GPS and similar satellite systems can fail or be jammed. Existing terrestrial systems, such as VOR and ADF are being switched off or are unreliable. Access to an alternative technical solution with adequate accuracy, low cost but different failure modes is important for the integrity of IFR navigation.
eLORAN is an evolution of the earlier LORAN system. It relies on a series of ground-based transmitters, supplemented by a digital signalling channel. Accuracy depends on the number/range of transmitters but can be 20 metres or better. It provides horizontal but not vertical (height) positioning. eDLoran adds local differential position corrections (similar to GBAS for GPS) to achieve 5 metre accuracy as proven in a recent trial at Rotterdam. High power transmitters (typically 1MW or more) deliver a signal 1 million times more powerful than GPS, reducing the risk of jamming.
In 2007, the US Administration announced adoption of the eLORAN system and spent $160 million on it. But the program was cancelled during budget cutbacks during 2010. Earlier this year, congress passed a bill barring further dismantling of LORAN sites while it reconsiders the situation.
Here in the UK, Trinity House (who look after Lighthouses) announced plans to deploy 7 transmitter sites between Aberdeen and Dover to service marine traffic, especially in the English Channel. The project was scheduled to complete summer 2014, but there has been no publicity of its recent status. Full UK port coverage is planned for 2019. Other European countries also have eLORAN capability, although Norway “decided to shut its sites down at end 2015”: http://uk.reuters.com/article/2014/05/13/shipping-gps-idUKL6N0NT66F20140513. South Korea is deploying their own eLORAN system after extensive GPS jamming attacks from their neighbour.
It does seem to be quite an effective solution for complete GNSS outage, and if widely adopted could provide a useful backup. It would provide the same lateral navigation guidance to at least RNP0.3 and as good as 5 metres but without vertical positioning. This should be more than adequate for en-route navigation and LNAV approaches. From a pilot’s perspective, perhaps an external iPad/Android receiver could be developed quite cheaply in the first instance, with certified kit following thereafter. The user wouldn’t notice any difference in using navigation software, except have a higher chance of receiving accurate positioning information.
I had not heard of eLORAN until recently. It does seem that the technology, mostly developed by a US company, would be a worthwhile national asset and may be deployed in Europe before North America.
My view would be to scrap the failed European Galileo project and spend the money on eDLoran immediately, with a view to covering airports as well as seaports.
Further reading:
Various publications by Greater Lighthouses Authority (UK & Ireland) including their long term eLoran strategy, GPS Jamming presentations etc.
US status reported early 2014I think it’s more an attempt of an old industry to make some money out of a horse so dead it doesn’t even smell anymore.
For en-route navigation, gyro platforms are fine and on board of every airliner. For terminal backup navigation, DMEs are the the most cost effective way. No need for eLORAN or other expensive solutions.
My view would be to scrap the failed European Galileo project and spend the money on eDLoran immediately, with a view to covering airports as well as seaports.
What exactly has failed about Galileo? The first satellites are up and the rest will come. The nature of an EU project made it a bit complicated and its issues transparent. Such undertakings tend to cost more and take longer than estimate and in order to get a big project through, you have to sell it as costing x billion and taking y years while knowing that both variables have to be doubled. It’s how the game works.
My view would be to scrap the failed European Galileo project…
Failed? Because two satellites of 30 didn’t reach their orbit? It takes a little more than that for a system failure.
AFAIK there are no plans regarding the installation of eLORAN chains other than along some coastal regions of the United States and the (still) United Kingdom.
I think, that a good backup for GPS would be “ground based satellites” which transmit their signals from fixed locations on the ground and can be received by normal GPS receivers runningh special software. China has been investigating this for some time (Link).
“ground based satellites"
Isn’t that what GBAS is supposed to be? I doubt however that GBAS will be largely deployed, because it’s quite expensive and SBAS good enough for most cases.
I find the claims about LORAN being unjammable quite amusing. The claim “1.3 million times stronger signal” which would mean something like -80dBm – hardly unjammable. Furthermore, LORAN operates roughly in the same frequency band as NDBs – the frequency band that gives you huge noise levels during thunderstorms, night time over the horizon propagation, costal effects, etc. Also, it’s the frequency band most affected by man made interference, from eg. (leaking) DSL cables, power line modems, etc.
