Hopes were fast fading Wednesday for recovering the CONTOUR (Comet Nucleus Tour) space mission in which Cornell astronomers were to have played a major scientific role. NASA ground controllers lost contact with the spacecraft after its main rocket engine fired on cue Aug. 15.
With the spacecraft apparently in three fragments and spinning away from Earth, the mission team continues checking for a signal that would indicate that the spacecraft, which was to explore the nuclei of at least two comets, is still capable of operating.
"All of us had so much invested in this mission that you have to continue hoping," said Jim Bell, Cornell assistant professor of astronomy. "I remain skeptical, however, as we all should, because I don't see how the spacecraft could have broken up like that."
Bell is a member of the CONTOUR scientific team, led by Joseph Veverka, Cornell professor of astronomy.
Two objects, believed to be spacecraft segments, were detected Aug. 16, the day after the solid rocket motor burn, and a third more distant object has since been found. The objects are now more than 2 million kilometers (about 1.25 million miles) from Earth, traveling at a steady 6.1 kilometers per second (3.8 miles per second or 13,600 miles per hour). The objects remain on a trajectory predicted by early observations -- although they now have traveled so far from the sun and Earth that more observations are unlikely, according to mission director Robert Farquhar of the Johns Hopkins University Applied Physics Laboratory (APL), which built CONTOUR and manages the mission for NASA. "We realize the possibilities are small, but we can't discount the idea that the spacecraft is still operable. We have to determine that before we give up," he said.
The trouble began on Aug. 15 when, after more than a month of circling the Earth, CONTOUR fired up its STAR-30 solid-propellant rocket motor. That firing was intended to take the spacecraft out of its parking orbit and into a heliocentric (sun-centered) Earth-return trajectory on its way to an encounter with Comet Encke in November 2003.
One theory about CONTOUR's fate is that the spacecraft, which was launched with such jubilation on July 3, broke apart when the motor was fired. The speculation is based on telescope images from several observatories showing three objects traveling along CONTOUR's predicted path.
If the spacecraft is indeed lost, said Bell, "it would be a scientific blow." He noted: "If you imagine picking up an astronomy textbook five years from now, it's as if the section on comets has been ripped out. There was so much new information that we were going to collect." The loss would also have human impacts, he said, in terms of students not hired, jobs supported by the mission lost and careers disappointed.
If the spacecraft is still capable of operating, by today (Aug. 22), it will have completed the first cycle of having each of its two transmitters attempt to send a signal through each of three antennas, according to APL. Near-continuous monitoring for CONTOUR will continue through Sunday using NASA's worldwide Deep Space Network's powerful 70-meter and 34-meter antennas. After that, efforts will be scaled back to once a week, a schedule that will be maintained until December when the spacecraft -- if it is still operating -- will come into a more favorable angle for receiving a signal from Earth.
However, Bell noted, the further the spacecraft spins away from Earth, the harder it will be to pick up signals from the low-gain antennas, which are difficult to detect from a distance. Signals from the spacecraft's high-gain antenna can only be detected if the antenna is pointed accurately at the Earth.
The high-gain antenna is likely to be in a more favorable orientation as the spacecraft passes close to Earth in the second week of December, although the chances of contacting CONTOUR then are small, according to APL. But, said Farquhar, "who knows, we might get lucky."
If not, said Bell, realistically it will be years before another such mission could be organized. "We were going to target the spacecraft closer to the heart of a comet than any other current or planned space mission," he said.
For up-to-date information, go to the CONTOUR home page at http://www.contour2002.org.
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