Basement-built jammers: new data defines the risk

Aviation International News » December 2002
May 9, 2008, 4:44 AM

The October announcement by Raytheon that it had won a Department of Defense contract–potentially worth $25 million–to develop next-generation anti-jamming systems for GPS underlines security specialists’ concern that GPS is now “an attractive target” for terrorists. But less well appreciated is the fact that non-military satellite facilities, such as the commercial communications satellite networks upon which international operators and segments of the U.S. civil and military depend, are also potential targets.

During Operation Desert Storm  in 1991, some 45 percent of the military’s communications traffic was via commercial satellites, according to an August 2 report by the General Accounting Office (GAO). Furthermore, according to the same report, all of the U.S. military’s satellite communication during operations in Somalia in 1993 was via Russian satellites.

Military sources told AIN that there are three main ways that GPS and communication satellite systems could be attacked. The first is a direct assault on the satellites in space orbit; the second is an attack on the ground-control segment; and the third is denial of satellite signals to users.

In the current environment there appears little likelihood of attacks on the satellites, although some believe this is not entirely out of the question. Certainly, the DOD’s GPS ground-control segment is securely guarded. But the GAO reported that commercial satellite control centers have little physical protection against a determined adversary.

The most likely threat to civil aviation within the continental U.S. appears to be disruption of the user signals. With GPS, the main signal interference techniques are jamming, where incoming signals cannot be adequately received; and “spoofing,” where signals appear normal but provide false positions. In the communications satellite case, jamming would most likely be via cyber attacks against the ground-station control system or by direct jamming of its uplinked signals to the satellite, thereby preventing their retransmission to airborne users.

And, while security experts caution against underestimating the capabilities of terrorists, they point out that GPS spoofing requires fairly specialized equipment, as does jamming the uplinked communications satellite signals. However, they are concerned about cyber attacks.

For domestic civil aviation operations, therefore, GPS jamming appears to be the major threat, and this has been recognized in the Department of Transportation’s March 6 action plan for mitigation of GPS interference. Under this plan, the DOT’s Office of Science and Technology (OST) was directed to “facilitate transfer of DOD anti-jam technology for civil use.”

However, OST officials told AIN that the DOD now appears unready to move quickly on this–possibly due to the present Iraq situation, where release of anti-jamming technology may be deemed contrary to current national security interests. According to an FAA official, while the DOD would prefer to release the technology to just one (potentially more secure) class of civil operators, this would inevitably risk protests from other classes on the grounds of flight safety alone. (On the other hand, economics may prevent proliferation–“nulling” anti-jam antennas could cost more than $80,000 each.)

By contrast, The Wall Street Journal recently reported the cost of a four-watt GPS jammer built from plans off the Internet could be as low as $40, and described the power of the received GPS signals as being one-thousandth that of a single Christmas tree light. The FAA’s traditional response to concerns about the low power of GPS signals has been to say that the next generation of satellites will transmit at much higher power, rendering cheap jammers ineffective. Unfortunately, the agency often fails to add that these new satellites are many years away.

In any event, the FAA has no stated policy regarding the installation and use of GPS anti-jamming equipment, and none appears to be in process, although AIN understands that certain unapproved anti-jam devices may now be offered
on the Internet. An informed FAA source suggested that such equipment could be installed, if it could be shown not to degrade normal GPS performance. But military tests have shown that some early, less sophisticated, “null steering” anti-jam units can also cut out valid signals from the same sector as the jammer.

Interference with a radionavigation aid is a federal offense, and until recently has required an FBI investigation before corrective action could be taken, making for a lengthy process. A new agreement with the Department of Homeland Security now allows local law-enforcement officials to act with the FAA in the event of jamming, with a suppression target of six hours from the first interference report. But this doesn’t include intermittent or moving jammers, which are likely to be preferred by terrorists.

Therefore, the watchword appears to be constant vigilance, with immediate reporting of any apparent anomalies to ATC and reversion to backup navaids. In fact, the FAA is expected to soon introduce a specific GPS-failure transponder code.

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