Evolutions of micro-vibrations in reaction wheels

The company Bradford Engineering is a supplier of reaction wheels which control the fine movement of satellites in flight. However, one set of reaction wheels for an ESA spacecraft showed that the existing design requires further technology consolidation. The fitst concern is that, reaction wheel induced disturbances, in the form of micro-vibrations, increase two to three times in amplitude after a qualification load. The second concern is that, the bearings after long term usage might be no longer well lubricated, and large micro-vibrations as well as frictions might be generated in this condition. These increases of micro-vibration would reduce the accuracy of observation made over great distances.
In the first part, the evolution of the micro-vibration with respect to environmental and mechanical loads is studied. The critical test, which makes the micro-vibration increase, is found, and the damaged bearing component is identified by the micro-vibration analysis.
In the second part, the long term oil loss in the reaction wheel is estimated. The oil absorption of the cotton phenolic cage, or ball retainer, is expected to be the most significant source of the oil loss. To estimate the oil uptake in the material, the oil absorption data are fitted with mathematical models, and the time to saturate and the saturation mass are obtained from the calculation.
These results help understand the causes of micro-vibration’s evolution and improve the future reaction wheel design.