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[mainiac]

The oxygen's more bound up in the aluminum than the iron, but then again mining oxygen from rocks is probably not the best way to obtain it. If you're not recycling your atmosphere (and other volatiles), you're not doing it right.

Yeah it's not a mining, the stuff is right on the surface.  Silicon dioxide is very common in moon dust.  You just need to pump enough electricity into the moon dust to separate the two elements.  This way some of the oxygen boils off as a gas which you can then capture while the silicon turns into rocks with a lower oxygen percentage.

[WillowLuman]

The thing is, you only need to mine for oxygen if you're building large scale, too large to make supplies from Earth cost-effective. If you're bringing in modules, they (should) come with their own air, and the initial resupply modules ought to bring extra compressed gas stores as well.

Also, bear in mind that nitrogen is an important, if inert, component. Breathing pure, or even high-saturation, oxygen can actually be poisonous (to say nothing of the fire danger). Ideally you'd want a 20-21% oxygen atmosphere.

[mainiac]

The thing is, you only need to mine for oxygen if you're building large scale, too large to make supplies from Earth cost-effective. If you're bringing in modules, they (should) come with their own air, and the initial resupply modules ought to bring extra compressed gas stores as well.

Also, bear in mind that nitrogen is an important, if inert, component. Breathing pure, or even high-saturation, oxygen can actually be poisonous (to say nothing of the fire danger). Ideally you'd want a 20-21% oxygen atmosphere.

Sending compressed gas from earth is expensive.  Every kilo you make on the moon is a huge cost savings.  Interesting point about nitrogen though.  I wonder if lower atmospheric pressure and alternative gasses like CO2 can do the trick.

[WillowLuman]

CO₂ is dangerous. It can take the place of oxygen in the lung's alveoli, preventing actual O2 from getting respirated even if its in abundance, and thus causing suffocation. It's not toxic per se, but it does stop oxygen from reaching your blood if there's too much of it, and by too much I mean 7% or more. A concentration of just 1% will make people constantly sluggish. It's best to stick with as close to Earth's atmosphere as possible, since that's what we're adapted for.

And once again, electrolysis of minerals is only more cost-effective if you're building a big colony. As far as resources go, compressed oxygen weighs a lot less than others, and it's already standard practice in building space stations to include a little extra packaged air in everything launched. Electrolysis of solid minerals, on the other hand, also requires a lot of energy, since you have to melt them first, and enough space to process tons of moon rock. So until you start trying to make the base big enough for hundreds of people, you probably won't need it. In either case, acquiring new oxygen molecules should not be a regular occurrence. If you're not recycling your used air, then you're not doing it right. A base wouldn't need regular shipments of air to breathe, but rather only need new air to fill newly constructed rooms (or in case of emergencies).

Interestingly, getting more air to fill new rooms on Mars would probably be easier, since Mars has an atmosphere, made almost entirely of CO₂. Electrolysis of gasses is a lot easier, since you don't have to melt them first.

[alway]

CO₂ is dangerous. It can take the place of oxygen in the lung's alveoli, preventing actual O2 from getting respirated even if its in abundance, and thus causing suffocation. It's not toxic per se, but it does stop oxygen from reaching your blood if there's too much of it, and by too much I mean 7% or more. A concentration of just 1% will make people constantly sluggish. It's best to stick with as close to Earth's atmosphere as possible, since that's what we're adapted for.

Yep, and further, CO2 in the blood is actually what triggers the feeling of being unable to breathe, not a lack of O2 in the blood. Between that and the effects mentioned above, you would basically drown in the air, complete with the gasping for breath and everything. So yeah, generally not all that useful an environment for humans.

[mainiac]

Electrolysis might take a lot of energy but energy is much easier to get in space then most materials.  Plunk down some solar cells and go to town.  Even if it takes a year or two to produce enough electricity for oxygen to return on your investment, that's a big savings long term.  It's a really simple process, extract the oxygen then dump the rock in a heap outside, not efficient but something that would be viable on the small scale.

