Ground control to Major Tim! Brit's spacewalk halted after NASA 'naut takes unexpected leak NASA called an early halt to a British astronaut's spacewalk after water leaked in his American colleague's spacesuit. The European Space Agency's Major Tim Peake and his NASA counterpart Colonel Tim Kopra had planned to spend over six hours outside the International Space Station replacing a faulty sequential shunt unit that …
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Astronauts have to purge nitrogen from their blood for hours by huffing pure oxygen before suiting up to avoid getting the bends
Is the pressure of the suits significantly lower than the one in the ISS? shouldn't the astronauts also decompress to suit pressure while living in the pure oxygen atmosphere (otherwise they will get oxygen poisoning)? Ho about using He/O mixtures then?
This has been discussed at lenth (and competent) in the comments on the article announcing the Two-Tim-spacewalk a couple of days ago.
Checking there.
So it seems to be about reducing suit stiffness due to high internal pressure.
This means you have to increase the oxygen content in breathable air to keep partial pressure of Oxygen constant.
Helium is used to replace Nitrogen in high-pressure environments because Nitrogen has toxic effects on the nervous system at high pressures. So this is not useful here. Using Helium also increases the problem of outgassing ("the bends") when pressure falls, so this is even less useful.
So this is all about a slow decompression to get to spacesuit-agreeable low-pressure while avoiding outgassing while keeping partial pressure of oxygen constant.
Maybe one should switch to Arthur C. Clarke rigid suits...
It'd be appropriate as far as I know; but you'd have to lift all the helium cylinders into orbit. Spose you could generate helium on-site but more complexity and cost of lifting the equipment. Also helium is a small molecule, so you can lose pressure more easily through smaller holes...not sure if the materials exist to satisfactorily contain helium in a vacuum. Appropriate, but at least more expensive and possibly not doable at all.
I sit corrected. According to Vic here:
http://forums.theregister.co.uk/forum/1/2016/01/13/peake_spacewalk/
...replacing nitrogen with helium is more iffy than I thought it was.
shouldn't the astronauts also decompress to suit pressure while living in the pure oxygen atmosphere (otherwise they will get oxygen poisoning)?
No. O2 poisoning occurs at high pressure, not low; even pulmonary roxicity wouldn't kick in for a couple of days at the pressures we're talking about.
Ho about using He/O mixtures then?
Heliox would increase the inert gas load, rendering them more susceptible to decompression injuries without any benefit.
This is why the clever people at NASA - who participate in decompression theory discussions - suggest their astronauts decompress on 100% O2 before suiting up.
Vic.
Oooh, that one's simple. There's nothing liquid in the suit besides water and possibly small amounts of urine (if you forgot to relieve yourself before suiting up). Similarly, there's nothing in there that is toxic in small amounts. Hence, tasting any liquid released inside the suit is safe enough. In the worst case scenario, it's a mild base and tastes really bad.
There are two sources of water in the suit, water from the cooling system which is cold, and water from the drinking bottle, which is warm as it is located on the chest. Luckily any urine spillage on long space walks is avoided through use of the space nappy, or space diaper as the Americans like to call it.
There are two sources of water in the suit, water from the cooling system which is cold, and water from the drinking bottle
There's also perspiration, should they exert themselves, and the breathing gas will be humidified to a minimum of 47mmHg[1]. If any part of the suit were to get suitably cold, that could easily condense.
Vic.
[1] That's the humidity of exhaled air; breathing anything drier than that means you will be losing water to your environment. Of course, being a rebreathing environment, the humidity should get to that level and stay there. Which is nice.
but that 'water' could have been any sort of chemical
It will be predominantly water.
Should that water have passed through the scrubber in the breathing loop, there will be other material in solution - NASA uses lithium hydroxide[1] as a scrubber material, so rather unpleasant, but in the concentrations we're talking about, it's not hazardous. Aside from that, the WOB of a wet scrubber is *much* higher (and so easily recognised), and it would surprise me[2] if they don't have telemetry to detect such conditions as well.
TL;DR: I can't see it being a real problem.
Vic.
[1] We Earth-bound rebreather divers usually use calcium hydroxide, meaning the "caustic cocktail" from a scrubber flood really isn't a big deal. But lithium hydroxide gets you more CO2 absorption for a given mass of material, and is less fussy about scrubber temperature.
[2] I haven't checked, so you probably should if you intend to quote this post...
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