Robust control of uncertain flexible spacecraft using disturbance observer based control strategies

Spacecraft with large flimsy structures impose an interesting and challenging design problem for on-board Guidance, Navigation and Control Systems (GNC) due to their flexible modes and possible significant uncertainties. This paper presents a new approach to this problem, namely disturbance observer based control (DOBC), where a disturbance observer is employed not only to estimate and cancel external disturbances but the influence of flexible modes and uncertainties. A two stages design procedure is proposed. It is shown that three design objectives, i.e. attenuation of external disturbance, suppression of flexible modes and robustness against uncertainties, can be achieved by the proposed scheme. The proposed technique is easy to implement and transparent to practitioners, and it shall have significant potential for AOCS of spacecraft with flexible structures and other space systems.