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Comment by credit_guy | Hacker News Reader

The big problem with Moon colonies is that the Moon lacks carbon and nitrogen. Hydrogen is also hard to come by.

Let's say we find a lava tube that is 15 meters in diameter and 100 meters long. That is about 70 thousand cubic meters, and would require about 70 tons of nitrogen to create an artificial atmosphere similar to the one we have here (we can ignore the oxygen, or which there is plenty in the lunar regolith). Bringing 70 tons of stuff from Earth is not impossible, but far from easy, even given Musk's Starship.

It is much more likely that initially we'll build something similar in volume to the International Space Station, where we were able to keep a breathable atmosphere for 20+ years. Which, by the way, has a volume of only about 1000 cubic meters (out of which only about 400 m3 habitable).

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My calculations for the volume of a 15m x 100m cylinder would be 17,671 m³ (π * (Diameter/2)² * Length). I think you calculated it with 15m as its radius.

For an atmosphere similar to the Earth's at sea level, you would only need to bring a single Starship with liquid nitrogen (~12k kg) or ammonia (~22k kg, which you could use the ammonia breaking process) to fill it up the volume. Starship can hold 100 tons in its cargo configuration. With a 15m radius you would still only need ~49k kg of liquid nitrogen or ~80k kg of liquid ammonia, which is doable in a single-ish Starship flight (maybe two with the ammonia if you couldn't use all of the cargo capacity).

This seems extremely doable on smaller sizes, and pretty doable for larger sized lava tubes (albeit expensive).

That’s not true. Regolith contains plenty of nitrogen and carbon. The moon is basically a giant Bussard collector.

“Similarly, carbon and nitrogen have also been implanted from the solar wind. The amount of nitrogen in a cubic meter of lunar regolith is similar to the amount of hydrogen-about 100 grams, or 3 percent of the nitrogen in a human body. The amount of carbon is twice that, the carbon beneath each square meter of the lunar surface is some 35 percent of the amount found tied up in living organisms per square meter of the Earth's surface.”

https://space.nss.org/settlement/nasa/spaceresvol4/lifesuppo...

So 70,000 tons of regolith? I'm not a moon engineer or anything, but I think given the choice of bringing 70 tons of nitrogen, or the equipment to process that amount of regolith over a reasonable scale you'd just bring the nitrogen.

Nice catch. Only it would not be 70000 tons, but one million tons of regolith.

On the other hand this is about 0.1 sqkm of lunar surface stripped and processed. This feels like a pretty small quarry mine on earth. Given that, it feels like it would probably be worth shipping the materials one would need to operate a quarry plus build the ISRU as without material environmental concerns you could process considerably more in a sustainable fashion than shipping elements from earth. The ISRU could extract all sorts of other useful materials -

Oxygen

Silicon (can be used to make plastics)

Iron

Aluminum

Magnesium

Sodium

Potassium

Phosphorus

Etc

Power would be abundant to fuel the reactions via solar radiation. So I wouldn’t write it off, I think regolith processing would be foundational for establishing any meaningful presence. Likely it can be entirely automated as well.

My impression was that it's mostly about particle pressure and 100% O_2 at 0.2 atmospheres would also be possible. ISS keeps with the normal atmospheric pressure and 80% nitrogen but from what one reads on the internet, that is more for compatibility reasons and not because we humans cannot sustain a pure oxygen, low pressure environment, once you go all in (and stay there for prolonged times).

A 100% O2 atmosphere would produce oxygen toxicity in the human body. Plus, it would create a huge fire hazard.

Now, it's possible that we could be ok with a gas mix that's different from the traditional 21% oxygen 78% nitrogen we have here. But we don't like to experiment on humans. A different gax mix would need a lot of long term testing on animals before we'd ever consider using it.

I believe you may be incorrect, the fraction is not the problem [1]. Apollo also ran with pure O2, even after an early accident under higher pressure [2].

> In such applications as extra-vehicular activity, high-fraction oxygen is non-toxic, even at breathing mixture fractions approaching 100%, because the oxygen partial pressure is not allowed to chronically exceed 0.3 bar (4.4 psi).

1. https://en.m.wikipedia.org/wiki/Oxygen_toxicity

2. https://www.popsci.com/why-did-nasa-still-use-pure-oxygen-af...

Is there any data about long term effects?

That's why I am writing 'at 0.2 atmospheres'! Under that condition, you do get neither any poisoning (which the internet claims appears at 1.4 atmospheres pure oxygen), nor a big fire hazard. You create other problems due to the lower air pressure like lower boiling temperature and more body heat retention but those might be engineered away... On SkyLab, astronauts supposedly experienced 75% oxygen, 25% nitrogen for upto 84 days (again at lower pressure). That's not really long term, but not short either.

100% oxygen at turned the crew of Apollo 1 into ash. It makes stuff like concrete and aluminum as flammable as wood.

That was 100% oxygen at 100% atmospheric pressure.

The lunar module was 100% oxygen at 5 PSI (atmospheric pressure is about 14 PSI.

I’m not a chemist but I think it’s not the percentage, but the number of atoms that counts.

https://history.nasa.gov/alsj/CSM08_LM_&_SLA_Overview_pp61-6...

The Apollo engineers knew this and it factored into their choice. For whatever reason not enough consideration was given to full up ground tests where the same atmosphere would be used, but at 1atm.

100 O2 at regular or reduced pressure?

You could cut this by about a third by using helium as a buffer gas. And cut it even further by reducing pressure and increasing oxygen percentage

TIL; when researching breathing gases I found "Hydrox". And yes, it's exactly what it sounds like and divers have successfully used it.

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