NASA counts down to nail-biter Pluto flyby

The flyby will allow scientists a close glimpse of the dwarf planet's surface for the first time

An unmanned NASA spacecraft is hurtling into the unknown, and will make a close shave past Pluto tomorrow, allowing scientists a close glimpse of the dwarf planet's surface for the first time.

But there were some jitters today as the $700 million spacecraft, called New Horizons, sped toward Pluto, the last undiscovered frontier in the solar system.

According to principal investigator Alan Stern, there is a one in 10,000 chance that the spacecraft could be lost in a collision with debris around Pluto, long considered the farthest planet from the sun until it was reclassified as a dwarf planet in 2006.

The closest approach is set for tomorrow at 7:49 a.m (1149 GMT), when the piano-sized spacecraft shaves by Pluto's surface at a speed of 30,800 miles (49,570 kilometers) per hour.

The first spacecraft to visit an unexplored planet since the NASA Voyager missions of the 1970s will be busy snapping pictures and collecting data, and will phone home later.

New Horizons will send a signal to Earth at 4:20 p.m (2020 GMT). It will take nearly five hours to reach scientists.

That means NASA won't announce until about 13 hours after the flyby, at 9:02 p.m (0102 GMT Wednesday), whether or not the spacecraft survived the high-speed encounter.

"While I don't lose sleep over this, the fact is, tomorrow evening is going to be a little bit of drama," said Stern.

"Until we pass that point tomorrow evening we won't really know with certainty that we cleared the system and that there were no debris strikes."

Stern said experts have searched for potential debris and haven't found any of concern.

But spaceflight is a risky business, and Stern described the Kuiper Belt, where Pluto resides on the edge of the solar system, as "more or less a shooting gallery, with lots of small primordial comets and other things much smaller than Pluto."

Never before has a spacecraft ventured into the Kuiper Belt, and New Horizons has been on its way there for more than nine years -- a journey of some three billion miles.

"We are flying into the unknown," Stern told reporters.