Anti-sway control of tethered satellite systems using attitude control of the main satellite

• It is tried to reduce libration of TSS system using satellite attitude maneuvers.
• Dynamic of tethered satellite system in planar motion is modeled using Lagrange method.
• Extended Kalman Filter is used to estimates states of the system.
• Using LQG method, a linear controller is designed to regulate libration of the tether.
• The designed controller succeeded to regulate libration of tether at low amplitudes.

In this study a new method 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, and the main satellite׳s actuators for attitude control are used as the only actuation in the system. The study considers planar motion of a two body TSS system in a circular orbit and it is assumed that the tether׳s motion will not change it. Governing dynamic equations of motion are derived using the extended Lagrange method. Controllability of the system around the equilibrium state is studied and a linear LQG controller is designed to regulate libration of the system. 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 feedback to the controller. The designed controller and observer are implemented to the nonlinear plant and simulations demonstrate that the controller lead to reduction of the tether libration propoerly. By the way, because the controller is linear, it is applicable only at low amplitudes in the vicinity of equilibrium point. To reach global stability, a nonlinear controller is demanded.