Timeline for Why is the EMU space suit pressurized to 4.3 psi specifically?
Current License: CC BY-SA 4.0
11 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jun 27, 2020 at 22:57 | comment | added | GlenPeterson | Humans also produce, er, occasional methane emissions that might have to be compensated for, but might not be especially publicized. I don't know if any hand cream, medical bandage, or anything else could outgas enough to matter. | |
| Jun 17, 2020 at 8:54 | history | edited | CommunityBot |
Commonmark migration
|
|
| Feb 2, 2019 at 23:30 | history | edited | Organic Marble | CC BY-SA 4.0 |
fixed flight rules link that JSC broke
|
| Jan 4, 2016 at 21:24 | comment | added | Nakedible | Actually yes, I just verified the same from ISS handbooks. There is a long camp-out at 10.7 psi, lots of breathing pure oxygen and finally 15 minutes long EMU nitrogen purge sequence where suit is vented and fed with pure oxygen. Considering the human body contains about 1 liter of dissolved oxygen, after all this is done, there can't be much nitrogen left in the blood stream to change the suit atmosphere - certainly not 8% in the normal case. | |
| Jan 4, 2016 at 20:32 | comment | added | Organic Marble | This, like many flight rules, may be extremely conservative since most EVAs are preceded by a long "prebreathe" on pure O2 designed to expel N2 from the crewmembers' bodies. In this nominal case I wouldn't expect much N2 to be exhaled, but the rule is presumably written to cover the case of an emergency EVA where a long prebreathe wasn't possible. | |
| Jan 4, 2016 at 20:23 | comment | added | Nakedible | Good point about the exhaled nitrogen - that would happen when transitioning from a two-gas environment. First I thought that the exhaled nitrogen would in no way reduce the partial pressure of the oxygen - but then I realized that the regulator in the EMU feeds oxygen if total pressure < 4.3 psi, instead of feeding oxygen if oxygen partial pressure < 4.3 psi, and that nitrogen isn't going anywhere except via leaking. However, I'm not 100% convinced about the "nice 1 psi margin" explanation. | |
| Jan 4, 2016 at 17:04 | comment | added | Organic Marble | Actually it was in the next rule, sorry, A13-54: Breathing 100 percent oxygen at sea level pressure will result in physiologic changes due to oxygen toxicity after 6 hours minimum. Since oxygen toxicity is proportional to the oxygen partial pressure and not the percent gas, longer exposures of 100 percent oxygen can be tolerated at lower pressures. For 100 percent oxygen at sea level, physiologic changes begin as mild (2 to 5 percent) asymptomatic decreases in vital capacity (the largest volume of air which can be exhaled voluntarily) beginning with fully inflated lungs. | |
| Jan 4, 2016 at 17:01 | comment | added | Organic Marble | I think so. There is a paragraph in the linked document, a few pages ahead of the block of text I quoted, that talks about O2 toxicity at higher pressures, but since it was in reference to the shuttle cabin atmosphere and not the EMU, I didn't really read it. Take a look if you like in the Flight Rules I linked to. | |
| Jan 4, 2016 at 15:55 | comment | added | honeste_vivere | I assume that 92% $O_{2}$ would be toxic if the pressure inside the suit were at 1 atm (~15 psi), right? | |
| Jan 4, 2016 at 2:16 | history | edited | TildalWave | CC BY-SA 3.0 |
ortography
|
| Jan 4, 2016 at 1:57 | history | answered | Organic Marble | CC BY-SA 3.0 |