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Sci-fi Life Support
Oct. 30, 2006: In Frank Herbert's epic ecological novel Dune (1965), set
on the fictitious desert planet Arrakis in another star system, water is
so precious that even perspiration and breath moisture are captured and
purified for drinking.
On real-life voyages to the Moon and Mars, science fact may end up
imitating science fiction. Indeed, scientists and engineers at NASA's
Marshall Space Flight Center (MSFC) are putting the finishing touches on
systems for capturing exhaled carbon dioxide and urine and turning them
into breathable oxygen and drinking water.
"Early space missions—Mercury, Gemini, Apollo—took with them all the
water and oxygen they needed and discarded liquid and gaseous wastes
into space," explains Robert Bagdigian of the MSFC. In short, the
astronauts' life-support systems were "open-loop"—meaning they relied on
resupply from Earth, something still true for the International Space
But for any long-duration missions to the Moon or Mars, "it makes sense
to close the loop"—that is, to recycle air and waste water instead of
just discarding them. Soon the ISS will be testing just such a
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The name of the project is Environmental Control and Life Support
Systems--better known by its acronym ECLSS (pronounced"EE-cliss").
Bagdigian is the ECLSS project manager.
"The Russians are ahead of us," says Robyn Carrasquillo, engineering
manager for ECLSS. "The original Salyut and Mir spacecraft were able to
condense humidity right out of the air and use electrolysis—an electric
current run through the water—to produce oxygen for breathing." NASA's
new regenerative ECLSS, to be launched to ISS in 2008, goes further: "it
can recover urine in addition to humidity."
Urine recovery is an engineering challenge: "Urine is so much dirtier
than ordinary humidity," Carrasquillo explains. "It can corrode hardware
and clog hoses." ECLSS uses a purification process called vapor
compression distillation: urine is boiled until the water in it turns to
steam. The steam—essentially clean water vapor except for some traces of
ammonia and other gases—rises into a distillation chamber, leaving
behind a concentrated brown soup of impurities and salts that
Carrasquillo charitably calls "brine" (which is discarded). The steam is
cooled and condenses back into liquid. This steam distillate is then
mixed with the humidity condensate, and the water further purified to
become potable. ECLSS can recover 100 percent of moisture in the air,
and 85 percent of the water in urine, resulting in a net overall
recovery efficiency of about 93 percent.
Stepping-stone to the stars. Regenerative ECLSS will get a field test
onboard the ISS
That's how it works on Earth. In space, there's an additional challenge:
"steam doesn't rise." Buoyancy requires gravity, and in the microgravity
of a spaceship, steam just "sits there." It doesn't rise naturally into
the distillation chamber. So in the version of ECLSS being completed at
Marshall for ISS, "we spin the entire distillation system to create
artificial gravity to separate the steam from the brine," says Carrasquillo.
Moreover, in microgravity human hairs, skin cells, lint, and other
impurities float around in the air instead of falling to the floor.
Thus, the processor requires an impressive filtration system. When clean
water emerges at the end, iodine is added to retard the growth of
microbes (chlorine, used to purify water on Earth, is too reactive and
hazardous to store and handle in space).
ECLSS hardwareThe regenerative water recovery system for ISS, weighing
about a ton and a half, will "produce half a gallon an hour, more than
the current of crew three needs," Carrasquillo says. "This will enable
the space station to support a total of six astronauts continuously."
The system is designed to produce potable water "meeting purity
standards better than most municipal water systems on the ground,"
In addition to providing drinking water for the crew, the water recovery
system will supply water to the other half of ECLSS: the oxygen
generation system (OGS). The OGS operates by electrolysis. It splits
water molecules into oxygen for breathing and hydrogen, which is vented
outside the spacecraft. "The air loop needs pretty clean water, so the
electrolyte cells don't get contaminated and foul," Bagdigian points out.
"Regeneration is far more cost-effective than resupplying the station
with water from Earth," Carrasquillo says, especially after the space
shuttle is retired in 2010.
Recycling up to 93 percent wastewater is impressive. But for missions of
months or years to the Moon or Mars, some later version of ECLSS must
achieve closer to 100 percent efficiency.
Then, astronauts would be ready to survive on our own solar system's
versions of Dune.
ECLSS in Iraq--Since April 2006, an Earth-bound application of a portion
of the ECLSS water recovery system has been being trucked from one rural
village to another in northern Iraq to filter particulates and
contaminants out of dirty groundwater or well water to provide residents
with clean drinking water. That portable system—about half the size of a
refrigerator including all its pumps and computer controls—purifies
water at a good clip of 4 gallons a minute, for a cost of only about two
cents a gallon.
Technical details of ECLSS appear in "Status of the Regenerative ECLSS
Water Recovery and Oxygen Generation Systems" by Robert M. Bagdigian,
Dale Cloud, and John Bedard (Paper 2006-01-2057) and in NASA Facts
"International Space Station Environmental Control and Life Support
System" (Pub 8-40399, May 2005).
ECLSS fact sheet
The Vision for Space Exploration