Finite-Time Convergent Integrated Relative Position and Attitude Control for Spacecraft Rendezvous

This paper addresses the problem of integrated relative position and attitude control of a spacecraft during the close-range rendezvous phase of a typical rendezvous and docking mission using sliding mode-based controllers, wherein the time of convergence to the desired states plays an important role in the success of the mission. Conventional sliding mode controllers ensure only asymptotic convergence to the equilibrium point. In this study, terminal sliding mode-based controllers have been proposed to ensure finite time convergence that is upper-bounded for any initial conditions. Further, a nonsingular terminal sliding mode controller, which avoids the singularity often seen in terminal sliding mode controllers, has also been developed using integrated relative position and attitude dynamics. The proposed techniques have been validated using numerical simulations and have been found to perform satisfactorily.