Post-capture attitude control with prescribed performance

The capture or docking of a spacecraft with a target spacecraft is an important component of future space debris capture and orbit servicing missions. One proposed concept includes using a robotic arm mounted on the chaser spacecraft to connect and manipulate the target's motion. This paper focuses on the post-capture attitude control of the target which will bring the target to rest and then control it in a prescribed way. The attitude control can be achieved by designing a robust control in the known chaser reference frame and treating the dynamics due to the uncertain inertia as an unknown disturbance. However, this can lead to poor performance since this uncertain torque can be large. In this paper, it is shown that the in-situ construction of the chaser-target dynamics can lead to improved performance. Based on the combined re-constructed model, a new disturbance observer based control with robust dynamic control allocation is developed. This approach is robust to the uncertainties in the re-constructed model and enables the prescription of convergence and stability properties. The proposed approach is demonstrated through numerical simulation of an actively controlled 12U CubeSat that has captured an inactive 12U CubeSat spacecraft.