Hopkins-built spacecraft to buzz 3 comets NASA funds mission set for launch in 2002

November 04, 1997|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

Three comets that make regular visits to the inner solar system will be buzzed early in the next century by a spacecraft to be built by scientists at the Johns Hopkins University Applied Physics Lab in Laurel.

The Comet Nucleus Tour, or CONTOUR mission -- proposed by APL and Cornell University -- won $154 million in NASA funding last month and is scheduled for launch July 4, 2002.

If all goes according to plan, CONTOUR will carry its cameras and analytical instruments to within 60 miles of Comet Encke in 2003, Comet Schwassmann-Washmann-3 in 2006, and Comet d'Arrest in 2008.

"APL has demonstrated that they can build spacecraft very efficiently, at very modest cost, and have them operate in top-notch fashion. That's the reason they were selected by NASA," said Joseph Veverka, a Cornell University astronomer and principal investigator for the CONTOUR mission.

APL's CONTOUR mission director, Mary Chiu, said the key to the lab's selection was a remarkable trajectory -- visiting three comets with one spacecraft. "It allowed us to design the spacecraft very conservatively, so we don't need new technology. We're using fairly standard spacecraft components."

CONTOUR was one of just two missions selected -- from among 34 applicants -- in the latest round of the National Aeronautics and Space Administration's Discovery series. The second is a $216 million Caltech mission called Genesis. Due for launch in 2001, it will collect samples of charged particles for a study of the solar wind.

The Discovery series is designed to deliver high-quality space science at costs that rank as bargain basement sales by NASA's past standards.

Previous Discovery missions have included the $270 million Mars Pathfinder mission that landed on the planet in July, and the $105 million Near Earth Asteroid Rendezvous (NEAR) spacecraft built at APL. NEAR photographed the asteroid Mathilde in June. It is scheduled to orbit the asteroid Eros in 1999.

A moon-mapping mission called Lunar Prospector is due for launch in January, and Stardust -- a mission to land on a comet and return samples to Earth -- is set for launch in 1999.

CONTOUR will not be the first spacecraft to fly past a comet. Halley's Comet was visited by five spacecraft in 1986, none of them American.

The European Space Agency's spacecraft Giotto snapped its last picture of Halley from more than 600 miles, Veverka said. It was a remarkable achievement, but left scientists eager to get closer.

"The plan right now is to get within about 60 miles" of CONTOUR's three targets, he said. "We fully expect images 25 times better than Giotto ever did. Instead of a city block, we will be able to see things the size of a small car."

Astronomers have studied comets for centuries, but they remain a tantalizing mystery.

Made mostly of ice, dust and frozen gases, they wander into the inner solar system, where solar energy warms them. The ice and gases begin to vaporize and spew into space. The solar wind -- charged particles and radiant energy from the sun -- blows them into the characteristic "tails" that make some comets -- like last spring's Comet Hale-Bopp -- so dramatically visible from Earth.

But "we still don't know how comets work, or exactly what they're made of," Veverka said. "Why do we care? The reason is that comets are probably the best-preserved pieces of the things that went into forming the big planets a long time ago."

"We have good information that the water in our oceans, the gases in our atmosphere and the molecules that made life all came from comets," he said. "We need to know what that stuff really is."

CONTOUR investigators -- 16 of them from universities, industry and government -- hope to learn more about diversity in the composition, structure and behavior of comets.

CONTOUR will carry four solar-powered scientific instruments, including two imagers to be built at APL. They will photograph the comets' nuclei and map the distribution of gases on their surfaces.

Scientists hope to learn, for example, what structures -- cracks or geysers, perhaps -- produce the plumes and jets of gas and dust they see through their telescopes.

Other instruments will analyze and identify the dust and gases streaming from the comets.

CONTOUR's trajectory is an innovative bit of space navigation devised by APL's Robert Farquhar.

About a month after launch aboard a Delta rocket, CONTOUR will fire a solid-fuel rocket booster. That push will carry it 25 million miles from Earth to its first target, Comet Encke, in November 2003.

After that first flyby, APL engineers will fire CONTOUR's gas thrusters to steer the spacecraft back toward Earth. A swing through Earth's gravity will give the spacecraft an energy boost for the 30-million-mile outbound flight to the next target, Comet Schwassmann-Washmann-3. It will get there in June 2006.

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