You have always dreamed of becoming an astronaut. You have studied the history of humans exploring space from the earliest days of the Soviet Cosmonauts and NASA's Mercury, Gemini and Apollo Programs. You watched the unbelievable video of men walking on the moon. You have been fascinated with each launch of NASA's space shuttles, the Russian Mir space station falling back to Earth, and the construction of the new International Space Station (ISS). This helps you to imagine yourself living and working in space - perhaps even traveling to another planet.

You did wonder what happened to the astronauts who were on the ISS when the U.S. Space Shuttles were grounded for a while in 2003. You were relieved that the three astronauts already on the ISS at that time returned on a Russian Soyuz spacecraft and a new crew of two astronauts was sent to replace them. One of the biggest concerns for the new crew was how long their food and water supplies would last before U.S. Shuttles or other vehicles carried new supplies to them. The other supply spacecrafts are smaller and cannot carry nearly as much as a Space Shuttle.

That started you thinking about how much astronauts depend on food, water, and other necessities brought up from Earth. What would happen, you wondered, on a much longer mission far away from Earth? A trip to Mars may last up to three years.-Would future astronauts run out of these supplies? How much water, for example, would they need for such a mission?

Knowing that astronauts require an average of 1.6 kg (0.4 gallons) of drinking water each day and an additional 27 kg (7.2 gallons) of water for other needs, you calculate how much water the crew would need for such a mission. Each person on a 1000-day mission to Mars would require about 28,600 kg (7729 gallons) of water and a crew of 6 would need 171,600 kg (46,378 gallons). That's enough water to fill a small swimming pool! Since each kilogram costs about $25,000 to launch into low Earth orbit and would cost much more to carry it all the way to Mars, it is very unlikely that astronauts will be able to bring this much water with them.

So what will they do? Part of the solution will be to make water from fuel cells, which combine hydrogen and oxygen to produce electricity and also make water as a by-product. Unfortunately, fuel cells will not produce nearly enough water to meet the needs of astronauts on a Mars mission. And although fresh water may exist on Mars, it's uncertain how much water is really available for astronauts to collect and use.

The solution is that future astronauts will rely on recycling, using every drop of water they have with them on their spacecraft or in their surface habitat over and over again. Water exhaled in their breath and evaporated sweat from their skin will be re-captured from the air. Hygiene water used for washing and even urine will be collected, cleaned, and reused! The difference is that here on Earth water is naturally recycled by rainfall, evaporation and the biosphere. This is called the water cycle. In space this recycling must be engineered as part of the crew's life support system using filters, scrubbers and other physical and chemical processes, as well as living plants and microbes. Not to worry though, NASA will make sure the re-cycled water is cleaner than the water you get from the faucet in your home.

The water used on the International Space Station (ISS) can be made from fuel cells. These fuel cells make electricity when they combine hydrogen and oxygen. When the atoms combine, you get electricity and H2O - water!

How can NASA clean the water on the ISS? This is done in three steps. First, the water passes through a filter. Next, layers of material remove more impurities as water moves through. Finally, a special reactor pulls out chemicals and kills bacteria and viruses. Then, the recycled water is ready.

Finally, you note with interest that NASA is using research on the ISS to help develop better ways to re-cycle the air, water, and food and that this research will enable future astronauts to venture far beyond low Earth orbit. For now, Mars will continue to wait for us to arrive. Who knows, perhaps Mars is waiting for you. Maybe your dreams are not so very far away, after all.