Dynamics and control of gimbal servo systems for control moment gyroscopes

As inertial actuators mounted on the spacecraft, single gimbal control moment gyroscopes (SGCMGs) can affect the attitude control accuracy to a great extent. However, SGCMGs can not output exact torques under the simple PID control strategies because they are actuated not only by the motor disturbances, but also by the gyroscopic disturbances resulted from the attitude motions of spacecraft. Therefore, a dynamic model is established for the gimbal servo systems based on the thorough analysis of SGCMG dynamics at first. Thus, an accurate description of the mutual influences between the spacecraft and the SGCMGs can be obtained. Then, a PID controller with a disturbance observer is designed for the gimbal servo systems. This algorithm not only has a simple form, but also can attenuate the effects of the disturbances, such as gimbal friction, ripple, and the gyroscopic torque. Simulation results indicate that the control algorithm is feasible.