The Attitude Control System Design for the Submillimeter Wave Astronomy Satellite

The Submillimeter Wave Astronomy Satellite (SWAS), the third Small Explorer spacecraft, has a sophisticated three-axis stellar pointing attitude, control subsystem. This mission requires slewing the satellite up to 3 degrees and settling on target within 15 seconds to a 57 arc-second accuracy once per minute. Hardware and software configuration will be briefly described. The spacecraft has many modes and submodes of increasing complexity and accuracy. These modes use a variety of routines including: Kalman Filtering, Magnetic Calibration, AutoTargeting, Slewing and Fine Control, Momentum Management, and Stellar Acquisition. Simulations have shown that the Attitude Control System (ACS) not only meets sub-arc-minute pointing but also high-rate slewing requirements. The SWAS ACS design clearly demonstrates the feasibility of a complex, sub-arc-minute accuracy attitude control system packaged in a small satellite.