ESA GNC Conference Papers Repository
Robust control design in a non-smooth h-infinity/mu setting for spacecraft microvibration attenuation
Motivations: There is an increasing need in modern spacecraft to meet rising pointing accuracy requirements . However, a variety of electrical and mechanical systems of a spacecraft generate mechanical vibrations that can propagate through the structure towards sensitive payloads. In the context of this work, the term microvibration refers to low-amplitude vibrations in the range of micro-g's, that typically occur in the range of frequencies between a few Hz up to 1 kHz. Since spacecraft are isolated systems, the mechanical energy associated with these disturbances must be dissipated into the system. Due to the low damping environment of space and structural resonances of the spacecraft, microvibrations can easily degrade the performance of various payload systems. To achieve high performance, it is thus necessary to provide viable solutions able to counteract the effects of microvibrations on satellite structural dynamics and the optical payload. Several works have identified mechanical spinning devices such as reaction wheel assemblies or control moment gyroscopes as the most significant source of microvibrations. These devices are used to achieve attitude control by acting as momentum exchange devices. During manufacturing, the flywheels are precisely balanced in order to minimize the vibrations that occur during operation. Nevertheless, even with extremely tight manufacturing tolerances, these devices generate residual vibrations due to mass imbalances and bearing imperfections. Paper contribution: In this context, the paper addresses the problem of mixed active-passive microvibration mitigation solution able to attenuate the vibrations generated by reaction wheels to the satellite structure. The solution relies on passive elastomer isolators for high frequency disturbance attenuation and a complementary active control strategy based on proof-mass-actuators for the low frequency. From an uncertain Linear Fractional Transformation (LFT) satellite model, this paper shows the preliminary results obtained in a collaborative work supported by Region Aquitaine and the European Space Agency (ESA). The design of the microvibration mitigation solution is formulated into the H-infinity/mu framework leading to a robust control strategy capable of achieving active attenuation performance across a wide range of reaction wheel speeds. An analysis procedure based on the structured singular value is used to assess the robust stability and nominal performance of the microvibration mitigation strategy. Time domain simulations based on a representative benchmark provided by ESA and Airbus Defence & Space are included to highlight the potential of the proposed solution.