Spacecraft attitude tracking via robust disturbance observer

Previous work has shown that the disturbance observer based control (DOBC) can improve the performance of spacecraft attitude control system for its good disturbance rejection ability. The disturbance rejection ability of DOBC is mainly determined by the disturbance observer. However, the conventional nonlinear disturbance observer for the disturbance with bounded derivative has an estimation error, thus leading to performance degradation. To solve this problem for spacecraft attitude tracking, we propose a composite control scheme. A robust disturbance observer (RDO) is proposed for spacecraft attitude tracking first. RDO not only avoids the re-estimation of spacecraft attitude variables and makes full use of the information of spacecraft dynamics, but also reduces the effects of disturbance model uncertainty on the observer estimation accuracy and achieves finite-time convergence. Second, the composite control scheme is developed by combining RDO with a nonlinear backstepping controller. The disturbance rejection ability of the closed-loop system is improved significantly by compensation of the output of RDO. Finally, numerical simulations are conducted to verify the effectiveness of the proposed method.