When a small, six-wheeled rover, no heavier than a bowling ball, rolls onto an ancient flood plain of Mars in 1997 to begin studying the parched and rocky landscape, its delicate electronics will be protected by a novel substance -- not new -- but never before used to keep a rover warm.
The material is called "aerogel" and it was first developed in the 1930s for scientific experiments. But aerogel is making its true debut now, 60 years later, as a substance with practical applications in the space program and, potentially, in the commercial marketplace.
Dr. Peter Tsou of the Jet Propulsion Laboratory began working with aerogel several years ago and came up with a form that could be flown on space shuttles to capture cosmic dust, microscopically small particles present in outer space, which is the centerpiece of his research.
"The substance is incredibly resilient in the space environment and it has proven to be an effective temperature shield," he said. "Aerogel is able to protect against heat and cold, but it cannot be frozen or destroyed by extremely hot temperatures. In fact, aerogel is not be affected by temperatures of less than 1,400 degrees Celsius (2,522 degrees Fahrenheit)."
This nearly weightless substance -- made from silicon dioxide -- is a form of sand and is now manufactured in Tsou's JPL laboratory. But by using the material for things other than capturing cosmic dust, Tsou quickly discovered that he could accomplish great feats.
Almost coincidentally and at his colleagues' request, Tsou went to work this year on a brand new application: outfitting the Mars Pathfinder rover with aerogel to replace the standard thermal insulation that had been proposed. Once he had developed the right form, Tsou was able to significantly reduce the rover's mass by more than 2.6 kilograms -- nearly six pounds or 20 percent of the rover's weight. That weight loss will cut the costs of the Pathfinder mission significantly.
The rover's previous insulation was also a form of silica, but powdered so that it required a special honeycomb structure to hold it in place, Tsou said. The honeycomb, which added much of the weight, was made of a substance like fiber paper. Because of all of the rover's electronic cabling, there are still heat leaks inside the bus which required electric power to protect the instruments.
The rover is part of the Mars Pathfinder mission, which is designed to place a small lander and rover on Mars in July 1997, following a December 1996 launch. When the lander spacecraft arrives at Mars, it will directly enter the Martian atmosphere and drop to the surface with the aid of parachutes and large balloons to soften its landing.
The aerogel being developed for Mars Pathfinder has some surprising properties, according to Tsou. It is somewhat like glass in that it is made of silica, and it has about the same melting point. Normal levels of coldness will not disturb the gel, nor will water. Tsou's strangely fluorescent form of the substance will fioat on water without absorbing moisture--the only form available that can make that claim
Aerogels can, however, absorb very large amounts of gas, because they are very porous. This porosity gives the substance a remarkable surface area. A cubic centimeter of aerogel -- about a quarter of the size of an average sugar lump -- has an effective surface area of 50 square meters.
Along with this capability, aerogel is also the lowest density solid material known in the world, according to Tsou. The aerogel used in his experiments has a density of 15 milligrams (.015 grams) per cubic centimeter (1 gram equals 35 thousandths of an ounce.)
As a poor conductor of heat, aerogel is an ideal insulator and, like glass, is impervious to ultraviolet radiation, Tsou said. Some scientists have suggested that aerogel would make an effective building insulation in cold and hot climates if placed between layers of window glass. But because aerogel is not entirely transparent, it would produce a frosted or smoky blue look.
Tsou will continue to use aerogel for his primary research project - capturing cosmic dust in space, including an experiment due to be sent to the Russian Mir space station in November -- but he has identified several other scientific and space applications. In additon, a host of investigators are now seeking commercial applications for this nearly weightless, translucent material. Possibilities include use as insulation for refrigerators and security safes, filters in advanced automobile catalytic converters and high-efficiency battery electrodes.
Tsou's work at the Jet Propulsion Laboratory is performed under contract to the Solar System Exploration Division of NASA's Office of Space Science, Washington D.C.
(Note to Editors: A color photograph of the Mars Pathfinder aerogel is available by contacting the IPL Public Information Office at 818-354-5011.)
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