Military Unscrambles GPS Signals

WASHINGTON, D.C.--Rarely can the government make thousands of scientists happy by simply flipping a switch. But at midnight tonight, military commanders will turn off a scrambling device on Air Force positioning satellites. Instantly, civilian receivers that depend on the spacecraft signals will become 10 times more accurate, providing researchers and commercial users with a highly reliable means to pinpoint locations.

Until now, only the U.S. military has had access to the highest degree of precision possible with the constellation of 24 Global Positioning Satellites (GPS) originally developed for the Navy. Civilian researchers--including geologists, ecologists, agricultural researchers, and weather forecasters--have had to make due with the scrambled version of the signals, which could only pinpoint a location to within a hundred meters or so. These scrambled GPS signals are commonly used to measure the movements of tectonic plates, map remote terrain, and locate animal and plant habitats. Unscrambling the signal will allow researchers to make more precise measurements. "This really opens up the field for scientists," says Charles Challstrom, director of the National Geodetic Survey.

National security agencies long resisted any move to improve GPS precision for civilian and commercial users, arguing that terrorists could make use of GPS signals. But after a fierce interagency battle, the Clinton Administration agreed in 1996 to stop scrambling the signal within a decade. Technical experts at the Defense Department came up with a way to rescramble those signals in case of a war earlier than anticipated, defense officials said at press conference today at the White House.