- US Army issues RFI for eLoran and GPS-integrated receivers
- Civil and military aviation communities are conscious of the need to deploy a reliable backup system for GPS
The US Army Contracting Command issued a request for information (RFI) from potential industry suppliers covering both stand-alone enhanced Loran receivers (eLoran) and receivers integrated with global positioning systems (GPS) on 14 January.
These receivers would be used on US Army and other Department of Defense maritime, aviation, or land vehicle platforms, and for position and timing purposes.
Interested responders were requested to provide a “rough order of magnitude” of individual unit costs, based on an order for 50,000 units.
The request was accompanied by a list of the characteristics of currently available equipment, along with a list of the characteristics of future equipment, assuming a five-year development effort. The latter included the predicted size, weight, power, and cost of fully integrated eLoran/GPS units, plus other anticipated needs, including operations in areas where GPS would be unavailable such as indoor, underwater, and urban environments.
The army’s request was not unexpected. In recent years, the US military has sought a solution to the threat of GPS jamming and ‘spoofing’ (an adversary’s transmission of false but more powerful GPS signals). Extensive evaluations of various combinations of transmissions via VHF omnidirectional range (VOR), distance measuring equipment (DME), and ground-based radar, carried out by the civil/military National Positioning, Navigation and Timing (PNT) Advisory Board, determined that none of these fully met the GPS backup requirement.
The PNT Symposium in October 2014 reached three principal conclusions: the Federal Aviation Administration (FAA) is dependent on GPS for navigation, surveillance, and network/infrastructure timing; most NextGen benefits currently rely on GPS and this reliance will increase in the future; and GPS is a very weak signal and therefore vulnerable to unintentional or intentional interference. The GPS signal is almost a billion times weaker than other navigation signals: inexpensive jamming and spoofing equipment and user tactics are widely available on the internet.
Even before the PNT Symposium, the US Army began its own assessment of eLoran’s capabilities, following successful trials by the General Lighthouse Authority in the United Kingdom. During one test off the UK east coast, held under typical GPS jamming conditions, one ship’s GPS position showed it to be several miles inland, whereas eLoran was unaffected.
While different in operation from the earlier Loran C navigation system, eLoran would continue to employ the very large antennas of its predecessor plus its extremely powerful, very long range, and essentially unjammable transmissions. In its enhanced form, the ‘raw’ Loran signals are electronically processed prior to their final transmission to compensate for several minor issues that tended to affect accuracy of the earlier Loran C.
Processing improvements in eLoran include corrections for differential terrain effects, performed by small local stations much closer to the user’s position (seven are under development in the United Kingdom and Ireland). These stations then pass the final position data to users over the worldwide GSM cellular network.
Tests by the Dutch Pilots’ Corporation (NLC) consistently demonstrated a five-metre accuracy standard, as have similar tests in the United Kingdom by Trinity House, which requires a near-GPS quality backup navigational aid to maintain safe separation for vessels in the English Channel.
Other nations, including China, Japan, Russia, Saudi Arabia, and South Korea – all of which still have Loran C infrastructure – are reportedly planning eLoran upgrades to their earlier installations.