Attitude and Articulation Control Subsystem (AACS)

Function

Provide Pointing Control of The Spacecraft during All Mission Phases, both Nominal and Off Nominal, and Attitude Knowledge of the Spacecraft Orientation Relative to Fixed Reference Frames. Also provides for articulation of the Solar Arrays and the High Gain Antenna.

Design Features

• 3-Axis Stabilized
• Celestial Sensor, Horizon Sensor, 4-pi Sun Sensors, and Inertial Measurement Unit Used in Various Combinations to Determine Attitude in Desired Reference Frames
• Fine Pointing Control Using Reaction Wheels
• Thrusters Used for Large Torque Capability, Reaction Wheel Momentum Unloading, Orbit Maintenance, Backup Attitude Control and Safe Mode
• Autonomous Periapsis Raise Maneuver Implemented in Safe Mode for Aerobraking
• Extensive Reuse of MO Hardware and Algorithms

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Flight Software Subsystem

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