In-plane adaptive retrieval method for tethered space robots after target capturing

After a target satellite is captured by the tethered space robot (TSR), the operator of TSR and the target satellite compose a combination with uncertain mass, inertia and tether junction position. The tether length, tether deflection and combination attitude are coupled seriously and control inputs are strictly limited, which make the retrieval of TSR very difficult. For the retrieval problem, the in-plane dynamic model is established using the Lagrangian method by considering the tether length, tether deflection and the combination attitude. An adaptive and anti-saturation control method is designed based on dynamic inversion theory. Firstly, an adaptive dynamic inversion retrieval controller is designed based on the online estimation of the combination mass, inertia and the tether junction position. Then, auxiliary variables are designed to compensate the inputs, which solve the problem of the limited control inputs. Finally, numerical simulations are conducted to validate the feasibility of the controller. Simulation results show that the online estimator can estimate the uncertain parameters fast and effectively. The retrieval controller can overcome disturbances of the tether deflection and combination attitude by limited inputs. The combination is retrieved stably and effectively along the designed trajectory.