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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.
 Right:
A dune-covered desert planet in our own solar system. [More]
"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
Station, today.
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 regenerative system.
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.
Above:
Stepping-stone to the stars. Regenerative ECLSS will get a
field test onboard the ISS. [More]
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).
Right:
ECLSS hardware. [More]
 The
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,"
Bagdigian adds.
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.
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Author: Trudy E.
Bell | Editor:
Dr. Tony Phillips | Credit: Science@NASA
| More
to the story... |
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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
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