Hubble 'scope gyro drama: Hey, NASA, have you tried turning it off and on again? Oh, you did. And it worked? Cool The classic “turn it off and turn it back on” strategy has worked once again for NASA, in that it may return the Hubble Space Telescope to active duty. On October 5, the venerable orbiting 'scope glitched out, and automatically put itself into hibernation to avoid any self-inflicted damage. Since then, its human controllers …
Hammer. Or a healthy blast of pressurised air to get rid of all that star dust. Just imagine how it must look in Hubble's bowels...
rotating the 'spare' units into service every few months, to keep something like this from happening again
(that was standard operating procedure when I was in the Navy - get the spare out of the supply system, and rotate it in, taking the next unit out of service and putting it back into 'spares' in the supply system).
Bob - I guess it depends what the dominant failure mode is. I assume space stuff is run-in before launch so they're not at the start of the bathtub, but if a component is more likely to fail when powering up then rotating is a bad strategy.
When I was at uni my housemate had a knackered Mini which was always a pain to start and once it got going he didn't like to turn it off - e.g. nipping into shops. He once left it running in the student car park for about half an hour because he'd left something in the lab and was on his own.
"rotating the 'spare' units into service every few months, to keep something like this from happening again"
My experience with ringing generators suggests that this is an excellent way of ensuring all units fail due to the same mechanical wear within a few days of each other. We stopped swapping 'spares' into service after that, instead just doing a changeover to ensure the spare worked and then changing back again to the normally working unit.
"Hubble uses reaction wheels to turn, so no fuel used."
Eh? Sorry, could you explain that to this rather coffee-deprived layman? Surely turning requires some change in velocity in the reaction wheels that would require some sort of energy expenditure? Or do you mean it uses electricity from solar panels and thus does not need to use propellant?
Yes, it uses electrical motors to spin, so the telescope rotates in the opposite direction.
However, this eventually results in "saturation" where the reaction wheels can't spin faster to move the 'scope.
"Desaturation" is usually done by firing rockets to hold it steady while the wheel is spun down... however this is an expensive telescope with very contamination sensitive optics, so you can't have rocket exhaust floating around. Instead they use magnetotorquers, which react against the Earth's magnetic field to to apply a small but steady torque.
Well then why don't they use the magnetotorquers themselves to control the attitude? Because the force is very very small, and can't be used for quick pointing maneuvers in something as large as HST. "Going to the next star" would take weeks.
"Well then why don't they use the magnetotorquers themselves to control the attitude? Because the force is very very small, and can't be used for quick pointing maneuvers in something as large as HST. "Going to the next star" would take weeks."
Oh, that's a shame, not being able to tell Hubble to "use the force, look"...
Actually, it's not vacuum stiction... it may be pitting in the bearings caused by electrical arcing caused by static buildup from the solar wind. This is a new theory.
http://esmats.eu/esmatspapers/pastpapers/pdfs/2017/bialke.pdf
https://www.youtube.com/watch?v=KibT-PEMHUU
Then they wouldn't need to use gyros on spacecraft. They could just lace the spacecraft with dozens of little EM Thrusters to have it point any which way you want, all solar powered and infinite lifespan.
Come on kids, hurry up already.
;-)
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