Attitude Control for Rigid Spacecraft via Disturbance Observer based Terminal Sliding Mode Controller

In this paper, a terminal sliding mode controller based on disturbance observer is designed for rigid spacecraft. A disturbance observer is first proposed for the unmeasurable disturbance. The disturbance estimation error converges to zero in finite time. By combining this proposed observer with the sliding mode control technique, then a finite time attitude control law is presented for the rigid spacecraft. The variable boundary layer saturation function is used in the design of the switching portion of the terminal sliding mode controller to reduce chattering. The convergence of the observer and closed-loop system is proved by the Lyapunov stability theory.