ON THE INVERSE CONTROL OF THE TETHERED SATELLITE SYSTEMS

The equations of motion for a class of Tethered Satellite Systems (TSS), undergoing planar motion in a Keplerian orbit, are derived. The system consists of a rigid platform from which a point mass subsatellite can be deployed or retrieved by a flexible tether. The model incorporates offset of the tether attachment point from the platform center of mass and its time dependent variation. The governing equations of motions are obtained using the Lagrangian procedure. The effect of system parameters on the dynamics is analyzed numerically. The thruster augmented active control strategy is used to regulate the tether swing with the platform dynamics controlled by a momentum gyro. It is shown that the control of only the rigid degrees of freedom is not sufficient as the flexible dynamics of the tether becomes unstable, particularly during retrieval. Passive dampers are proposed to control the flexible dynamics. Effectiveness of the control strategy is assessed through its application to several cases of practical importance.