When you're on a camping trip, you might have to pack your own food and maybe something to filter or treat water that you find. But imagine your campsite is in space, where there's no water, and packing jugs of water would take up room when every inch of cargo space counts. That's a key challenge engineers faced when designing the International Space Station .
Author
- Berrin Tansel
Professor of Civil and Environmental Engineering, Florida International University
Before NASA developed an advanced water recycling system, water made up nearly half the payload of shuttles traveling to the ISS. I am an environmental engineer and have conducted research at Kennedy Space Center's Space Life Sciences Laboratory. As part of this work, I helped to develop a closed-loop water recovery system.
Today, NASA recovers over 90% of the water used in space. Clean water keeps an astronaut crew hydrated, hygienic and fed, as it can use it to rehydrate food. Recovering used water is a cornerstone of closed-loop life support , which is essential for future lunar bases, Mars missions and even potential space settlements.
NASA's environmental control and life support system is a set of equipment and processes that perform several functions to manage air and water quality, waste, atmospheric pressure and emergency response systems such as fire detection and suppression. The water recovery system − one component of environmental control and life support − supports the astronauts aboard the ISS and plays a central role in water recycling.
Water systems built for microgravity
In microgravity environments like the ISS , every form of water available is valuable. The water recovery systems on the ISS collect water from several sources, including urine, moisture in cabin air, and hygiene - meaning from activities such as brushing teeth.
On Earth, wastewater includes various types of water: residential wastewater from sinks, showers and toilets; industrial wastewater from factories and manufacturing processes; and agricultural runoff, which contains fertilizers and pesticides.
In space, astronaut wastewater is much more concentrated than Earth-based wastewater. It contains significantly higher levels of urea - a compound from urine - salts, and surfactants from soaps and materials used for hygiene. To make the water safe to drink, the system needs to remove all of these quickly and effectively.
The water recovery systems used in space employ some of the same principles as Earth-based water treatment . However, they are specifically engineered to function in microgravity with minimal maintenance. These systems also must operate for months or even years without the need for replacement parts or hands-on intervention.
NASA's water recovery system captures and recycles nearly all forms of water used or generated aboard the space station. It routes the collected wastewater to a system called the water processor assembly, where it is purified into safe, potable water that exceeds many Earth-based drinking water standards .
The water recovery and treatment system on the ISS consists of several subsystems .
Recovering water from urine and sweat
The urine processor assembly recovers about 75% of the water from urine by heating and vacuum compression. The recovered water is sent to the water processor assembly for further treatment. The remaining liquid, called brine, still contains a significant amount of water. So, NASA developed a brine processor assembly system to extract the final fraction of water from this urine brine.
In the brine processor assembly, warm, dry air evaporates water from the leftover brine. A filter separates the contaminants from the water vapor, and the water vapor is collected to become drinking water. This innovation pushed the water recovery system's overall water recovery rate to an impressive 98% . The remaining 2% is combined with the other waste generated.
The air revitalization system condenses moisture from the cabin air - primarily water vapor from sweat and exhalation - into liquid water. It directs the recovered water to the water processor assembly, which treats all the collected water.
Treating recovered water
The water processor assembly's treatment process includes several steps.
First, all the recovered water goes through filters to remove suspended particles such as dust. Then, a series of filters removes salts and some of the organic contaminants, followed by a chemical process called catalytic oxidation that uses heat and oxygen to break down the remaining organic compounds. The final step is adding iodine to the water to prevent microbial growth while it is stored.
The output is potable water - often cleaner than municipal tap water on Earth .
Getting to Mars and beyond
To make human missions to Mars possible, NASA has estimated that spacecraft must reclaim at least 98% of the water used on board. While self-sustaining travel to Mars is still a few years away, the new brine processor on the ISS has increased the water recovery rate enough that this 98% goal is now in reach . However, more work is needed to develop a compact system that can be used in a space ship.
The journey to Mars is complex , not just because of the distance involved, but because Mars and Earth are constantly moving in their respective orbits around the Sun.
The distance between the two planets varies depending on their positions. On average, they're about 140 million miles (225 million km) apart, with the shortest theoretical approach, when the two planets' orbits bring them close together, taking 33.9 million miles (54.6 million km).
A typical crewed mission is expected to take about nine months one way. A round-trip mission to Mars, including surface operations and return trajectory planning, could take around three years. In addition, launch windows occur only every 26 months, when Earth and Mars align favorably.
As NASA prepares to send humans on multiyear expeditions to the red planet, space agencies around the world continue to focus on improving propulsion and perfecting life support systems. Advances in closed-loop systems, robotic support and autonomous operations are all inching the dream of putting humans on Mars closer to reality.
Berrin Tansel does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
