In this work, a friction-induced vibration model for water-lubricated bearings (WLBs) is developed. The model incorporates interfacial mechanical effects, including the stiffness and damping coefficients of the water film, contact stiffness of asperities, elastic deformation of the bush, etc. To evaluate the friction-induced vibration state, i.e., stability of WLBs, complex eigenvalue analysis is employed. A frictional noise experiment for a WLB is performed to validate the effectiveness of the developed model. Based on this model, the stability diagram of friction-induced vibrations in WLBs under various parameters is obtained, and the effects of key parameters, such as radial clearance, angular groove amplitude, and boundary friction coefficient, on the stability are investigated. Numerical results indicate that increasing the boundary of friction, surface roughness, radial clearance, and angular groove amplitude elevates the risk of unstable friction-induced vibration. Furthermore, numerical studies reveal the existence of a critical rotational speed at which friction-induced vibration transitions from being unstable to stable. As the rotational speed approaches the critical value, the risk of unstable friction-induced vibration rapidly decreases. Within the hydrodynamic lubrication regime, the maximum vibration attenuation index tends to remain constant, regardless of any further increases in the rotational speed.

The control moment gyroscope(CMG) is a critical actuator in spacecraft attitude control systems. In the vacuum of space, heat generated by the CMG is primarily dissipated through thermal conduction and radiation, resulting in substantial temperature rises that may compromise system stability and reliability. Consequently, analyzing the CMG ’s temperature field and maintaining its operating temperature within acceptable limits is essential. This study focuses on a 70 Nms single-frame CMG, for which a thermal simulation model is developed to investigate temperature distribution and assess the effects of rotational speed, applied torque, and bearing preload on thermal behavior. The model, validated against experimental data, achieves an average temperature prediction accuracy of 93.87%. Results reveal that temperature at various measurement points is highly sensitive to changes in rotational speed. The lower end of the rotor shaft exhibits a pronounced responsiveness to torque, while both ends of the rotor shaft are significantly influenced by bearing preload. The maximum observed temperature increase is 5.2 ℃ at the lower end of the rotor shaft, whereas the frame experiences the smallest increase at 1.72 ℃. The presented temperature field modeling approach offers valuable insights for optimizing the design of control moment gyroscopes and facilitating operational diagnostics of spacecraft systems.

During operation of the space robot joint, there are periodic changes in the load and speed of the harmonic reducer. Because the flexspline is a flexible mechanism, the transmission error of the harmonic reducer is related not only to manufacturing but also to load. The key to improve the precision of harmonic reducer is to reveal the relationship between transmission accuracy and load. In this paper, considering the influence of internal friction and external load, the prediction model is established for transmission error of harmonic reducer. The model has been optimized considering the load fluctuations and sudden changes during operation. The influence of load and speed is discussed on the transmission error. The influence of load on transmission error is more serious. The model can predict the transmission error of the harmonic reducer under variable speed and load. The results show that the transmission error in the operating state is much larger than the transmission error in the stable operation. The accuracy of stable transmission error, operational transmission error, and dynamic lost motion is more than 90%. The research will provide an effective reference for the high-precision operation of space robot.