Nonlinear optimal control of spacecraft approaching a tumbling target

This paper addresses the control of spacecraft to approach and align with a tumbling target. In order to complete the task, the spacecraft is required to perform large position and attitude maneuvers with sufficient accuracy. In addition, the flexible motion induced by large angular maneuvers needs to be minimized. The primary contribution of this work is to consider the control of position, attitude, and flexible motion in one unified optimal control framework. The 6-DOF rigid body dynamics and coupled flexible structure dynamics are highly nonlinear and lead to a challenging control problem. The thetas - D nonlinear optimal control technique is employed to design an integrated controller for this problem by solving the associated Hamilton-Jacobi-Bellman (HJB) equation in an approximate analytical form via a perturbation process. The closed-form controller offered by this method is easy to implement onboard especially for this problem with a large state-space. Numerical results show that the proposed controller exhibits good tracking performance even under large moment of inertia uncertainties.