| Variable Structure Control Systems (VSCS) are a class of nonlinear systems which change the structure of the controls when a set of prescribed hypersurfaces are reached in the phase space. The theory represents a real-time implementable approach to control in contrast to algorithmic approaches, and therefore eliminates the computational burden. This dissertation applies the VSCS theory to maneuvering of a rigid spacecraft with four momentum exchange wheels and maneuvering of a flexible spacecraft. General nonlinear equations of motion are presented for the three-axes maneuver of the rigid spacecraft and for a single axis maneuver of the flexible spacecraft. Three methods are presented for designing variable structure control logics. The theory is demonstrated for set point regulation, tracking, disturbance accommodation, spin-up and robust maneuvers of a specific spacecraft configurations.; A practical problem in the implementation of VSCS theory is the possibility of chatter about hypersurfaces known as "sliding regimes." Three methods of chatter alleviation are introduced. Specifically, the methods are: a boundary layer approach, asymptotic reaching of sliding regimes, and digital input prefiltering. Illustrative examples are given for a single-axis rest-to-rest maneuver of a flexible spacecraft, demonstrating the success of the three methods in alleviating the chatter phenomenon. In association, robustness to parameter uncertainties is also illustrated. The spillover problem is checked via a modal approach.; This study demonstrates that Variable Structure Control is a promising alternative methodology to maneuvering of spacecraft. |
