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Comment by notimetorelax | Hacker News Reader

There’s only one atmosphere of pressure from inside to outside. Under the sea the direction is reversed and pressure is much higher.

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Spacecraft are pressurized to much less than one atmosphere, because it reduces the stress on the craft, and the weight of the air supply.

I was curious and went to look up how low it was, and the references I can find online say that the ISS, the Space Shuttle, and the Crew Dragon are all at 1 atm.

It does say that the pressure in the Space Shuttle was decreased to about 70% atm for 24h before EVA.

Apollo was 1/3 atm 100% oxygen.

https://en.wikipedia.org/wiki/International_Space_Station

https://space.stackexchange.com/questions/5690/why-is-the-br...

https://www.google.com/search?q=pressure+inside+the+space+sh...

https://www.google.com/search?q=pressure+inside+the+apollo+c...

Likewise commercial aircraft.

This is actually a terrible idea, because to keep the air breathable you'd have to raise the oxygen fraction, making fire risk much worse. (Inert gases in air suppress fires by carrying away heat, making it harder to sustain a flame.)

People live on mountains just fine.

This exact same problem exists on mountains, which is why there are no permanent settlements above 5,100m. The Apollo pressure mentioned above (1/3rd atm) is roughly equivalent to an elevation of 8,500m, well into the "death zone" for a normal atmospheric mix.

Yes, I know about the death zone. But air pressure is significantly less in Denver, and many town are much higher.

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