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LIVE: STS-125 Flight Day 4 - EVA-1
by
Chris Bergin
on 14 May, 2009 00:49
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#1
by
mikes
on 14 May, 2009 08:39
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#2
by
EirikV
on 14 May, 2009 08:47
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#3
by
Chris Bergin
on 14 May, 2009 08:47
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#4
by
tva
on 14 May, 2009 08:53
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There used to be a camp-ut with pure oxygen in the air-lock on EVA's staged from the ISS.
They did not do it now. Why ?
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#5
by
EirikV
on 14 May, 2009 08:54
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Sunset from orbit. Hope they catch one of 'em sunrises with that IMAX cam.
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#6
by
EirikV
on 14 May, 2009 09:04
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#7
by
kneecaps
on 14 May, 2009 09:47
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There used to be a camp-ut with pure oxygen in the air-lock on EVA's staged from the ISS.
They did not do it now. Why ?
Because the Orbiters airlock is too small to comfortably spend the night in. The ISS airlock is much larger.
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#8
by
Analyst
on 14 May, 2009 10:00
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The airlock size is the same. The ISS campout does not happen in the actual airlock, but in the Quest module, which contains the airlock, but also some normal space (The 4.5m cylinder with the CBM on one side and the actual airlock on the other.). They close the door between Node-1 and Quest for the campout.
Analyst
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#9
by
John44
on 14 May, 2009 10:02
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#10
by
cb6785
on 14 May, 2009 10:19
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#11
by
ItsyAndy
on 14 May, 2009 10:23
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The airlock size is the same. The ISS campout does not happen in the actual airlock, but in the Quest module, which contains the airlock, but also some normal space (The 4.5m cylinder with the CBM on one side and the actual airlock on the other.). They close the door between Node-1 and Quest for the campout.
Analyst
Anyway, don't they need to prepare breathing pure oxygen like for EVAs on the ISS? Something I am missing?
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#12
by
kneecaps
on 14 May, 2009 10:30
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Anyway, don't they need to prepare breathing pure oxygen like for EVAs on the ISS? Something I am missing?
As I understand it the reduced cabin environment is the first step. The EVA team will pre-breath pure oxygen while in the airlock to purge remaining nitrogen. (i'm no expert on these matters so anybody chip in with corrections).
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#13
by
psloss
on 14 May, 2009 10:39
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As I understand it the reduced cabin environment is the first step. The EVA team will pre-breath pure oxygen while in the airlock to purge remaining nitrogen. (i'm no expert on these matters so anybody chip in with corrections).
Right, they would be in "continuous campout" in ISS EVA prep terminology, since the crew module pressure was lowered to 10.2 psi on Flight Day 2. But shuttle crews have been doing this for 25 years; the ISS campout is something like a modified protocol. Depress to 10.2 is standard for all standalone shuttle flights with EVAs -- and a modified version was done for ISS assembly missions with EVAs from the shuttle airlock.
(If you listen to the air-to-ground, I believe the '10.2 servicing' or '10.2 maintenance' calls are during the post-sleep period.)
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#14
by
Ronsmytheiii
on 14 May, 2009 11:19
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#15
by
Ronsmytheiii
on 14 May, 2009 11:22
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#16
by
Ronsmytheiii
on 14 May, 2009 11:23
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ready to tape ops in the bay
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#17
by
Ronsmytheiii
on 14 May, 2009 11:25
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#18
by
Ronsmytheiii
on 14 May, 2009 11:29
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#19
by
Mike_1179
on 14 May, 2009 11:30
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The airlock size is the same. The ISS campout does not happen in the actual airlock, but in the Quest module, which contains the airlock, but also some normal space (The 4.5m cylinder with the CBM on one side and the actual airlock on the other.). They close the door between Node-1 and Quest for the campout.
Analyst
Anyway, don't they need to prepare breathing pure oxygen like for EVAs on the ISS? Something I am missing?
The goal is to purge nitrogen out of their blood. Air is 78% oxygen, meaning there's a lot of it dissolved in your blood. At low pressures, that nitrogen can come out of solution (while in your bloodstream) and create bubbles. This is know as "the bends" to divers. These emboli can vary from painful to debilitating to leathal, so there is a protocol to purge this nitrogen from the EVAs bloodstream.
You could do it by breating pure oxygen for about three hours, the nitrogen in your blood would diffuse out because there is a higher partial pressure of N2 in your blood than in the gas in their lungs. To reduce the amount of time they need to pre-breathe 100% O2, you can lower the ambient pressure.
When you lower the air pressure from 14.7 to 10.2, you lower the partial pressure of nitrogen in that air - it's still 78% N2, there's just less molecules of it in the air, so that causes some of the N2 in your blood to diffuse out. After spending an entire night at 10.2 psi, you only need to pre-breath 100% O2 for one hour instead of three.