In Search Of Comets
A Boeing Delta 2 rocket boosted a small NASA spacecraft into a preliminary parking orbit Wednesday, the first step in an open-ended journey that will carry the armored craft within 60 miles or so of at least two comets.
The $159 million Comet Nucleus Tour - CONTOUR - project is 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," said Colleen Hartman, director of NASA's solar system exploration division.
"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 Johns Hopkins University Applied Physics Laboratory, CONTOUR is 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 journey began at 2:48 a.m. Wednesday when the first stage of CONTOUR's Delta 2 rocket ignited with a ground-shaking roar and a sky-lighting flash of fire, instantly pushing the craft away from pad 17 at the Cape Canaveral Air Force Station.
"We're on our way!" Veverka said from NASA's control center.
After spending less than an hour in a low-altitude, roughly circular orbit, the flight plan called for a final Delta rocket firing to boost the solar-powered CONTOUR into an elliptical orbit with a high point of more than 71,000 miles and a low point of just 124 miles.
If all goes well, a small solid-fuel rocket will fire Aug. 15 to boost CONTOUR into an orbit around the sun.
That orbit will repeatedly bring the spacecraft back to Earth for gravity-assist flybys that will boost CONTOUR's velocity and change its trajectory as required. To save money, the spacecraft was designed to hibernate between flybys and comet encounters.
The first Earth flyby is targeted for Aug. 15, 2003. Three months later, on Nov. 12, 2003, CONTOUR will streak past comet 2P/Encke at some 55,000 mph, passing within 62 miles or so of its icy nucleus.
"We first of all want to know how comets work," Veverka said. "We also want to know what comets are made of and finally, we want to know what the diversity, chemically, is amongst the comets."
During the Encke flyby, CONTOUR's side-looking camera will be able to snap pictures at least 10 times sharper than any ever taken, revealing the precise size of the nucleus, its shape, its rotation, brightness and color. Other instruments will map the comet's structure and chemical composition.
"We'll be making detailed chemical analysis of the gas and dust being released by the comet and we will obtain the best ever pictures and spectral maps of the comet's nucleus," Veverka said.
After the Encke flyby, CONTOUR will go back into hibernation until another Earth flyby on Aug. 14, 2004. Two more such encounters, on Feb. 10, 2005, and Feb. 10, 2006, are needed to set up the encounter with comet Schwassmann-Wachmann 3 on June 19, 2006.
"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 is officially scheduled to end Sept., 30, 2006. But the spacecraft's solar orbit will permit flight controllers to target a third comet if a worthwhile target is identified.
By Bill Harwood