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Active Vibration Isolation System For Space Applications

par Lafarga Nebot, Vicente
Président du jury Hendrick, Patrick
Promoteur Collette, Christophe
Publication Non publié, 2024-06-21

Thèse de doctorat

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Résumé :

Mechanical vibrations propagating through the structure of a spacecraft can be detrimental to mission success whether by presenting a direct threat to the structural integrity of the spacecraft and sensitive scientific instruments during launch, or, in the case of much smaller amplitude loads called microvibrations, by inducing jitter of the line-of-sight of instruments and increasing noise levels of observations.The transmission of such harmful vibrations can be mitigated by mounting sensitive payloads or sources of disturbance on passive isolating suspensions. While these passive systems are effective in filtering the vibrations occurring at frequencies above their own resonance, they end up amplifying the disturbances occurring at the suspension modes themselves. The curbing of the responses of these suspension modes can be achieved by resorting to elastomeric materials, but this approach is often accompanied by a degradation of the higher frequency isolation.Alternatively, active vibration isolation systems present the big advantage of virtually eliminating the amplification by the suspension modes, while at the same time not degrading the high-frequency isolation present in undamped suspensions. This thesis investigates innovative concepts for active vibration isolation systems suited to spacecraft. It is based on soft suspensions, in which the load-path consists of integrated sensors and actuators, and therefore privilege simplicity, reliability, low mass and low power consumption which are essential characteristics for a space equipment. Two distinct applications were addressed. For the case of reduction of the high mechanical loads generated by launch vehicles and imposed on spacecraft, the concept of a hybrid isolator was explored. By adding a passive layer in parallel to an active system developed earlier, which consists of piezoelectric stack shunted to a resistive-inductive load. This configuration allows to dissipate part of the mechanical energy in the system, reducing the power consumption of the active system, while at the same time providing fallback-damping performances in case of failure of the active component.The second application provided filtering of microvibrations. It was implemented as a Stewart Platform with its six legs formed by non-contact voice-coil actuators. These voice-coil actuators are self-sensing, in which the monitoring of their voltage and current produces an estimate of the relative velocity of the two sides of the platform and enables the active damping of the suspension modes. The concept was validated experimentally with the test model of a reaction wheel and an isolation performance of -65 dB was obtained at 270 Hz. This consists of an improvement with relation to the vibration isolation systems described in the state-of-the art of space applications.