Coupled rotational and translational modeling of two satellites connected by a tether and their robust attitude control using optimal offset approach

Abstract

In this study, the robust sliding mode attitude control of a tethered satellite system using optimal tether offset in the presence of perturbations and uncertainties is investigated. The three main goals of this study are: (1) comprehensive modeling of two satellites connected by a tether considering the coupling between their attitude and position, (2) finding a robust attitude control for both satellites, and (3) reducing the reaction wheels’ power consumption for attitude control utilizing the tether tension. In this regard, the 6 DOF governing equations of the coupled nonlinear rotational and translational dynamics of a two-satellite tethered system in the presence of perturbing forces are derived. Additionally, the offset of the tether attachment points from the center of mass of both satellites is modeled, which results in the coupling of two satellites’ dynamics. The tether tension force acts as external force and moment on each satellite which is used by an optimization method for attitude control of satellites along with their reaction wheels. The simulation results show that the designed sliding mode control stabilizes the attitude of both satellites in the presence of uncertainties and perturbations. Moreover, the optimal offset control saves the energy usage of reaction wheels up to 55 percent.