Space Station based tethered payload - Control strategies and their relative merit

Abstract

A mathematical model is proposed here for studying the dynamics of the Tethered Satellite System (TSS) that consists of a plate-type space station from which a tether supported subsatellite is deployed or retrieved. The rigid body dynamics of the tether, subsatellite and space station are analyzed accounting for the mass of the tether as well as a three dimensional offset of its point of attachment. Controllability of the linearized equations is established numerically and a comparative study of three different control strategies conducted. The strategies employ thrusters, tension in the tether line or motion of the offset of the attachment to achieve control of the system subjected to a relatively large initial disturbance. Results suggest that, in the stationkeeping mode, the tension control strategy damps a given disturbance in the shortest time, however, a t an expense of the energy. On the other hand, the offset control proves to be the most efficient in terms of energy consumption, but now the response to disturbance persists over a long duration. In addition, the performance of the thruster control, tension control, and offset control strategies, as well as as their combinations are analyzed during retrieval of the tether. Results suggest that the thruster-offset hybrid controller is most effective in damping out given disturbances.