ESA GNC Conference Papers Repository

This paper describes the functional architecture and presents the control law of an attitude control system designed for a large scientific satellite with high accuracy and stability pointing requirements, such as those necessary during the fine pointing operations. The satellite dynamical motion has been reproduced by an accurate software simulator implementing the error models of the sensors and actuators currently being part of the on-board system configuration of state-of-the-art space missions; moreover the main disturbances affecting the satellite motion during its mission are considered. The control system architecture includes an optimal estimator, the well-known Multiplicative Extended Kalman Filter, modified for the time delay correction of the star tracker by means of a forward state propagation for a correct implementation of measurement update. This estimator is cascaded with a second one specifically used for disturbance torques estimation. The estimation task is then coupled with a linear optimal control algorithm combined into an error feedback output regulator, based on a space system design involving the exosystems of the disturbances and reference profiles. The reported simulations highlight the high performances of the algorithm, capable of fully satisfying a stringent pointing error requirement. Lastly, the proposed attitude control system is capable of tracking not only step reference trajectories but also sinusoidal time varying signals within a disturbed environment and promises robust performances also in case of possible actuators faults.