When GPS falters, where will the military turn?

Whether you use it to find the closest grocery store or guide an artillery shell to its target, GPS has become the most ubiquitous navigational tool since the North Star.

Using 32 satellites in circular orbits around the Earth, the Global Positioning System is capable of providing time and location information in all weather conditions anywhere there is unobstructed sight to four or more satellites. The Defense Department created it, beginning in the 1970s, and achieved full operational capability in 1995, at that time with 24 satellites. The military has since relied heavily on GPS for such things as navigation, target tracking, and missile and artillery guidance.

But as useful as the system is, the technology is vulnerable to attack.

The relatively weak signals sent out by the satellites can be spoofed by stronger signals, sending receivers off-course. One example is the Iran-US RQ-170 incident in which an Iranian cyber warfare unit spoofed a UAV into landing in Iran. Students from the University of Texas at Austin also have conducted tests in which they took control of drones and an $80 million yacht using GPS spoofing.

The signal can also be jammed with small, low-power devices that can be easily bought on the Internet and have been used to hide locations or commit crimes. Last year, an engineer from New Jersey, in an effort to hide his whereabouts from his employers, used one of the devices to jam an airport GPS navigation system whenever he passed by.

GPS Block IIR(M) satellite

With its dependence on GPS and other satellite-based communication tools for nearly everything, DOD has begun raising questions about the weaknesses of the system.

“Needless to say, that is a capability that we are going to just have to sustain. The world wouldn’t have it any other way,” Gen William Shelton, chief of the Air Force Space Command, said at a breakfast on Feb. 7 discussing the new GPS III system, as reported by National Defense Magazine. “Do we have too much dependence on GPS? That is the question we are starting to ask across the Department of Defense. The answer is not to get off GPS, however. That will never be the answer in my view.”

The new GPS III system is expected to affordably replace legacy GPS satellites and improve anti-jamming capabilities. The system includes a new military code, or M-code, that uses a different frequency than public signals and is more resistant to jamming.

Regardless, the military has recognized the need for back-up navigation systems and has begun developing new technologies to meet the demand.

For instance, the Defense Advanced Research Projects Agency has been developing chip-scale inertial measurement units (IMUs) and chip-scale atomic clocks. The program has been focusing on shrinking the size of atomic clocks and IMUs to a single chip the size of an apple seed. By combining inertial movement information and the exact timing of atomic clocks, the chip should be able to function as a GPS-free navigational tool.

Meanwhile, engineers in the U.K. have taken a different approach. At a conference at the U.K.’s National Physical Laboratory (NPL) on Feb. 12, researchers described a system using low-cost sensors that can pick up information about the environment, such as terrain height and magnetic fields, which would then be cross-referenced with a database in real time to determine locations. 

These systems would still require an initial GPS reference, however, and would be a mid- to long-term solution to the problem.

Another possible solution derives itself from World War II-era technology. Loran, short for Long Range Navigation, enabled ships and aircraft to determine location and speed from low-frequency radio signals that are transmitted by radio beacons. Made obsolete by GPS, the system was shut down in 2010. However, a new, digitized-version of the system, called eLoran, has been gaining ground as a possible GPS back-up system.

eLoran signals are nearly unjammable due to their high power; the signals have about 1.3 million times more power than GPS signals. The radio towers are land-based, meaning that they are not susceptible to space debris or space warfare and can operate concurrently with GPS, but can only provide a certain range.

Several countries have already implemented eLoran, including South Korea, which has been affected by North Korean GPS jamming, and the U.K. for use in maritime shipping. Meanwhile, the United States is still trying to come up with a plan to implement the system. While several departments such as DOD and the Homeland Security and Transportation departments have an interest in the system, none of them want to pay for the entire program as budgets continue to shrink.

While exploring possible solutions to the GPS back-up problem, DOD also is developing contingency plans for the worst, with the services holding “a day without space” training exercises featuring degraded communications and GPS capabilities.


About the Author

Joey Cheng is an editorial fellow with Defense Systems.

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