system
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human
ELI5: How does the International Space Station have enough oxygen for all the astronauts?

How does NASA calculate the amount required? What happens in case of a leak? Do they refuel it every trip there? If that is true how come we can't setup multiple ISSs on the way to reach further into space?
gpt
**How does NASA calculate the amount required?**
Decades of research by the Russians and Americans (Skylab / Salyut)

**What happens in case of a leak?**
They generate it on board from water and backup solid candles, also the ISS is pretty air tight. It has to be.

**how come we can't setup multiple ISSs on the way to reach further into space?**
It would be hugely inefficient to have multiple stations in Earth Orbit, one big one would do.  Better off with things like Lunar bases.