COVARIANCE CONTROL DESIGN FOR HUBBLE-SPACE-TELESCOPE

To improve the response to unexpected thermally induced disturbances, two new controllers are designed for the Hubble Space Telescope (HST) using covariance control techniques. The first controller minimizes th e required control effort subject to inequality constraints on the out put covariance matrix. The second controller is designed to satisfy bo th output covariance constraints and controller covariance constraints . The importance of the controller covariance constraint is to properl y scale the controller for digital implementation in the control compu ter using fixed-point arithmetic. We provide a technique to integrate modeling, control design, and signal processing (in HST's fixed-point control computer), since these problems are not separable. Covariance control can easily ac commodate the roundoff error and computational t ime delay. Compared with the existing HST controller design, the resul ts show that the required pointing error specifications can be achieve d with 85% less control effort and that the error due to the finite-wo rdlength implementation of the controller can easily be included in th e optimal control design process.