Bearing health monitoring and life extension in satellite momentum/reaction wheels

Bearing faults in momentum/reaction wheels and control moment gyros are a significant life- and performance-limiting factor in spacecraft. Even when complete failure does not occur, problems with excessive bearing torque and torque noise can drain power and negatively impact vibration sensitive instruments. The failure mechanisms in these applications and the monitoring technologies needed are significantly different from most terrestrial and aircraft systems. This paper describes field experience and experimental data on bearing faults in satellite applications, and presents new monitoring technologies that allow optimal control of lubrication, thus extending life and preventing torque anomalies. These include a unique wireless sensor that measures cage temperature and motion, which are shown to be sensitive indicators of lubrication effectiveness. The technologies described may also be useful in aircraft applications such as hanger bearings where loss of lubrication, rather than contact fatigue, is the primary failure mechanism