Robust nonlinear control for spacecraft rendezvous and docking with disturbance observer

This paper presents a robust nonlinear control strategy for a cooperative spacecraft rendezvous and docking maneuver with coupled attitude and position dynamics. The nonlinear and coupled models of relative attitude and relative position motions are expressed in the pursuer body-fixed frame, respectively. Both parametric uncertainties and disturbances are estimated together by a second-order nonlinear disturbance observer. A robust control strategy based on feedback linearization is developed. It is proved that the states of the closed loop systems are uniformly ultimately bounded in presence of parametric uncertainties and disturbances by using Lyapunov theory. Theoretical conclusions are demonstrated by numerical simulations.