DOD to step up defense of GPS signals
- By Bob Brewin
- Mar 21, 1999
The Defense Department plans to add a new set of military anti-jam frequencies to the next series of military Global Positioning System (GPS) satellites to protect its users in what a top DOD official called "navwar," or navigation warfare.
New generations of precision munitions as well as U.S. attack aircraft can tap into highly precise military signals broadcast by the existing GPS constellation, but the Pentagon has serious concerns about the vulnerability of those signals to jamming by enemies who view such efforts as an inexpensive way to render U.S. "smart" weapons less smart.
Mike Shaw, assistant for GPS, positioning and navigation in the Office of the Assistant Secretary of Defense, said that if the current GPS constellation of 24 satellites, which can provide DOD users with positioning information accurate within meters, has "one weakness, it is [its] anti-jam capabilities."
Two years ago the Russians introduced a low-cost GPS jammer at the Paris Air Show for sale on world markets. Shaw, speaking last week at the Coast Guard-sponsored Civil GPS Service Interface Committee meeting in Alexandria, Va., said "it would not surprise me" if potential U.S. adversaries possessed GPS jamming systems.
Shaw declined to say whether one of the adversaries DOD is worried about includes Iraq, where the United States has conducted since last December its most sustained air operations since the Vietnam War.
Navwar concerns will dictate the design of the new GPS satellites, Shaw said, with DOD designating "protection, prevention and preservation" as its top priorities.
Air Force Col. Neil McCasland, chief engineer for the DOD GPS Joint Program Office, said that he believes there are "a number of deficiencies in the military signals" on the existing GPS satellites that can be corrected in the next generation. The new satellites will incorporate technologies that "optimize [them] for high anti-jam capabilities," including "spot beams" that can be used to boost GPS signals in a specific region.
McCasland said the current GPS satellites are susceptible to jamming because of a relatively low power output, and DOD plans to provide higher power on the spot beams and install new antennas on the spacecraft to further boost power.
But, McCasland added, this will require "significant changes to the spacecraft," and DOD does not have much time to make the design changes. "In order to have constellation sustainment, we need to order [the redesigned GPS satellites] in ."
DOD's efforts to test the vulnerability of the existing system could have an impact on other users of the GPS system. However, these users, including Transportation Department administrations, do not want to interfere.
DOT, which along with DOD jointly manages the DOD constellation on behalf of both civil and military users, continues to endorse DOD testing of the GPS constellation for anti-jam capabilities and does not plan to arbitrarily deny permission to conduct such tests.
The Coast Guard operates a nationwide enhanced GPS system for marine navigation that provides position information accurate to within 10 meters. Another DOT agency, the Federal Aviation Administration, plans to start operating its own enhanced GPS system next year that is designed to replace all ground-based navigation systems.
Joe Canny, DOT assistant secretary for transportation policy, said DOT does not want DOD "jamming in areas that would effect maritime or aviation safety.... We certainly don't want them testing while an airplane is on a final approach to O'Hare [Airport]." But Canny added that the DOT understands the Pentagon's need to test the vulnerabilities of the system.
"Both civil and military users have to be accommodated," Canny said, "and we can't do that by drawing lines.... DOD will have to continue to test the system, and the civil user community will have to work with that. Accommodations will have to be managed from both sides."