Nonlinear MPC based coordinated control of towed debris using tethered space robot

Using tethered space robot (TSR) for active debris removal (ADR) is promising but subject to collision and entanglement due to the debris tumbling. To detumble the towed debris, this paper proposes the nonlinear model predictive control (NMPC) based coordinated control strategy. The TSR consists of a gripper for capture, thrusters and a tethered manipulator (TM) with variable length to which the tether is attached. The proposed strategy works in the way that the TM coordinates with the thrusters for de-tumbling by changing its length accordingly so that the tension torque can be adjusted. The attitude model of the debris is first established, followed by the definition of attitude equilibrium. The NMPC is then designed with the prediction model discretized by 4-order Runge-Kutta method. Simulation results validate this strategy and show that the debris attitude can maneuver to the equilibrium smoothly in the presence of the constraints on TM and thrusts.