Variable structure slewing control and vibration damping of flexible spacecraft

Abstract

The question of attitude control and elastic mode stabilization of a spacecraft (orbiter) with “beam-tip mass” type payload is considered. It is assumed that bounded but unknown disturbance torques are acting on the spacecraft. Based on variable structure system theory, a discontinuous three-axis moment control law is derived to control the attitude of the spacecraft. Although, this control law accomplishes attitude trajectory tracking, it excites the elastic modes of the beam. A modal velocity feedback design is presented to damp the elastic oscillations using additional actuators at the tip of the beam. Simulation results are presented to show that rotational maneuvers and vibration stabilization can be accomplished in the closed-loop system in spite of disturbance torques and uncertainty in the system.