The LORAN wavelength is about 3km, roughly 10000 times longer than GPS. Antennas scale with wavelength, so while your eLORAN receiver might be portable, any reasonably performing antenna won’t be. “Small antennae” (relative to the wavelength) tend to be narrow band (or badly lossy), so using them would negatively affect navigation performance.
DCF77, the german timepulse transmitter, operates at a similar frequency (77.5kHz). Their antenna, while impressive in size, it has a Q too high (i.e. it is still too small) so that it negatively affects the accuracy of their pulse per second timepulse!
So to conclude, when LORAN was developed a century ago, it was necessary to design it like it is, because it wouldn’t have been possible otherwise with the technology at the time. But nowadays, the system just doesn’t make any sense anymore.
Isn’t that what GBAS is supposed to be?
GBAS (Ground Based Augmentation System) transmits differential correction information over VHF from groundstations but still relies on the basic GNSS satellites to provide positioning. It’s not independent and would fail if GNSS wasn’t available. This is similar to SBAS (Satellite Based Augmentation Systems such as WAAS, EGNOS) where the correction data is sent by separate geostationary satellites.
unjammable
Not unjammable – I doubt if any radio signals could ever claim to be that inpenetrable – but I can’t see a bunch of cheap (e.g. Far Eastern) LORAN jammers being offered on eBay etc. for mass consumer use at low prices as we see today for GPS. They would have a much smaller potential market so probably not worthwhile to make.
Failed? Because two satellites of 30 didn’t reach their orbit?
4 satellites launched so far. Only 2 working. 2/30 sounds much better than 2/4. I’d say that wasn’t a great success to date. It certainly leaves plenty of room for improvement. I just question whether this is the best use of funds when there are other GNSS systems available for use. I can’t see mass consumer equipment (including much of the costly aviation kit) being upgraded to use Galileo just for the European market when plenty of low cost GPS stuff is available already.
EGNOS was and is a much more useful investment.
good backup for GPS would be “ground based satellites” which transmit their signals from fixed locations on the ground
I had not heard of that option. I wouldn’t know if this is intended only for en-route/high altitude or short range/approach phase. Presumably it would have to be near line of sight, so couldn’t be used for relatively low level GA point to point navigation.
I do not think LORAN signals can realistically be jammed. With a signal strength so much better than GPS, it would take more equipment that you can hide in one – or ten – large trucks.
The great advantage of LORAN for aviation would be that it is so completely complementary to GPS. The two systems simply do not have each other’s weaknesses. I would imagine that with two boxes with both LORAN and GPS recievers integrated, there would not really be a realistic single failure mode left.
In the US LORAN-C provided IFR en-route, terminal and non-precision approach navigation for more than 20 years until it was shut down in the beginning of 2010. (See the Flying Magazine July 1990 issue, where J. Mac McClellan reviews the then revolutionary King KLN 88 after having flown it himself for a year.) Accuracy seem to be comparabel to GPS and can be augmented locally in the same way as GPS – LAAS/ DGPS/GBAS.
I suspect that the historically long time span without significant conflicts in most of the Western World has made us close our eyes to how easy and cheap it is for anybody to jam GPS reception. NDBs and VORs are now being steadily decomissioned in most countries, and multiple-DME lack coverage, are much less accurate and recievers are too expensive for GA generally. In this picture LORAN seems an ideal backup to the GPS system.
Q. How accurate could a digital magnetic compass be made?
and multiple-DME lack coverage, are much less accurate and recievers are too expensive for GA generally
I’ve always been of the impression the multiple DME recivers are very accurate.
The expensive is just like everything in aviation – regulatory with my 90 quid mobile phone being far more advanced.
The accuracy of DME is 0,25NM + 1,25% of the distance. And of course DME navigation is restricted by line-of-sight, which is probably why it is not regarded as a primary means of navigation for GA. GA tends to fly low and land at places with no DME in “sight”.
The accuracy of eLORAN is reportedly 8 meters. LORAN C was around 100 meters.
Let’s bring back the eAdcock radio range. ELoran, come off it.
I am not sure why people are so in need of a GPS backup when they happily flew with a single VOR.
GA doesn’t need anything more than GPS and multiple GPS if in controlled airspace IMHO.
