NIRSpec wheel support mechamisms' central duplex bearings cryogenic test restults

Abstract

RUAG Aerospace Austria (RAA) has the privilege to develop the Wheel Support Mechanisms for the Filter Wheel and the Grating Wheel of the Near Infrared Spectrograph (NIRSpec) Instrument of the James Webb Space Telescope (JWST).
One of the key components of the wheel support mechanisms is the bearing which shall
1. have highest accuracy,
2. withstand cryogenic operating temperatures of 30K
3. have low friction torque during low temperature operation while
4. withstanding considerable launch loads at ambient temperature

The chosen bearing is a custom-made hard preloaded flanged duplex ball bearing lubricated with sputtered MoS2 in back to back configuration with a patented thermal off-load device in order to realize the diametrically opposed requirements 3 and 4 above.
Two batches of bearings were procured, and component level testing of the first bearing models was performed. This paper describes the lessons learnt during component level testing, failure recovery, and correlation of the test results with the predictions.