Nonlinear disturbance observer-based robust control for spacecraft formation flying

This paper proposes a composed control approach by combining a nonlinear disturbance (NDO) observer and an asymptotic tracking control (ATC) for spacecraft formation flying system subject to nonvanishing disturbances. In this paper, the multiple disturbances that act on spacecraft from space environment and uncertain mass are considered as unknown external disturbances. The proposed NDO is used to estimate and compensate for the disturbances through feedforward. Stability of the composite closed-loop system is provided using Lyapunov theory. It is shown that the proposed composite controller can significantly enhance disturbance attenuation ability and achieve robust tracking in the presence of the parameter uncertainty and external disturbances. Simulations results are included to demonstrate the effectiveness of the proposed control scheme. Robust dynamic performance and position control accuracy are effectively improved.