Five years of traveling through the solar system will culminate in a few minutes of glory for a comet-chasing spacecraft today.

Stardust launched from Cape Canaveral in 1999. Today, it will come within about 186 miles of the nucleus of Wild 2, but in some ways, its close encounter will mark only the halfway point of its journey.

In two years, it’s coming back to Earth, with comet dust samples packed away for analysis. They could yield clues to the start of our solar system.

“We are traveling to the very edge of the solar system, and we are traveling back in time billions of years, the time when the sun and Earth and other planets formed,” said Don Brownlee, principal investigator for the mission.

Stardust will take several dozen pictures of the nucleus of the comet. More importantly, it will sweep past Wild 2 while wielding a paddle-like dust collector. The paddle’s ingenious “aerogel” — a glassy material slightly denser than air — can collect particles traveling six times the speed of a bullet.

The collector has two sides. At times during its travels, which included a gravity-assisted slingshot boost during one of its Earth orbits, Stardust pointed one side of the collector forward. For Wild (pronounced “vilt”) 2, its other side is exposed.

Scientists can look at the path of particles through the gel to determine whether they came from the interstellar-dust side or the comet-dust side, mission manager Ed Hirst said.

The collector, which pops up from the top of the spacecraft, was deployed in late December for its encounter with the comet.

“In order to collect these particles, we have to put our spacecraft in harm’s way,” said Tom Duxbury, project manager.

During its flyby, the spacecraft is under its own control. Six minutes from its closest point, it turns so that its navigation camera is pointed toward the nucleus of Wild 2.

“This will probably be the most tense period of the mission, where the spacecraft controls itself,” Duxbury said.

After the pass, “we then immediately stow the collector back in the sample return capsule,” he said.

When Stardust hits the Utah desert on Jan. 15, 2006, its cosmic dust collector will be carried to Johnson Space Center in Houston before it’s opened again.

“From an engineering standpoint, it’s nervous time,” Allan Cheuvront said earlier this week. He’s the Stardust spacecraft engineer for Lockheed Martin Space Systems, which built the craft.

Lockheed Martin helps manage several NASA missions from Denver: Stardust, Mars Global Surveyor, Mars Odyssey, Genesis and the Spitzer Space Telescope.

Cheuvront is confident in Stardust’s success, partly because it had a dress rehearsal when it swung by asteroid Annefrank in November 2002.

“There’s nothing like doing it for real as opposed to faking something,” he said.

“We demonstrated the vast majority of the spacecraft actions as it went by, the mirror tracking and everything, even though we didn’t actually see the asteroid until we were right in close,” said Joe Vellinga, Lockheed Martin Space Systems program manager.

As for what the nucleus of Wild 2 will look like, he isn’t sure. Given pictures of similar objects taken by other missions, “it’s probably something like a potato,” Vellinga said.

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