To the Solar System’s edge

The three-stage Atlas will hurl the spacecraft from earth at a record 36,000 mph, fast enough to pass the moon in nine hours—an Apollo mission takes two and a half days—so that it can reach Jupiter in just 13 months. A gravity assist from the giant planet, which also will serve as a test bed for New Horizons’ seven instruments, is to speed the craft on.

Once near its target, in 2015, the spacecraft is to conduct about five months of studies, including a dash that takes it within 6,200 miles of Pluto’s surface and 16,800 miles from the its large moon, Charon. Mission scientists said, it will also study two smaller moons, found late last year by the Hubble Space Telescope, and any new features discovered in transit.

The three-billion-mile journey to Pluto will take at least nine and a half years, and the compact robot craft will have to conserve energy. So for most of the flight, it will be in a state of hibernation, sending a brief weekly signal back to earth to report its condition and being awakened by mission control only once a year for an instrument check.

But the payoff at the end of the mission will be worth the wait, said Alan Stern of the Southwest Research Institute in Boulder, Colorado, the mission’s principal investigator and team leader. ‘‘This is in a real sense the capstone of the initial missions to explore the planets,’’ Dr Stern said. ‘‘Pluto, its moons and this part of the solar system are such mysteries that New Horizons will rewrite all of the textbooks.’’ Pluto, discovered in 1930 by astronomer Clyde Tombaugh, is the first known example of a new class of planetary bodies called ice dwarfs, Stern said. Scientists think these cold bodies, which number in the hundreds beyond Neptune in the Kuiper Belt, represent some of the original building materials of the solar system.

Stern dismisses recent debate on whether Pluto is really a planet, since it and its ilk are so different from the four rocky inner worlds like earth and Mercury, and the four giant, gaseous outer planets like Jupiter. Ice dwarfs are the most populous group of major bodies in the solar system, he said. ‘‘Just as a Chihuahua is still a dog, ice dwarfs are still planetary bodies,’’ he said. ‘‘The misfit becomes the average. Pluto-like objects are more typical in our solar system than the nearby planets we first knew.’’ Once New Horizons completes its studies of the Pluto system, it will be redirected to one or two other Kuiper Belt objects that will be selected later.

The 1,054-pound spacecraft is about the size and shape of a grand piano. It was designed and built by the Johns Hopkins University Applied Physics Laboratory in Laurel, Mayland, which is also managing the mission for NASA. The budget is about $700 million, including launching costs and 10 years of operations.

Since New Horizons will operate too far out to use solar power, it will draw power from a plutonium-fueled thermoelectric generator that produces 200 watts. The use of the highly radioactive plutonium is controversial.

William Gibson, the mission’s science payload manager, said the craft’s instruments include three cameras to take visible light, infrared and ultraviolet images and three spectrometers to study composition and temperatures of Pluto’s thin atmosphere and surface. The instruments are the most compact, energy-efficient designs ever flown on a planetary mission, he said.

The spacecraft also carries a University of Colorado dust counter, the first experiment entirely designed and operated by students to fly on a planetary mission. This is the only experiment that will not hibernate during the mission.

(New York Times)