The 2001 Mars Odyssey, formerly MGM (Mars Global Mapper), is the remaining part of the
Mars Surveyor 2001 Project, which originally consisted of two separately launched
missions, The Mars Surveyor 2001 Orbiter and the Mars Surveyor 2001 Lander. The lander
spacecraft was cancelled as part of the reorganization of the Mars Exploration Program at
NASA. The orbiter, renamed the 2001 Mars Odyssey, will nominally orbit Mars for three
years, with the objective of conducting a detailed mineralogical analysis of the planet's
surface from orbit and measuring the radiation environment. The mission has as its primary
science goals to gather data to help determine whether the environment on Mars was ever
conducive to life, to characterize the climate and geology of Mars, and to study potential
radiation hazards to possible future astronaut missions. The orbiter will also act as a
communications relay for future missions to Mars over a period of five years.
The 2001 Mars Odyssey launched on 7 April 2001 at 15:02:22 UT (11:02:22 a.m. EDT).
During the cruise to Mars, in August, the MARIE instrument failed to respond during a
routine data transfer and was put into hibernation. Attempts to revive the instrument were
successful in March 2002 and MARIE began taking scientific data from orbit on 13 March.
The star tracker camera is having difficulties with too much stray light, it is thought
that this will not affect its operation severely. After a seven month cruise the
spacecraft reached Mars on 24 October 2001 at 02:26 UT (23 October 10:26 p.m. EDT). The
spacecraft used a 19.7 minute main-engine propulsive maneuver to transfer into an 18.6
hour elliptical capture orbit and used aerobraking until 11 January 2002, when the
spacecraft pulled out of the aerobraking orbit into a 201 × 500 km orbit. This orbit was
trimmed over the next few weeks until it became a 2-hour, approximately 400 × 400 km polar
science orbit on 30 January 2002. The Orbiter will act as a communications relay for the
Mars 2003 Rovers, scheduled to arrive in January 2004, and possibly other future missions.
Data will be collected from orbit until the end of the 917 day nominal mission in July
2004. The spacecraft will continue to act as a communications relay until October 2005.
The 2001 Mars Odyssey carries
- the Mars Radiation Environment Experiment (MARIE), which will measure the near-space
radiation environment as related to the radiation-related risk to human explorers,
- the Thermal Emission Imaging System (THEMIS), which will map the mineralogy of the
Martian surface using a high-resolution camera and a thermal infrared imaging
spectrometer,
- the Gamma-Ray Spectrometer (GRS), which will map the elemental composition of the
surface and determine the abundance of hydrogen in the shallow subsurface.
- star cameras.
The main body of the 2001 Mars Odyssey is box-shaped, 2.2 meters × 1.7 meters × 2.6
meters. The spacecraft has a launch mass of 725.0 kg, including 348.7 kg of fuel. The
orbiter is divided into two modules, the upper equipment module holds the equipment deck
which supports the engineering components and the science instruments. Above the equipment
module, connected by struts, is the science deck, holding the star cameras, high energy
neutron detector, UHF antenna, the THEMIS instrument and a deployable 6 meter boom holding
the gamma sensor head for the GRS. A set of solar array panels extends out from one side
of the main bus. A parabolic high-gain dish antenna is mounted on a mast extending from
one corner of the bottom of the bus. The MARIE instrument is mounted inside the
spacecraft. The lower part of the bus is the propulsion module. The main engine, a
hydrazine and nitrogen tetroxide rocket which can produce 65.3 kg thrust, is mounted in
the bottom part of the propulsion module, along with the fuel, oxidizer and helium
pressurization tanks.
Attitude control is provided by four 0.1 kg thrusters and the spacecraft can be turned
using four 2.3 kg thrusters. The spacecraft is three-axis stabilized using three primary
reaction wheels and one backup. Navigation is provided by a Sun sensor, star camera, and
inertial measurement unit. Power is provided by the gallium arsenide solar cells in the
solar panel and a 16 amp-hr nickel hydrogen battery. Communications between the orbiter
and Earth are in X-band via the high-gain antenna and communications between the orbiter
and any Mars landers are via the UHF antenna. Thermal control is achieved using a system
of heaters, radiators, louvers, insulating blankets and thermal paint. Command and data
handling is through a RAD6000 computer with 128 Mbytes RAM and 3 Mbytes of non-volatile
memory. [NASA]