Mars Climate Orbiter
Detailed Flight System Description
The Mars Climate Orbiter is 3-axis stabilized in all mission phases following separation from the launch vehicle. The primary attitude determination is via star camera and an inertial measurement unit, and is backed up by analog sun sensors. Reaction wheels provide primary attitude control during most mission phases, and are desaturated via RCS thrusters. Because of IMU lifetime concerns, the IMUs will be turned off during significant portions of Cruise and Mapping, and the vehicle operated in all-stellar mode. except during maneuvers. The RCS thrusters also provide attitude control during Trajectory Correction Maneuvers, Mars Orbit Insertion, aerobraking drag pass, Orbital Trim Maneuvers, and safe mode [until rates are damped, at which point RW control is used]. In all, four 5-lbf thrusters are used for Trajectory Correction Maneuvers and pitch/yaw control. Four 0.2-lbf thrusters are used for roll control. The Orbiter C&DH uses the RAD6000 processor. The X-band link with Earth employs Cassini Deep Space Transponders, 15 W RF solid state power amplifiers (SSPA's), one 1.3 m transmit/receive high gain antenna (HGA), one transmit-only medium gain antenna (MGA), and one receive-only low gain antenna. A 10 Watt RF UHF system supports the 2-way link with the Lander. The 3-panel, single wing solar array (SA) uses GaAs/Ge solar cells and also functions as the primary drag brake during aerobraking. The batteries are NiH2 CPV batteries, while the electrical power electronics are based on the SSTI spacecraft electronics. The thermal control subsystem is passive, with louvers to control the temperature of the batteries and SSPA's and combinations of MLI, Kapton, paints, and dedicated radiators for certain other components. Both thermostatically controlled and computer controlled heater circuits are used. The Orbiter equipment module (EM) is a composite truss structure with titanium end fittings and two Aluminum honeycomb panels with composite face sheets. The solar array and HGA track the Sun and Earth, respectively, with 2-axis gimbals. The propulsion subsystem is dual mode, employing a bipropellant main engine for Mars Orbit Insertion (MOI) and TCM (hydrazine) thrusters for all other propulsive events. Most subsystem components are redundant, with critical items cross strapped.
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