DOT adopts plan to ensure GPS back-up for navigation

Washington DC
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Acceptance by all US Department of Transportation agencies of the recommendations made by the Volpe Center report on GPS signal vulnerability has led the DOT to adopt an action plan to ensure existing radionavigation systems support GPS adequately.

From the viewpoint of aviation and other safety-critical transport applications, the report’s most important and controversial recommendations established that GPS signals were vulnerable to jamming, intentional or unintentional, and that GPS could not be relied on for sole-source navigation.

The report – which was released publicly on 10 September – concluded that back-up navigation systems were needed. This conclusion was so unpopular to the DOT and FAA that they allegedly kept the report under wraps for more than a year, as they tried to find a way to persuade the Volpe National Transportation Systems Center to soften its recommendations.

However, the Volpe Center did little if anything to amend the thrust of the report. And today, announcing the DOT’s decision to put the action plan into effect, US Transportation Secretary Norman Mineta said the DOT would ensure GPS vulnerabilities would “not affect the safety and security of our transportation system as we work to ensure that GPS fulfills its potential as a key element” of US transportation infrastructure.

The DOT action plan lists six major areas of action to maintain infrastructure viability. These are:

  1. Ensuring that adequate back-up systems are maintained
  2. For the DOT to maintain its partnership with the US Department of Defense (DOD) to continue modernizing GPS by adding additional civil signals at new frequencies
  3. Facilitating the transfer of appropriate anti-jam technology from the US military to commercial manufacturers for civil use
  4. Working with the electronics manufacturing and transportation industries to develop GPS receiver standards
  5. Working with state and local transportation departments to promote education advising users about GPS vulnerabilities
  6. Completing a detailed assessment of US radionavigational capabilities across all transportation modes to identify the most appropriate mix of systems – in terms of a balance between capabilities and cost – to serve along with GPS for at least the next decade. This review would include completing the inter-agency evaluation of the long-term need to continue the US Loran-C network.

The DOT’s director for radionavigation, Mike Shaw, says the department does not yet have a definitive idea of the specific actions that will be involved in pursuing the six initiatives.

However, Shaw stresses the DOT has no preconceived bias as to which existing radionavigation systems should be kept and which should be decommissioned. It plans to establish a task force next year to focus on the problem.

Only by polling all of its mode-specific agencies to find the mix that works best for each transport mode and synthesizing their preferences to achieve a workable balance between cost and adequate functionality will the DOT learn which systems it can dispense with, he says.

“In the end we are hoping for a reduced number of mixes [of different radionavigation systems] to serve everyone,” Shaw remarks, noting that the FAA only finished last month its review of Loran-C functionality for aviation. Other aviation radionavigation systems to be assessed will include instrument landing systems, microwave landing systems and VOR/DME equipment.

Shaw concedes much of the basic analytical work on the usefulness of different radionavigation systems as back-ups for GPS has been done “at various levels with various organizations”. New to the action plan, however, is the idea of taking a comprehensive look at how well these systems support GPS across the range of transportation modes.

The DOT also believes its work with the DOD on introduction of new civil GPS frequencies, such as the 1227.60MHz ‘L-2’ second frequency to be introduced next year and the 1176.445MHz ‘L-5’ third signal for 2005, is particularly important.

Along with work to help transfer declassified military anti-jamming technologies to the civil sector, Shaw says introducing additional civil GPS frequencies is highly important in increasing the robustness of the signal against interference.

Shaw says the DOT is now involved in the US government’s GPS 3 program study, which aims to design and develop a new generation of GPS satellites for 2009 and beyond, offering greatly increased functionality for a range of applications.

The existing GPS satellites were launched from 1978 onwards and their signals were only made available for civil use in 1993. “In many respects we’re trying to do things with the current constellation that weren’t thought of the in the ’70s and that the system wasn’t designed to do,” says Shaw.

He concedes that a larger constellation of GPS satellites – as a Heritage Foundation report recommended to the White House last month – would be desirable in terms of signal clarity, but points out the cost and funding implications involved might make the idea unworkable.