Suboptimal Repointing Maneuver of a staring-mode spacecraft with one DOF for final attitude

This paper addresses the problem of suboptimal control for repointing maneuver of a staring-mode spacecraft where the optical axis is required to point to the target orientation. Different from the traditional reorientation maneuver, the angle of the spacecraft around the optical axis does not need to be controlled. First, a simple yet efficient representation for repointing error is introduced and kinematical descriptions are established correspondingly. Then, two different control algorithms are proposed for repointing control of a staring-mode spacecraft. The first one is the inverse optimal PD-like controller that drives the spacecraft to complete repointing maneuver and the optimality properties of the proposed control law are investigated by using dynamic programming theory. The other one is a control Lyapunov function (CLF) based suboptimal control scheme incorporated with the idea of equivalent control in sliding mode control theory. The switch mechanism between CLF control and sliding mode control is established where only one control switch is needed when the state reach the sliding surface. Compared with the classical CLF method, the sliding mode based CLF approach not only guarantees the optimality, but also enhances the system robustness against model uncertainties and disturbances. Finally, numerical investigations are conducted to demonstrate the utility and optimality of the proposed control algorithm.