Picture an astronaut opening a hatch with nothing on: how do astronauts breathe in space? They do not breathe space at all. They carry or generate their own air inside pressurized cabins and suits.
On the International Space Station, that air comes from a chain of hardware: oxygen made from water, carbon dioxide removed or recycled, and suits for work outside. Those same functions define the technology needed for a mars base, and the wider picture of orbital hardware is covered in Technology In Space: How Modern Innovations Are Powering Exploration, Satellites, And Life Beyond Earth In 2026 – Decolonizemars.
Air, pressure and the suit boundary
The most common misunderstanding is that space is just very thin air. Earth’s atmosphere is 21% oxygen, but breathing needs two things at once: oxygen and surrounding pressure. A cabin or a suit has to provide both, which is why astronauts outside the station need suits to give them oxygen and air pressure.
The table below sets four everyday assumptions against what the evidence supports. Each row points to a section later in the article.
| Assumption | What is supported | Design consequence |
|---|---|---|
| Space is thin air a person could adapt to | Even with air in the lungs, low pressure in space would make that air expand and could burst the lungs | Pressure must be supplied, not only oxygen |
| Oxygen is only ever carried up in tanks | The ISS electrolyses water into hydrogen and oxygen, and the oxygen goes into the cabin atmosphere for the crew to breathe | Water becomes a breathing resource |
| Exhaled carbon dioxide is simply dumped | Hydrogen from electrolysis is combined with crew-exhaled carbon dioxide in a recycling step | Waste gas becomes a feedstock |
| Moisture from breath is lost | Humidity condensate from the crew’s breathing and sweat is collected and reprocessed | Cabin humidity feeds the water supply |
The mechanisms in the table come from Washington State University’s Ask Dr. Universe explainer and the Royal Society of Chemistry’s feature on how astronauts breathe.
Oxygen on the ISS: made from water
Every breath on a station orbiting about 250 miles above Earth at 17,500 mph depends on hardware inside the hull, according to the Royal Society of Chemistry. The central idea is that the crew’s oxygen is manufactured on board rather than only stored.
Electrolysis and the Oxygen Generation System
Oxygen production on the ISS relies on electrolysis, the process associated with the Oxygen Generation System. Electrolysis splits water into hydrogen and oxygen. The oxygen is released into the cabin atmosphere, where the crew breathes it.
What this means for planning
Because oxygen comes from water, the life support system is as much a plumbing and chemistry problem as a breathing problem. Anything that wastes water also shrinks the oxygen supply. That is why recovering water from breath and sweat sits alongside oxygen generation rather than in a separate department, and why the hydrogen left over from electrolysis has to go somewhere useful.
Carbon dioxide removal and recycling
Removing carbon dioxide is the other half of keeping cabin air breathable, and it is not a finished problem. The Royal Society of Chemistry reports that getting better at pulling carbon dioxide out of the air to improve air quality has become a NASA priority. The pieces fit together like this:
- Scrubbing and absorbents. Carbon dioxide scrubbers and absorbent materials take the gas out of cabin air. New absorbent materials have been tested in flight, which shows the technology is still being improved.
- Chemical recycling. In the Sabatier reaction, hydrogen from electrolysis is combined with the carbon dioxide the crew exhales. The products are methane and water.
- Reuse and venting. The water is reused. The methane is currently vented overboard, a visible gap in an otherwise recycling design.
For readers weighing designs, the useful judgement is that carbon dioxide handling and oxygen generation are linked. Hydrogen produced in one step is consumed in the other, so a change to either affects both. Outside the station, a different set of hardware has to do the same job in a much smaller volume.
Spacesuits as portable life support
A spacesuit is a small personal spacecraft: it gives an astronaut outside the station oxygen and air pressure. A simple mask could deliver oxygen but could not hold the body against the low-pressure environment of space, which is why the suit has to enclose the astronaut.
Reading a suit as a life support system
The station’s functions are divided between large machines, but a suit has to carry its own supply and keep the astronaut at a survivable pressure while still allowing movement. That is the practical reason suits are treated as equipment systems rather than clothing. Anyone comparing spacewalk systems should ask two questions of any design: where does the oxygen come from, and what holds the pressure.
When breathing systems fail
Life support failure is not one event. The supported evidence points to three distinct hazards: losing the oxygen supply, losing pressure, and creating an atmosphere that is itself dangerous.
- Loss of oxygen supply. On the ISS, oxygen comes from electrolysis of water, so the water loops that feed it are part of the safety case.
- Loss of pressure. A suit or cabin that cannot hold pressure exposes the lungs to the low-pressure environment described earlier.
- A hazardous atmosphere. Cabin air can be breathable and still unsafe if its composition invites fire.
The third hazard has the clearest historical record. In January 1967, three astronauts died in the Apollo 1 pre-flight cabin fire after an electrical spark ignited the 100% oxygen in the cabin. As the same account explains, in a 100% oxygen atmosphere materials that are normally non-flammable can become fuel. The lesson is that more oxygen is not automatically safer, and the gas mix is a safety decision as much as a breathing one.
From the ISS to a Mars base
The ISS is a template for a Mars base, not a ready-made answer. The same chain applies: make oxygen, remove carbon dioxide, recycle water, and protect crews in suits. The difference is how tightly the loops must close.
The Royal Society of Chemistry reports that the station’s water recycling currently loses about 10% of the water molecules each time they go through the loop. The team it describes aims for 2% for a Mars mission. Because water is the feedstock for oxygen, that gap is a direct measure of how much engineering remains.
- Water losses. Cutting per-loop loss from about 10% toward 2% is the stated target for a Mars mission.
- Carbon dioxide handling. Better removal is already a NASA priority, and venting methane is the clearest place where the current loop is not closed.
- Suits. Surface work would still require the oxygen and pressure functions described above.
The practical takeaway is to judge any Mars life support concept by its recycling losses and by how its oxygen, carbon dioxide and water loops depend on one another.
Frequently asked questions
| Question | Answer |
|---|---|
| How long has the ISS supported crews? | Its lab has been continuously occupied since November 2000, typically with three to six people on board, according to the Royal Society of Chemistry. |
| How does the station recycle water without a heat source? | A vacuum pump lowers the pressure, which drops the boiling point of the water inside, so it can boil without a heat source, as described in the same feature. |
| How was oxygen delivered in Apollo-era systems? | Pure oxygen was stored in small bottles under very high pressure, and a regulator reduced that pressure to a very low pressure a crew member can breathe, according to a public radio report. |