Regarding the nitrogen thing, why would you just lower the atmospheric pressure to 25% so you don't need much nitrogen to get by?  It would be a slight problem for plants but one that could be overcome with fertilizers and the right strains of bacteria.  It wouldn't cause lung collapse because the change would be the same inside and outside the body.

[Remalle]

Watching with interest.

[WillowLuman]

Electrolysis might take a lot of energy but energy is much easier to get in space then most materials.  Plunk down some solar cells and go to town.  Even if it takes a year or two to produce enough electricity for oxygen to return on your investment, that's a big savings long term.  It's a really simple process, extract the oxygen then dump the rock in a heap outside, not efficient but something that would be viable on the small scale.

Regarding the nitrogen thing, why would you just lower the atmospheric pressure to 25% so you don't need much nitrogen to get by?  It would be a slight problem for plants but one that could be overcome with fertilizers and the right strains of bacteria.  It wouldn't cause lung collapse because the change would be the same inside and outside the body.

Because low pressure over long periods of time has effects on people, and a higher concentration of Oxygen makes the atmosphere extremely flammable. You need N₂, because 50% or even 30% oxygen just isn't safe. Low-pressure rooms are for acclimating to avoid the bends; we don't keep our subs or our spacecraft at acclimation chamber conditions throughout because they're not suitable for daily existence.

[MaximumZero]

How have I missed this until now? I love space!

[mainiac]

Because low pressure over long periods of time has effects on people

Such as..?

[WillowLuman]

Because low pressure over long periods of time has effects on people

Such as..?

The lower the pressure, the thinner the air, the less O2 delivered to the blood with every breath. See Altitude Sickness. 25% of normal pressure is roughly equivalent to 11,000 meters in altitude, well within the zone where people have trouble breathing and must limit their activity. How exactly does lowering the pressure reduce the need for Nitrogen, anyway? What does that have to do with the relative concentration of gasses in the air?

[LordSlowpoke]

Lower pressure means that you need more oxygen by percentage to comfortably continue regular activity, I guess. Pretty unsafe though.

[WillowLuman]

And as we all know, more oxygen% = more flammable. At even 30%, rapid, total immolation of the pressurized space might be possible.

[mainiac]

The lower the pressure, the thinner the air, the less O2 delivered to the blood with every breath. See Altitude Sickness. 25% of normal pressure is roughly equivalent to 11,000 meters in altitude, well within the zone where people have trouble breathing and must limit their activity. How exactly does lowering the pressure reduce the need for Nitrogen, anyway? What does that have to do with the relative concentration of gasses in the air?

People have trouble because the partial pressure of oxygen is low, not because the pressure of the air is low.

And ignition happens because the partial pressure of oxygen is high, not because the percentage of oxygen is high.

[WillowLuman]

Lower total air pressure = lower partial pressure of the component gasses. Pressure is irrelevant for fire danger except at exceptional lows, and at those lows people would not be able to survive for even a few minutes. In your proposed environment, people would need oxygen masks on at all times just to function normally.

Again, the pressure you propose is equivalent to being at 11,000 meters (11 kilometers) in altitude on Earth, an altitude at which people cannot live their daily lives. It's in the tropopause, the boundary zone between the troposphere and the stratosphere. People may spend days at such altitudes while mountaineering, but must return to lower places soon. The highest dwelling with permanent human inhabitants (and not transitory ones, like camps) is only at about 6,400 meters in altitude.

Also, you haven't answered my question:

The lower the pressure, the thinner the air, the less O2 delivered to the blood with every breath. See Altitude Sickness. 25% of normal pressure is roughly equivalent to 11,000 meters in altitude, well within the zone where people have trouble breathing and must limit their activity. How exactly does lowering the pressure reduce the need for Nitrogen, anyway? What does that have to do with the relative concentration of gasses in the air?