From: LARRY KLAES (ljk4_at_msn.com)
Date: Fri Dec 05 2003 - 08:27:40 PST
----- Original Message -----
From: Ron Baalke - Mars Exploration Program
Sent: Wednesday, December 03, 2003 11:59 AM
To: ljk4_at_msn.com
Subject: Membranes on Mars
http://science.nasa.gov/headlines/y2003/03dec_membranes.htm
Membranes on Mars
NASA Science News
December 3, 2003
Thin membranes developed by NASA-funded researchers could
help people go to Mars--and clean the air here on Earth.
Dec. 3, 2003: The ideal technology for space travel would
be simple, robust, reliable, lightweight, and
volumetrically efficient. It would have no moving parts, which would make
it less likely to break. It would be a passive technology, not requiring
any energy from the outside. It would be small. It would be light. An
ideal technology for space, says chemical engineer Doug Way, is the
membrane.
Well, OK, membranes can't do everything. Membranes won't boost us into
space. And they won't carry us to Mars. But membranes could solve some of
the problems of traveling there. And once we arrive, they could help us
get back.
Basically, membranes are a semi-permeable barrier. They're like a wall,
except that gases, and even liquids, can seep through them. But--here's
the key point--different molecules move through membranes at different
rates. Membranes can therefore be used to sort things out, separating one
type of molecule from another.
Doug Way of the Colorado School of Mines and Lockheed
engineer Larry Mason are working on a NASA-funded project
that uses membranes to help produce rocket fuel from the
Martian atmosphere. The principle is simple: The Martian
atmosphere is 95% carbon dioxide (CO2). Using membranes,
explorers could extract some of that CO2, which when
mixed with hydrogen and then heated yields methane--a useful propellant
for rockets or rovers.
Water is a byproduct of this type of methane production, called the
Sabatier process (discovered by the French chemist Paul Sabatier in the
nineteenth century). What's more, water can be electrolyzed into oxygen,
for breathing, and hydrogen, which can be used to produce another round
of methane.
Although the Martian atmosphere is almost pure CO2, it's not pure enough
for the Sabatier process. Carbon dioxide must be separated from the other
atmospheric gases before it's processed. Otherwise unused gases--mostly
nitrogen and argon--build up, and will eventually keep the procedure from
working. Way and Mason are developing a membrane that will separate out
CO2.
The specialized polymers that make up these membranes, some of
which were developed at the Idaho National Environmental and
Engineering Laboratory, are engineered to increase carbon dioxide
solubility. "We add in groups of molecules that are polar--they carry an
electric charge," says Way. Because carbon dioxide molecules are also
polar, they're attracted to charged groups in the membrane.
The membranes are tested in a special chamber that simulates the Martian
environment, explains Larry Mason. The device, which is about a meter
high, is divided into two compartments. One contains a Mars-like
atmosphere, and the other side contains a vacuum. They?re separated by a
membrane that's about one square inch in surface area. A mass
spectrometer measures how easily each gas moves into the vacuum side.
"In the best [membrane] material we've found," says Way, "at Martian
conditions, CO2 was transferred across the membrane about 50 times faster
than nitrogen."
"Right now," adds Mason, ?we?re screening different candidate materials
to find the ones that permeate CO2 the best. Once we find that, we can
concentrate on getting enough through in an appropriate amount of time,
by changing the amount of area, packaging it, and so on."
The researchers want to design a device that produces a gas that's 99.8
percent CO2 at a rate of 2.5 liters per minute. To do that, Way says,
will require quite a bit of membrane. Although the membrane is very
thin--about 25 microns, one-quarter of the diameter of a strand of
hair--it will probably need to be about 300 square feet in area, the size
of a small room. All that will have to fit into a package of about 1
square foot.
But a membrane that separates CO2 from other gases can do more than
provide the raw material for rocket fuel. "This is fundamental
technology," says Mason. "It's got all kinds of uses."
It could, for example, be used to filter air on the space station or on a
spaceship bound for Mars. Carbon dioxide, which is a waste product of our
metabolism, must continually be removed from the atmosphere of
self-contained spacecraft. Membranes that are permeable only to carbon
dioxide would be perfect, says Mason. "The CO2 would just passively go
through the membrane into a holding chamber--or out into space. Oxygen
and other gases would stay intact inside the habitat."
These membranes could potentially help slow global
greenhouse warming, too. "There's some thought," says Mason,
"that a membrane could be used in extracting CO2 from factory smoke
stacks--reducing the amount of carbon dioxide that's dumped into the
atmosphere." Such an application still lies in the future, he says.
"The biggest potential Earth-application," adds Way, "is the removal of
CO2 from natural gas. CO2 is the most common contaminant in natural gas
besides water vapor. Membrane separations are one of the primary
processes used to filter natural gas so that it meets pipeline
specifications of less than 2% CO2." This is a big deal because "the
natural gas industry is huge--more than 100 billion dollars per year in
retail value," according to Way.
To Mason, "the most exciting part of this technology is the fact that it
may leverage us to actually go to Mars and live and work there someday."
And, in the meantime, there are plenty of uses for it right here on
Earth.
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