Experts debate NAS-wide GPS jamming threat

 - March 28, 2011, 8:10 AM

At press time, the first of three monthly reports of the technical arguments between experts from LightSquared and the GPS community over GPS jamming was about to be issued. LightSquared proposes to offer NAS-wide high-speed voice and Internet service under a waiver of FCC satellite rules that would permit such transmissions from 40,000 powerful ground stations in the 1525 to 1559 MHz band allocated to low-powered satellite signals. That band is next to the 1560 to 1610 MHz band containing the sole civil GPS frequency, reportedly a billion times weaker than LightSquared’s signals.

Garmin simulations showed that spillover from LightSquared’s stations started to interfere with a TSO’d GPS airborne receiver at 13.8 miles and totally jammed it at 5.6 miles. Garmin warned of potential “widespread severe GPS jamming,” that would “deny GPS service over vast areas of the United States.” LightSquared asserted that GPS would be unaffected, and that the ongoing three months of testing and analysis would confirm that hypothesis. Nevertheless, the Departments of Defense, Transportation, Commerce and Homeland Security, as well as the civil GPS Industry Council, filed objections with the FCC, citing “significant interference concerns.” Separately, FAA sources warned AIN of potentially “serious impacts” on NextGen.

However, LightSquared suggested that jamming avoidance was not entirely its responsibility, implying that GPS users should also take preventive steps. In March 10 testimony before the House Subcommittee on Commerce, Justice and Science Appropriations, Trimble Navigation vice president and general counsel Jim Kirkland rejected that approach, stating that “LightSquared must bear the costs of preventing interference emanating from [its] devices, and if there is no way to prevent interference, it should not be permitted to operate.”

Space-based Augmentation Systems

In separate satnav news, an EASy II-equipped Dassault Falcon 900LX has been the first private aircraft to fly LPV approaches to 250-foot minimums using the European Geostationary Navigation Overlay Service (Egnos)–a Waas equivalent. Waas and Egnos are space-based augmentation systems that provide ILS-equivalent Category I approach guidance without the need for ground stations.

Seven successful approaches to Pau-Pyrenees Airport in the mountainous region of southwest France confirmed Egnos precision, estimated as being close to one foot on the runway. In this instance, Egnos was correcting GPS signals, but in the future it will also support Europe’s Galileo and, possibly, Russia’s Glonass satellite navigation systems.

Russia and the FAA employ different management styles. Earlier this year, a large Russian rocket carrying three Glonass satellites fell into the Pacific after launch, due to incorrect fuel loading. Russian President Medvedev promptly fired two top space agency officials. Shortly before, the U.S. DOT had reported that Eram, an essential NextGen traffic management system already accepted by the FAA, would require five more years and cost an additional $500 million before it could meet agency specifications. No FAA staff changes were announced.

In fact, when all the numbers have been added up, the FAA will doubtless boast that it saved a large amount (but nowhere near $0.5 billion) of its FY09 and FY10 Waas budgets by not having to cover monthly payments for the lease of space for the Waas transponder on the Galaxy 15 satellite. That satellite went rogue in April last year, when it set off for an unscheduled nine-month stroll an eighth of the way around the world, miraculously dodging 15 other GEOs as it went. Galaxy engineers finally corralled it in January almost 45 degrees west of its original location, disabled its wanderlust circuits and headed it back east to resume normal Waas augmentation. Fortunately, the FAA always has two Waas GEOs in orbit, so there was little loss of continental U.S. coverage during Galaxy 15’s absence. o