Nonlinear control of sway in a tethered satellite system via attitude control of the main satellite

In this study a new nonlinear control approach is introduced to suppress libration of a tethered satellite system (TSS). It benefits from coupling between satellites and tether libration dynamics. The control concept uses the main satellite attitude maneuvers to suppress librational motion of the tether. To achieve this goal, the main satellite attitude control actuators are used as the only actuation in the system. The study considers planar motion of a two body TSS system in a circular orbit. Governing dynamic equations of motion are derived using extended Lagrange method. Controllability of the system about equilibrium state is studied and a nonlinear controller is designed using feedback linearization method to regulate libration of the system. By studying the conditions of feedback linearization method, stability of the controller is also proved. Tether tension and satellite attitude are assumed as only measurable outputs of the system. The Extended Kalman Filter (EKF) is used to estimate states of the system to be used as the feedback to the controller. By implementing the controller and observer on the system, simulations demonstrate that the controller lead to reduction of the tether libration from large amplitudes.