In the previous activity, you were introduced to the idea that air and water need to be recycled in space in order for long missions to be successful. In this activity, you will take a closer look at water and air in space.

Transporting anything to the space station is extremely expensive. And you know what’s really heavy? Water. Tanks of water can't be constantly shipped up to the International Space Station, so the station has a complex water system that squeezes every last drop of available, drinkable liquid out of the environment. That leaves astronauts drinking a filtered mixture that includes recycled shower water, old astronaut sweat, and urine. The station also keeps about 530 gallons of water in reserve in case of an emergency.

The NASA water system on the International Space Station (ISS) collects moisture from breath and sweat, urine from people and research animals, and runoff from sinks and showers to keep the station hydrated. According to Layne Carter, who manages the ISS water system, “It tastes like bottled water, as long as you can psychologically get past the point that it’s recycled urine and condensate that comes out of the air."

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The International Space Station (ISS)

While this can be done for the International Space Station, it can't be done on a long space flight. Scientists have to figure out an even better recycling system for long space flights. Water takes up a lot of space, so the more water you take, the bigger the ship has to be. The bigger the ship, the more power it takes to move it. It gets to the point where it can become impossible at this time to undertake any flights to other planets. And this is only dealing with water.

So, what about air? On Earth, we have a constant supply of fresh air. We breathe in oxygen and breathe out carbon dioxide. These gases get recycled by plants through the process of photosynthesis. The plants take in carbon dioxide and release oxygen. But what happens in the tiny, confined cabins of spacecraft, like the space shuttle or space stations?

Most spacecraft carry their own supply of oxygen with them and may have one backup system. However, the missions of these spacecraft last a short time. The International Space Station was designed for long-term spaceflight and has been in orbit since 1998. So how is oxygen made aboard the ISS? It's handled in one of three ways: using oxygen generators, pressurized oxygen tanks, or solid fuel oxygen generators (also called oxygen candles).

The primary method is accomplished by the oxygen generators: the Russian-made Elektron and the U.S. Environmental Control and Life Support System (ECLSS). These devices make oxygen from water by a process called electrolysis, during which an electric current passes through water from one positively-charged electrode, called an anode, to another negatively-charged electrode called a cathode. There's a small concentration of salt in the water to conduct electricity because water itself is a poor electrical conductor. In the process, water gets split into hydrogen gas and oxygen gas.

In the second method, oxygen is not made but rather delivered to the ISS from Earth. When space shuttles dock at the station, they pump oxygen into pressurized tanks at the airlock nodes. They also pump nitrogen gas into other pressurized tanks at those airlocks. The station's atmospheric controls mix the gases in the correct proportions to Earth's atmosphere and circulate the mixture through the cabin.

The third method is a backup system that makes oxygen through chemical reactions. The system is called the solid fuel oxygen generator (SFOG), also called oxygen candles.

In future space stations or space colonies, NASA scientists hope to create oxygen and eliminate carbon dioxide naturally by growing plants. The plants would supply breathable air and would also be a food source for the astronauts.

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Solid Fuel Oxygen Generator (SFOG)