While engineers have not yet confirmed the objects are, in fact, pieces of the $159 million CONTOUR, mission director Robert Farhquar said "I'm not very optimistic."
"We always have hope that things are going to turn out all right," Farhquar told reporters late today. "And up until a little while ago, I had a lot of hope."
But the grainy Spacewatch image shows two smeared trails against a star field that presumably represent what's left of CONTOUR. The objects are about 250 kilometers apart and one is much brighter than the other.
"Although this isn't conclusive, it's not very encouraging," said Farhquar. "We haven't given up, but this is pretty bad news."
Ground controllers at the Johns Hopkins University Applied Physics
Laboratory lost contact with CONTOUR early Thursday following an "in-the-blind" rocket firing to boost the craft out of Earth orbit. CONTOUR was launched July 3 into an elliptical parking orbit. Thursday's rocket firing, scheduled for 4:49 a.m. EDT, was designed to put the craft into an orbit around the sun that would enable it to encounter at least two comets, one in 2003 and another in 2006.
Ground controllers were not in contact with CONTOUR at the time of the rocket firing, which was scheduled to occur at the low point of the craft's elliptical orbit a scant 140 miles above the Indian Ocean. Engineers using NASA's Deep Space Network tracking antennas expected to regain contact at 5:35 a.m. But no signals were received.
Engineers initially held out hope CONTOUR had suffered a non-catastrophic malfunction that temporarily left it in protective "safe mode" and unable to communicate with Earth.
In the absence of contact with ground controllers, CONTOUR's on-board computer was programmed to re-orient the spacecraft and to phone home after 24 hours. That deadline came and went today without a peep from the spacecraft.
Farhquar said engineers using a large radar dish at Goldstone, Calif., and Aericibo, Puerto Rico, will be aimed at the Spacewatch targets over the weekend in a bid to gather more conclusive data. Other optical telescopes also will join in the hunt.
In the meantime, ground controllers will continue to explore other options in hopes the spacecraft is still intact and suffering from a non-catastrophic malfunction that might have disabled its radio system.
Another onboard timer will hit zero Monday, triggering another attempt to contact Earth, and there's a chance engineers will pick up telemetry then.
But Farhquar said he's not optimistic.
"We're fairly certain, after seeing these images, the spacecraft has left earth orbit and that the motor fired," he said. "I wrote my first paper on getting to comet Encke (one of CONTOUR's targets) in 1972. So I've been at this for 30 years so I would have liked to have gotten some images. I haven't given up, but it's pretty bleak."
The Comet Nucleus Tour - CONTOUR - project was the latest in a series of missions designed to probe the nature of these "dirty snowballs," the role they played in the solar system's evolution and the degree to which they seeded Earth with the compounds necessary for life.
"Comets are exotic objects, coming to us from the farthest reaches
of our solar system," Colleen Hartman, director of NASA's solar system exploration division, said before launch.
"Cometary nuclei are actually remnants from the creation of the outer solar system planets," she said. "They also may be the source of much of the water we find in the Earth's oceans. In fact, there's some speculation that human beings are made of comet dust."
Built by the Applied Physics Laboratory, CONTOUR was the second in a series of three NASA missions devoted to cometary exploration.
The first - Stardust - was launched in 1999. If all goes well, it will collect samples of gas and dust from comet Wild 2 in 2004 and bring the material back to Earth in 2006 for detailed laboratory analysis.
NASA plans to launch yet another comet mission in 2004 that will fire an 800-pound copper-tipped bullet into the nucleus of comet Tempel 1. The resulting cloud of debris will be studied by instruments aboard the Deep Impact mothership as well as by astronomers on Earth.
"Comets remain mysterious objects, they are indeed the most abundant and least understood bodies in our solar system," said CONTOUR principal investigator Joseph Veverka of Cornell University.
"And they're important because they are the best preserved pieces of the solid materials out of which the planets formed 4.6 billion years ago.
"Contour's main purpose is to investigate the nature and the diversity of comets in unprecedented detail," he said. "The way we're going to do that is by getting our spacecraft closer to a comet nucleus than has ever been achieved before."
The flight plan called for CONTOUR to streak past the comet 2P/Encke on Nov. 12, 2003, passing within 62 miles or so of its icy nucleus.
Then, on June 19, 2006, CONTOUR was to sail by comet Schwassmann-Wachmann.
"We have two comets that could not be more diverse," said co-investigator Donald Yeomans of NASA's Jet Propulsion Laboratory. "Encke is a tough, blackened, old comet. ... It's what we call a transition object, a comet that likely is on its way from being a comet that outgasses to perhaps an object that's lost its ability to outgas and cannot be differentiated from an asteroid.
Schwassmann-Wachmann 3, on the other hand, "is a young fragile object, it split off at least three pieces in late 1995 for no obvious reason," Yeomans said. "It's probably a rubble pile-type structure that's held together by little more than its own self gravity.
"And if indeed some of these pieces have left the interior of the main nucleus exposed, then we'll get a chance to look at the structure of the interior of this comet."
The CONTOUR mission was officially scheduled to end Sept.30, 2006. But the spacecraft's solar orbit was designed to permit flight controllers to target a third comet if a worthwhile target is identified.
By Bill Harwood