LINEAR-QUADRATIC-GAUSSIAN-BASED CONTROLLER-DESIGN FOR HUBBLE-SPACE-TELESCOPE

Large changes in the thermal environment as the nubble Space Telescope (RST) orbits Earth cause thermal distortion in the solar arrays that in turn cause the solar arrays to vibrate. The original HST controller was not designed to attenuate disturbances due to vibration of flexible members of the HST, and hence the solar array motions led to very noticeable degradation in pointing control. Using classical techniques, Marshall Space Flight Center in conjunction with Lockheed Missiles and Space Company developed modified HST controllers that were able to suppress the influence of the vibrations of the solar arrays on the line-of-sight (LOS) performance. Substantial LOS improvement was observed when two of these controllers were implemented on orbit. This paper describes the development of modified HST controllers by using linear quadratic Gaussian (LQG) design. Two design approaches are considered. The first approach is a one-step process that designs a controller that satisfies both the tracking/integral requirements and the disturbance rejection requirements. The second approach, first designs a controller that satisfies the tracking/integral objectives and then designs a parallel controller that preserves the tracking properties while achieving the disturbance rejection properties. The latter approach was used because it was found to more easily lead to high-performance controllers. The results clearly demonstrate that LQG-based controller design is capable of yielding high-performance controllers for the HST.