Robust active control for microvibration mitigation in high stability space missions

The present work describes the development of an innovative Active Vibration Control (AVC) solution for science and observation satellite missions requiring ultimate pointing accuracy in a broad frequency domain. Amongst all the on-board equipment including mobile parts, the most critical sources of microvibrations are reaction wheels, which generate multi-frequency and time-varying harmonic disturbances. For the majority of state-of-the-art satellites, microvibration mitigation is handled by passive isolators performing a good high frequency disturbance rejection. The active control in conjunction with passive isolation aims at complementing this rejection in the low frequency band and improving the global pointing stability. The complex time-varying nature of the control problem calls for sophisticated active control techniques to handle robustness and performances issues. Linear Parameter-Varying (LPV) control, devised in the 90's, appears extremely suitable in terms of compliance with plant time-varying properties and mathematically proven robustness and performance properties. However, LPV synthesis techniques prove too conservative for this complex non-academic application and succeed in mitigating only narrow frequency domains. Inspired by the gain scheduling concept, an original notch-based control structure using non-smooth mu-synthesis techniques is proposed and shows less conservatism than LPV methods. In the intent to further enlarge the mitigation band, bumpless transfer switching and control signal blending among multiple controllers designed for the mitigation of adjacent regions are also implemented. The robustness and attenuation performance assessment campaign on an experimental hardware test bench demonstrates the effectiveness of the proposed active control solution and suggests that the active/passive isolation strategy is a reliable and a practical candidate solution for future high stability missions.