Adaptive Fixed-Time Six-DOF Tracking Control for Noncooperative Spacecraft Fly-Around Mission

This brief is devoted to the fixed-time six-DOF tracking control problem for noncooperative spacecraft fly-around mission in the presence of the parameters uncertainties and disturbances. First, a new and coupled six-DOF relative motion dynamic model without using any target orbital information is established. Subsequently, a novel nonsingular fixed-time terminal sliding mode (NFTSM) with bounded convergence time in regardless of the initial states is designed, which not only can circumvent the singularity problem, but also has faster convergence performance than fast terminal sliding mode. By employing the designed NFTSM and the adaptive technique, a continuous adaptive nonsingular fixed-time fast terminal sliding mode control strategy with no information of the mass, inertia matrix, and disturbances is proposed, which can eliminate the chattering phenomenon and guarantee the fixed-time reachability of the relative position and attitude tracking errors into the small regions containing the origin. Finally, the performance of the proposed control schemes is demonstrated by numerical simulations.