Dynamic modelling and coordinated controller designing for the manoeuvrable tether-net space robot system

Capturing the non-cooperative space debris has gained increasing attention in the past decades. As an alternative of the rigid robot, the flexible tether-net space robot systems (TNSRS), like ROGER, are proposed by many research institutes, which can significantly reduce the risk of capturing process. However, their poor manoeuvrability and the lack of abilities to keep the net shape may lead to the failure of the capture process. Thus, a manoeuvrable tether-net space robot system (MTNSRS), as a potential approach to improve TNSRS, is proposed. In order to simplify the dynamics, we introduce the assumption that the Young’s modulus of the cord in the net is infinite when in tension while it is zero when being slack. Then, the contact dynamics of rigid robots is employed to solve the unilateral constraints within the above assumption, and the T3 element is introduced to approximate the shape of the net. Furthermore, the coordinated controller for MTNSRS is designed by transferring the inverse dynamics to be a double-level optimization problem. Finally, the simulation results show that without active control, the net will gradually close in the approaching phase, and this process will be significantly accelerated even by a small dragging force in the connecting tether. It is also shown that our controller can ensure MTNSRS to successfully capture the target and can resist the effects of initial state errors, measurement noise and kinetic parameter errors.