Dynamics and Aerodynamic Control of a Cross-Track Tether Satellite System

The objective of this paper is to analyze the dynamics and control strategy of a novel type of formation flight architecture, enabling unprecedented space mission capabilities. We propose a tether satellite system composed by two, flying in LEO, connected by a linear tether maintained in tension along the cross-track direction, with respect to the orbit, i.e., perpendicular to the motion and radial directions. A three-dimensional multibody model was developed, intro- ducing the equations of relative dynamics centered in an orbiting reference frame. To simulate the conditions of LEO, several mathematical models taken from the literature were used. By uti- lizing this model and verifying that this configuration is intrinsically unstable, it was concluded that the system needs continuous control to be stabilized. As a result, the model of the dynamics was linearized and an optimal LQR controller was introduced. Once the linear control law was validated by simulating its application on the full system model, aerodynamic surfaces were next introduced to generate the force required for control by taking advantage of the rarefied atmo- sphere. The proposed control strategy is tested by extensive numerical simulations. Finally, the proposed aerodynamic stabilization approach was compared to a gyroscopic stabilization alterna- tive strategy.