Where does oxygen for astronauts come from? Are we just constantly sending rockets with tanks of oxygen up to the ISS?


Where does oxygen for astronauts come from? Are we just constantly sending rockets with tanks of oxygen up to the ISS?

In: 42

Water. Electrolysis is used to split hydrogen from oxygen. Hydrogen is useful fuel, oxygen is breathable air.

It’s pretty self sufficient. There’s no way they could keep running up everything they need constantly so the ISS recycles a lot.

Oxygen can be made through electrolysis. This is where using electricity you can turn water into oxygen and hydrogen. The hydrogen can then be combined with the carbon dioxide the astronauts breathe out to turn back into water…… and some methane.

The air filtration systems remove the moisture from the air (from the astronauts breathing and sweating) and recycle it for either drinking or turning into air.

Water is also reclaimed from the waste that the astronauts produce. Shower water is also reclaimed.

This severely limits any resupply runs they may need.

Mostly by passing electricity through water. When done properly, this will split the water molecules into hydrogen and oxygen, in a process called electrolysis.

So where do they get the water? Some of it is sent up by supply missions, but a lot of it comes from recycling and purifying waste water, including urine and sweat.

That is almost what is done. What is launched to ISS is water that is split into oxygen and hydrogen by electrolysis with power from the solar cells.


It is not just new water that is split but also urine, sweat, and moisture that is breath out are clean and recycled. In our metabolism, we use oxygen both to create carbon dioxide and water so some of the recycled water oxygen comes from the air that is breathed in.


The reason water is launched and not pure oxygen is that is simpler and lighter to store.

Liquid oxygen needs to be cooler than −182.96 °C; −297.33 °F so you need a complex, heavy, and energy-consuming cooling system to do that.

The density of oxygen as gas is quite low so you need high pressure to store a significant amount. High pressure means you need a tank that can handle that and they are heavy. It is not just weight that is a limit when you launch stuff to space, volume is another limitation

Both will expand in volume if heated up or released from a tank, which is a potential hazard in a confined environment like ISS

Liquid water is simple to store and can have the same temperature as is maintained for the crew. Water is 88% oxygen by weight.

The result is launching water is the most cost-efficient, simple, and safest way to deliver oxygen there.

Ther are tanks with pressurized oxygen gas on ISS. So you have a buffet for the produced oxygen and as a backup if there is a problem with the electrolysis. So you might have oxygen for a week stored so you can fix the problem in the electrolysis equipment and in the case of the work leave the station without needing to rush it.

Air is like a recipe. It can be made by other things like water!

Water also is a bit of a recipe and, as it turns out, up in space they constantly clean it up and re-use it. A portion of that water gets cooked up along with funky things like what the astronauts breath out and then a cool machine can turn that into more air!

This machine also removes funky things that the astronauts don’t want to be breathing in or taking in, just like the fan over an oven takes away yucky things like smoke.

And just like this a bit of a water goes a long way up in space to be drank or cooked up to create more air! (Called by adults “Oxygen”)

Now, keep on dreaming young one! 👨‍🚀👩‍🚀