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57 votes
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Why aren't spacecraft and spacesuits pressurised to 2.5 psi (17 kPa) of pure oxygen?

The sum of all partial pressures in the lungs must add up to the ambient pressure. The composition of gas inside the lungs includes the vapor pressure of H₂O at body temperature which is about 0.9 psi....
Woody's user avatar
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35 votes
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Why would oxygen be stored as a super critical fluid?

The same system was used on Shuttle - allow me to discuss that, the design philosophy applies to Apollo as well (Shuttle deleted the fans though, and had a special Avoid-Apollo-13-circuit in the O2 ...
Organic Marble's user avatar
34 votes
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Do rockets deplete the oxygen on earth?

Let's start with a Fermi estimate: The atmosphere has a mass of about 5.15×1018 kg, 20% of that is oxygen. A rocket launch uses on the order of 106 kg of oxygen. To use up all the oxygen (and ...
Hobbes's user avatar
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30 votes
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What does "stirring tanks" mean?

There was no "slush" in the Apollo cryo tanks. The O2 and H2 in the tanks were stored at conditions that made them supercritical fluids. The critical pressure for O2 is ~ 730 psi, the Apollo tanks ...
Organic Marble's user avatar
30 votes

What stages of distress occur to a person when there is a small hull breach in space?

To understand subjective symptoms of a hull breach, it is important to remember that respiratory drive (the sensation of shortness of breath) is driven by blood CO2 level, not blood O2 level. As long ...
Woody's user avatar
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23 votes

Is oxygen present in the sun?

The sun is not "burning" in the sense you are used to: there is no chemical reaction going on. Instead, there is a very high pressure in the core of a star (like our sun) due to the high mass that ...
DarkDust's user avatar
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23 votes
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Self-sustainable Hermetically Sealed System: Humans & Plants

This is being done with biosphere 2 and several similar projects and found to be very complicated. Specifically in a small sealed system there is little buffering or inertia available if one element ...
GremlinWranger's user avatar
21 votes
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What is the advantage of using Helium over Nitrogen when used for pressurising LOx?

As suggested by OrganicMarble in a comment, nitrogen is miscible with oxygen (you can thus make liquid air). According to NASA Technical Paper 2464, this is a major concern because using "...
TooTea's user avatar
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21 votes
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Are there any short-term survivable locations in the solar system, outside of Earth?

As already commented by Fred, Venus is your best bet. Not at surface level – both temperature and pressure are way too high there – but at ca. 50 km elevation, where both are actually quite similar to ...
leftaroundabout's user avatar
16 votes

Are there any short-term survivable locations in the solar system, outside of Earth?

No place other than Earth has available oxygen. This limits survivability. Nevertheless, if a body is cooled down significantly, the immediate deadly effects of anoxia can be pushed away as much as ...
SE - stop firing the good guys's user avatar
15 votes
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Is atmospheric skimming for propellant feasible?

It is easy enough to analyze this in terms of conservation of momentum, we'll assume the velocity through the atmosphere to be 7.8km/s, that is LEO orbital velocity - in actuality it'll be a little ...
Blake Walsh's user avatar
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14 votes
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Why is the EMU space suit pressurized to 4.3 psi specifically?

This is what Kenneth S. Thomas and Harold J.McMann have to say about it in U.S. Spacesuits: Operating pressures: The Shuttle extravehicular mobility unit (EMU) has an operating pressure of 4.3 ...
Phil_12d3's user avatar
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14 votes
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How long were the Apollo astronauts allowed to breathe 100% oxygen at 1 atmosphere continuously?

There are two different effects of oxygen toxicity, the Lorrain-Smith-effect and the Paul-Bert-effect. See Wikipedia. The Lorrain-Smith-effect may occur at a partial oxygen pressure above 0.5 bar for ...
Uwe's user avatar
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14 votes

Why aren't spacecraft and spacesuits pressurised to 2.5 psi (17 kPa) of pure oxygen?

A mix of 79 % nitrogen and 21 % oxygen at a pressure of 1 atm, 14.7 psi or 1.01 bar is more fireproof than pure oxygen at a pressure of 0.21 atm, 3.087 psi or 0.212 bar. The partial pressure of oxygen ...
Uwe's user avatar
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13 votes

What stages of distress occur to a person when there is a small hull breach in space?

