A combined positive position feedback and variable structure approach for flexible spacecraft under input nonlinearity

This paper is concerned with vibration control of a flexible spacecraft in the presence of parametric uncertainty/external disturbances as well as control input nonlinearity through distributed piezoelectric sensor/actuator technology. To satisfy pointing requirements and simultaneously suppress vibrations, two separate control loops are adopted. The first uses piezoceramics as sensors and actuators to actively suppress certain flexible modes by designing positive position feedback (PPF) compensators which add damping to the flexible structures in certain critical modes. The second feedback loop is designed based on an output feedback sliding mode control (OFSMC) design where control input nonlinearity is taken into consideration. Simulation studies for the proposed control strategy on a flexible spacecraft demonstrate the effectiveness of the proposed approach.