Robust Control of Spinning Tethered Satellite System Pendular Motion

We develop control laws for the pendular motion of a spinning tethered satellite system. The control laws are developed using a simplified system model that contains unknown disturbance terms that account for unmodeled dynamics in the simplified model. Principles of sliding mode and adaptive nonlinear control design are used to develop control laws that drive the pendular motion to a desired reference motion in spite of the effects of unmodeled dynamics. The effectiveness of the control laws is tested by applying them to a much more physically realistic system model than that used in their derivation. In all cases tested, the control laws are successful in controlling the pendular motion of the more physically realistic model about the desired reference motion. The main disadvantage of the control laws is that they require relatively large steady-state control inputs to account for the unmodeled dynamics and hold the pendular motion on the reference motion. Any problems associated with these large steady-state inputs could be avoided by simply turning the control off after the reference motion has been reached and accepting the small deviations from the reference motion due to unmodeled dynamics.