CONTROL OF AN ORBITING PLATFORM SUPPORTED TETHERED SATELLITE SYSTEM

Abstract

A mathematical model is proposed for studying the dynamics of the Tethered Satellite System (TSS) consisting 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 relatively large initial disturbances. Results suggest that, in the stationkeeping mode, the tension control strategy damps a given disturbance in the shortest time, however, at 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 longer duration. In addition, 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 show that the thruster-offset hybrid controller is the most effective in damping given disturbances.