Precision CMG Control for High-Accuracy Pointing

Extremely precise gimbal control, as is necessary for CMG (Control Moment Gyro) high-accuracy-pointing control systems, is obtainable and has been demonstrated for large single-gimbal CMGs. A proportional-plusintegral control law, where the integral gain is substantially greater than the gradient of the gimbal "stiction" profile, makes possible wide bandwith control of gimbal rate at extremely low levels. The stiffness of structures between the rotor rim and the vehicle in the CMG output axis should be substantially greater than the integral gain in order to maintain control-loop stability with the relatively high gain required. A bandwidth of 20 Hz at 0.005 sec gimbal rate, producing 0.05 ft-lb output torque, has been demonstrated for a 600 ft-lb-sec CMG. This unit also produced 100 ft-lb output torque at 10 /sec gimbal rate, demonstrating a dynamic range in output torque of at least 2000 :1. Further improvement is feasible.