Active gravity-gradient stabilization of a satellite in elliptic orbits

A tether can be utilized as an efficient actuator for the purpose of satellite attitude control. The tether tension generates a strong passive gravity stabilization effect. The combination of tether tension with a movable attachment point mechanism results in an effective and low cost active controller. This paper reviews the concept and presents the dynamical characteristics of the configuration. It then demonstrates that a feasible three-axis control can be achieved by means of only two actuators. The primary contribution is the development of a control law that works for eccentric orbits. In this case, the dynamical system that represents the configuration becomes periodic in time, and thus impossible to control by using constant gains. The solution is a periodic control law. A combination of Floquet transformation and sampled state periodic hold feedback control is proposed as an effective pointing method for small-eccentricity orbits. (C) 2000 Elsevier Science Ltd. All rights reserved.