Controllers at the Johns Hopkins University’s Applied Physics Laboratory are checking out NASA’s nuclear-powered New Horizons probe after a successful pre-programmed reactivation Saturday night, preparing for an unprecedented flyby of Pluto and its five known moons on July 14.

At 9:53 p.m. EST on Dec. 6 the 70-meter Deep Space Network antenna at Canberra, Australia, received a signal from the 478-kg (1,050-lb.) spacecraft indicating that it had switched from hibernation to active mode for the 18th time since it was launched on Jan. 19, 2006. It will remain active until after it passes within about 6,000 mi. of Pluto and returns all of the data it collects as it approaches, encounters and recedes from the dwarf planet’s system.

"This is a watershed event that signals the end of New Horizons crossing of a vast ocean of space to the very frontier of our Solar System, and the beginning of the mission’s primary objective: the exploration of Pluto and its many moons in 2015," stated principal investigator Alan Stern of the Southwest Research Institute in Boulder, Colorado, after the wakeup call.

At a range of more than 2.9 billion miles from Earth, the speed-of-light signal took 4 hr., 26 min. to reach Earth. The probe was still 162 million miles from Pluto. Powered by a radioisotope thermoelectric generator that produces electricity from the heat of decaying Plutonium 238, its seven instruments are programmed to map all six bodies in the Pluto system, draw composition and temperature maps of Pluto and its largest moon Charon, and determine if the two are geologically active.

"New Horizons is on a journey to a new class of planets we’ve never seen, in a place we’ve never been before," stated Hal Weaver of APL, the New Horizons project scientist. "For decades we thought Pluto was this odd little body on the planetary outskirts; now we know it’s really a gateway to an entire region of new worlds in the Kuiper Belt, and New Horizons is going to provide the first close-up look at them."

The instrument suite consists of a visible/infrared imager/spectrometer; an ultraviolet imaging spectrometer, a passive radiometer to measure the composition and temperature of Pluto’s tenuous atmosphere; a long-range reconnaissance camera dubbed Lorri that will begin imaging the dwarf planet and its moons on Jan. 15; a solar wind and plasma spectrometer and an energetic particle spectrometer to measure the interaction of the atmosphere with the solar wind, and a student-built counter to measure dust impacts on the spacecraft.

Once it passes Pluto, New Horizons will turn around to look at the thin atmosphere backlit by the Sun, a maneuver planned with the help of imagery from the Hubble Space Telescope. But by May, when the spacecraft still has 10 weeks to go before its flyby, Lorri should be producing higher resolution imagery of the surfaces than the is possible with Hubble from its position in Earth orbit. Those images will trickle back to Earth at a glacial data rate of 1 kbps because of the low power – 12-watts - and vast distances to be covered.

Plans call for New Horizons to conduct a post-Pluto mission into the distant Kuiper Belt, which will take another 3-4 years and take the probe 4 billion miles from the Sun. When initial attempts with large ground-based telescopes to identify Kuiper Belt Objects in range for a flyby were unsuccessful, Hubble was pressed into service again last summer and spotted three candidate KBOs, one of them "definitely reachable," according to the New Horizons team.