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US Scientists Search for Silent Spacecraft - 2002-08-27


U.S. scientists are trying to re-establish contact with a lost spacecraft launched last month to rendezvous with comets. But they admit they are not optimistic about its prospects.

The Contour spacecraft has been silent since August 15, when it was supposed to leave Earth's orbit on its way to close fly-bys of comets. The U.S. space agency NASA's global network of huge dish antennas has not picked up a signal from the spacecraft and ground telescopes have observed three pieces, instead of one, in its expected flight path.

Robert Farquhar, the mission director at the Johns Hopkins University Applied Physics Laboratory near Washington, admits this discovery is not a good omen. "Obviously we're not very optimistic given that kind of data," he said. "We're not very optimistic about the chances of ever recovering Contour again, but we haven't given up totally because there is an obligation to make sure that the spacecraft is indeed lost."

Johns Hopkins ground controllers, who are operating the mission for NASA, continue listening for a signal. But they have reduced their full-time search to just once weekly for eight hours. Mr. Farquhar says they will make a final effort at full-time monitoring in early to mid-December when the alignment between Earth and Contour's flight path improves, giving the team the best chance for regaining contact. "That's our best hope, but even then we don't have a lot of hope that we'll recover it," says Mr. Farquhar.

Johns Hopkins University scientists do not know what happened to Contour. They say the best case would be if the main spacecraft remains intact and that the two other objects witnessed through telescopes are pieces of protective thermal material or a dust shield that broke off.

However, they suggest that a more realistic explanation would be an explosion in the solid fuel rocket motor or fuel system when the motor fired to leave Earth orbit. Another possibility is that the spacecraft broke apart as it spun as designed at 60 revolutions per minute because of what they call a dynamic imbalance.

The eight-sided Contour craft was supposed to fly within 100 to 300 kilometers of three comets between next year and 2008 to get the sharpest images yet of a rocky, icy nucleus. Researchers want to study comet chemistry because these bodies are thought to be remnants of the material from which the solar system formed.

The Johns Hopkins team is already planning to reconstruct the mission for a launch in 2006. Contour project scientist Joseph Veverka of Cornell University says the second mission would aim for the same comet targets. "We had selected these targets for specific scientific reasons, and so to the extent possible, we would like to maintain at least some of those targets," he says. "That seems to be possible, so there is nothing that seems to stand in the way of a Contour-II except raising the funds to make it possible."

Mission officials say a second Contour would be cheaper since its development is complete and only the spacecraft and its instruments must be built.

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