Flexible spacecraft attitude maneuvering and vibration damping using variable structure control input shaping

A generalized scheme based on the output feedback variable structure control (OFVSC) and input shaping (IS) technique has been proposed for the rotational maneuver and vibration suppression of an orbiting spacecraft with flexible appendages. The proposed control design process is the design of the attitude controller followed by the design of a flexible vibration attenuator. The attitude controller using only the attitude and angular rate information for the flexible spacecraft consists of a linear feedback term and a discontinuous feedback term. By combining the linear term with the discontinuous term, very good disturbance rejection and robustness can be achieved with a lower control effort that would be required from either control when used independently. The linear gain and the discontinuous gain are designed so that the sliding surface exists and is globally reachable. With this attitude controller in place, the dynamics of the closed-loop system is studied and any harmonics in the response are eliminated using IS technique, which requires information about the natural frequency and damping of the closed-loop system. This information is used to modify the input such that the flexible modes are not excited. The proposed control strategy has been implemented on a flexible spacecraft, which is a hub with symmetric cantilever flexible beam appendages and can undergo a single axis rotation. The results have proven the potential of this approach to control flexible spacecraft.