NASA Launches Comet Probe
Special to The Washington Post
Wednesday, July 3, 2002; 7:38 AM
CAPE CANAVERAL, (July 3) - NASA launched a small spacecraft today that will fly within 60 miles or so of a pair of comets in 2003 and 2006, part of an unprecedented effort to understand the role such "dirty snowballs" played in the solar system's evolution.
In so doing, researchers hope to map out the chemical composition and structure of comets in never before recorded detail and to determine to
what degree comets might have seeded Earth with the water and organic compounds necessary to support life.
"Cometary nuclei are actually remnants from the creation of the outer solar system planets," said Colleen Hartman, director of NASA's solar
system exploration division. "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."
The Comet Nucleus Tour - CONTOUR - spacecraft was built by the Johns Hopkins University Applied Physics Laboratory. It is the second of
three NASA missions devoted to the study of comets.
The first, called Stardust, was launched in 1999. If all goes well, it will snare samples of dust and debris from comet Wild 2 in 2004 and return the material to Earth two years later for detailed analysis.
The third mission, known as Deep Impact, is scheduled for launch in 2004. The goal of this project is to fire what amounts to an 800-pound bullet into the nucleus of comet Tempel 1, kicking up a cloud of debris that will be studied by a battery of instruments.
"Comets remain mysterious objects, they are indeed the most abundant and least understood bodies in our solar system," said Joseph
Veverka, CONTOUR principal investigator. "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."
Perched atop a $50 million Boeing Delta 2 rocket, the $109 million CONTOUR began its open-ended mission at 2:48 a.m. today, lighting up the night sky for miles around as it roared away from complex 17 at the Cape Canaveral Air Force Station.
Launch originally was scheduled for Monday, but the flight was put on hold while engineers investigated how a small amount of dust-like
material got on the spacecraft. In the end, the contamination was judged harmless and launch was set for today.
The three-stage Delta 2 boosted CONTOUR into a parking orbit with a high point of around 71,300 miles and a low point of just 124 miles. If all
goes well, a small solid-fuel rocket will fire at the low point of the orbit on Aug. 15, propelling CONTOUR into an orbit around the sun.
That orbit is designed to repeatedly bring the spacecraft back to the vicinity of Earth for velocity-boosting flybys, using the planet's
gravity to supply the energy that otherwise would have to be provided by rocket fuel.
In between flybys and comet encounters, CONTOUR will electronically hibernate, a cost-cutting strategy that minimizes the amount of human
interaction and tracking required.
The first Earth flyby, on Aug. 15, 2003, is designed to fine-tune CONTOUR's trajectory to its first target, comet 2P/Encke, and to give
ground controllers a chance to calibrate its instruments. Three months later, on Nov. 12, 2003, the spacecraft will streak past Encke
at some 55,000 mph, fast enough to make the trip from Baltimore to Washington in two seconds.
During the high-speed flyby, at a close approach distance of just 62 miles or so, CONTOUR's side-looking camera will be able to snap
pictures at least 10 times sharper than any ever taken, revealing surface features as small as 13 feet across.
After the Encke flyby, CONTOUR will go back into hibernation and head back toward Earth for another gravity-assist flyby on Aug. 14, 2004.
Two more such flybys, on Feb. 10, 2005, and Feb. 10, 2006, are needed to set up the encounter with comet Schwassmann-Wachmann 3 on June 19,
Unlike Encke, which is a mature, highly evolved - and thus less active -comet, Schwassmann-Wachmann 3 is a much younger, much more dynamic body, giving scientists a chance to study the full range of cometary evolution.
"SW-3 is a young, fragile object, it split off at least three pieces in late 1995 for no obvious reason," said Donald Yeomans, a comet
expert at the Jet Propulsion Laboratory and a CONTOUR co-investigator. "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 is officially scheduled to end Sept., 30, 2006. But the trajectory is designed to permit flight controllers to send
the spacecraft on to a third comet if a worthwhile target is identified.
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