurate and reliable navigation system. The U.S. Navy and U.S. Air Force were developin... | https://en.wikipedia.org/wiki?curid=11866 |
21,663 | To increase the survivability of ICBMs, there was a proposal to use mobile launch platforms (comparable to the Soviet SS-24 and SS-25) and so the need to fix the launch position had similarity to the SLBM situation. | https://en.wikipedia.org/wiki?curid=11866 |
21,664 | In 1960, the Air Force proposed a radio-navigation system called MOSAIC (MObile System for Accurate ICBM Control) that was essentially a 3-D LORAN. A follow-on study, Project 57, was performed in 1963 and it was "in this study that the GPS concept was born." That same year, the concept was pursued as Project 621B, whic... | https://en.wikipedia.org/wiki?curid=11866 |
21,665 | Updates from the Navy TRANSIT system were too slow for the high speeds of Air Force operation. The Naval Research Laboratory (NRL) continued making advances with their Timation (Time Navigation) satellites, first launched in 1967, second launched in 1969, with the third in 1974 carrying the first atomic clock into orbi... | https://en.wikipedia.org/wiki?curid=11866 |
21,666 | Another important predecessor to GPS came from a different branch of the United States military. In 1964, the United States Army orbited its first Sequential Collation of Range (SECOR) satellite used for geodetic surveying. The SECOR system included three ground-based transmitters at known locations that would send sig... | https://en.wikipedia.org/wiki?curid=11866 |
21,667 | With these parallel developments in the 1960s, it was realized that a superior system could be developed by synthesizing the best technologies from 621B, Transit, Timation, and SECOR in a multi-service program. Satellite orbital position errors, induced by variations in the gravity field and radar refraction among othe... | https://en.wikipedia.org/wiki?curid=11866 |
21,668 | During Labor Day weekend in 1973, a meeting of about twelve military officers at the Pentagon discussed the creation of a "Defense Navigation Satellite System (DNSS)". It was at this meeting that the real synthesis that became GPS was created. Later that year, the DNSS program was named "Navstar." Navstar is often erro... | https://en.wikipedia.org/wiki?curid=11866 |
21,669 | The effect of the ionosphere on radio transmission was investigated in a geophysics laboratory of Air Force Cambridge Research Laboratory, renamed to Air Force Geophysical Research Lab (AFGRL) in 1974. AFGRL developed the Klobuchar model for computing ionospheric corrections to GPS location. Of note is work done by Aus... | https://en.wikipedia.org/wiki?curid=11866 |
21,670 | After Korean Air Lines Flight 007, a Boeing 747 carrying 269 people, was shot down in 1983 after straying into the USSR's prohibited airspace, in the vicinity of Sakhalin and Moneron Islands, President Ronald Reagan issued a directive making GPS freely available for civilian use, once it was sufficiently developed, as ... | https://en.wikipedia.org/wiki?curid=11866 |
21,671 | Initially, the highest-quality signal was reserved for military use, and the signal available for civilian use was intentionally degraded, in a policy known as Selective Availability. This changed with President Bill Clinton signing on May 1, 2000, a policy directive to turn off Selective Availability to provide the sa... | https://en.wikipedia.org/wiki?curid=11866 |
21,672 | Since its deployment, the U.S. has implemented several improvements to the GPS service, including new signals for civil use and increased accuracy and integrity for all users, all the while maintaining compatibility with existing GPS equipment. Modernization of the satellite system has been an ongoing initiative by the... | https://en.wikipedia.org/wiki?curid=11866 |
21,673 | As of early 2015, high-quality, FAA grade, Standard Positioning Service (SPS) GPS receivers provided horizontal accuracy of better than , although many factors such as receiver and antenna quality and atmospheric issues can affect this accuracy. | https://en.wikipedia.org/wiki?curid=11866 |
21,674 | GPS is owned and operated by the United States government as a national resource. The Department of Defense is the steward of GPS. The "Interagency GPS Executive Board (IGEB)" oversaw GPS policy matters from 1996 to 2004. After that, the National Space-Based Positioning, Navigation and Timing Executive Committee was es... | https://en.wikipedia.org/wiki?curid=11866 |
