ADAPTIVE ROBUST TRACKING FOR FLEXIBLE SPACECRAFT IN PRESENCE OF DISTURBANCES

The paper deals with trajectory tracking for a flexible spacecraft, su bject to a gravity-gradient disturbance, under parameter uncertainties . The controls are gas jets and reaction wheels, and the measured vari ables describe the attitude and angular velocity of the rigid part. Th e flexible dynamics is treated as an additional disturbance acting on a rigid structure. First, an adaptive control is designed with only th e gravity-gradient disturbance acting on the spacecraft; second, it is proved to be effective also in the presence of disturbance due to the flexibility, provided that appropriate robustness conditions on the c ontroller gains are satisfied. These conditions use partial knowledge of the parameters describing the elastic dynamics. Simulations show th e good performance of such control scheme and demonstrate its applicab ility even in the presence of input saturation.