The fact that you are breathing in oxygen right now is proof of just how amazing our planet’s ecosystem is. Human beings, and other animals, must breathe oxygen to live. However, when they do, they turn that oxygen into carbon dioxide. And, carbon dioxide is a gas that can be harmful to animals. If there were only animals living on Earth, life would not last very long. Luckily, animals share the planet with plants. Plants use carbon dioxide, and make oxygen. This cycle is what lets animals and plants live together on Earth.

With that in mind, how can astronauts breathe in space? People have been living on the International Space Station (ISS) for almost 3 ½ years now. During this time, the astronauts have grown a few plants. However, they didn’t grow nearly enough to produce all of the oxygen needed to support two or three people. And, in space, crew members can’t just open a window to get some fresh air. So, why hasn’t the ISS run out of oxygen?

The main source of oxygen on the Space Station is a Russian system called Elektron. This system uses electricity to split water into hydrogen and oxygen gasses. The Space Station’s solar panels are used to create the electricity needed. The Space Shuttle or Russian cargo supply ships can be used to bring the needed water to ISS. Plus, the Station has systems that are used to recycle the water that is already onboard. Right now, about 98 percent of the water on the ISS is recycled. Even the small amounts of water released by the astronauts when they sweat and breathe are reused.

The oxygen created by the Elektron system is released into the air on the Station. The hydrogen that is created is vented out into space. One day, NASA hopes to install a system that would combine the hydrogen with carbon dioxide the astronauts exhale to make water. This water could then be used to make even more oxygen!

In case there is a problem with the Elektron system, the ISS also has backup supplies of oxygen. One of these backups is “perchlorate candles.” Burning perchlorate inside a metal canister creates enough oxygen for one astronaut for 1 day. There are about 100 of these candles on the Station. Plus, there is several months’ worth of oxygen in two storage tanks attached to the Station airlock.

The life support system on the Space Station has to do more than just make sure there is enough oxygen. It also has to remove other gases from the air. One of these gases is carbon dioxide. Carbon dioxide is removed from the air by a special device. It uses a material called zeolite to clean the gas from the air. The carbon dioxide is then vented into space. The ISS life support system also uses charcoal filters to remove harmful substances from the air.

Another concern is air pressure. Normal air pressure on the Space Station is 14.7 pounds per square inch (psi). This is the same as at sea level on Earth. While members of the ISS crew could stay healthy even with the pressure at a lower level, the equipment on the Station is very sensitive to pressure. If the pressure were to drop too far, it could cause problems with the Station equipment.

To prevent a drop in air pressure, extra nitrogen gas is kept on the ISS. The nitrogen is often used to keep the air pressure on the Station at safe levels. This system had to be used earlier this year. It was used to restore air pressure when a leak formed in a hose in the Destiny Laboratory Module. The leak caused air pressure on the Station to drop to 14.0 psi. Luckily, the Expedition 8 crew was able to find the leak and fix it.

On Earth, we rarely think about breathing. And, we hardly ever think about the complex ecosystem that is working to make it possible. Just like the Earth’s atmosphere, the ISS life support system has many different complicated parts. And, all of them must work together perfectly. But, thanks to advanced technology and extra backup systems, astronauts living in space don’t have to worry about their next breath of air.