Water is one of the most crucial provisions an astronaut will need to live and work in space. Whether orbiting Earth, working at a lunar base, or traveling to Mars, astronauts must save as much water as possible. On the International Space Station, each crewmember is allocated about two liters of water daily. Such conservation means the crew must stretch the ration by collecting, cleaning, and reusing wastewater, condensate in the air, and urine. For future deep space missions, astronauts will need even greater amounts of water. To help them save this precious commodity, research engineers at NASA's Ames Research Center in California are following several different but complementary avenues to develop dependable ways of recycling water.
Forward osmosis is a technology that has been around since the 1960s, and in use as a water recycling system since the late 1990s or early 2000s. In the design of Sustainability Base, a 50,000-square-foot, lunar-shaped building at Ames, NASA innovations originally engineered for space travel and exploration are providing a showcase for NASA technology and an evolving exemplar for the future of buildings.
As part of Sustainability Base's design, NASA researchers installed a new forward osmosis water recovery system in the building. This system, in combination with other water-saving technologies integrated into the building, is expected to reduce water consumption in Sustainability Base by more than 90 percent.
Designed by scientists for use on the International Space Station, the system cleans greywater (water that drains from the bathroom sinks and showers) and then recycles it in the building to flush toilets and urinals. The system is an example of NASA technology that both benefits Sustainability Base immediately, and also allows the building to be a testbed to perfect the technology.
According to NASA Ames engineer Michael Flynn, the system is one of the first larger-scale forward osmosis systems that has been developed. “It uses a membrane-based system. There are a couple things that prevent terrestrial water recycling. One is the need to have double plumbing in the building, meaning that you collect, for instance, hygiene water and water from the toilet separately. Water from the toilet, of course, poses a human health issue, so you don't really want to recycle that directly into potable water.”
The greywater is not inherently hazardous, so it's a good source to treat for water recycling. But to do that, explains Flynn, “you need to have basically a new building. You need to have two sets of plumbing. What NASA brings to the table that’s really unique is the ability to make water recycling technologies very, very small, and fully automated. So the idea is that you could take a water recycling system and put it into an existing building by just simply putting it under the counter area in the bathroom, or putting it in a closet outside of the bathroom. It doesn't require new construction.”
Construction of the first-generation forward osmosis secondary treatment system (FOST) was recently completed at NASA Ames. The system was recently shipped to NASA's Johnson Space Center in Houston to undergo integrated testing with the membrane-aerated bioreactor. That system is a smaller version of the one in Sustainability Base, and is sized to support a crew of four on a long-duration space flight mission.
The Water Wall
The Water Wall concept is a new direction for NASA life support systems. Said Flynn, “It comes from the fact that spaceflight is very expensive and we need to take measures to reduce the cost. One of the ways to reduce the cost from a life support perspective is, of course, to not have a life support system. Now that is impossible -- you need to keep the astronauts alive -- but by combining different functions, one can get as close to that as possible. The mass that would be required for water recycling can be combined with other functions to produce a total system that has little overall mass.”
The Water Wall approach does that based on the need to have radiation protection. On a mission to Mars, astronauts will receive a very high radiation dose. Mitigation measures need to be taken in order to prevent that from happening. One of he ways to do that is to provide a water layer around the outside of the spacecraft that would absorb the radiation. The other way is a polyethylene liner around the outside of the spacecraft.
“If they're using the water, it could only be used for life support functions,” said Flynn. “The simplest idea is that it could be a storage tank where your fresh water comes from. A little more complicated would be a storage tank with another section on it that would be where all the wastewater went. So you would need a wastewater tank and a storage tank.”
According to Flynn, NASA has developed technologies that actually put a membrane between those two layers and allow the dirty water to turn into fresh water. “We can create a situation where the tanks are just continually recycling each other. And we can also do that with solid waste treatment and with air revitalization, carbon dioxide sequestration, and thermal control. We can take all those functions and integrate them into this radiation protection Water Wall liner,” Flynn explained.
“If you can use that liner to do your life support function,” said Flynn, “then you can conceivably greatly reduce the mass required for providing life support. And that's the basic concept of the Water Wall approach. Current NASA technologies are mechanically complex. There are machines that recycle water; they have gears and motors. The Water Wall concept is a much more inherently passive approach, so it should also provide a much higher level of reliability, redundancy, and backups. And for a Mars mission that might take 600 to 900 days, that reliability is a big plus because if the life support systems fail on a mission like that, it could cost people their lives.”
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