Application of Ultrasonic Motor to Control of Moment Gyroscope Gimbal Servo System

Attitude control system is one of the most important subsystems in a spacecraft. As a key actuator, the control moment gyroscope (CMG) mainly determines the performance of attitude control system. Whereas, the control accuracy and output torque smoothness of the CMG depends more on its gimbal servo system. Considering the constraints of size, mass and power consumption for a small satellite, here, a mini-CMG is designed, in which the gimbal servo system is driven by an ultrasonic motor. The good performances of the CMG are obtained by both the ultrasonic motor and the rotary inductosyn. The direct drive of gimbal improves its dynamic performance, with the output bandwidth above 20 Hz. The angular and speed closed-loop control obtains the 0.02 °/s gimbal rate, and the output torque resolution better than 2×10-3 N·m. The ultrasonic motor provides 1.0 N·m self-lock torque during power-off, with 12 arc-second position accuracy.