OPTIMAL SLIDING-MODE CONTROL OF A FLEXIBLE SPACECRAFT UNDER STOCHASTIC DISTURBANCES

A new optimal sliding-mode (OSM) controller is developed for a linear stochastic system and applied to the Middeck Active Control Experiment (MACE), which represents the control structure interaction problem fo r a precision spacecraft. The OSM controller minimizes the expected va lue of a quadratic objective function consisting of only states with t he constraints that esimated states always remain on the intersection of sliding hyperplanes. This controller is designed for two subsets of MACE problems: a single-input, single-output gimbal inertial pointing problem and a three-input, three-output torque wheel attitude control problem. Using numerical simulations, performance of the OSM controll er is compared to that of the classical linear quadratic Gaussian cont roller. The OSM controllers are digitally implemented on the developme nt model of MACE. The experimental results are shown to be in good agr eement with theoretical results.