CONTROL OF TETHERED SATELLITE SYSTEMS IN PRESENCE OF TETHER FAILURES

摘要

The attitude stabilization of a satellite represents one of the important applications of tethers. We consider this application and examine cases when tether deployment suddenly stops and tether breakage occurs. The TSS model considered in this study comprises of two identical tethers of equal length connecting the downward-deployed-auxiliary mass to two distinct points symmetrically offset from the satellite mass center. The Lagrangian formulation procedure is utilized to obtain the governing equations of motion of the TSS moving in a circular orbit. Due to the relatively short tether length considered in this study, it is assumed that the tether dynamics does not affect the orbital dynamics. Next, a nonlinear controller based on sliding mode control as well as an adaptive nonlinear controller is developed for the tether offset variations that ensure desired attitude control of the satellite. Finally, for a detailed assessment of the proposed controllers, the set of governing TSS equations of motion is numerically integrated. The effects of external disturbances on system response are then examined and compared to responses obtained using a linear controller. The robustness of the adaptive controller is then tested for varying system parameters. The concept proposed may be useful for future space missions.