A gyro drift and dynamics state estimator for satellite attitude control systems utilizing a star mapper

A recursive estimator satellite with substantially rigid body dynamics is presented which provides filtered estimates of gyro width, disturbing angular acceleration, body angular velocity and attitude. The estimator is based on a Kalman filter with the following innovations: a low-level fictitious covariance matrix element to facilitate estimation of the disturbing angular acceleration, and a modified gain matrix which permits real-time model iterations and gyro sampling at a much higher rate than star mapper sampling. The part of the matrix relevant to star mapper output is adapted to enable the correction to the model to be applied continuously, thereby avoiding stepping of the state measurement relative to new star mapper measurements. Digital simulation results are given for a complete control system in which two control loops are completed by state-variable feedback, comprising a linear gyro-drift control law and a nonliner gas jet control law.