Spacecraft and Subsystems
The Mars Climate Orbiter is a box shaped spacecraft about 2.5 m wide and 4 m high, consisting of stacked propulsion and equipment modules. An 11 square meter solar array wing is attached by 2-axis gimbal to one side and a 1.3 m diameter high-gain dish antenna is attached by 2-axis gimbal to a mast at the top of the propulsion module. The MARCI and PMIRR instruments, as well as a UHF antenna and battery enclosure, are mounted to the bottom of the equipment module. Launch mass is constrained to be no more than 643 kg including 289 kg of propellant.
Propulsion is achieved via a bi-propellant (hydrazine/nitrogen tetroxide) main engine, mounted with the propellant tanks in the propulsion module, and hydrazine thrusters. The orbiter is 3-axis stabilized. Attitude control and maneuvering capability is provided by four 5-lbf thrusters (pitch/yaw) and four 0.2-lbf thrusters (roll) in combination with reaction wheels. Attitude is determined using an inertial measurement unit, a star tracker, and analog Sun sensors with knowledge of 25 mrad and stability of 1.5 mrad/(1 sec) and 3 mrad/(3 sec).
Spacecraft power is provided by 3 panels of GaAs/Ge solar cells on the single-wing solar array. Power is stored in nickel hydride (NiH2) common pressure vessel batteries. Thermal control is achieved through a combination of louvers, MLI, Kapton, paints, radiators and heater circuits. Communications with Earth are in X-band using Cassini Deep Space Transponders and 15 W RF solid state power amplifiers through the 1.3 m high gain antenna for both uplink and downlink, a medium gain transmitting antenna, and a low-gain receiving antenna. A 10 W UHF system is used for 2-way communications with the Mars Polar Lander. A RAD6000 processor is used for on-board command and data handling.