Supplementary answer For your timeline, it's important to note that the pressure drop is not even remotely linear. The flow through the leak is large at first because the differential pressure is ...
Organic Marble's user avatar
12 votes
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Isn't electrolysis of water less efficient for a space craft than pressurized oxygen tanks?

As Andrew Thompson's comment hints, it's a matter of tankage mass vs the trifling extra mass of hydrogen. Tankage is no small thing; it's the main reason hydrolox ($H_2 / O_2$) rockets, despite their ...
Nathan Tuggy's user avatar
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12 votes

What does "stirring tanks" mean?

From this NASA pdf: At 46:40:02 Mission Elapsed Time during the Apollo 13 mission, both oxygen tank fans were powered on, hopefully to get a more accurate reading of the tank pressure. In fact,...
Uwe's user avatar
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11 votes
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Decision Factors for using 100% $ O_2 $ cabin atmosphere in early US space program

Despite a higher risk of a fire, pure oxygen also has some advantages. First, the internal pressure of the vessel is only a fifth of a normal breathing mix, allowing less structural load on the hull ...
SE - stop firing the good guys's user avatar
11 votes
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Martian Carbon Dioxide Turbine Oxygen Generator

Yes, in principle to both questions, why not? However we can calculate the maximum energy you could get from the generator. The vapour pressure of $CO_2$ at 0C is around 4MPa, so in a perfect world, ...
Steve Linton's user avatar
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10 votes

Is atmospheric skimming for propellant feasible?

It can be made to work, but it would be quite different from the typical SF depiction. As Blake points out, you can't gain anything from mass that is already moving faster than rocket exhaust. However,...
Quentin Clarkson's user avatar
10 votes
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Can a machine process and run on $CO_2$ and $H_2O$ for an $O_2$ by product?

Can electrolysis of water provide fuel for the generator where both water and liquid carbon dioxide is utilized in one self sustaining machine? NO. A 'self sustaining machine' would be a perpetual ...
Hobbes's user avatar
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10 votes

Is oxygen present in the sun?

There is oxygen and many other elements on the Sun. The "burning" you refer to is fusion, it does not require oxygen. Oxygen is created by: 12 C + 4 He ------> 16 O + energy. In case you are ...
Rob's user avatar
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9 votes
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Has solidifying liquid propellant been considered for space exploration?

The melting point of hydrogen isn't much lower than its boiling point (6K), so the temperature isn't necessarily that much of an obstacle. However, using solid fuel requires either melting it, or ...
Nathan Tuggy's user avatar
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9 votes

Why is the EMU space suit pressurized to 4.3 psi specifically?

Apparently, it's because putting a person in the suit prevents the atmosphere from being pure O2. The Space Shuttle Flight Rules (Rule A13-53) state: ONE-GAS ENVIRONMENT (EMU) - IF THE PRESSURE IN ...
Organic Marble's user avatar
9 votes
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How much oxygen can MOXIE produce?

The answer is up to around 10g/hour. The experiment will be run multiple times throughout the lifetime of the rover and each run will be for about an hour. A full scale version for use on a human ...
Slarty's user avatar
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9 votes
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How much algae would you need to fully support a person?

I was recently involved in a feasibility study for using Chlorella vulgaris algae for generating medical oxygen using solar energy in off-grid medical facilities. Bottom line: it requires one cubic ...
Woody's user avatar
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8 votes
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Oxygen toxicity vs Apollo mission preparation

Reading the listed Wikipedia article, it is evident that these experiments were done at pressure, the same pressure that would be experienced at 90 feet of water. I've been trying to find a better ...
PearsonArtPhoto's user avatar
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8 votes

Why would oxygen be stored as a super critical fluid?

I'm not a chemist but I'll go out on a limb and suggest a way to resolve some issues in comments. It looks to me as though as long as you are above both the critical pressure and critical temperature ...
uhoh's user avatar
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8 votes

What effects did the different air pressure and air composition in certain spacecraft have on astronauts?

The partial pressure of oxygen (ppO2) should be higher than about 0.16 bar and lower than about 0.4 to 0.5 bar for longer exposition of some days up to a week. So breathing pure oxygen for a week is ...
Uwe's user avatar
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7 votes

Isn't electrolysis of water less efficient for a space craft than pressurized oxygen tanks?

The ISS does receive regular shipments of oxygen as a gas in specially built, very high pressure (about 6000 psi or 400 atmospheres), scary looking tanks, as pointed out in this interesting answer. ...
uhoh's user avatar
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