4 ms·

> The reason Kepler ran out of fuel when it did was that it was expending more maneuvering fuel for attitude control because two of its four reaction wheels fai

> The reason Kepler ran out of fuel when it did was that it was expending more maneuvering fuel for attitude control because two of its four reaction wheels failed. Hubble and the ISS also had similar failures. And to calm down anyone afraid of JWST sharing the same fate - construction of reaction wheels have been changed some time ago to make them significantly more reliable. The source of issues on Hubble, Kepler, FUSE, Hayabusa, Dawn and TIMED was electrical arcing between metal parts of reaction wheels. Static charge was building up like when you rub a ballon against your head. That charge caused arcing that in turn caused metal pitting and increased friction leading to failures. That failure mode was understood only in late 2007, when Kepler was already fully build and ready for launch. JWSt uses new generation ceramic bearing in its reaction wheels, they have been used in spacecrafts since 2010 with great performance.

dtgriscom 5y ago
Great info: citation? More details?
- terramex 5y ago
  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.
- Laremere 5y ago
  Scott Manley video: https://www.youtube.com/watch?v=KibT-PEMHUU https://www.youtube.com/watch?v=KibT-PEMHUU

dtgriscom 5y ago

Great info: citation? More details?

terramex 5y ago
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.
Laremere 5y ago
Scott Manley video: https://www.youtube.com/watch?v=KibT-PEMHUU https://www.youtube.com/watch?v=KibT-PEMHUU