Disturbance-Observer-Based Robust Relative Pose Control for Spacecraft Rendezvous and Proximity Operations Under Input Saturation

This paper investigates the robust relative pose control for spacecraft rendezvous and proximity operations subject to input saturation, kinematic couplings, parametric uncertainties, and unknown external disturbances. Relative rotational and relative translational nonlinear system models are first derived, and relative attitude and relative position controllers are then proposed, respectively. The kinematic couplings, parametric uncertainties, and unknown external disturbances in dynamical models are treated as compound disturbances, and nonlinear disturbance observers are developed and incorporated into the relative pose control design, which can avoid the assumption on the bounded derivatives of compound disturbances. Meanwhile, input saturation effect of the control torques and forces is compensated by synthesizing the outputs of the auxiliary systems into the controllers. Based on the proposed disturbance observers and auxiliary systems, saturated attitude synchronization and position tracking controllers are developed to reject the unknown compound disturbances and ensure the convergence of the relative pose and velocities. The stability of the closed-loop system is rigorously proved in the Lyapunov framework; relative pose and velocities ultimately converge to the small neighborhoods of the origin in spite of input saturation and model uncertainties. Simulation experiments validate the performance of the proposed robust saturated control strategy.