Here is a paper detailing metal reaction wheels failure modes going into detail on how charge was built up and solar influence on this process: https://www.esma

Here is a paper detailing metal reaction wheels failure modes going into detail on how charge was built up and solar influence on this process: https://www.esmats.eu/esmatspapers/pastpapers/pdfs/2017/bialke.pdf https://www.esmats.eu/esmatspapers/pastpapers/pdfs/2017/bial... I cannot find primary source for JWST using ceramic bearings right now, but I know they are manufactured by Rockwell Collins Deutchland and have good track record: https://jwst.nasa.gov/content/forScientists/faqScientists.html#wheels https://jwst.nasa.gov/content/forScientists/faqScientists.ht... TELDIX (today owned by Rockwell Collins Deutchland) invented use of ceramic bearing in reaction wheels for spacecraft use in 1978: https://patents.google.com/patent/DE3027209A1/en https://patents.google.com/patent/DE3027209A1/en so it would make sense that JWST uses ceramic bearings. Other manufacturers (ITHACO) have switched to ceramic too.