Identification of reaction wheel assembly disturbances based on variable modal frequencies

Micro-vibrations of the reaction wheel assembly (RWA) can have a negative impact on spacecrafts' attitude control, surveillance, and measurement. Evaluating the micro-vibration magnitude during the design stage is possible by establishing an accurate dynamic model of the RWA disturbance characteristics and identifying the relevant parameters. Doing so can provide references for spacecraft design and development, ultimately leading to more efficient and effective spacecraft operations. However, the conventional methods of modeling and identifying the RWA and of predicting the distribution and magnitude of the disturbing force/torque are limited, as it relies on stable and constant modal frequencies. In the development mission of a satellite, a specific scenario is found that the modal frequency of the RWA changes with speed. This study proposes a novel modeling and parameter identification method for the RWA disturbances based on variable modal frequencies and is advantageous in this scenario. The RWA's dynamic model is considered a covariant system related to the rotational speed. Additionally, frequency-domain and time-domain models have been established for the RWA's translational and swinging motions. Simultaneously, the identification method of the model parameters is developed, which involves identifying the harmonic factors, the variable modal frequencies, and the amplitude coefficients. Finally, the method is validated by numerical simulations and experiments. The results indicate that the proposed method offers excellent identification performance, surpassing conventional methods in model accuracy and identification performance. This achievement holds significant reference value in the micro-vibration suppression and optimization design of spacecraft.