21,675 | The U.S. Department of Defense is required by law to "maintain a Standard Positioning Service (as defined in the federal radio navigation plan and the standard positioning service signal specification) that will be available on a continuous, worldwide basis," and "develop measures to prevent hostile use of GPS and its ... | https://en.wikipedia.org/wiki?curid=11866 |
21,676 | On February 10, 1993, the National Aeronautic Association selected the GPS Team as winners of the 1992 Robert J. Collier Trophy, the US's most prestigious aviation award. This team combines researchers from the Naval Research Laboratory, the USAF, the Aerospace Corporation, Rockwell International Corporation, and IBM F... | https://en.wikipedia.org/wiki?curid=11866 |
21,677 | Francis X. Kane (Col. USAF, ret.) was inducted into the U.S. Air Force Space and Missile Pioneers Hall of Fame at Lackland A.F.B., San Antonio, Texas, March 2, 2010, for his role in space technology development and the engineering design concept of GPS conducted as part of Project 621B. | https://en.wikipedia.org/wiki?curid=11866 |
21,678 | On October 4, 2011, the International Astronautical Federation (IAF) awarded the Global Positioning System (GPS) its 60th Anniversary Award, nominated by IAF member, the American Institute for Aeronautics and Astronautics (AIAA). The IAF Honors and Awards Committee recognized the uniqueness of the GPS program and the e... | https://en.wikipedia.org/wiki?curid=11866 |
21,679 | On December 6, 2018, Gladys West was inducted into the Air Force Space and Missile Pioneers Hall of Fame in recognition of her work on an extremely accurate geodetic Earth model, which was ultimately used to determine the orbit of the GPS constellation. | https://en.wikipedia.org/wiki?curid=11866 |
21,680 | On February 12, 2019, four founding members of the project were awarded the Queen Elizabeth Prize for Engineering with the chair of the awarding board stating "Engineering is the foundation of civilisation; there is no other foundation; it makes things happen. And that's exactly what today's Laureates have done - they'... | https://en.wikipedia.org/wiki?curid=11866 |
21,681 | The GPS satellites carry very stable atomic clocks that are synchronized with one another and with the reference atomic clocks at the ground control stations; any drift of the clocks aboard the satellites from the reference time maintained on the ground stations is corrected regularly. Since the speed of radio waves (s... | https://en.wikipedia.org/wiki?curid=11866 |
21,682 | Each GPS satellite carries an accurate record of its own position and time, and broadcasts that data continuously. Based on data received from multiple GPS satellites, an end user's GPS receiver can calculate its own four-dimensional position in spacetime; However, at a minimum, four satellites must be in view of the r... | https://en.wikipedia.org/wiki?curid=11866 |
21,683 | Conceptually, the receiver measures the TOAs (according to its own clock) of four satellite signals. From the TOAs and the TOTs, the receiver forms four time of flight (TOF) values, which are (given the speed of light) approximately equivalent to receiver-satellite ranges plus time difference between the receiver and G... | https://en.wikipedia.org/wiki?curid=11866 |
21,684 | In practice the receiver position (in three dimensional Cartesian coordinates with origin at the Earth's center) and the offset of the receiver clock relative to the GPS time are computed simultaneously, using the navigation equations to process the TOFs. | https://en.wikipedia.org/wiki?curid=11866 |
21,685 | The receiver's Earth-centered solution location is usually converted to latitude, longitude and height relative to an ellipsoidal Earth model. The height may then be further converted to height relative to the geoid, which is essentially mean sea level. These coordinates may be displayed, such as on a moving map displa... | https://en.wikipedia.org/wiki?curid=11866 |
21,686 | Although usually not formed explicitly in the receiver processing, the conceptual time differences of arrival (TDOAs) define the measurement geometry. Each TDOA corresponds to a hyperboloid of revolution (see Multilateration). The line connecting the two satellites involved (and its extensions) forms the axis of the hy... | https://en.wikipedia.org/wiki?curid=11866 |
21,687 | It is sometimes incorrectly said that the user location is at the intersection of three spheres. While simpler to visualize, this is the case only if the receiver has a clock synchronized with the satellite clocks (i.e., the receiver measures true ranges to the satellites rather than range differences). There are marke... | https://en.wikipedia.org/wiki?curid=11866 |
