EXPLOITING CORIOLIS ACCELERATION TO REDUCE LIBRATION OSCILLATIONS DURING RETRACTION OF TETHERED SATELLITE SYSTEMS

Tethered satellite systems enable formation ying missions by providing a physical connection between satellites. However, retraction of tethered systems is an unstable process. Several works have proposed complex control methods to stabilize this process. Recently, a simple, heuristic bang-bang control algorithm was found to be effective at significantly reducing libration angles by introducing short periods of extension during the retraction phase, thereby exploiting Coriolis acceleration. In this paper, an analytical method is derived for the determination of effective retraction/extension speeds for a bang-bang control. The performance of the derived control profiles are validated by comparison to optimized bang-bang profiles, and the effect of the final speed is investigated. Additionally, particle swarm optimization is leveraged to optimize switch times and tether length rates for control profiles with varying numbers of extension/retraction switches. It is determined that speeds of retraction and extension contribute greatly to the libration motion of the tethers, and that proper speed selection is especially critical when the formation is near its equilibrium state. Accurate switch timing is also found to be particularly important, as slight variations can signifficantly affect the tether libration response. While a greater number of switches is found to improve the tether response and reduce retraction time, the achievable gains may not be sufficient to justify the much increased complexity.