De-spinning of tethered space target via partially invariable deployment with tension control

This paper focuses on the dynamics and control problems of deploying a small tethered payload from a massive spinning target in space such that the target can be gradually de-spun via the induced torque by the tether tension. The deployment control task is subject to a special limit that the control action should be made only by regulating the tether tension which needs to be kept at a positive level all the time. The basis of the proposed control law is on the identification of ‘partially invariable’ deployment motions, in which the length rate of the tether and its angle with respect to the target are kept invariable by regulating the tether tension, thereby de-spinning the massive target in a smooth and stable manner. Moreover, a model predictive control law which explicitly accounts for control constraint and nonlinear dynamics is developed to achieve and retain the partially invariable deployment for the tethered system. Successful de-spinning of the tethered target by the proposed control scheme is demonstrated by numerical case studies in which partially invariable motions are achieved in a rapid manner and retained afterward.