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Ideas that Gel
February 11, 2002
The most obvious ideas are not always clear. Take aerogel for instance, a
transparent, smoky blue substance that's been especially manufactured to
bring home a piece of a comet, among other things.
This exotic substance, commonly referred to as "frozen smoke" for its hazy
appearance, has many unusual properties and can withstand extreme
temperatures. Its versatility was obscured until it got into the hands of some
NASA researchers. They saw through the haze and realized the
possibilities. The result was the development of a novel use of aerogel for
space exploration.
Much Ado About Nothing
Aerogel is a silicon-based solid with a porous, sponge-like structure in which
99.8 percent of the volume is empty space. By comparison, aerogel is 1,000
times less dense than glass, another silicon-based solid. Discovered in the
1930s by a Stanford University researcher, aerogel is the world's lightest
solid.
NASA's Jet Propulsion Laboratory in Pasadena, Calif., altered the original
recipe to come up with an exciting new way to use aerogel for space
exploration. This particular JPL-made aerogel approaches the density of air,
but it is durable and easily survives launch and space environments. JPL
used aerogel to insulate the electronics box on the Mars Pathfinder
Sojourner rover, which explored the red planet in 1997.
Strong Enough To Stop a Bullet in its Track
The Stardust mission, currently on its way to comet Wild 2 (pronounced Vilt
2), will use aerogel to encapsulate interstellar and comet dust particles and
bring samples home in 2006. When Stardust encounters the comet, the
particles will be traveling up to 6 times the speed of a rifle bullet. To collect
these delicate particles, each smaller than a grain of sand, aerogel will
gradually slow them to a stop without damaging them or altering their shape
and chemical composition.
The aerogel on Stardust was developed and manufactured at JPL. It is less
dense at the impact face where the particle encounters the aerogel and yet
has a gradually increasing density as the particle burrows deeper and slows
to a stop. This is a similar concept to the use of progressive lens in
eyeglasses.
Collecting Dust
The aerogel aboard the Stardust spacecraft is fitted into a tennis
racket-shaped collector grid. One side of the collector will face toward the
particles coming from the comet, while the reverse, or B side, will be turned
to face the streams of interstellar dust at various points in the mission's
seven year journey.
When a piece of comet dust hits the aerogel, it buries itself in the material,
creating a carrot-shaped track up to 200 times its own length. This slows it
down and brings the sample to a relatively gradual stop. After the comet
encounter, the aerogel collector will retract into a sample return capsule and
return to Earth for logging and storage by scientists at NASA's Johnson
Space Center in Houston, where research scientists throughout the world
will be able to study and analyze these unique particles.
Clear Uses of Aerogel
Because of its unique combination of physical properties--thermal,
acoustical, optical and electronic--aerogel holds incredible potential for
Earthly uses.
However, compared to other standard commercial materials, aerogel is still
rather costly. Thus, despite the fact that it would make a superior insulator
for your home or cooler, you are not likely to see it put to use as such in the
near future.
Meanwhile, researchers at JPL are working to improve on the properties
and performance of aerogel. By making aerogel more versatile, it might
become competitive as a commercial material. Until then, researchers keep
looking to the sky, anxiously awaiting the return of the smoky blue
substance, which will bring home a souvenir from space.
Aerogel Fast Facts
It is 99.8% Air
Provides 39 times more insulation than the best fiberglass insulation
Is 1,000 times less dense than glass
Was used on the Mars Pathfinder Sojourner rover
Will catch a piece of a comet on the Stardust mission
Will be used to insulate the batteries of the 2003 Mars Exploration Rovers
Source; http://www.jpl.nasa.gov/news/features.cfm?feature=490
