Set to visit and study at least two comets, NASA's CONTOUR (Comet Nucleus Tour) spacecraft should provide the first detailed look at the differences between these primitive building blocks of the solar system and answer questions about how comets act and evolve as they speed toward the sun.

CONTOUR is scheduled to lift off from Cape Canaveral Air Force Station, Fla., on a three-stage Boeing Delta II expendable launch vehicle during a 25-day launch window that opens at 2:56 a.m. on July 1. The spacecraft will orbit Earth until Aug. 15, when it should fire its main engine and enter its comet-chasing orbit around the sun. NASA TV is scheduled to provide live coverage of the launch beginning at 1:30 a.m.

The $159 million CONTOUR is the sixth mission in NASA's Discovery Program of lower cost, scientifically focused exploration projects. The university's Applied Physics Laboratory manages the mission, built the spacecraft and its two cameras, and will operate CONTOUR during flight.

Mary C. Chiu, CONTOUR project manager at APL, says, "The key to the CONTOUR mission is to visit a diverse range of comets, from an evolved comet such as Encke to a younger comet like SW3 or even a new comet never seen in this part of the solar system. Our mission plan gives us that flexibility." The encounter with Encke is scheduled for Nov. 12, 2003, and that with Schwassmann-Wachmann 3 for June 19, 2006.

CONTOUR will examine each comet's "heart," or nucleus, which scientists believe is a chunk of ice and rock, often just a few kilometers across and hidden from Earth-based telescopes beneath a dusty atmosphere and long tail.

"The CONTOUR mission will be NASA's second mission dedicated solely to exploring these largely unknown members of our solar system," says Colleen Hartman, director of NASA's Solar System Exploration Division. NASA's other operating mission, Stardust, is on its way to bring a sample of a comet back to Earth; next year, Deep Impact will launch to join its fleet of comet-exploring spacecraft. "These missions all help us find answers to the fundamental questions of how our planet may have formed and evolved, and how life may have begun on Earth and perhaps elsewhere in the universe," Hartman says.

The eight-sided solar-powered craft will fly as close as 62 miles to each nucleus, at top speeds that could cover the distance between Baltimore and Washington, D.C., in two seconds.

CONTOUR's principal investigator, Joseph Veverka of Cornell University, says, "Comets are the solar system's smallest bodies, but among its biggest mysteries. We believe they hold the most primitive materials in the solar system and that they played a role in shaping some of the planets, but we really have more ideas about comets than facts. CONTOUR will change that by coming closer to a comet nucleus than any spacecraft ever has before and gathering detailed, comparative data on these dynamic objects."

Veverka leads a science team of 18 co-investigators from universities, industry and government agencies in the United States and Europe.

CONTOUR's four scientific instruments will take pictures and measure the chemical makeup of the nuclei while analyzing the surrounding gases and dust. Its main camera will snap high-resolution digital images showing car-sized rocks and other features on the nucleus as small as about 13 feet across. It also will search for chemical "fingerprints" on the surface, which would provide the first hard evidence of comet nuclei composition.

The targets were selected because of their diversity and relative closeness to Earth during encounter time--less than 50 million kilometers--allowing astronomers to observe the comets during the encounters. Encke has been seen from Earth more than any other comet; it's an "old" body that gives off relatively little gas and dust but remains more active than scientists expect for a comet that has passed close to the sun thousands of times. Schwassmann-Wachmann 3, on the other hand, was discovered just 70 years ago and recently split into several pieces, intriguing scientists with hopes that they might see fresh, unaltered surfaces and materials from inside the comet.

CONTOUR's orbit loops around the sun and back to Earth for annual "gravity swings" toward its targets; these maneuvers bend CONTOUR's trajectory and help it reach several comets without using much fuel. CONTOUR will cruise unattended between comet encounters and Earth swingbys in a spin-stabilized "hibernation" mode, helping the mission reduce operations and communications costs.

For more information on CONTOUR, go to www.contour2002.org.