How does the ISS get more oxygen? Do they have a device that can create more, or do they simply send shipments of O2?
In: Physics
They make oxygen gas from water, which is 16/18^ths oxygen by weight. Water is resupplied regularly. It requires a much lighter container than oxygen as gas or a cryogenic liquid.
The ISS produces oxygen through the **electrolysis** of water. Each molecule of water contains two hydrogen atoms and one oxygen atom. Running a current through water causes these atoms to separate and recombine as gaseous hydrogen (H2) and oxygen (O2). Hydrogen that’s leftover from splitting water will be vented into space. The electrolysis is carried out by the oxygen generators: the Russian-made Elektron and the U.S. Environmental Control and Life Support System (ECLSS).
Shouldn’t the tag be chemistry?
Here’s a [good article on the ISS oxygen generation](https://www.cnet.com/news/breathe-deep-how-the-iss-keeps-astronauts-alive/).
You can get oxygen from breaking down water (electrolysis). All you need is electricity, which is convenient in space, because electricity doesn’t have to be shipped from Earth; you can get electricity from solar panels.
Water’s H2O, so breaking down water also gives you hydrogen. You can use the hydrogen to turn CO2 into H2O and CH4 (the Sabatier reaction). This is convenient because the astronauts are all breathing out CO2.
So with the Sabatier reaction, you’re turning two waste products (hydrogen and CO2) into a valuable resource (water) and one waste product (CH4, also known as methane).
About 80% of the oxygen on the ISS is recycled, the remaining amount has to be replenished by supply ships.
As an addendum, the Perseverance rover is carrying a device to turn CO2 back into oxygen, in part as a potential upgrade for the ISS.
So in the future there may be a closed system. But right now, the water option is the simplest (produces oxygen to breathe and the hydrogen is used to process theC O2)
Only partially related, but Smarter Every Day on YT recently did a video on oxygen generation on a submarine. Very interesting. https://youtu.be/g3Ud6mHdhlQ
others have provided good information, but the ISS also has what are called “oxygen candles”, packs of chemicals that produce oxygen when burned. they are very compact and stable for an oxygen source, allowing them to be stored in individual compartments, but are saved for emergencies as burning *anything* in space is generally a bad idea.
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