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antennas on the backshell, lander and rover, transmissions during the next hour or
more will consist of simple signal tones coded to indicate the accomplishment of critical
activities. For example, a change in tone will tell controllers when the spacecraft has
successfully jettisoned its cruise stage about 15 minutes before hitting the atmosphere.
During the descent through the atmosphere, about 36 ten-second signal tones will be
Before its first night on the surface of Mars, each rover may deploy its high-gain anten-
na for use the following morning. The rovers will be able to communicate directly with
Earth at transmission rates greater than 11,000 bits per second using this antenna.
About a minute before each lander drops to the martian surface, another important
communication method -- relay through Mars orbiter spacecraft -- will begin to be used.
An antenna mounted on each lander will transmit status information to the orbiting
Mars Global Surveyor from the time the descending lander emerges from the backshell
until ground impact. If that antenna survives the first bounce, it will continue to relay
information for a few minutes as the lander bounces and rolls to a stop. The orbit of
Mars Global Surveyor will be adjusted in preceding weeks to place it over the landing
vicinity during those crucial minutes to receive the transmissions. The orbiter will later
transmit the data to Earth.
Throughout each rover's surface mission, a rover-mounted antenna will be able to
communicate with Mars Global Surveyor and Mars Odyssey for several minutes once
or twice per sol while each of the two orbiters pass overhead via a UHF link at 128,000
bits per second. Plans call for using direct-to-Earth communications for transmissions
critical to mission success, but about half the total data returned from the rovers could
be relayed via the orbiters. One engineering goal for the project is to demonstrate
relay capability at least once with the European Space Agency's Mars Express orbiter,
which is due to begin circling Mars in December 2003.
Planetary Protection Requirements
avoids harmful contamination of celestial bodies.
Rover spacecraft must comply with requirements to carry a total of no more than
300,000 bacterial spores on any surface from which the spores could get into the mart-
ian environment. Technicians assembling the spacecraft and preparing them for
launch frequently cleaned surfaces by wiping them with an alcohol solution. The plane-
tary protection team carefully sampled the surfaces and performed microbiology tests
to demonstrate that each spacecraft meets requirements for biological cleanliness.
Components tolerant of high temperature, such as the parachute and thermal blanket-
ing, were heated to 110 C (230 F) or hotter to kill microbes. The core box of each
compartments are also isolated in this manner.
Another type of precaution is to be sure that other hardware doesn't go to Mars acci-
dentally. When the Delta’s third stage separates from the spacecraft, the two objects
are traveling on nearly identical trajectories. To prevent the possibility of the Delta's
third stage hitting Mars, that shared course is deliberately set so that the spacecraft
The NASA planetary protection officer is responsible for the establishment and
enforcement of the agency’s planetary protection regulations.
Launch Safety
The rovers use small amounts of radioactive materials in two science instruments and
to prevent electronics from getting too cold during martian nights. NASA has safely
used radioactive materials for four decades in a variety of scientific instruments and for
spacecraft heating or electrical power when necessary.
There is little radiological danger to the public from a Mars Exploration Rover 2003
launch accident. Analysis performed for the mission's environmental impact statement
indicates that the chance of an accident occurring during launch is about 1 in 30. Most
accidents would not present a threat to the radioisotope heater units onboard the
spacecraft because of the rugged design of the units. There are also small-quantity
radioactive sources on board the spacecraft (curium-244 and cobalt-57) that are used
for instrument calibration or science experiments. Since these small sources of
curium-244 and cobalt-57 have relatively low melting temperatures compared to the
plutonium dioxide in the radioisotope heater units, these radioactive materials would
likely be released in an early launch accident (i.e., the first 23 seconds of launch). The
chance of an early launch accident that releases any radioactive material is about 1 in
If a launch-area accident resulting in the release of radioactive sources were to occur,
spectators and people off-site in the downwind direction could be exposed to small
quantities of radionuclides. The person with the highest exposure would typically
receive less than a few tens of millirem. (The average annual dose from naturally
occurring sources of radiation in the United States is about 300 millirem per year.) No
health consequences would be expected with this level of radiation exposure.
Precautionary measures include deployment of radiological monitoring teams and
remote air monitoring stations at strategic locations at the launch site. A radiological
control center at Kennedy Space Center would coordinate any local emergency actions
required during the pre-launch or early launch phases of the mission in the event of a
launch mishap.
In the event of a radiological release, federal, state and county agencies would deter-
mine an appropriate course of action for any areas outside the Cape Canaveral Air
Station-Kennedy Space Center site based on actual monitoring information.
Each of the two Mars Exploration Rover spacecraft resembles a nested set of Russian
dolls. The rover will travel to Mars tucked inside a folded-up lander wrapped in
airbags. The lander in turn will be encased in a protective aeroshell. Finally, a disc-
shaped cruise stage is attached to the aeroshell on one side and to the Delta II launch
vehicle on the other.
Cruise stage
The cruise stage provides capabilities needed during the seven-month passage to
Mars but not later in the mission, such as a propulsion system for trajectory correction
maneuvers. Approximately 2.6 meters (8.5 feet) in diameter and 1.6 meters (5.2 feet)
tall, the disc-shaped cruise stage is outfitted with solar panels and antennas on one
face, and with fuel tanks and the aeroshell on the other. Around the rim sit thrusters, a
star scanner and a Sun sensor.
The propulsion system uses hydrazine propellant stored in two titanium tanks. Since
the the entire spacecraft spins at about 2 rotations per minute, fuel in the tanks is
pushed outward toward outlets and through fuel lines to two clusters of thrusters.
Each cluster has four thrusters pointing in different directions.
The star scanner and Sun sensor help the spacecraft determine its orientation. Since
the rover's solar arrays are tucked away inside the aeroshell for the trip, the cruise
stage needs its own for electrical energy. The arrays can generate more than 600
watts when the spacecraft is about as far from the Sun as Earth is, and about half that
much when it nears Mars.
The cruise stage also carries a system for carrying excess heat away from the rover's
computer with a pumped freon loop and rim-mounted radiators.
Entry, Descent and Landing System
The system for getting each rover safely through Mars' atmosphere and onto the sur-
face relies on an aeroshell, a parachute and airbags. The aeroshell has two parts: a
heat shield that faces forward and a backshell. Both are based on designs used suc-
cessfully by NASA's Viking Mars landers in 1976 and Mars Pathfinder in 1997.