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Mission Accomplished: Probe Hits Comet
PASADENA, Calif. -- NASA's Deep Impact spacecraft completed a flawless journey to oblivion early today, slamming into an onrushing comet to vaporize itself in an Independence Day blaze of glory.
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Scientists and engineers at NASA's Jet Propulsion Laboratory cheered as spectacular images taken by a second "fly-by" spacecraft positioned nearby confirmed that the "impactor" had scored a perfect bull's-eye, smacking into comet Tempel 1 at its lower edge at 1:52 a.m. EDT, spewing dust and ice in a column of debris that lit up the heavens.
"Oh, my God, look at that!" shouted Donald Yeomans, an astronomer at the laboratory, as the first images were posted. "There's considerably more [debris] than I thought. It looks enormous."
The fly-by spacecraft, stationed 5,350 miles from the comet at impact, used two cameras and an infrared spectrometer to record the event and its aftermath for 13 minutes, then turned away in "shield mode" as the comet passed by only 310 miles away, traveling at a relative speed of 23,000 miles per hour.
In addition, the impactor itself carried a camera that sent back crystal-clear pictures of ridge-like features, apparent craters and sinkholes and other pockmarks that grew to dominate its field of vision as the spacecraft closed in on the comet at 6.4 miles per second. The last image was sent only three seconds before the crash.
"It was just phenomenal, we didn't have to exercise one contingency plan," said Rick Grammier, project manager of the Jet Propulsion Laboratory. "We're minus one spacecraft -- the impactor has been totally vaporized," but the fly-by spacecraft emerged 40 minutes after impact none the worse for its close encounter with the comet.
Besides the spacecraft images, a network of about 60 Earth- and space-based telescopes, along with thousands of amateur astronomers, were standing by to participate in the first-ever globally coordinated effort to watch an object dig a crater in a comet.
By assessing the shape and size of the crater and chemically analyzing the debris that belched from it, scientists hope to gain new insights into the composition of the solar system at the time of its formation 4.5 million years ago.
Comets, composed mostly of dust and ice, periodically migrate in from deep space, their outer layers burning away as they approach the sun. To get to the ancient material within, Deep Impact needed to punch through the boiling crust.
"A lot of scientists think most of the water and hydrocarbons on the Earth came from comets," said University of Maryland astronomer Michael A'Hearn, lead scientist for the mission. "With this experiment we will see how the inside of the comet is different from what we see from the ground."
Deep Impact, with the impactor attached to the fly-by spacecraft, was launched Jan.12 for an Independence Day rendezvous with Tempel 1, about 83 million miles away and hurtling through space at 66,000 mph. Early Sunday morning, the spacecraft was 547,000 from the comet, traveling in the same direction, but at 43,000 mph. If everything went as planned, the Manhattan Island-sized comet would overtake the 820-pound impactor like an express train.
At 2:07 a.m. EDT Sunday, the fly-by spacecraft released the impactor, then did a 14-minute "divert burn" to take it out of harm's way and put it into position to watch its erstwhile companion be obliterated 24 hours later.
The impactor, by contrast, locked on to the approaching comet. Grammier said both the impactor and the fly-by spacecraft were only a little over a half mile from their preferred tracks, "phenomenal" accuracy after nearly six months in space.
It only got better. As Sunday unfolded, the impactor periodically sent its position back to the fly-by spacecraft, which passed it back to Earth via the Deep Space Network along with descriptions of its own status.
At the laboratory two teams of engineers (red shirts for the impactor, blue shirts for the spacecraft) evaluated the information. No problems: "It's an understatement to say that the flight team is excited," Grammier said Sunday afternoon.
Two hours before impact, both spacecraft began operating independently. There was a 7.5-minute delay in receiving signals from Earth, too long to wait as the time to collision dwindled away. The spaceships were on their own.
Ninety minutes away the impactor made the first of three scheduled course corrections, using its camera to point at the comet's brightest spot. Thirty-five minutes away, the impactor made a second correction.
"The first correction actually pulled it off the comet," Yeomans said. "The second one put it back where it started."
And the third, with only 12 ½ minutes left, aimed the impactor at the lower right-hand corner of the comet, a bright spot at five o'clock with plenty of sunlight for the fly-by spacecraft's two cameras and infrared spectrometer. The fly-by spacecraft picked the same spot.
The comet grew in the impactor's camera. It looked like a giant potato, pockmarked and gouged, but also with smooth surfaces. Cross-hairs in the camera focused on a smooth spot next to a possible crater with squiggly ridges above it and to the right.
Ten minutes out, controllers announced that the last change had brought the impactor on course with an error of only 0.23 per cent. Applause echoed through the control room, then stopped.
Twenty seconds to impact. Then the time had passed. The impactor's radio signal was lost, but confirmation that the spacecraft had fulfilled its mission would come only when the fly-by cameras produced an image of the impact itself.
Meanwhile, the impactor's images were still transmitting: "Our spacecraft's doing remarkably well for something that's about to be vaporized," said Yeomans, providing commentary as events unfolded. "Our brave little spacecraft is in a very hostile environment."
Five minutes later, the first fly-by image appeared. The comet's lower right-hand quadrant had erupted in a brilliant, unmistakable explosion of light. Cheers erupted in the control room as picture after picture flashed on screens lining the walls, each one more spectacular than the one that preceded it.
"That's plenty of confirmation, no question about that," exulted Yeomans. "I can't believe they pay us to have this much fun."
[url="http://www.washingtonpost.com/wp-dyn/content/article/2005/07/04/AR2005070400267.html"]Source...[/url] |
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Moscow astrologist takes NASA to court
MOSCOW, July 4 (RIA Novosti) - Moscow's Presnensky Court has postponed until July 28a suit filed by Moscow astrologist Marina Bai against NASA over the Deep Impact project, Bai's lawyer said Monday.
"The trial has been postponed, as a NASA official failed to turn up at court," said Alexander Molokhov.
Bai demanded that the project - which culminated on Monday when a NASA probe collided with the Tempel 1 comet - be cancelled as an affront to her spiritual values, and because it upset the natural balance in the universe.
NASA experts said the project aimed to determine the composition of the comet and to prepare measures in case of a comet or an asteroid threatening Earth.
Experts deny any risk that the crash could alter the comet's trajectory and make it crash into the Earth. The comet weighs up to 250 billion metric tons, so the probe, which weighs 350 kg, was unlikely to cause significant orbital change.
"It was like mosquito hitting a 747," said Professor Iwan Williams from University of London, according to the BBC.
Equally absurd, said scientists, are fears that the parts of the comet disturbed by the blast will pollute the atmosphere, prevent solar rays from reaching the Earth, and cause eternal winter. Such speculation is complete nonsense, said Alexander Yakushev, a researcher at the Russian Academy of Sciences' Space Research Institute. |