NASA uses a laser to track a spacecraft

GREENBELT, Md., Sept. 28 (UPI) -- NASA scientists say they are conducting the first laser-ranging effort to track a spacecraft beyond low-Earth orbit on a daily basis.

"On certain nights, an arresting green line pierces the sky above NASA's Goddard Space Flight Center in Greenbelt, Md.," the space agency said. "It's a laser directed at the moon, visible when the air is humid. No, we're not repelling an invasion. Instead, we're tracking our own spacecraft."

Goddard scientists said the laser's green beam is directed toward the Lunar Reconnaissance Orbiter spacecraft that's in orbit around the moon. Twenty-eight times per second, scientists fire the laser that travels about 250,000 miles to hit the minivan-sized spacecraft that's moving at nearly 3,600 miles per hour.

The distance measurements are accurate to about 4 inches, NASA said, noting microwave stations tracking the LRO measure its range to a precision of about 65 feet.

"Current lunar maps are not as accurate as we'll need to return people safely to the moon," said Ronald Zellar, a member of the laser ranging team. "In order to make an accurate map, first you need to know where you are. Knowing the precise range to LRO is necessary for its instruments to produce much more accurate maps, with errors reduced to the size of humans or rovers."

More information about Goddard's laser ranging facility is available at http://lrolr.gsfc.nasa.gov/.