Stability Enhancement for Flexible Space Structure Control

This paper illustrates the use of linear-quadratic Gaussian/loop transfer recovery (LQG/LTR) techniques for the active control of a flexible space structure which is an optical support structure. LQG compensators are designed for three actuator/sensor placements on the structure where the reduced-order model consists of only 18 elastic modes. The state-feedback (LQ) portion of each design meets stringent line-of-sight performance requirements in the face of two wideband disturbances impinging on the structure. Conditions on the open loop transfer matrix, broken at the plant input, are stated for the robustification of the LQG designs to the 132 high frequency elastic modes excluded from the design model. Through loop transfer recovery, with LQ dynamics as the target, closed-loop stability is maintained with all 150 elastic modes for two of the actuator/sensor selections. Difficulties in achieving performance robustness are noted.