Spacecraft Reaction Wheel Failures

[Homer J Simpson]

Random YouTube find, interesting.......

Also a lot of other good content on his channel.

[Brumby]

Curious.

I came across this video and watched it yesterday

[Berni]

Oh yes Scott is the best guy to watch on youtube for anything space related. I came across him a long time ago because of his informative Kerbal Space Program videos (Its a pretty engineering focused game so it has drawn me in in the past).

[digsys]

Oh GREAT !! With MY luck, I'll draw the short straw to go out and fix them !! Better cancel my Foxtel ... <grumble>

[T3sl4co1l]

Hmm, interesting. I know bearings can run as a kind of heat engine when driven with a bunch of amperes; I wonder how that's affected by lubricant type, speed and clearance.

I suppose these bearings would be made a little differently, so as to keep friction low -- but I wonder how much effect that has on the observations?  Could it be worthwhile to use a tighter bearing (assuming you stuck with metal -- going to ceramic is a better move here), at the expense of initially higher torque but longer life?

Ball bearing design is something I don't know anything about (beyond the basics) either...

Tim

[Ian.M]

So the whole problem could have been avoided with a tiny carbon brush running on the center of the end of the reaction wheel axle, similar to the brushes VCR head motors used to have to ensure the upper drum was properly grounded.

[PA0PBZ]

Guys, if you watch it to the end you will learn that they switched to ceramic bearings some 10 years ago already.
(And they didn't fail - yet)

[ruffy91]

Just read the failure analysis PDF. It's a very interesting read.

[PointyOintment]

Hmm, interesting. I know bearings can run as a kind of heat engine when driven with a bunch of amperes; I wonder how that's affected by lubricant type, speed and clearance.

More info on that: http://www.electricstuff.co.uk/bbmotor.html (new content since I last read that page, many years ago!)

[james_s]

Just read the failure analysis PDF. It's a very interesting read.

Where might that be?

[David Hess]

It has been known for decades that even tiny electrical arcing will damage bearings and you will sometimes find discharge brushes used to remove static charge when non-conductive parts are used in a drive train.  I am surprised that spacecraft designers did not consider this and space charge in a vacuum for so long.

Designing electronics for space must be fun.  Not only do you have reliability, temperature, and cooling to worry about, but a vacuum environment better than any vacuum tube ever made.

[T3sl4co1l]

Designing electronics for space must be fun.  Not only do you have reliability, temperature, and cooling to worry about, but a vacuum environment better than any vacuum tube ever made.

No, it's not that good -- if it were as good as the interior of a 12AX7 this probably wouldn't be a problem (not enough radiation to cause a problem in the given time frame?).  Low Earth orbit is a few thousand times worse than that, or, comparable to a gassy/leaky tube.  Interplanetary I think is comparable; and interstellar, better (more comparable to, uh, LHC has a really high vacuum inside, doesn't it?).

At least, that's what I recall, LEO is like ~mid utorr, and interplanetary and interstellar go down a few orders of magnitude from there (each).

Tim

[Beamin]

I would describe that guy as a manly Scotsman. His name perfectly describes him. Lich Richard Machowitz or "Dick Macho".