Stabilizing tethered satellite systems using space manipulators

The use of space manipulators to stabilize a two-body tethered satellite system (TSS) during the stationkeeping and retrieval phases, is considered. The uncontrolled motion of the system in the stationkeeping phase is marginally stable, while during the retrieval phase it is unstable. The stabilization is carried out by means of a two-link space manipulator, similar to the CANADARM. The motion is considered to be planar and the joint torques are considered as inputs. The equations of motion for the system are analytically generated, using FLXSIM, a symbolic computer code based on Kane´s method. For the stationkeeping phase, the equations of motion are linearized around the trim condition (fixed point) and the LQR method is used to devise a state-feedback based controller for the system. The results prove the method to be practical. For the retrieval case, with a non-autonomous set of equations, a modified feedback linearization technique is employed to alleviate the problem of not having enough inputs for the standard feedback linearization technique