http://stardust.jpl.nasa.gov/tech/aerogel.htmlAerogel Quick Facts
It is 99.8% Air
Provides 39 times more insulating than the best fiberglass insulation
Is 1,000 times less dense than glass
Was used on the Mars Pathfinder rover
Catching Comet Dust
Particle Captured in Aerogel
The primary objective of the Stardust mission is to capture both cometary samples and interstellar dust. Main challenges to accomplishing this successfully involve slowing down the particles from their high velocity with minimal heating or other effects that would cause their physical alteration. When the Stardust Spacecraft encounters the Comet Wild 2, the impact velocity of the particles will be up to 6 times the speed of a rifle bullet. Although the captured particles will each be smaller than a grain of sand, high-speed capture could alter their shape and chemical composition - or even vaporize them entirely.
To collect particles without damaging them, Stardust uses an extraordinary substance called aerogel. This 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, which is another silicon-based solid. When a particle 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. Since aerogel is mostly transparent - with a distinctive smoky blue cast - scientists will use these tracks to find the tiny particles.
Aerogel Capabilities
Aerogel is not like conventional foams, but is a special porous material with extreme microporosity on a micron scale. It is composed of individual features only a few nanometers in size. These are linked in a highly porous dendritic-like structure.
Crayons On Aerogel
Over A Flame
This exotic substance has many unusual properties, such as low thermal conductivity, refractive index and sound speed - in addition to its exceptional ability to capture fast moving dust. Aerogel is made by high temperature and pressure-critical-point drying of a gel composed of colloidal silica structural units filled with solvents. Aerogel was prepared and flight qualified at the Jet Propulsion Laboratory (JPL). JPL also produced aerogel for the Mars Pathfinder and Stardust missions, which possesses well-controlled properties and purity. This particular JPL-made silica aerogel approaches the density of air. It is strong and easily survives launch and space environments. JPL aerogel capture experiments have flown previously and been recovered on Shuttle flights, Spacelab II and Eureca.
"Tennis Racket" Shaped Collector
Aerogel Dust Collector
Under Construction
The aerogel aboard the Stardust Spacecraft is fitted into a "tennis racket" shaped collector. This is unfolded from the protective Sample Return Capsule to expose it to space during flight. One side of the collector will be faced towards the particles in Comet Wild 2, while the reverse, or B side, will be turned to face the streams of interstellar dust encountered during its journey.
When hypervelocity particles are captured in aerogel they produce narrow cone-shaped tracks that are hollow, and can easily be seen in the highly transparent aerogel by using a stereomicroscope. This cone is largest at the point of entry, and the particle is held intact at the point of the cone. This provides a method for determining which direction the dust came from, and is the basis of the approach of using single slabs of aerogel to collect both cometary and interstellar dust from both sides.
After the encounter with Comet Wild 2, the aerogel collector will be retracted into the Sample Return Capsule (SRC) and returned to Earth for detailed analysis by scientists at the NASAs Johnson Space Center.
Link to NY Times story Using the Right Bait to Catch a Comet
By CHRIS DIXON
Published: January 20, 2004
ASADENA, Calif. ? On Jan. 2, NASA's Stardust spacecraft flew through a 14,000-mile-an-hour hail of debris from the Wild 2 comet. Under this withering barrage, the ship's objective was not only to survive, but to use a collector made of a bizarre substance to gather an unaltered sample of five-billion-year-old dust and gas ejected by the comet.
This seemingly impossible task has been the 20-year quest of Dr. Peter Tsou, the deputy principal investigator for the Stardust. On a quiet afternoon at the Jet Propulsion Laboratory, Dr. Tsou showed off a three-centimeter cube of silica aerogel, the substance that he used to catch the comet's tail.
At around 0.003 grams per cubic centimeter of material ? only about three times as dense as air ? aerogel is pure silicon dioxide. Not only is it the least dense solid in existence, it is also such a remarkable insulator that a layer of it surrounds the most vital electronics on the Mars rover Spirit. But the most striking feature, at least to the naked eye, is that up close, the cube looks like a blurry hologram.
"When you look at this," says Dr. Tsou, holding the aerogel up, "you don't know where to focus. That's why some people call it solid smoke."
Made of 99.6 percent empty space, the little cube is indeed barely there, with a density one-hundredth that of the hand that holds it.
To make this strange material, scientists start with a liquid alcohol like ethanol and mix it with silicon dioxide to form a gel. Then, through a process called supercritical drying, the alcohol is forced out of the gel, typically with high-pressure carbon dioxide. With this drying process, the gel does not collapse or lose its volume. It appears holographic because the silicon dioxide scatters shorter wavelengths of light much like air in the daytime sky.
In the mid-1980's, Dr. Tsou ventured to the Los Alamos National Laboratory in search of a material that would allow him to collect particles moving at three to six miles per second without destroying either the particles or their collector. "I approached many scientists," he said. "They said, `Come on, that's ridiculous.' At J.P.L., we have a tech guru. I paid him to do a report, and he said, `It's not possible.' "
Dr. Tsou had considered using many thin foil layers or a polymer foam to catch the particles, but in space, radiation and temperature extremes quickly degrade foams. Because foams and foils are opaque, finding the captured interstellar particles would have been a problem.
While at Los Alamos, he said, he noticed a cube of an odd material on a laboratory windowsill. It was a form of aerogel that Los Alamos had tested and rejected for its nuclear fusion experiments.
The material was not new. In 1931, Steven S. Kistler was a pioneer in making the substance at the College of the Pacific in Stockton, Calif., now the University of the Pacific. But, Dr. Tsou said, the material was not used much, except in powdered form as a nontoxic anti-caking agent for food.
In the 1980's, Dr. Tsou and others began to work with the material. "It has 14 Guinness Book of World Records-type properties," Dr. Tsou said. "It's the lowest density of any solid, and it has the highest thermoinsulation properties. Though it would be very expensive, you could take a two- or three-bedroom house, insulate it with aerogel, and you could heat the house with a candle. But eventually the house would become too hot."
Additionally, aerogel slows soundwaves to about 10 percent of their speed in air, and because it has such a vast surface area for its volume, its use as a filtration agent could increase the capacity of desalination plants a thousandfold.
Because aerogel is transparent and releases light when struck by certain high-energy radiation, it provides an excellent means of counting atomic particles. It also has incredible compressive strength. "It can take 2,000 times its body weight without damage," Dr. Tsou said. NASA's Web site shows a 2-gram cube of aerogel (less than 0.1 ounce) supporting a 2.5-kilogram brick (about 5.5 pounds).
"It's better than anything you can think of," said Glenn Tsuyuki, a manager with the Mars rover project.
Because of its ability to keep electronics on both the 1997 Mars Pathfinder and the current rover, Spirit, at room temperature in the face of minus-100-degree cold, aerogel will probably remain the insulator of choice on Mars missions for some time, Dr. Tsuyuki said.
He added that he had proposed aerogel as the collection medium for a future flight studying dust in the upper Martian atmosphere.
"I would imagine that there are ideas out there that we haven't even thought of," he said.
Topic: Now this stuff is just too cool (Read 7219 times)