Speeding at 24,000 mph (38,600 kph), Stardust zoomed by comet Tempel 1 on Monday night, snapping six dozen high-resolution pictures along the way. At nearest approach, the craft passed within 112 miles (180 kilometers) of the potato-shaped comet - closer than the original prediction.
Instead of erupting in cheers, mission controllers at the NASA Jet Propulsion Laboratory puzzled over why images from the flyby were not downloading in the order that they want.
NASA had planned to wow the world by playing back the images in reverse order, starting with five close-up shots of Tempel 1's nucleus. Instead, the first images to pop up on scientists' computer screens showed the comet as a tiny speck.
"We still don't understand fully why this didn't work the way we planned," said Chris Jones, an associate director at the Jet Propulsion Laboratory, which managed the mission.
On "The Early Show," co-anchor Jeff Glor reported on the spacecraft flyby. Click on the video below for his full report.}
All the flyby pictures were stored aboard Stardust. "They're not lost," Jones said.
The glitch means scientists will have to wait several more hours for everything to download to study changes on the comet's surface.
The Valentine flyby, which occurred 210 million miles (338 million kilometers) from Earth, is the second time that Tempel 1 has been visited up close.
Onboard dust detectors revealed Stardust took several hits as it swooped past Tempel 1. The craft is armed with bumpers designed to protect it from comet shards as large as half an inch.
"We made it through," said mission control commentator Mykal Lefevre, of Lockheed Martin Space Systems in Denver.
Shortly after closest approach, Stardust turned its antenna toward Earth to begin the downlink. The playback was delayed an hour due to inclement weather at a ground station in Spain.
When the close-up images didn't show up as planned, project leaders were seen pacing around mission control or huddling in groups to troubleshoot.
Space enthusiasts who stayed up all night watching the coverage streamed over the Internet by NASA grew weary and signed off from Twitter and other social networking sites after failing to get an up-close peek.
Comets are like frozen time capsules because they're thought to contain primordial material preserved from the aftermath of the solar system's birth some 4.5 billion years ago. Studying comets could yield clues to how the sun and planets formed.
The last time NASA visited Tempel 1, it ended in violence. In 2005, Deep Impact fired a copper bullet that slammed into the surface and gouged a crater. The high-speed collision spewed such a huge plume of dust that it obscured Deep Impact's view.
It was not immediately known whether Stardust photographed the Deep Impact crater.
Launched in 1999, Stardust's original destination was comet Wild 2, where it scooped up minute interstellar dust and comet grains that were later stored in a capsule and jettisoned to Earth. The $300 million mission gave scientists their first collection of comet bounty gathered in space.
Since Stardust had ample fuel after visiting Wild 2, NASA in 2007 tapped it for a $29 million fling with Tempel 1 - cheap by space mission standards.
Hours before the dalliance, two scientists who met while working on the mission got engaged. During a presentation to team members, Steve Chesley, of NASA's Near-Earth Object Program office, slipped in an extra PowerPoint slide that read: "Will you marry me?"
Jana Pittichova, of the University of Hawaii, who has imaged the comet through ground telescopes, responded by running across the room and hugging Chesley.
The ring came from - where else? - a jewelry company named Stardust.
"It's Valentine's Day. It's a Stardust ring. It's a Stardust mission," Chesley said.
Unfortunately for Stardust, its comet-chasing days are over after traveling 3.5 billion miles (5.6 billion kilometers). It has about a cup of hydrazine fuel left - not enough to visit another target.