Robust adaptive control for relative motion of spacecraft under input saturation

This paper investigates the integrated control of attitude and orbit for the relative motion of a spacecraft in the presence of input saturation constraint. First, using unit dual quaternion, a mathematic model of the six-degree-of-freedom relative motion for the spacecraft is introduced, and an error dual quaternion is adopted to describe the relative attitude and position of the spacecraft. Second, an adaptive controller, which is robust enough to model the uncertainties of the spacecraft and its bounded external disturbances, is proposed to deal with input saturation. Moreover, it is proved by a rigorous theoretical analysis of the Lyapunov method that the whole resulting closed-loop system is globally and asymptotically stable. Finally, numerical simulations are performed to demonstrate the validity and effectiveness of the presented approach. Compared with other approaches, the new one has the following properties: 1) control input saturation can be explicitly restrained; 2) faster convergence rate and improved robustness can be obtained.