Fixed-Time Terminal Sliding Mode Control for Close-Range Rendezvous

The problem of the relative position and attitude coupled control for rendezvous and docking is investigated in this paper, which takes the external disturbances into consideration and assumes that the target spacecraft is freely tumbling. An adaptive 6-DOF control scheme is proposed based on the concept of the fixed-time stabilization. Besides, the singularity problem is solved through a switch function which not only makes the settling time estimable, but also the estimated value is independent of the initial values of states. Then the stability proof is accomplished by the development of a Lyapunov function. The numerical results show that this method achieves good performance and robustness.