AN OPTIMAL APPROACH TO COMPUTER CONTROL OF A HIGHLY COUPLED SATELLITE ATTITUDE LOOP

Linear-Quadratic-Gaussian optimal control theory provides a uni-fied approach to controller synthesis. The pitch and array drive loop of the DMSP Block 5D spacecraft, which represents an interesting control problem because of actuator coupling, is considered as an example. A discrete-time optimal feedback control law timed to match the Block 5D's flight computer is determined. New cross feeds result that are not pres-ent in the current control laws, derived by classical compensation, which exploit the array drive motor's reaction torque on the satellite body to enhance body pointing at the expense of array error. Reaction wheel ac-tivity can, in certain cases, be reduced by a factor of five. The requirement of full state knowledge is met by an estimator developed according to discrete time Kalman filtering theory. Several measurement-options were considered which included rate integrating gyros as currently exist on the satellite, a 2-D star mapper sensing catalogued stars, and the combination of a star mapper and rate gyro measurements