Active and Passive Disturbance Isolation for High Accuracy Control Systems

Micro-vibrations are a major contributor to the performances of an in-creasing number of Earth observation and space science missions because line of sight stability requirements get tighter with increasing resolution and longer in-struments integration time. These mission performances are sensitive to the pres-ence of disturbance sources such as wheels, cryocoolers and solar array drive mechanisms. For the majority of Astrium's satellites, microvibrations attenuation is widely handled by considering passive isolators set at the reaction wheels inter-face. This solution allows guaranteeing good rejection of high frequency disturb-ances while providing sufficient performances for the current missions. However, this so-called “passive” solution provides limited isolation at low frequency which could be insufficient for future mission needs. The work presented in this paper results from research activities led by Astrium Satellites and the European Space Agency on the design of optimized passive/active solutions for large frequency band microvibrations insulation. The preferred solution is based on a passive iso-lator coupled with an active control system in charge of rejecting disturbances in the low frequency band. Two kinds of active controllers have been designed and implemented. The first one is based on an adaptive disturbance cancellation scheme operating in the output demodulated space while the second one is formulated and managed in the H∞/µ setting. The plant model, used for the con-trollers design procedure, has been derived from a prior ARMAX-type MIMO identification procedure considering input/output experimental time measurements collected on the real system. The two control solutions have been implemented on a dedicated hardware test bench facility and a robust performances assessment campaign has been performed demonstrating more than 20dB disturbance rejection even on a partially modeled structure.