Integrated relative position and attitude control of spacecraft in proximity operation missions with control saturation

In this paper, an integrated relative position and attitude control scheme is proposed for a pursuer spacecraft approaching a spatial target in proximity operation missions. Relative translation and rotation dynamics of spacecraft are both presented, and further integratedly considered due to mutual couplings, which leads to a six degrees-of-freedom (6-DOF) control system with input saturation. To simultaneously achieve relative position and attitude requirements, an adaptive backstepping control law is designed, where an auxiliary signal is employed to cope with control saturation, and a first order filter is introduced to overcome the "explosion of terms" problem. Within the Lyapunov framework, the controller guarantees the stability of the closed-loop system in the presence of bounded disturbances and unknown system parameter. Numerical simulation demonstrates the effect of the proposed control law.