Relative Position and Attitude Coupled Control for Autonomous Docking with a Tumbling Target

An integrated coupled control strategy for a servicing spacecraft autonomously approaching and docking with a freely tumbling target is studied. To implement capturing successfully, the docking port of the servicing spacecraft should be always pointing to the docking port of target during close rendezvous and docking, which involves proximity maneuvering of coupled position and attitude simultaneously. The integrated coupled control is accomplished through a robust sliding mode control for coupled relative position and attitude tracking. In order to design the integrated coupled control law, the integrated coupled dynamics of relative position and attitude is established through relative position vector and relative attitude quaternion. Then, based on the integrated coupled dynamics, an integrated coupled control law is designed through a robust sliding mode control technique which is constructed by two sliding surfaces. The convergence of sliding surfaces and tracking error are guaranteed in presence of unknown but bounded disturbances and model uncertainties. The robustness of the proposed control law to measurement noise is also analyzed. Finally, three numerical simulation scenarios are conducted and the results validate the effectiveness and robustness of the integrated coupled control law.