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Space Fills Void Aerogel Created

Material: The light, strong compound was born in the 1930s. Now extraterrestrial projects will put the 'solution waiting for a problem' to test.


Able to stop a speeding bullet! More insulating than ordinary fiberglass! So lightweight it's almost as light as air!

For some space applications, scientists can't rely on man or steel. Instead, it's aerogel to the rescue.

Sometimes called "solid smoke" because of its extraordinarily low density and the bluish cast it takes when light shines on it, aerogels once were little more than a scientific curiosity.

The material, created in the 1930s, is made of silicon dioxide, the basic material in glass. It is extremely light and strong--able to support more than 4,000 times its own weight. One variety of aerogel developed at the Jet Propulsion Laboratory holds the Guinness record for world's least dense solid, weighing in at 3 milligrams per cubic centimeter.

In addition, aerogels are excellent thermal insulators, can withstand wild temperature fluctuations and resist the effects of ultraviolet light.

"It has all these unique properties all wrapped up into one material all at once," said Steven Jones, the scientist at the Jet Propulsion Laboratory who developed the Guinness record version. "It's a solution waiting for a problem."

Space exploration has supplied the problems. The characteristics of aerogel, to take one example, make it the perfect candidate to go where no space mission has gone before: to the tail of a comet.

Stardust, an unmanned spacecraft launched in 1999, will use aerogel to capture fragile dust from the tail of Comet Wild-2 in 2004. Scientists predict the aerogel will trap particles as small as 1/50 the width of a human hair moving six times faster than a rifle bullet.

Aerogels have other uses in space exploration. Consider insulation. When engineers set out to design a rover to survey the surface of Mars, they found the machine was several kilograms too heavy. Using lightweight aerogels for the insulation solved the problem. The materials also will be used on two larger Mars vehicles that are planned.

What is it about aerogel that gives it those amazing properties?

It's a solid foam, said Sidney Perkowitz, professor at Emory University in Atlanta and author of "Universal Foam: From Cappuccino to the Cosmos" (Walker & Co., 2000).

A foam, says Perkowitz, is simply open spaces of one kind of material embedded in another material. Swiss cheese, for example, is a solid foam. Meringues and souffles also owe their light and airy textures to a foamy structure.

Foams have unique properties that are different from their individual parts, Perkowitz said. Soap suds offer an example. "Air is transparent, water is transparent," he said. "You mix both together, and light behaves differently."

Aerogels have a microscopic ''open-pore'' design, reminiscent of a sponge or a net, which makes the materials only slightly denser than air.

To make aerogels, scientists mix liquid silica with a solvent to form a Jell-O-like solid. Scientists then remove the solvent using extreme heat and pressure to preserve the gel network.

The structure of aerogel interferes with the way the substance transfers light, sound and thermal energy. Although 99% of the mass of an aerogel is made of air filling its empty pores, each individual pore is so small it prevents the air molecules within it from interacting with other molecules.

On Stardust's mission to Wild-2 (pronounced "vilt," after its Swedish discoverer), blocks of aerogel arrayed in a honeycomb-like tray on a collector shaped like a tennis racket will trap dust particles from the comet's tail. After making a couple of swings around Earth, Stardust will fly within 93 miles of Comet Wild-2 in 2004.

The aerogel will act like shrink-wrap to preserve the particles' original "fluffy" shape and chemical composition, said Peter Tsou, a deputy investigator for the project.

Each bit of dust will carve a track shaped something like a carrot into the block of aerogel, melting the material and encasing itself in a little glass shell. Other cushiony materials such as polystyrene would disintegrate into a powder when exposed to ultraviolet light in space, Tsou said.

When Stardust returns home in 2006, researchers will extract the particles for study.

Maintaining the original structure and composition is important, Tsou said, just as they are to an archeologist excavating a site. If you were a researcher, "would you prefer a chip of a vase or a bottle of atoms of a vase?" he asked.

Comets essentially are hunks of ice and rock that are left over from the solar system's formation, so analyzing the comet dust "will tell us about the start of the solar system," said Donald Brownlee, a University of Washington professor and the primary investigator of the mission.

But not just any comet dust will do.

"More importantly, we want fresh comet," Tsou said.

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