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#80
by
JayP
on 27 Jun, 2009 02:18
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I see that sounds quite hard to solve, why wasn't it considered in the design that a dynamic failure of the inner pressure pane will likely make the redundant outer one fail as well, makes it sound like it isn't actually that redundant, especially since tempered glass tends to fail completely when it fails.
Why does the Shuttle use glass instead of high strength plastics? is it because of its age?
It isn't just normal tempered glass, it's made of an aluminosilicate compound that was chosen for its high mechanical strength. The inner pane is only 5/8 of an inch thick but the middle pane is 1.3 inches thick. It might be damaged in a blowout but would probably hold. The reports that are saying that it would fail are being a bit alarmist. Plastics like polycarbonate wouldn't withstand the thermal conditions of reentry. Don't worry, the guys who designed this knew what they were doing.
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#81
by
JayP
on 27 Jun, 2009 02:25
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If the knob is made out of aluminum, it will be highly susceptible to mercury amalgamation. Remove the knob by taping off the area to prevent excess mercury from escaping, then paint some on and wait for it to oxidize the aluminum away, weakening the part until it can be removed. The glass won't care one bit about having the mercury in it.
I'm sure that overall the small amount of hazmat would not be an issue to clean up.
Aaron
You really want to contaminate the inside of the cabin with MERCURY!!. The stuff woun't bee seen again until some astronaut inhaled it on orbit. Where that knob is, there would be no way to put something under it to catch any that dripped without dissasembaling the panel that its traped behind. Oh wait, that would free the knob anyway wouldn't it
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#82
by
Danny Dot
on 27 Jun, 2009 03:27
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Why can't they just pump the cabin up to 14.7 psi gauge while it is sitting in the OPF? They must do some type of pump up for leak checks all the time. Apollo I fire was largely due to pumping the cabin up to the proper 100% O2 gauge pressure.
For shuttle this would make for 30 psi air in the cabin. Is there a fire hazard with this.
Danny Deger
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#83
by
Chris Bergin
on 27 Jun, 2009 04:11
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I think that can only be done at the pad. I know that's going to lead to people asking why they can't roll her out and send her with a stack to the pad, but I'm sure they've more than thought of all the proceedures and put them in a running order. First thing's first with Monday's low pressurization and dry ice, then they'll move on to the next option and so on if the knob doesn't come loose.
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#84
by
Jorge
on 27 Jun, 2009 04:14
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Why can't they just pump the cabin up to 14.7 psi gauge while it is sitting in the OPF? They must do some type of pump up for leak checks all the time.
I think the equipment in the OPF can only muster 2-3 psig.
You don't need 14.7 psig for a leak check.
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#85
by
Danny Dot
on 27 Jun, 2009 04:25
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Why can't they just pump the cabin up to 14.7 psi gauge while it is sitting in the OPF? They must do some type of pump up for leak checks all the time.
I think the equipment in the OPF can only muster 2-3 psig.
You don't need 14.7 psig for a leak check.
Why can't they have Atlantis pump herself up to 14.7 psi gauge. She does it all the time on orbit. Maybe the instruments in Atlantis will not work to 30 psi absolute.
Maybe doing this is risky, but it sounds like NASA is willing to take some risk at this point.
There certainly is a reason, or they would do it. I will say again, I know these guys are the best. They will get this problem resolved.
Danny Deger
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#86
by
aaronsb
on 27 Jun, 2009 07:00
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Actually, yes.
* A small amount of mercury paste won't "drip" anywhere.
* A fume extraction hood next to the site to remove any vapors would be simple and easy.
* If you look at the photos, ksc folks have already managed to slip some materials under the offending knob to catch anything that might slip or fall.
It's not like there aren't other rather toxic items that need to be dealt with occasionally nearby, like hydrazine in the RCS.
Also, people are suggesting things like inflating the orbiter to 14 psi differential, which might have unknown effects on components inside the orbiter's pressure hull, and strapping the orbiter back on it's ferry and flying around with a team to unstick the knob in flight? Those sound a little more risky than a small controlled chemical procedure.
Of course, I'm just a deskchair speculator, so I may be wrong on a lot of assumptions here.
