"From the day we built GPS, we've been working on ways to overcome jamming," said Lt. Col. John Carter, chief of space requirements at the Pentagon. "We're very confident we can do that."

GPS is a constellation of satellites that emit electronic signals while orbiting the Earth. A GPS receiver gathers the signals from multiple satellites overhead, then triangulates those signals to calculate its precise location. Those receivers can be hand-held or mounted in ships, aircraft, vehicles and precision guided munitions.

The United States routinely installs GPS guidance packages in standard 500- 1,000- and 2,000-pound bombs to create the Joint Direct Attack Munitions. The JDAM typically strikes within 13 meters of its target.

According to reports, Iraq has acquired several Russian-made transmitters capable of jamming the GPS signal.

In general terms, someone could "jam" a radio signal by transmitting a more powerful signal on the same frequency. Carter equates the practice with trying to listen to a conversation on the other side of the room while another person shouts in your face.

While the tactic may seem easy to accomplish, Carter said he would not encourage anyone to take the job.

"Anyone who (transmits) on the battlefield can be found, and anyone who can be found can be targeted," he said. "When the bad guys are picking jobs, (they) don't want to pick 'GPS jammer.'"

A GPS jammer is not a silver bullet to prevent precision bombardment, Carter said, because the Air Force has more than one way to put steel on target.

"Oftentimes we get sucked into looking at individual engagements, and warfare is not an individual engagement," he said. "It's the sum of all the actions you take. We have a lot of arrows in our quiver."

Those include the inertial navigation system within the JDAM, its primary navigation system, which is fully capable of guiding the weapon to its target. The Air Force also employs laser- and optically-guided munitions, as well as free-falling bombs.

The Air Force also is looking ahead to ensure future GPS satellites are more jam-resistant, beginning with the current crop of modified GPS IIRs.

"One of the features of the modification is something called flexible power, which increases the power level radiated from the GPS," said Peter B. Teets, undersecretary of the Air Force and chief of the National Reconnaissance Office.

That power increase will provide some anti-jam capability, but Teets said the real improvement will come when the GPS III is introduced in about 10 years.

"We recognize the fact that GPS can be jammed," Teets said. "We're taking steps to make it much more jam-resistant on the satellite side, on the control-element side and on the user-equipment side.

"I think we're doing the necessary smart things to enable GPS to serve us well," Teets said.

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