Covariance control design for Hubble Space Telescope
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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 the required control effort subject to inequality constraints on the output covariance matrix. The second controller is designed to satisfy both output covariance constraints and controller covariance constraints. The importance of the controller covariance constraint is to properly scale the controller for digital implementation in the control computer 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 accommodate the roundoff error and computational time delay. Compared with the existing HST controller design, the results show that the required pointing error specifications can be achieved with 85% less control effort and that the error due to the finite-wordlength implementation of the controller can easily be included in the optimal control design process. 1995 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.
