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#20
by
kevin-rf
on 08 Jun, 2012 13:51
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Since it was being discussed off topic in another thread I thought I would ask this in the Hubble thread.
I have never under stood how (and why) Hubble's CMG's (Gyro's) wore out and broke. Anyone have any insight and a reasonable layman's explanation for it?
Is it bearings, is it rotors or stators fowling up.
I just don't understand, I would have thought in Zero G you can use a magnetic bearing that keeps the shaft centered, or an air bearing, and a brushless motor. I'm just a little curious what the issue was.
I look at all the spin stabilized GEO birds over the decades and how the motor's despun the antenna's. They seemed to last the life of the satellite.
Though, wasn't it the gyro's that did in the International Ultraviolet Explorer.
Just looking for a layman's explanation.
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#21
by
Lee Jay
on 08 Jun, 2012 14:12
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#22
by
kevin-rf
on 08 Jun, 2012 15:03
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So the working theory is corrosion of wires. So a material choice issue. I was not expecting that answer.
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#23
by
Lee Jay
on 08 Jun, 2012 15:05
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So the working theory is corrosion of wires. So a material choice issue. I was not expecting that answer.
Better read it more carefully. It wasn't the wires or the fluid, it was the way the fluid was injected.
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#24
by
kevin-rf
on 08 Jun, 2012 16:15
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Yes, oxidation of the wires by the fluid reacting with O2 in the pressurized air. In my book that is a materials compatibility issue.
If the working fluid can break down and create corrosive residue when exposed to O2, then either a different fluid should be used (which is most likely not realistic) or an O2 (or corrosive residue) scavenger should be inserted. Either as an additive or built into the chamber. Switching to an N2 pressurization removes the bulk of the O2 contamination, but is it 100% removed?
Maybe just a rant,
I was really expecting some sort of strange physical wear down effect that limited the life of a component or two.
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#25
by
Lee Jay
on 08 Jun, 2012 16:33
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It's quite simple to purchase extremely pure N2.
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#26
by
Prober
on 13 Jun, 2012 15:34
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The last service mission of Hubble was fantastic to watch.
My question would be about the storage of video of that mission.
Does NASA keep all the hours of video of that mission?
If So, how would I request a DVD's of it?
What would be the proper process?
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#27
by
catdlr
on 14 Jun, 2012 01:46
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#28
by
Naito
on 15 Jun, 2012 13:04
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Another question about the gyros: how come they don't get saturated like the ISS gyros? Hubble doesn't have any thrusters to desaturated them with right?
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#29
by
Jim
on 15 Jun, 2012 14:14
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Another question about the gyros: how come they don't get saturated like the ISS gyros? Hubble doesn't have any thrusters to desaturated them with right?
It has torque bars that react against the earth's magnetosphere for desaturation.
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#30
by
AnalogMan
on 15 Jun, 2012 14:28
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Another question about the gyros: how come they don't get saturated like the ISS gyros? Hubble doesn't have any thrusters to desaturated them with right?
As Jim said, magnetic torquers - there is a little more info in this old thread:
http://forum.nasaspaceflight.com/index.php?topic=17121.0
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#31
by
Hog
on 10 Sep, 2014 16:15
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HST service Mission #4, was executed in 2009.
1) If STS was to be retired in 2016 and a final Servicing Mission #5 was planned for 2015, what modifications would be a priority for this hypothetical HST Service Mission?
b)Guesses on how much Service Mission #5 would extend HST's service life?
2) If ISS was on orbit at it's current inclination of 51.6° and HST was to be launched afterwards. Would planners have launched HST on a different orbit other than 28.5°
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#32
by
wolfpack
on 10 Sep, 2014 17:36
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HST service Mission #4, was executed in 2009.
1) If STS was to be retired in 2016 and a final Servicing Mission #5 was planned for 2015, what modifications would be a priority for this hypothetical HST Service Mission?
b)Guesses on how much Service Mission #5 would extend HST's service life?
2) If ISS was on orbit at it's current inclination of 51.6° and HST was to be launched afterwards. Would planners have launched HST on a different orbit other than 28.5°
1) Probably gyroscopes and some method of propulsive deorbit.
2) No. It doesn't make sense to give up orbital altitude for orbital inclination. What in deep space do you want to photograph that can't be photographed from 28.5 deg?
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#33
by
Hog
on 10 Sep, 2014 23:42
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HST service Mission #4, was executed in 2009.
1) If STS was to be retired in 2016 and a final Servicing Mission #5 was planned for 2015, what modifications would be a priority for this hypothetical HST Service Mission?
b)Guesses on how much Service Mission #5 would extend HST's service life?
2) If ISS was on orbit at it's current inclination of 51.6° and HST was to be launched afterwards. Would planners have launched HST on a different orbit other than 28.5°
1) Probably gyroscopes and some method of propulsive deorbit.
2) No. It doesn't make sense to give up orbital altitude for orbital inclination. What in deep space do you want to photograph that can't be photographed from 28.5 deg?
Thanks
2) I wasnt thinking of imaging capability, I was thinking more in terms of the HST servicing missions having the posibility of using the ISS as a safe haven.
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#34
by
Proponent
on 11 Sep, 2014 08:30
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Although Hubble's 11-tonne mass doesn't sound like a lot compared to the 20+ tonnes that the Shuttle could haul to LEO, I'll bet the Shuttle would have really struggled to lift Hubble to 600 or so kilometers at 51.6°.
The payload capability of a typical expendable launch vehicle would decrease by -- making a WAG here -- 10-ish percent as the altitude is raised from LEO to 600 km and the inclination is increased by 20-30 degrees. The same would be true for the Shuttle, but with the Shuttle plus payload weighing, what, 100 t, the decrease in payload capability would be (0.1-ish)(100 t) = 10 t. Take a due-East LEO capability of 20-some tonnes, reduce it by 10 t or so, and it's not obvious that the Shuttle could lift Hubble to its operational orbit if the inclination were raised to 51.6°.
EDIT: "it's" -> "its" in final sentence
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#35
by
Jim
on 11 Sep, 2014 09:56
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Around 650lbs of capability for every degree of inclination and 100 lb per nautical mile of altitude
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#36
by
wolfpack
on 11 Sep, 2014 19:02
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2) I wasnt thinking of imaging capability, I was thinking more in terms of the HST servicing missions having the posibility of using the ISS as a safe haven.
HST is a big satellite with no thrusters for station keeping. I don't think you'd want it in exactly ISS's inclination.
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#37
by
kevin-rf
on 12 Sep, 2014 00:23
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Another point is because of the South Atlantic Anomaly (Van Allen dips down over the South Atlantic) you want to be in as low an inclination as possible. The radiation speckles the CCD's.
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#38
by
wolfpack
on 12 Sep, 2014 00:43
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Another point is because of the South Atlantic Anomaly (Van Allen dips down over the South Atlantic) you want to be in as low an inclination as possible. The radiation speckles the CCD's.
Good point. Here's another - beta angle. Thermals are worse at higher inclinations.
More I think about it, you really want a telescope as close to equatorial as you can get. Looking out into space, go 0 deg. Looking back at Earth (clouds and bad guys), go polar.
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#39
by
jgoldader
on 14 Sep, 2014 02:18
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Yet another point--the low-inclination orbit made the original Hubble Deep Field possible, as the telescope cound stare at a single place in space near the north celestial pole for days straight without worry of occultation by the Earth during an orbit. I'm almost certain that the Deep Fields, among HST's greatest achievements, would have been impossible from a high-inclination orbit.
