Automatic mass balancing of three-axis rotational spacecraft simulator

Spherical air-bearing-based spacecraft simulators are widely used to research spacecraft attitude dynamics and control techniques. To simulate the microgravity environment for the ground spacecraft simulators, the effects of the torque of gravity should be minimized. So, the center of rotation of the spacecraft simulator should be exactly aligned with the center of gravity. This paper presents an automatic mass balancing method. The attitude stability control is designed as an inner loop of the system, and automatic mass balancing is designed as the outer loop of the system. When the system is stable, the position of the center of gravity is calculated by the output torque of the reaction wheel. Then three proof masses on linear motion stages are actuated to compensate for the center of gravity offset from the center of rotation in real time. The control law is designed using parameter optimization based on the parameters of the loop which are measured by the experiment. The tracking-differentiator is applied to torque information processing, which effectively reduces motor moving repeatedly and improves the efficiency of automatic mass balancing. The method is successfully implemented in three degrees of freedom spacecraft simulation experiments.