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Set to visit and study at least two comets, NASA’s Comet Nucleus Tour () 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 July 1 at 2:56 a.m. (EDT). The spacecraft will orbit Earth until Aug. 15, when it should fire its main engine and enter its comet-chasing orbit around the sun. is scheduled to provide live coverage of the launch beginning at 1:30 a.m. (EDT)

CONTOUR’s flexible four-year mission plan includes encounters with comets Encke (Nov. 12, 2003) and Schwassmann-Wachmann 3 (June 19, 2006), though it can add an encounter with a “new” and scientifically valuable comet from the outer solar system, should one be discovered in time for CONTOUR to catch it. 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,” said Dr. Colleen Hartman, Director of the Solar System Exploration Division, Headquarters, Washington. “CONTOUR joins our other operating mission, , which is on its way to bring a sample of a comet back to Earth. Next year, will launch to join our 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 began on Earth and perhaps elsewhere in the universe.”

The 8-sided solar-powered craft will fly as close as 100 kilometers (62 miles) to each nucleus, at top speeds that could cover the 56 kilometers between Washington and Baltimore in two seconds. A 5-layer dust shield of heavy Nextel and Kevlar fabric protects the compact probe from comet dust and debris.

“Comets are the solar system’s smallest bodies, but among its biggest mysteries,” says Dr. Joseph Veverka, CONTOUR’s principal investigator from , Ithaca, N.Y. “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.”

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, the CONTOUR Remote Imager/Spectrograph (CRISP), will snap high-resolution digital images showing car-sized rocks and other features on the nucleus as small as 4 meters (about 13 feet) across. CRISP will also 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 (31 million miles) — 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.

“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,” says Mary C. Chiu, CONTOUR project manager at The Johns Hopkins University Applied Physics Laboratory (), Laurel, Md. “Our mission plan gives us that flexibility.”

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.

The $159 million CONTOUR is the sixth mission in NASA’s of lower cost, scientifically focused exploration projects. APL manages the mission, built the spacecraft and its two cameras, and will operate CONTOUR during flight. NASA’s , Greenbelt, Md., provided CONTOUR’s neutral gas/ion mass spectrometer and , Schwetzingen, Germany, built the dust analyzer. NASA’s , Pasadena, Calif., will provide navigation and Deep Space Network (DSN) support. Cornell’s Veverka leads a science team of 18 co-investigators from universities, industry and government agencies in the U.S. and Europe.

More information on CONTOUR is available on the Web at .