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 flexib le members of the HST, and hence the solar array motions led to very n oticeable degradation in pointing control. Using classical techniques, Marshall Space Flight Center in conjunction with Lockheed Missiles an d Space Company developed modified HST controllers that were able to s uppress the influence of the vibrations of the solar arrays on the lin e-of-sight (LOS) performance. Substantial LOS improvement was observed when two of these controllers were implemented on orbit. This paper d escribes the development of modified HST controllers by using linear q uadratic Gaussian (LQG) design. Two design approaches are considered. The first approach is a one-step process that designs a controller tha t satisfies both the tracking/integral requirements and the disturbanc e rejection requirements. The second approach, first designs a control ler that satisfies the tracking/integral objectives and then designs a parallel controller that preserves the tracking properties while achi eving the disturbance rejection properties. The latter approach was us ed because it was found to more easily lead to high-performance contro llers. The results clearly demonstrate that LQG-based controller desig n is capable of yielding high-performance controllers for the HST.