Bandwidth-Limited Robust Nonlinear Sliding Control of Pointing and Tracking Maneuvers

It is shown in this paper how multiaxial spacecraft tracking and pointing maneuvers, with known control bandwidth and given tracking error bounds, can be implemented by variable structure control, in the presence of uncertain vehicle and target dynamics. To this end, it is shown how to select a nonlinear sliding surface relating attitude and rate variables, as well as a Lyapunov function in the surface variables that absorbs multiplicative model uncertainties, thereby simplifying the computation of control corrections. It is then shown how a boundary layer envelope can be designed, within which the components of the surface error dynamics can be modeled as the outputs of designer-selected decoupled low pass filters. Closed loop stability conditions, accounting for the coupling between the attitude error dynamics and the surface error dynamics are then obtained.