The thing is that nonconductive surfaces charge up much more readily than grounded conductive surfaces, so it's not obvious that the change to ceramic bearings was indicative of a spacecraft charging culprit.
Also, there is a spectrum of particle energies such that low energy particles deposit on the surface of materials, but the higher energy particles plow through and can deposit within a material, or plow straight through it. Of course there are fewer of the high energy particles, so it takes much more time to deposit enough charge that way until you get a breakdown, compared to charges depositing on a material first surface and then blowing off above some charge density whose potential exceeds a breakdown threshold. Ken Javor Phone: (256) 650-5261 From: Edward Price <[email protected]> Reply-To: Edward Price <[email protected]> Date: Tue, 21 Aug 2018 22:12:59 +0000 To: <[email protected]> Conversation: Satellite Reaction Control Wheel Failures Subject: [PSES] Satellite Reaction Control Wheel Failures I just happened to come across the topic of low reliability of Reaction Control Wheels in satellites over the past 30 years. (RCW¹s are used to electrically control the pointing direction of satellites and deep space probes.) It was noted that RCW¹s would often fail due to increased bearing friction, and that the failures were correlated to Solar Coronal Mass ejections and solar flares. Recent studies seem to point to micro-ESD events across the ball bearings of the RCW¹s, causing erosion of the races and particulate contamination of the ball lubricant. It was said that the RCW¹s were contained in conductive housings, so there should be some decent shielding effectiveness from that. But, if that¹s true, how can the satellite external environment lead to electrical charging of the RCW¹s? This may be a problem that was accidently fixed, as about 15 years ago, bearing concerns led to replacing the Rockwell 60 hardness ball bearings with ceramic bearings that were much harder, and coincidentally, also non-conductive. RCW failures then dropped dramatically. Possibly the value of the ceramic bearings was not their hardness but their non-conductivity. Here¹s a popular video that can get you introduced to this issue: https://www.youtube.com/watch?v=KibT-PEMHUU Ed Price WB6WSN Chula Vista, CA USA - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
