<h2>AAS  96-162</h2><h2>DEVELOPMENT OF ROBUST REDUCED ORDERED DIGITAL CONTROLLER FOR LARGE ORBITING PLATFORMS IN DISCRETE-TIME DOMAIN</h2><h4>A. J. Ericsson-Jackson, NASA Goddard Space Flight Center; P. M. Bainum and G. Xing, Howard University</h4><h2> Abstract </h2>Engineers are proposing the construction of large platforms to be utilized as a base for orbiting space structures. These large space structures are typically highly flexible. Their modeling may require a large number of significant elastic modes, resulting in a highly ordered mathematical model. To reduce the on-line control computation time it is necessary to design the controller/estimator based on a reduced-order system model. Through the utilization of the linear quadratic Guassian/loop transfer recovery (LQG/LTR) technique a reduced order controller/estimator system has been designed, while providing robustness recovery and avoiding system sensitivity in the presence of parametric uncertainties. This robust control synthesis methodology, LQG/LTR guarantees a certain minimum performance and allows one to assess properly stability robustness parameters in the frequency domain that were difficult to characterize effectively in a time-domain setting. This work specifically tests for additive uncertainty robustness due to the dynamic errors of unmodelled higher elastic modes.<br><br>