A towing orbit transfer method of tethered space robots

Towing transfer is considered as an effective but challenging countermeasure for the space debris removal. To ensure the safe transfer, an entire towing transfer method for the dumbbell-like combination of TSR and debris is proposed in this paper. A time-energy optimal orbit is first designed using the Gauss pseudospectral method. Then, the effects of tether length and spacecraft mass on the equilibrium position are analyzed, which provides a basis for the selection of attitude command. Finally, a LQR based orbit compensator is adopted to maintain the orbit and the computed torque PID theory is employed to design the control law for tracking the expected tether length, in-plane and out-of-plane angles. Besides, an anti-windup module is added to the controller due to the actuator saturation. Simulation results show that the transfer is fulfilled by optimal thrust, and the proposed attitude control is effective in the presence of the thrust constraints.