Spacecraft and Subsystems
The Mars Surveyor 2001 Orbiter is being rescoped based on the Mars '98 Orbiter design. The original design called for a square equipment deck approximately 1 meter across attached on the edges to a pair of solar panel wings. A 1.1 meter Cassegrain high-gain dish antenna is mounted to another edge of the engineering deck on a 2-axis gimbal. A table-like science deck is supported above the equipment deck. During science orbit operations the solar array and engineering and science decks are constrained to lie in the orbital plane, with the normal to the solar arrays and decks perpendicular to the nadir direction and the long axis of the solar array collinear with the orbital velocity vector. The engineering deck holds a hydrazine tank, propulsion systems, radiator, and batteries. Star cameras, the Martian Radiation Environment Experiment (MARIE), neutron detector, the Thermal Emission Imaging System (THEMIS), the Gamma-Ray Spectrometer (GRS) boom, and a UHF antenna are mounted on the science deck. The GRS boom extends out normal to the science deck with the GRS mounted on the end.
Power is provided by 7 square meters of GaAs/Ge solar cells. The power subsystem provides power switching and unregulated 28Vdc, and energy storage with a 16 amp-hour nickel hydrogen common pressure vessel battery. Reaction wheels provide primary control to maintain the orbiter in a nadir tracking orientation, with periodic momentum desaturation maneuvers with the RCS thrusters. Attitude determination is performed using star cameras, with a near-zenith boresight orientation, and ring laser gyro IMUs. Temperature is maintained through use of a capillary pumped loop thermal control subsystem and 0.7 square-meter nadir-oriented radiator. The command and data handling subsystem uses redundant RAD6000 processors and provides a total of 256 Mbytes of volatile memory.