Coupling dynamics modelling and optimal coordinated control of tethered space robot

Abstract

Tethered space robots use tethers to replace rigid arms and have more flexibility than a traditional space robot, which gives it wide application prospect in future on-orbit servicing missions. Before carrying out elaborate manipulations, tethered operation robots need to approach the target. In order to save fuel in the approaching phase, various coordinated control methods that employ tethers and thrusters together are investigated in the literature. However, the increasing mass of the tether and the distributed force acting on the tether will affect the position and attitude of the robot, which is neglected in previous studies and can degrade the performance of the control system. Here, in order to involve these factors, coupled dynamics and coordinated control theories are combined and applied. Firstly, a coupling dynamics model for the tethered space robot system is built based on the Hamilton principle and the linear assumption. Then, based on the dynamics model, we design an optimal coordinated controller which can minimize the fuel consumption by using the hp-adaptive pseudospectral method and the classical PD controller. Finally, the advantages of the proposed method and the performance of the designed controller are validated by the numerical simulation.