Two nonlinear control approaches for retrieval of a thrusting tethered subsatellite

This paper presents an analysis of the dynamics and control of the pitch and roll motion during retrieval of a Tethered Satellite System, consisting of the Space Shuttle Orbiter and the tethered satellite. Two nonlinear control designs are investigated and compared. The first approach uses visual observation of the line-of-sight angle and phase-plane switch logic to generate simple rules for orbiter pilots. The second uses a controller designed using computational sliding mode techniques. It assumes more precise sensing of system state, and would be implemented using subsatellite jets.