Reprieve for loran in DHS budget

 - February 27, 2008, 4:58 AM

Just when many thought loran was dead, it is coming back, albeit in a different guise. The President’s recently released FY2009 budget includes funding for the Coast Guard to continue operating the current loran network in readiness for its upgrade in 2009 to enhanced loran (eLoran). The system is an advanced version of the legacy system where, instead of its transmitters operating in regional groups, or chains, each station transmits individually, as a component of a much larger configuration covering the continental U.S. and beyond.

Flight trials by the FAA’s Atlantic City Technical Center typically received more than 25 separate, but simultaneous, eLoran position lines, which were then processed in similar fashion to that used in the “all in view” GPS satellite technique, and the most accurate position derived. While the resulting accuracy was not equal to GPS, it was substantially better than traditional loran, and for much of the time was remarkably close to the satellite positions.

System Reinvention
But the move to eLoran does not signal its return as simply a rehashed older navaid. In fact, the transition to–and subsequent management and operation of– eLoran will next year move from the Coast Guard to the National Protection and Programs Directorate of the Department of Homeland Security (DHS). This is be- cause the DHS has chosen it as the backup timing source for national infrastructure elements that depend on GPS time, reflecting the fact that navigation is now of less strategic importance to the nation than the availability of highly accurate timing signals transmitted from GPS. Since the development of GPS in the 1970s, the system’s timing signals have become essential components of the nation’s critical infrastructure–such as communications, utilities and banking–where knowledge of position is irrelevant. However, a severe GPS outage today could cripple these services.

Is such an outage likely? It’s certainly possible, because GPS signals are weak and can be jammed easily. The potential threat is real, which is why a backup is urgently required. The DHS chose eLoran on the unanimous recommendation of an expert panel that found there was no other backup that had the capabilities of eLoran in the three most critical areas. First, it has near-GPS timing accuracy, to meet the country’s super-precise Stratum 1 time standards. Second, its signals are essentially unjammable; and third, it has failure modes that are totally different from GPS. That last is important. While Europe’s Galileo and other nations’ GPS-like satnavs in development all share the high accuracies of GPS, they also share its vulnerabilities, so they can’t be backups. But several of those nations also operate their own loran networks and are expected to convert them to eLoran.

So should operators be thinking about buying an eLoran avionics unit to back up thaeir GPS? Right now, no, but that might be necessary later. The no is because it seems highly unlikely that there would be much demand for “standalone” eLoran avionics units, and therefore none are expected on the market. What seems much more likely is that because the National Airspace System will depend heavily on GPS-supported ADS-B, Homeland Security could require that eLoran be integrated with the ADS-B’s GPS as an autonomous backup navigation sensor.