Breathing Easy on the Space Station

Life support systems on the ISS provide oxygen, absorb carbon dioxide, and manage vaporous emissions from the astronauts themselves. It's all part of breathing easy in our home in space.

Many of us stuck on Earth wish we could join (at least temporarily) the crew aboard the International Space Station (ISS). Floating effortlessly from module to module, looking down on Earth from a breathtaking height of 350 kilometres.... It's a dream come true for innumerable space lovers.

But be careful what you wish for! Living on the Space Station also means hard work, cramped quarters, and... what's that smell? Probably more outgassing from a scientific experiment or, worse yet, a crewmate.

With 3 to 7 people sharing a small enclosed volume on the still-growing Space Station, air management is critical.

Life support systems on the ISS must not only supply oxygen and remove carbon dioxide from the cabin's atmosphere, but also prevent gases like ammonia and acetone, which people emit in small quantities, from accumulating. Vaporous chemicals from science experiments are a potential hazard, too, if they combine in unforeseen ways with other elements in the air supply.

So, while air in space is undeniably rare, managing it is no small problem for ISS life support engineers.

Making oxygen from water

NASA An artist's rendering of the ISS

Most people can survive only a couple of minutes without oxygen, and low concentrations of oxygen can cause fatigue and blackouts.

To ensure the safety of the crew, the ISS will have redundant supplies of that essential gas.

"The primary source of oxygen will be water electrolysis, followed by O₂ in a pressurised storage tank," said Jay Perry, an aerospace engineer at NASA's Marshall Space Flight Centre working on the Environmental Control and Life Support Systems (ECLSS) project. ECLSS engineers at Marshall, at the Johnson Space Centre and elsewhere are developing, improving and testing primary life support systems for the ISS.

Most of the station's oxygen will come from a process called "electrolysis," which uses electricity from the ISS solar panels to split water into hydrogen gas and oxygen gas.

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).

The oxygen that people breathe on Earth also comes from the splitting of water, but it's not a mechanical process. Plants, algae, cyanobacteria and phytoplankton all split water molecules as part of photosynthesis -- the process that converts sunlight, carbon dioxide and water into sugars for food. The hydrogen is used for making sugars, and the oxygen is released into the atmosphere.