GNSS Vulnerability: The Unresolved Problem


In May 2009, Professor Brad Parkinson of Stanford University testified before a congressional committee in Washington, DC on the danger of a ‘brownout’ of the GPS constellation, due to some satellites reaching the end of their useful lives before replacements could be launched, writes Bob Poole.
Parkinson gets attention when he speaks about GPS, because earlier in his career, as US Air Force Colonel Brad Parkinson, he served as the chief architect of the GPS programme. And while the ‘brownout’ problem has apparently been resolved, the larger problem of GPS/GNSS vulnerability has not been.
Although ever-increasing portions of the world economy depend on GNSS, not only for navigation but also for precise positioning (e.g. in surveying and in farm irrigation) and timing (e.g., electronic time-stamping of financial transactions), there is still no back-up system in place, or even in an agreed-upon planning stage.
Back in 2007, the US Department of Transportation and Department of Homeland Security set up an Independent Assessment Team to assess the seriousness of GPS vulnerability and weigh the pros and cons of potential back-up systems. This group of experts was chaired by Professor Parkinson.
Its unanimous recommendation was that a modernized version of LORAN, called eLORAN, was the best choice, all things considered. LORAN is a long-range navigation system put in place in the 1950s, primarily for oceanic navigation. It operates in a completely different frequency band (100 kilohertz), compared with GPS at 1.5 gigahertz. Jamming eLORAN is possible, but requires a huge and conspicuous source of power. And while eLORAN is not as effective as GPS, it can serve as an adequate back-up. In addition, its cost is quite modest.
GPS Back-up
The Independent Assessment Team’s recommendation was accepted by both DHS and DOT, and DHS announced in February 2008 that it would begin implementing eLORAN as the GPS back-up. But then a strange thing happened. The report disappeared from public view, and the federal Office of Management & Budget continued its long-standing effort to zero-out funding for LORAN (including development efforts for eLORAN) in the Coast Guard’s budget.
In early 2009, the new Obama Administration’s budget called for terminating LORAN, and in February 2010 the Coast Guard ceased LORAN-C transmissions. (In announcing the impending termination, the agency urged users to shift to GPS!)
Since that time, concerns about GPS jamming have arisen in both the U.S. and the U.K. Inexpensive GPS jammers are available via the internet for as little as $150, and truckers using such jammers on I-95 next to Newark airport have made it impossible for the FAA to certify a Honeywell Ground-Based Augmentation System for operation at that airport.
Two more-recent events have increased people’s awareness of the GNSS vulnerability. One was warnings from many scientists that upcoming solar storms could short-circuit electric power grids and disrupt GNSS signals.
The other was the U.S. Federal Communications Commission’s premature approval of a plan by  broadband communications company Lightsquared to install up to 40,000 terrestrial base stations operating on L-band frequencies adjacent to the L1 band used by GPS (both civil and military). Both the FAA and the Defense Department raised objections, and avionics firm Garmin presented test data showing ‘disastrous interference’ with GPS receivers from a simulated Lightsquared base station.
Concerns
In response, the FCC has required the company to work with the GPS community to assess the interference problem. The working group submitted their test protocol to the FCC on Feb. 25, but both DOT and DOD expressed concerns about its inadequacies in a letter to the FCC dated March 25.
As these concerns were being raised, the Royal Academy of Engineering in London released a report early in March called Global Navigation Space Systems: Reliance and Vulnerabilities. Like previous reports from various expert bodies in the United States, it documented the growing worldwide use of GNSS, not only in transportation but also in agriculture, finance, and numerous other fields. It reminded readers that all GNSS applications are vulnerable not only to failure but to disruption and interference, both from nature (e.g., solar flares) and from human causes, both inadvertent interference and deliberate jamming.
This report underscores two points which are often not appreciated by the aviation community:

  • GNSS vulnerability affects a vast portion of economic activity, not just aviation or transportation;
  • GNSS vulnerability is a global problem.

Consequently, back-up system(s) must be across-the-board (not aviation-specific) and global in nature.
Like most previous assessments that meet the above criteria, the Royal Academy report identified eLORAN as the best available option as the back-up system. That was also the conclusion of those taking part in the Global Navigation Satellite Systems (GNSS) Interference, Detection, and Monitoring Conference in London in March.
As the largest single GNSS user and provider, the United States, in my view, has a special responsibility to make implementation of a GNSS back-up capability a high priority. If the Obama Administration is aware of some heretofore unknown defect in eLORAN that makes it unsuitable as the GPS backup, it should make that information public, before Europe and the rest of the world move forward. And in that case, it also has an obligation to propose an alternative that is both suitable for all applications (not just aviation or transportation) and usable worldwide.
Robert Poole is Director of Transportation Policy at the Reason Foundation, a think tank based in Los Angeles. An MIT graduate and former aerospace engineer, he is a member of the Air Traffic Control Association and of the U.S. Government Accountability Office’s National Aviation Studies Advisory Panel.
Read more:
UK study reveals extent of GPS jamming
LightSquared cannot coexist with GPS: official report
SmartPath GBAS trials to thwart jammer threat
Aircraft divert in wake of large solar storm