You really want to contaminate the inside of the cabin with MERCURY!!. The stuff woun't bee seen again until some astronaut inhaled it on orbit. Where that knob is, there would be no way to put something under it to catch any that dripped without dissasembaling the panel that its traped behind. Oh wait, that would free the knob anyway wouldn't it
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#87
by
JPK
on 27 Jun, 2009 08:48
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The orbiter is made mostly of aluminum. Thus mercuary vapor could weeken the window frame. So any thin that could dislove or chemically
attack the knob is probabbly out.
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#88
by
kevin-rf
on 28 Jun, 2009 02:58
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Dumb Hg question, but I assume that knob is anodized, does Hg eat through the anodize the same way it eats through Al?
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#89
by
trout007
on 28 Jun, 2009 03:46
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#90
by
JayP
on 28 Jun, 2009 17:10
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Actually, yes.
* A small amount of mercury paste won't "drip" anywhere.
* A fume extraction hood next to the site to remove any vapors would be simple and easy.
* If you look at the photos, ksc folks have already managed to slip some materials under the offending knob to catch anything that might slip or fall.
It's not like there aren't other rather toxic items that need to be dealt with occasionally nearby, like hydrazine in the RCS.
Also, people are suggesting things like inflating the orbiter to 14 psi differential, which might have unknown effects on components inside the orbiter's pressure hull, and strapping the orbiter back on it's ferry and flying around with a team to unstick the knob in flight? Those sound a little more risky than a small controlled chemical procedure.
Of course, I'm just a deskchair speculator, so I may be wrong on a lot of assumptions here.
What exaxtly were you thinking of mixing the mercury with to make a "paste"? mercury is a liquid at room tempature
The difference between this and things like the RCS is that this is inside the CM. I don't believe they would ever intoduce a toxic chemical to it if there is another choice, and there is always the possibility of a spill when working with chemicals. You can never assume that it won't get loose. Also, a fume hood wouldn't help very much, since the real threat is globs of mercury floating around the cabin.
I do agree that the ideas of preasurising the cabin are equally farfetched. It's up to the guys at the cape, but I think the only trully safe way to go is to remove the panel. They would have to remove it anyway if the get the knob out and it turns out the window has to be replaced. The only downside is that it will take a really long time to do.
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#91
by
bobthemonkey
on 28 Jun, 2009 17:36
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#92
by
Danny Dot
on 28 Jun, 2009 19:18
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Mercury paste is an actual substance; I don't know what they use to make the paste however.
German Commandoes were issued with it in WW2 to smear over Allied aluminium structures. Apparently.
Anyway, here is something from popsci on it.
http://www.popsci.com/scitech/article/2004-09/amazing-rusting-aluminum
Interesting post. It might work. On the toxic aspect, most of the filling in my teeth are almost 100% mercury. Before it hardened, it was a nice to spread paste. I used to routinely play with the stuff as a kid. It can't be all that bad that it can't be handled in in the cockpit.
Danny Deger
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#93
by
phardacre
on 28 Jun, 2009 23:11
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The following is a light hearted comment hope its not out of place and is meant for humour only.
Obviously the answer is to tie a length of rope around the knob and put the other end over the nose of Endeavour then when she launches she will yank it out, a bit like having a tooth pulled, can't beleive all those nasa boffins didn't see that one.
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#94
by
mgreb
on 29 Jun, 2009 00:55
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I wonder if there is any way to EDM the thumbwheel in two. I guess the electrolite and electrical current would be a problem.
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#95
by
MikeMi.
on 29 Jun, 2009 18:34
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How is pressurization going? Someone know sth more?
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#96
by
Chris Bergin
on 29 Jun, 2009 18:38
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How is pressurization going? Someone know sth more?
In work. Won't be until much later today until the removal attempt. Will have an article updating status in an hour or so.
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#97
by
MikeMi.
on 29 Jun, 2009 20:13
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How is pressurization going? Someone know sth more?
In work. Won't be until much later today until the removal attempt. Will have an article updating status in an hour or so.
Good to know, thanks
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#98
by
Nomadd
on 29 Jun, 2009 21:10
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Lots of ways to cut or dissolve the knob, but it's not that simple. When the knob breaks from removal of part of it's material the high points that are jammed into the window could and probably would slip, possibly causing further damage. About the only way to loosen it safely is shrink the knob or make the space it's in bigger. 1st one didn't work so it's up to the 2nd one (pressurization).
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#99
by
Chris Bergin
on 30 Jun, 2009 02:25
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