The countdown clock is ticking toward a January liftoff of NASA’s New Horizons spacecraft bound for Pluto and the Kuiper Belt.

"The spacecraft and instruments are undergoing a very rigorous test program over the next few months," said New Horizons Principal Investigator Alan Stern of the Southwest Research Institute in Boulder, Colorado. "This begins with systems testing, and then proceeds to shake tests and space environment thermal vacuum testing," he told SPACE.com.

Also among a series of steps still to be undertaken is launch approval of the nuclear-powered probe. The power source for New Horizons is a radioisotope thermoelectric generator (RTG). It uses heat from the decay of plutonium dioxide to produce electricity.

On March 29 and 30, NASA will host meetings at the Florida Solar Energy Center in Cocoa – a research institute of the University of Central Florida -- where the public can comment on a New Horizons Draft Environmental Impact Statement (DEIS) and learn more about the proposed mission.

After reviews are completed under the National Environmental Policy Act, if NASA decides to proceed with the mission, the spacecraft would await presidential approval to launch next January.

New Horizons is to be launched aboard an Atlas 5. The piano-sized probe would cross the entire span of the solar system -- in record time -- and conduct flyby studies of Pluto and its moon, Charon, in 2015. New Horizons would also voyage into the Kuiper Belt of smaller, icy objects.

[See also: Hearing set tonight on nuclear Pluto mission]