Loran to die young?

Domestic loran C, with years of reliable service behind it and a large installed base of users, might be headed for the scrap heap; a possible victim of both GPS and tight budgets. Sources within the radionavigation community say that the Coast Guard, in an effort to save money, could turn off loran as soon as 1998.

This shutoff date differs substantially from the 2015 date stated in the 1992 Federal Radionavigation Plan (FRP). This latter date was chosen to provide a reasonable overlap in coverage between GPS and loran. With tight budgets and with the widespread user acceptance of GPS as receiver prices drop, the Coast Guard and the Department of Transportationofficially responsible for civilian radionavigation systems, as operated by the Coast Guard and Federal Aviation Administration (FAA)are now considering the possibility of an early demise for both Omega and loran. “The pot is boiling on this issue,” said John Weseman, chief of the radionavigation division at Coast Guard Headquarters. “The final mix of systems is being looked at. But there haven’t been any firm decisions at this point.”

The 1994 FRP will be distributed in early 1995 and will reflect official policy. It could well call for an early loran shutdown. One big factor in loran’s fate will be user reaction. “We look closely at what we hear from users,” said Weseman. “It’s difficult to make a case if you don’t have enough input from users. But as program manager for the Coast Guard, I want to do my best to make sure that users get what they need.”

GPS has come on strong in the last few years with prices dropping and receivers finding their way aboard a growing percentage of vessels. (One survey put radionavigation receiver ownership at 52% for loran and 20% for GPS.) Still, GPS has a long way to go to equal the loran user baseestimated at more than one million in the U.S., with about $500 million invested in receiver equipment. Under an accelerated loran shutdown program, those users would be forced to switch to GPS for radionavigation. That wouldn’t be a great hardship for the average recreational navigator, but for those who have time and money invested in loran data, such as fishermen, the change might be less appealing. Many commercial fishermen use loran receivers to locate and then avoid snags, since a snag can be costly in torn or lost nets.

Operating the domestic loran system costs about $17 to $20 million a year. That figure pales when compared to the more than $500 million yearly estimated requirement for running GPS (part of this estimated cost involves the procurement and launch of satellites). On the basis of incremental cost, the added capability that loran gives mariners would seem to be a good deal. Of course, eliminating loran might help to free up funds for the five-year, $15 million program to install differential GPS capability on radiobeacons. (The Coast Guard’s differential GPS system will remove the error purposely introduced into GPS signals by the Air Forceperhaps not the most efficient way to operate a radionavigation system. The irony of this situation has been lost on the Department of Defense, who steadfastly insists that the error is necessary for national security purposes. Developments in GPS signal processing, however, are making this argument increasingly less viable.)

One irony of an early loran shutdown is that full domestic loran coverage for aviation users wasn’t achieved until 1991 when new loran chains were built in the mid-continental part of the U.S. In addition, many of the older tube-type transmitters at East Coast stations, and several other stations around the country, have been replaced with new solid-state units that should still have decades of operational life.

Two radionavigation systems may not make much sense from a cost control viewpoint: if GPS and loran do the same job in U.S. waters, why keep both of them going? Other than the previously reviewed cost differential between loran and GPS, plus the large loran user base, there are navigational aspects that bear consideration.

It is, in fact, the very redundancy of two systems that makes sense to navigators. The cardinal rule of navigation is not to rely on any one source of data. A navigator should always use as many inputs as possible in determining position. Using GPS alone is not an intelligent way to navigate a vessel. (Even with loran shut off, there certainly would be other methods a navigator could employ: radar, celestial, visual bearings, DR, depth readings, horizontal sextant angles, vertical sextant angles, etc.)

Since loran and GPS are so different in frequency, architecture, and method, they are highly independent of each other and a failure in one system would not affect the other. This type of redundancy is highly desirable from a navigational standpoint.

While loran is a “mature” radionavigation system (its antecedents lie in radionavigation systems developed during World War II for bomber navigation), R&D has been done in recent years to improve loran performance and possibly even change the nature of the system. Some experimental studies have looked at tying all loran stations together to a tight time reference (down to 20-nanosecond accuracy) using either time transfer via satellite links or employing GPS as a time reference. Doing this would allow for both masterless and cross-chain loran use. Any selection of stations could be used, either within a chain or across different chains. And with a tightly controlled time base, loran stations could be used in the range-range mode. One could determine the range to various stations to determine a fix. Used in this way, loran could be tied into a GPS position fix as if it were a satellite range.

Tying loran into a GPS fix might seem like overkill, but it actually addresses a problem with something called integrity monitoring. This is a problem that has some worldwide aviation authorities wary of using GPS for precision approach and landing of civilian aircraft. Integrity monitoring arises due to the architecture of GPS. The system was designed to provide a user with four satellites in view. By employing the signals from four satellites, one can determine latitude, longitude, and altitude. However, since one is using all the available satellites, there is no way to check on the integrity of the fix should one satellite malfunction. Because of this, an airliner on a low-visibility landing using GPS might be led astray.

Integrity checking is not just for airliners; it is something that navigators do all the time. A good navigator is always evaluating the data to see if it makes sense. Loran can provide this type of input for those using GPS.

Loran has a built-in integrity alarm called “blink.” Should a station get out of tolerance, it broadcasts the blink indicator. This warns navigators that the station is not to be trusted. There is also the possibility of modulating differential GPS corrections onto loran signals. DGPS corrections can then be sent along to a DGPS-capable receiver. Such an approach would require modification of existing receivers and the addition of demodulation circuitry to new loran units.

From the point of view of a thinking user, loran allows one to make some decisions about using the system; the navigator can get “into the loop” somewhat. Users can choose either TD or lat/long readouts, secondary stations can be user-selected, one can shift chains, change the zero crossing point for sampling the pulse, etc. The workings of GPS, on the other hand, are those of the classic “black box.” There is virtually no way for the user to insert him or herself into the loop (except for properly plotting GPS fixes and integrating them with DR and other navigational inputs).

Even though loran’s days may be numbered here in the U.S., loran seems to have a bright future worldwide. Various nations have decided to either upgrade or install new loran stations in their home waters. The Japanese have taken control of loran stations in the western Pacific from the U.S. Coast Guard. New transmitters have been installed or will soon be installed in Korea, China, India, France, Norway, Ireland, and Germany. Meanwhile, Spain, Portugal, and Italy are also considering constructing chains. “Loran is growing worldwide,” said Gene Brusin of Megapulse, Inc., which manufactures solid-state loran transmitters. “Other countries see it as a highly accurate, dependable network.”

Still, the budgetary pressures are substantial, and even though the FRP gives a shutoff date of 2015, that may change. “The FRP is a plan; it isn’t set in concrete,” says Weseman at Coast Guard HQ. “Budgets are tight, and this year there will be close oversight on these systems.”

Given the large user base, the money invested in loran equipment, the increasing worldwide use, and the possibility of improvements to loran capabilities, there are some very good reasons to maintain the original shutoff date and keep loran on the air. However, unless loran users make their opinions known by writing, calling, faxing, or e-mailing their Congressional representatives, then the Coast Guard and the Department of Transportation may well decide to retire loran within the next few years.

By Ocean Navigator