July 2, 1998 It might sound like something from a popular science fiction movie, but a University of Washington astronomy professor's nearly two-decade dream of launching an unmanned spacecraft to collect interstellar dust from a comet is close to coming true.
Stardust will blast off from Cape Canaveral, Fla., in February. It will be the fourth mission in NASA's Discovery series, which captured public imagination a year ago with Mars Pathfinder. It will be the first mission since Apollo to return samples of space material to Earth for analysis.
UW professor Donald Brownlee, the principal investigator for the project, expects to find clues about the formation of the solar system and perhaps the universe itself.
"We hope to understand how comets were formed and what they're made of," he said. "We expect them to be the preserved building blocks of the outer planets." Brownlee began considering such a mission in1980. The idea was explored seriously five years later when Halley's comet approached Earth, but it was deemed unworkable then.
For Stardust's 7-year, 3.1-billion-mile journey, solar panels will power the spacecraft to encounter Wild 2, a comet that altered course in 1974 after a close encounter with Jupiter. Now instead of circling among the outer planets in our solar system, Wild 2 (pronounced vihlt 2) travels among the inner planets. It was discovered in 1978 during its first close approach to Earth.
Wild 2's recent arrival to the planetary neighborhood makes the $200 million Stardust mission possible. In 2004, the craft will pass about 75 miles from the main body of the comet. That's close enough to trap small particles from the comet's coma, the gas-and-dust envelope surrounding the nucleus. A camera built for NASA's Voyager program will transmit the first-ever close-up comet pictures back to Earth. Though the encounter will last about 12 hours, Brownlee says the really intense activity will be over in a matter of minutes.
The collection system will extend from the spacecraft and trap particles as they collide with it. To prevent damaging or altering the particles - each smaller than a grain of sand and traveling as much as nine times the speed of a bullet fired from a rifle - the collector uses a unique substance called aerogel. Often called "frozen smoke," aerogel is a transparent blue silica-based solid that is as much as 99.9 percent air. It is as smooth as glass, something like plastic foam without the lumps. A block the size of a person weighs less than a pound but can support the weight of a small car.
On the trip to Wild 2, the aerogel-equipped collection panel will be deployed to trap interstellar particles traveling in space. During the encounter with the comet, some 242 million miles from Earth, the opposite side of the panel will gather bits of comet dust. Trapped particles will leave a telltale trail through the aerogel that scientists will follow to find the grains and extract them. Upon leaving the comet, the collection panel will retract into its capsule.
Once the Stardust capsule parchutes into Utah's Great Salt Desert in 2006, the particles it collects will go to Johnson Space Center in Houston and then be parceled out to various research facilities, including the University of Washington. Because comets are about equal parts ice and dust, Brownlee believes the particles will be cryogenically preserved interstellar dust left from the birth of the solar system some 4.6 billion years ago. Such grains can be found only in the outer solar system, he believes, because heat has destroyed them nearer the Sun.
Brownlee's previous work collecting cosmic dust particles led to their being named Brownlee particles. Cosmic dust was brought back to Earth on Gemini missions in the 1960s. Later, high-flying U2 planes and balloons gathered particles from different levels in the atmosphere, and space dust even has been collected from the ocean floor. "A comet mission is the logical extension," Brownlee said.
The project is being carried out by a consortium that includes the Jet Propulsion Laboratory and Lockheed Martin Astronautics. When it came to picking a name, Brownlee said, it just seemed appropriate to select "Stardust," the title Hoagy Carmichael put on a popular tune that since has been recorded by numerous artists, including Willie Nelson and Ringo Starr.
"I liked it because most spacecraft missions had weird, bizarre names. They were acronyms for something," he said. "This isn't an acronym for anything. It's just a name that people know."
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