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Comment by EuanReid | Hacker News Reader

I forget who said it, but there's a quote about how _of course_ we know more about space than the bottom of the ocean - in space we only have to deal with one atmosphere.

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>only have to deal with one atmosphere.

A difference of one atmosphere?

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

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...

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.

Likewise commercial aircraft.

The one atmosphere that telescopes are looking through. It is nowhere near as problematic as looking through seawater.

But space telescopes exist where you don't have to deal with one atmosphere.

This is about sub sea pressure where it reaches a thousand atmospheres. So a space telescope in zero atmosphere doesn't help.

Fry: "How many atmospheres can the ship withstand?" Professor: "Well, it's a spaceship, so I'd say anywhere between zero and one." s02e12

futurama comes to mind. the spacecraft can withsthand any level of atmosphere between 0 and 1

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