Stability enhancement for control of flexible space structures

This paper demonstrates the application of linear-quadratic-Gaussian/ loop transfer recovery (LQG/LTR) techniques to the active control of a flexible spaceborne optical support structure. LQG compensators are designed for three actuator/ sensor placements on the structure in the context of an 18-mode reduced-order structural model. The state-feedback (LQ) portion of each design meets stringent line-of-sight performance requirements in the face of two wide-band disturbances impinging on the structure. Conditions on the open-loop transfer matrix, broken at the plant input, are stated which make more robust the response 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 goal, closed-loop stability in the presence of all 150 elastic modes is maintained for two of the actuator/sensor selections. Difficulties in achieving performance robustness are noted.