NASA has given the go-ahead for the Cornell University-led Comet Nucleus Tour, or Contour, mission. The agency said the mission has passed a critical review and the building of the spacecraft can begin.

Cornell will lead and direct the $158 million mission to conduct close-proximity comet flybys. The spacecraft is scheduled for launch in July 2002, with the precise launch date to be decided in the next year or two.

The principal investigator on the mission is Joseph Veverka, professor of astronomy at Cornell and chair of the astronomy department. Other Cornell researchers on the team are Steven W. Squyres, professor of astronomy, who will interpret the geology of the comets; James Bell, assistant professor of astronomy, who will interpret the spectral maps of the comets; and Peter C. Thomas, senior research associate, who is a leading expert in determining the size and shape of irregular objects like comets.

David Jarrett of NASA's Discovery Program, said, "After successful completion of both the preliminary design review and an independent confirmation assessment, the Contour team is well on its way toward completing the spacecraft design."

The launching of Contour is timed to encounter and study Comet Encke in November 2003 and Comet Schwassmann-Wachmann-3 in June 2006. The mission has the flexibility to include a flyby of Comet d'Arrest in 2008 or to retarget itself to approach an unforeseen cometary visitor to the inner solar system. Mission scientists are hopeful they will have the opportunity to study a newly discovered comet, such as Comet Hale-Bopp, which was discovered by amateur astronomers in 1995.

The spacecraft, to be launched aboard a Delta rocket, will be outfitted with a solar array for power and a high-gain antenna for communication with Earth. The Contour spacecraft will venture about 30 million miles from Earth to study the comets. Building of the spacecraft at the Applied Physics Laboratory at Johns Hopkins University, which is managing the mission, begins this month.

The nucleus of a comet is its heart, believed by scientists to be a tiny, irregular chunk of ice and rock. To date only one comet nucleus has ever been viewed with a spacecraft: Comet Halley in 1986. The spacecraft will fly past at least two comets and take far better pictures than those of Halley. It will also collect and analyze dust to reveal the comet's makeup, greatly improving our knowledge of key characteristics of comet nuclei and providing an assessment of their diversity.

The mission also will clear up the many mysteries of how comets evolve as they approach the Sun and their ices begin to evaporate.

The spacecraft will fly by each comet at the peak of its activity, close to the Sun. During each encounter, the target comet will also be well situated in the night sky for astronomers worldwide to make concurrent observations from the ground. The spacecraft will fly by each comet at a distance of about 100 kilometers (62 miles).

Related World Wide Web sites: The following sites provide additional information on this news release. Some might not be part of the Cornell University community, and Cornell has no control over their content or availability.

-- Comet Nucleus Tour: http://stardust.jpl.nasa.gov/comets/Contour.html

-- NASA Discovery Program: http://discovery.nasa.gov