Simple, inexpensive jammers threaten GPS.

• Author: Parsons, Dan
• Position: Inside Science + Technology

* When hunting for a particular restaurant or driving to a business meeting in an unfamiliar city, the global positioning system can be a lifesaver.

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The satellite constellation also provides the backbone for nearly every navigational system used by the U.S. military. It is one of the tools that Air Force officials repeatedly describe as a "must have" in operations from routine training to combat missions on the ground, at sea and in the air.

Gen. William Shelton, commander of U.S. Space Command, said in June that the 31-satellite GPS system in orbit is "performing extremely well."

"This constellation just keeps on ticking," he said.

Such a valuable asset to the U.S. military and commercial sector, GPS presents a juicy target to potential adversaries and criminals alike, the Department of Homeland Security has recognized. Industry, acting on those concerns, is preemptively developing technologies to protect the GPS signal and identify anyone trying to disrupt its transmission.

The Air Force awarded contracts for the first eight satellites of the next-generation GPS constellation that will improve its capability and security. But back on Earth, technology has progressed to where portable, inexpensive, readily-available jammers threaten the GPS signal for commercial, civilian and military users.

GPS receivers have shrunk to fit inside a smartphone or in the dashboard of a car. But the same developments have made the signal that guides a person to the grocery store, or a warship into a harbor, vulnerable to interference.

An inexpensive Chinese-made jammer the size of a pack of playing cards can scramble a GPS signal enough to make trucks invisible to GPS tracking. Multiple jammers in one area have the potential to throw ships off course or interfere with airline navigation, Kevin Farrell, general manager for ITT Exelis' position, navigation and timing division, told National Defense.

Exelis recognized the vulnerability and preemptively developed a device that can turn the GPS infrastructure around on those trying to disrupt it. Signal Sentry can detect and geolocate the jamming signal so authorities can stop the interference.

"Jamming is a technology that is very simple and is available at the entry level--you can buy a $20 GPS jammer from the Chinese to keep your boss from knowing where you are delivering goods," Farrell said. "We have proactively developed the ability to geolocate multiple jammers and give law...