A comparison of LQR control design with current baseline design for the man-tended version of Space Station Freedom

Two control systems were compared for the MB-6 configuration of Space Station Freedom, with the objective being to improve if possible the performance of existing baseline control laws. The first control system used the existing baseline control laws: control moment gyro (CMG) for attitude control, alpha joint control, and beta joint contol. The second control system was designed using the linear quadratic regulator (LQR) algorithm, which produces an optimal controller with excellent stability characteristics for this application (60° phase margin and 6-dB gain margin). It was shown that the alpha joint controller worked nearly as well without CMG measured velocity as an input as it did with that extra input available. Further, the measurements used by the existing baseline control laws were seen to be the most important ones for each of the three control laws. Rigid-body stability margins could not be much improved with additional measurement inputs