Magnetic torquer control with thruster augmentation

Abstract

Apparatus and a method is presented for controlling yaw and roll excursions in a spacecraft having on-board components such as magnetic torquers, a roll thruster, momentum wheels, a wheel controller, an earth sensor, and a Digital Integrating Rate Assembly (DIRA). An observer module on the spacecraft receives inputs containing information comprising the unbiased roll error from the earth sensor, yaw momentum measured from the wheel speeds, and commanded yaw and pitch momentum output from the wheel controller, and produces therefrom output signals indicative of yaw estimate, yaw momentum estimate and torque disturbances estimate. A controller module on the spacecraft receives the output signals and combines them with inputs containing information comprising minimum yaw error and roll thrust yaw controller gain and minimum yaw error and roll thrust yaw momentum controller gain, and produces therefrom a signal for commanding the operation of the magnetic torquers to change roll momentum when within the dead band of the signal and, alternatively, for commanding the operation of both the magnetic torquers and the roll thruster to change roll momentum when the threshold of the dead band is exceeded. By so doing, the yaw attitude and yaw excursions are controlled.