Active vibration suppression in flexible spacecraft with mismatched uncertainty via sliding mode/shaped input control

A generalized scheme based on output feedback sliding mode control (OFSMC) in conjunction with input shaping technique is discussed for a linear uncertain system with an unknown but bounded parametric uncertainty and external disturbance, and is utilized in a flexible spacecraft for rotational nameuver control and active reduction of elastic vibration during maneuvering operation. The configuration of the proposed approach is that the input shaper is implemented outside the feedback loop, which is designed for the reference model and achieves the exact reduction of residual vibration by modifying the existing command; while for the feedback loop, the feedback controller based on the sliding mode control is implemented to make the closed-loop system behave like the reference model with input shaper and suppress the residual vibrations. The robustness against the parametric uncertainty and external disturbance is achieved through the proper selection of control gains. An attractive feature of this OFSMC algorithm is that the parametric uncertainties of the system need not satisfy the so-called matching condition or invariance conditions provided certain bounds are known. Simulation results for the spacecraft model show precise trajectory control and satisfactory vibration suppression.