Fixed-Time Disturbance Observer-Based Composite Controller for CMG Gimbal Servo Systems With Prescribed Performance

Based on prior failures of the control moment gyroscope (CMG) deployed on the International Space Station, the velocity of the gimbal should be kept within the preset range. Furthermore, the high-maneuvering tasks of the spacecraft require fast convergence of the gimbal servo system. However, the tracking performance is particularly vulnerable to disturbances (e.g. cogging torque and nonlinear friction), thereby leading to performance degradation of the CMG and the spacecraft. To address the problem, this paper proposes a fixed-time disturbance observer-based fixed-time sliding mode controller that can preassign the gimbal velocity-tracking transient performance (maximum overshoot, convergence time) and steady-state performance (accuracy). Notably, both the disturbance-estimation errors and the gimbal velocity-tracking errors are rigorously proven to converge to the expected bounded regions within a fixed time that is independent of the initial state. Finally, the hardware-in-the-loop experiments demonstrate the effectiveness and advantages of the proposed method.