Magnetic Bearing for Reaction Wheels in Space Applications

Reaction wheels are used as actuators for attitude control of satellites. Ball bearing is being used in reaction wheel application since many decades. Even small variations in friction torque in ball bearings affects the pointing stability of the satellites used for high resolution imaging application. Also the bi-directional operation of reaction wheel requires frequent zero speed crossing. The stiction present in ball bearing wheels affects the stability during zero speed cross over. Magnetic Bearings have distinct advantages over conventional bearings, like zero friction (due to non-contact operation), no lubrication, long life, less power, etc. Absence of lubrication in magnetic bearing makes it compatible to harsh environments like vacuum. It provides smooth zero speed cross over due to negligible stiction, which is advantageous to achieve better pointing stability. The context of this paper benchmarks the design, simulation and test results of a two axes actively controlled magnetic bearing. The wheel is designed to have adequate slew rate capability to ensure non-contact operation during satellite maneuvers.