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Just a year after it was dispatched on the first mission to Pluto and the Kuiper Belt, the APL-built New Horizons spacecraft is on the doorstep of the solar system's largest planet — about to swing past Jupiter and pick up even more speed on its voyage toward the unexplored regions of the planetary frontier.

The fastest spacecraft ever launched, New Horizons will make its closest pass to Jupiter on Feb. 28, threading its path through an "aim point" 1.4 million miles (2.3 million kilometers) from the center of Jupiter. Jupiter's gravity will accelerate New Horizons away from the Sun by an additional 9,000 miles per hour — half the speed of a space shuttle in orbit — pushing it past 52,000 mph and hurling it toward a pass through the Pluto system in July 2015.

At the same time, the New Horizons mission team is taking the spacecraft on the ultimate test drive — using the flyby to put the probe's systems and seven science instruments through the paces of a planetary encounter. More than 700 observations of Jupiter and its four largest moons are planned from January through June, including scans of Jupiter's turbulent, stormy atmosphere and dynamic magnetic cocoon (called a magnetosphere); the most detailed survey yet of its gossamer ring system; maps of the composition and topography of the large moons Io, Europa, Ganymede and Callisto; and an unprecedented look at volcanic activity on Io.

The flight plan also calls for the first-ever trip down the long "tail" of Jupiter's magnetosphere, a wide stream of charged particles that extends tens of millions of miles beyond the planet, and the first close-up look at the "Little Red Spot," a nascent storm south of Jupiter's famous Great Red Spot.

"Our highest priority is to get the spacecraft safely through the gravity assist and on its way to Pluto," says New Horizons Principal Investigator Dr. Alan Stern, of the Southwest Research Institute, Boulder, Colo. "But we also have an incredible opportunity to conduct a real-world-encounter stress test to wring out our procedures and techniques for Pluto, and to collect some valuable science data."

The Jupiter test matches or exceeds the mission's Pluto study in duration, data volume sent back to Earth, and operational intensity. Much of the data from the Jupiter flyby won't be sent back to Earth until after closest approach, because the spacecraft's main priority is to observe the planet and store data on its recorders before transmitting information home.

"We designed the Jupiter encounter to prove out our planning tools, our simulation capabilities, our spacecraft and our instrument sensors on a real planetary target, well before the Pluto encounter," says Glen Fountain, New Horizons project manager at The Johns Hopkins University Applied Physics Laboratory (APL), Laurel, Md., which built and operates the spacecraft. "If the team needs to adjust anything before Pluto, we'll find out about it now."

The mission team at APL, SwRI and other institutions has learned much in a hectic year since New Horizons lifted off from Cape Canaveral Air Force Station, Fla., last Jan. 19. The spacecraft has undergone a full range of system and instrument checkouts, instrument calibrations and commissioning, some flight software enhancements, and three small propulsive maneuvers to adjust its trajectory. Operational highlights of the past year included long-distance snapshots of both Jupiter and Pluto, and a flyby of asteroid 2002 JF56 (recently named "APL" by the International Astronomical Union).

With closest approach to Jupiter coming 13 months after launch, New Horizons will reach the planet faster than any of its seven previous visitors. Pioneers 10 and 11, Voyagers 1 and 2, Ulysses and Cassini all used Jupiter's gravity to reach other destinations; NASA's Galileo orbited the planet from 1995-2003.

New Horizons also provides the first close-up look at the Jovian system since Galileo, and the last until NASA's Juno mission arrives in 2016. "The Jupiter system is incredibly dynamic," says New Horizons Jupiter Encounter Science Team lead Dr. Jeff Moore, of NASA Ames Research Center, Moffett Field, Calif. "From constant changes in Jupiter's magnetosphere and atmosphere, to the evolving surfaces of moons such as Io, you get a new snapshot every time you go there."

After an eight-year cruise from Jupiter across the expanse of the solar system, New Horizons will conduct a five-month-long study of Pluto and its three moons in 2015, characterizing their global geology and geomorphology, mapping their surface compositions and temperatures, and examining Pluto's atmospheric composition and structure. Then, as part of a potential extended mission, New Horizons would conduct similar studies of one or more smaller worlds in the Kuiper Belt, the region of ancient, rocky and icy bodies far beyond Neptune's orbit.

The New Horizons science payload includes imaging infrared and ultraviolet spectrometers, a multi-color camera, a long-range telescopic camera, two particle spectrometers, a space-dust detector and a radio science experiment. The compact, 1,050-pound spacecraft, drawing electricity from a single radioisotope thermoelectric generator, currently operates on slightly more power than a pair of 100 -watt light bulbs.

New Horizons is the first mission in NASA's New Frontiers Program of medium-class spacecraft exploration projects. Stern leads the mission and science team as principal investigator; APL manages the mission for NASA's Science Mission Directorate. For more information on New Horizons, visit: .