Nonlinear output tracking and disturbance rejection for autonomous close-range rendezvous and docking of spacecraft

A new control scheme of nonlinear output tracking and disturbance rejection for autonomous close-range rendezvous and docking of spacecraft is proposed in a closed-loop structure. The robustness of the proposed control scheme is achieved through the sum of output-feedback control and state-feedback control as a closed-loop control structure. The designs of both control laws are based on full, 6-degrees-of-freedom, nonlinear dynamic models, which are transformed into a linear-like form using a state dependent Ricatti equation technique. The proposed control scheme ensures closerange rendezvous and meets the state tracking conditions for docking such that the convergence of state tracking errors should be ensured in the presence of unknown disturbances and uncertainties of the system parameters. Compared with the conventional state-dependent Ricatti equation method, the proposed control scheme yields superior state tracking performance and robustness in the presence of external disturbances and uncertain system parameters. The 6-degreesof- freedom numerical simulation results are presented to verify the effectiveness and capability of the proposed control scheme for autonomous close-range rendezvous and docking.