Abstract: Control moment gyros bearing unit is a core component of spacecraft attitude control system. Its performance directly affects the control accuracy and life of spacecraft attitude control system, even endangers the safety of spacecraft. The friction torque and its fluctuation are the key performance indexes of the bearing for control moment gyros bearing unit. Based on the tribology and dynamics of rolling bearing, the nonlinear dynamic differential equations of the control moment gyros bearing unit with six degrees of freedom are established. GSTIFF (gear stiff) integration algorithm with variable step is used to solve the dynamic differential equations. The influences of different working environment that with/without gravity, working conditions that revolution and rotation, the axial preload and cage pocket clearance on the amplitude and fluctuation of bearing friction torque are analyzed. The analysis results show that: the preload has a significant effect on the friction torque of flywheel bearing unit, too large or too small preload is not conducive to reducing the friction torque and its fluctuation. For the flywheel bearing unit analyzed in this paper, the optimal preload is 50~55N; the cage stability is significantly affected by gravity, and the cage is more stable under the condition without gravity; too small pocket clearance will increase the friction torque, and too large pocket clearance will increase the friction torque fluctuation. For the flywheel bearing unit analyzed in this paper, the clearance ratio should be controlled between 0.6 and 0.8.

Key words: attitude control, control moment gyros, bearing unit, revolutionrotation, friction torque