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


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


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.