Switching Control for Guaranteeing the Safety of a Tethered Satellite

There are many problems in a tethered satellite system, such as the danger of the tether being cut by space debris and difficulty in analyzing the tether because of its flexibility. Moreover, because a tether cannot be pushed, control tension is constrained to be nonnegative during deployment and retrieval of the tethered satellite. Therefore, it is difficult to guarantee that the tethered satellite will not collide with the mother ship or that the tether will not entangle itself with the mother ship. A method is proposed to guarantee the safety of a tethered satellite. To operate a tethered satellite safely while avoiding the situations described, a switching control algorithm is constructed for satellite deployment and retrieval. A model in which the tether has neither mass nor flexibility is used to construct a switching control algorithm. Because this model is linear when the dimensionless input is constant, conditions for guaranteeing safety can be derived analytically. Then, the obtained conditions are applied to a simulation with a model in which the tether has mass and flexibility to show the validity of the conditions for guaranteeing safety.