21,688 | The description above is representative of a receiver start-up situation. Most receivers have a track algorithm, sometimes called a "tracker", that combines sets of satellite measurements collected at different times—in effect, taking advantage of the fact that successive receiver positions are usually close to each ot... | https://en.wikipedia.org/wiki?curid=11866 |
21,689 | The disadvantage of a tracker is that changes in speed or direction can be computed only with a delay, and that derived direction becomes inaccurate when the distance traveled between two position measurements drops below or near the random error of position measurement. GPS units can use measurements of the Doppler sh... | https://en.wikipedia.org/wiki?curid=11866 |
21,690 | GPS requires four or more satellites to be visible for accurate navigation. The solution of the navigation equations gives the position of the receiver along with the difference between the time kept by the receiver's on-board clock and the true time-of-day, thereby eliminating the need for a more precise and possibly ... | https://en.wikipedia.org/wiki?curid=11866 |
21,691 | Although four satellites are required for normal operation, fewer apply in special cases. If one variable is already known, a receiver can determine its position using only three satellites. For example, a ship on the open ocean usually has a known elevation close to 0m, and the elevation of an aircraft may be known. S... | https://en.wikipedia.org/wiki?curid=11866 |
21,692 | The current GPS consists of three major segments. These are the space segment, a control segment, and a user segment. The U.S. Space Force develops, maintains, and operates the space and control segments. GPS satellites broadcast signals from space, and each GPS receiver uses these signals to calculate its three-dimens... | https://en.wikipedia.org/wiki?curid=11866 |
21,693 | The space segment (SS) is composed of 24 to 32 satellites, or Space Vehicles (SV), in medium Earth orbit, and also includes the payload adapters to the boosters required to launch them into orbit. The GPS design originally called for 24 SVs, eight each in three approximately circular orbits, but this was modified to si... | https://en.wikipedia.org/wiki?curid=11866 |
21,694 | Orbiting at an altitude of approximately ; orbital radius of approximately , each SV makes two complete orbits each sidereal day, repeating the same ground track each day. This was very helpful during development because even with only four satellites, correct alignment means all four are visible from one spot for a fe... | https://en.wikipedia.org/wiki?curid=11866 |
21,695 | , there are 31 satellites in the GPS constellation, 27 of which are in use at a given time with the rest allocated as stand-bys. A 32nd was launched in 2018, but as of July 2019 is still in evaluation. More decommissioned satellites are in orbit and available as spares. The additional satellites improve the precision o... | https://en.wikipedia.org/wiki?curid=11866 |
21,696 | The MCS can also access Satellite Control Network (SCN) ground antennas (for additional command and control capability) and NGA (National Geospatial-Intelligence Agency) monitor stations. The flight paths of the satellites are tracked by dedicated U.S. Space Force monitoring stations in Hawaii, Kwajalein Atoll, Ascensi... | https://en.wikipedia.org/wiki?curid=11866 |
21,697 | Satellite maneuvers are not precise by GPS standards—so to change a satellite's orbit, the satellite must be marked "unhealthy", so receivers don't use it. After the satellite maneuver, engineers track the new orbit from the ground, upload the new ephemeris, and mark the satellite healthy again. | https://en.wikipedia.org/wiki?curid=11866 |
21,698 | The operation control segment (OCS) currently serves as the control segment of record. It provides the operational capability that supports GPS users and keeps the GPS operational and performing within specification. | https://en.wikipedia.org/wiki?curid=11866 |
21,699 | OCS successfully replaced the legacy 1970s-era mainframe computer at Schriever Air Force Base in September 2007. After installation, the system helped enable upgrades and provide a foundation for a new security architecture that supported U.S. armed forces. | https://en.wikipedia.org/wiki?curid=11866 |
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