Approaching Control Based on Mobile Tether Attachment Points

The orbit control during the approaching target phase is one of the key missions for the TSR and has been studied by many researchers. A new method is proposed by S. Pradeep to determine the tension control law, which is designed based on theorems in analytical mechanics. Nakamura discussed the collaborative control of the tension (controlled by the service satellite) and thruster (controlled by tethered robot) in approaching the target of the tethered retriever but the attitude is not considered. A boundary control was proposed for station keeping of a tethered satellite system in the literature, but the proposed boundary controller does not constrain the tension in the tether to be positive. V.J. Modi investigated an off-set control strategy that uses a manipulator mounted on the platform to regulate the tether swing. The corresponding state feedback controller is designed using a graph theoretic approach and the tethered system is successfully regulated by the controller. Some particular laws of deployment/retrieval leading to analytical solutions for the small in-plane and out-of-plane motions of the system are obtained and then these results are extended to a massive tether. To fulfill the station-keep control of the rotating TSS along halo orbits, a nonlinear output tracking control scheme based on the h-D technique is proposed. This approach overcomes some limitations such as on-line computations of the algebraic Riccati equation and is easy to implement.