Underactuated control of swing in orbit debris towing removal via tether space robots

Towing removal using tethered space robot is a promising method for the ever increasing space debris population. The tether libration is one of the obstacles for its on-orbit application. For the space debris does not have any driving force and the tether is not a suitable control input, transfer thrusts on tug are remaining control inputs for libration suppressing. It consequently becomes an underactuated control problem. A dynamical model of debris towing removal system (DTRS) is established firstly. Then, an anti-windup hierarchical sliding mode control law is studied for the constrained and underactuated transfer thrusts on the tug. Simulation results show that the tether librational motion is suppressed and the controller is feasible. Under the transfer thrusts on tug, the orbit radius, true anomaly and tether librational angle are tracked to their desired states accurately.