Water on the
Space Station
NASA
Science News
Rationing and recycling will be an
essential part of life on the International Space
Station. In this article, Science@NASA explores where
the crew will get their water and how they will (re)use
it.
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to this story (requires RealPlayer)
November
2, 2000 -- Future astronauts poised to blast off for an
extended stay on the International Space Station (ISS)
might first consider dashing to the restroom for a quick
splash at the lavatory, or better yet, a luxurious hot
shower. Once on board the ISS, spacefarers are in for a
steady diet of sponge baths using water distilled from
-- among other places -- their crewmates breath!
If you're squeamish, read no farther,
because the crew will eventually include lab rodents --
and they'll be breathing, too. All of the denizens of
the space station lose water when they exhale or sweat.
Such vapors add to the ambient cabin humidity, which is
eventually condensed and returned to the general water
supply.
Sometimes it's better not to think
about where your next glass of water is coming from!
Rationing and recycling will be an
essential part of daily life on the ISS. In orbit, where
Earth's natural life support system is missing, the
Space Station itself has to provide abundant power,
clean water, and breathable air at the right temperature
and humidity -- 24 hours a day, 7 days a week,
indefinitely. Nothing can go to waste.
In this article, the first of a series
about the practical challenges of living in space,
Science@NASA will examine how the Space Station's
Environmental Control and Life Support System (ECLSS),
under continuing development at the Marshall Space
Flight Center, will help astronauts use and re-use their
precious supplies of water. Future installments will
explore air management, thermal control and fire
suppression -- in short, all of the things that will
make the Space Station comfortable and safe.
Making a Splash in Space
Before recycling can begin, there has
to be some water to start with.
"We
have plenty of water on the Space Station now,"
says Jim Reuter, leader of the ECLSS group at the
Marshall Space Flight Center. "The Russian module
Zarya is packed with contingency water containers (CWCs)
that were carried over from the Space Shuttle during
assembly missions earlier this year. They look like
duffle bags and each one holds about 90 lbs."
"But it's expensive to ferry
water from Earth," he added. "We have to
recycle. There's already a Russian-built water processor
in orbit that collects humidity from the air. Here at
Marshall we're building a regenerative system that will
be able to recycle almost every drop of water on the
station and support a crew of seven with minimal
resupplies."
Right: Shuttle pilot Terry
Wilcutt during STS-76 with 7 contingency water
containers destined then for the space station Mir.
The ECLSS Water Recycling System (WRS),
developed at the MSFC, will reclaim waste waters from
the Space Shuttle's fuel cells, from urine, from oral
hygiene and hand washing, and by condensing humidity
from the air. Without such careful recycling 40,000
pounds per year of water from Earth would be required to
resupply a minimum of four crewmembers for the life of
the station.
Not even research animals are excused
from the program.
"Lab animals on the ISS breath
and urinate, too, and we plan to reclaim their waste
products along with the crew's. A full complement of 72
rats would equal about one human in terms of water
reclamation," says Layne Carter, a water-processing
specialist at the MSFC.
It might sound disgusting, but water
leaving the space station's purification machines will
be cleaner than what most of us drink on Earth.
"The water that we generate is
much cleaner than anything you'll ever get out of any
tap in the United States," says Carter. "We
certainly do a much more aggressive treatment process
(than municipal waste water treatment plants). We have
practically ultra-pure water by the time our water's
finished."
Mimicking Mother Earth
On Earth, water that passes through
animals' bodies is made fresh again by natural
processes. Microbes in the soil break down urea and
convert it to a form that plants can absorb and use to
build new plant tissue. The granular soil also acts as a
physical filter. Bits of clay cling to nutrients in
urine electrostatically, purifying the water and
providing nutrients for plants.
Water excreted by animals also
evaporates into the atmosphere and rains back down to
the Earth as fresh water -- a natural form of
distillation.
Above: When water
evaporates from the ocean and surface waters, it leaves
behind impurities. In the absence of air pollution,
nearly pure water falls back to the ground as
precipitation.
Water purification machines on the ISS
partly mimic these processes, but they do not rely on
microbes or any other living things.
"While you try to mimic what's
happening on Earth -- which is so complicated if you
really think about it -- we have to use systems that we
can control 100 percent," said Monsi Roman, chief
microbiologist for the ECLSS project at MSFC. ECLSS
depends on machines -- not microbes -- because, "if
a machine breaks, you can fix it."
The water purification machines on the
ISS will cleanse wastewater in a three-step process.
The first step is a filter that
removes particles and debris. Then the water passes
through the "multi-filtration beds," which
contain substances that remove organic and inorganic
impurities. And finally, the "catalytic oxidation
reactor" removes volatile organic compounds and
kills bacteria and viruses.
Every Drop Counts
Once the water is purified, astronauts
will do everything possible to use it efficiently.
"On the ground, people flick on the faucet and they
probably waste a couple of liters of water just because
it's free and the water pressure is high," notes
Carter.
"On the ISS, the water pressure
will be about half what you might experience in a
typical household," Carter said. "We don't use
faucets on the ISS, we use a wash cloth. It's much more
efficient. If you're an astronaut, you'll wet the wash
cloth with a spray nozzle and then use the cloth to wash
your hands."
On the space station, people will wash
their hands with less than one-tenth the water that
people typically use on Earth. Instead of consuming 50
liters to take a shower, which is typical on Earth,
denizens of the ISS will use less than 4 liters to
bathe.
Even with intense conservation and
recycling efforts, the Space Station will gradually lose
water because of inefficiencies in the life support
system.
"We
will always need resupply, because none of the water
reprocessing technology that is available right now for
space flight ... is 100 percent efficient. So
there's always some minimal loss," said Marybeth
Edeen, deputy assistant manager of environmental control
and life support at NASA's Johnson Space Center.
Water is lost by the Space Station in
several ways: the water recycling systems produce a
small amount of unusable brine; the oxygen-generating
system consumes water; air that's lost in the air locks
takes humidity with it; and the CO2 removal systems
leach some water out of the air, to name a few.
Above: One of the
"nodes" that will become a part of the Space
Station. The ECLSS life support equipment will be housed
in Node 3, which is scheduled to be attached to the
station in October 2005.
Lost water will be replaced by
carrying it over from the Shuttle or from the Russian
Progress rocket. The Shuttle produces water as its fuel
cells combine hydrogen and oxygen to create electricity,
and the Progress rocket can be outfitted to carry large
containers of water.
NASA scientists will continue to look
for ways to improve the life support systems of the
Space Station, reducing water losses and finding ways to
reuse other waste products. If the water recycling
systems can be improved to an efficiency of greater than
about 95 percent, then the water contained in the
Station's food supply would be enough to replace the
lost water, Edeen said.
"It takes processes that are
slightly more efficient than we have developed for the
space station to do that," Edeen said. "Those
are the next generation water processing
systems. Those are being developed now, but they're
not ready for space flight yet."
The ECLSS life support system will
join the Space Station as part of Node 3, which is
scheduled to launch in October 2005. Until then, the
environment inside the ISS will be maintained primarily
by life support systems on the Russian Zvezda Service
Module.
Related Links
International
Space Station -- NASA's Web page for the
International Space Station
Wheels
in the Sky -- Science@NASA article about
humanity's dreams of a space station from the science
fiction fantasies of the Nineteenth Century to Wernher
von Braun's catalytic vision in the 1950s
Advanced
Life Support Web Page -- from the Johnson Space
Flight Center
Environmental
Control and Life Support Systems -- describes the
life support systems being developed at Marshall Space
Flight Center
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