Disturbance observer based fault-tolerant control for cooperative spacecraft rendezvous and docking with input saturation

A robust nonlinear control strategy is presented for a cooperative spacecraft rendezvous and docking maneuver, where the pursuer spacecraft is subject to input saturation and actuator faults. The nonlinear coupled models for relative attitude and relative position dynamics are expressed in the pursuer body-fixed frame. A novel control strategy based on feedback linearization framework is developed, and a second-order disturbance observer is employed to estimate and compensate all uncertainties including parametric uncertainties, external disturbances, input saturation and actuator faults. It is proved that the closed-loop systems are uniformly ultimately bounded by using Lyapunov theory. Numerical simulations are given to illustrate effectiveness of the proposed control strategy.