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AS FAR as Logan Scott was aware, the date was 28 September 2017 and he was at a conference centre in Portland, Oregon. But that was not what most of the smartphones around him seemed to think. Many of them were displaying a location somewhere in Europe. Others were saying it was January 2014 and refusing to send texts or emails.

Fittingly, the conference was about global navigation, and the problems began as Scott was presenting a talk on how GPS receivers can be fooled. He borrowed a detector and tracked down the source. It turned out that a GPS signal generator used for testing had not had its terminals properly capped.

The mistake was soon put right, but a deliberate attack could be far more destructive. GPS, originally developed by the US military for defence purposes, is now used for everything from power grids to financial trading, ambulances to air traffic control. To reduce the risks of relying on it, the European Union is building its own satnav, Galileo, a system that has become a political football in the UK鈥檚 negotiations to leave the union. But perhaps backing up satellites with more satellites isn鈥檛 such a stellar idea. Instead, a more down-to-Earth technology, with its roots in the second world war, could be re-enlisted in our defence.

We have become used to the power of satnav. Pull out your phone and it will give you your position in seconds. To reach this nirvana of navigation we have travelled a tortuous road, built by pioneers who understood how the dimensions of space and time are intertwined (see 鈥�Getting there鈥�).

Time is also at the heart of satnav systems such as the Global Positioning System. Each of the 31 GPS satellites sends out a time signal from atomic clocks on board. A receiver on the ground can work out its own location from how long it takes those signals to arrive.

GPS receivers are small and cheap, and the most accurate can give time to within a nanosecond and position to within millimetres. This has made satnav indispensable not just for navigation but also for any system that depends on precise timing. It allows power grids to manage the interplay of supply and demand, synchronises data transfer in phone and other communications networks, and time-stamps financial trades.

The trouble is, the signal comes from more than 20,000 kilometres up and is very weak by the time it reaches us. A cheap, pocket-sized signal-jamming device can easily overpower it. Consultant engineer , who often appears as an expert witness in court cases, says he is 鈥渟eeing such devices used by criminals all the time鈥�. For instance, some high-tech car thieves use satnav jammers to avoid being tracked as they drive away.

A more insidious threat is spoofing: the use of a signal to overpower the satellite and fool devices into giving a false position and time. This is what Scott saw in Portland, albeit in accidental form. In that case, although the signal leaking out of the spoofing device was a tiny, it was enough to, in effect, transport much of the conference centre to another place and time. And it disabled email and text because the incorrect date took phones outside the validity of their security certificates, Scott thinks.

A sophisticated spoofing attack, broadcast at a higher power across a whole city, could cause far worse problems. That鈥檚 something 鈥渁 technically literate terrorist would find quite straightforward鈥�, says Last.

There are many other threats. A cyberattack could disrupt satellite control. The owners of satellite constellations could simply withdraw open access to their positioning signals. Accidental software glitches have been known to mess up the signals too. And outbursts of plasma from the sun can cause turmoil in the magnetic shield around Earth, which in rare cases could disable satellites.

It鈥檚 possible to reduce some of these threats; we can make receivers smarter, and prosecute people who use jammers and spoofers. New systems such as Galileo will boost the resilience of satnav overall; it would be difficult for a cyberattack to take them all out at once (see 鈥�The four constellations鈥�). And Galileo users can pay for authenticated signals that are harder to spoof.

But all these defences are limited, which is why Last champions a more comprehensive backup. Enter Loran, developed in the second world war to help aircraft pilots find their way. The name is short for long-range navigation, and the principle is similar to that of GPS 鈥� masts transmit a synchronised radio signal and a receiver compares the travel time of different signals to work out its position. The most recent version of this technology, Loran-C, was used around the world for decades, especially by ships, until the spread of GPS in the 1980s.

By 2004, the US government had recognised the vulnerability of GPS and called for a backup system. A few years later the Department of Homeland Security announced it would be that had been in the works since the mid-1990s. The new version was synchronised to Coordinated Universal Time, which is needed for time-stamping financial trades. It could also be made more accurate by adding differential stations, fixed receivers that transmit position corrections to nearby users.

Even better, eLoran is very difficult to jam or spoof. The signal is tens of thousands of times stronger than GPS, because the transmitters are no more than 1000 kilometres away and do not have to rely on tiny power sources as satellites do. What鈥檚 more, eLoran signals have a wavelength of 3000 metres, compared with around 20 centimetres for satellite navigation systems. You need a big antenna to transmit those long wavelengths effectively, just as a bassoon can produce lower, longer-wavelength notes than a piccolo. A jammer would be a bulky thing for criminals to handle. 鈥淵ou would probably call attention to yourself,鈥� says Last.

The system needed road-testing to show it would be a robust defence. But before that could get going, jamming of the political sort left the project in limbo. In 2009, funding was unexpectedly cut thanks to 鈥渟ome minor bureaucrats in the Office of Management and Budget鈥�, says Dana Goward, who worked on the programme at the US Coast Guard, and now heads the Resilient Navigation and Timing Foundation charity. In 2010 the US turned off its Loran stations.

On the other side of the Atlantic the beacons still burned, and the General Lighthouse Authorities of the UK and Ireland soon demonstrated a prototype eLoran system using nine old Loran stations across north-western Europe. One of a series of sea trials took place in March 2012: eLoran equipment was installed at the port of Dover in the UK and on a research ship, and the system was calibrated to account for the distorting effects of local land masses. The trials showed that eLoran is accurate and dependable enough to meet even the strict requirements for coastal navigation and harbour approach, with a positioning accuracy of better than 10 metres. It can also give time to about 100 nanoseconds. That鈥檚 less accurate than GPS but good enough for most applications, including the timing needed in electricity grids and even high-speed financial trades.

Things were looking promising, but then politics intervened again. Some of the masts involved in the trials were in France, Norway, Germany and Denmark 鈥� but in 2015 those countries decided to turn them off. The UK government asked Norway to at least mothball their four stations, but instead the country blew them up. According to Last, this is because of Galileo. 鈥淗aving spent 鈧�10 billion on the project, the last thing governments want to hear about is its vulnerability,鈥� he says. 鈥淭his is what has stopped eLoran.鈥�

Or maybe just paused it. John Garamendi and Frank LoBiondo, two US congressmen, wanted to see a backup for GPS. So in 2017 they sponsored an amendment to a defence act that awarded $10 million to a demonstration project. 鈥淲e鈥檝e got real money now,鈥� says Goward. 鈥淭here鈥檚 blood in the water.鈥�

Over in the UK, a 2018 government included a recommendation that critical national infrastructure employ backup systems 鈥� and a government group is now meeting to work out exactly what to do. South Korea is working on an eLoran system for shipping, after claims that North Korea has jammed GPS in the vicinity of Seoul harbour. Russia, Saudi Arabia and other countries are looking at similar technologies too.

鈥淎 jamming device for long wavelengths would be a bulky thing for criminals鈥�

Compared with setting up a new satellite constellation, getting eLoran running would be a breeze. The UK already has a transmitter at Anthorn in Cumbria delivering eLoran timing. Adding two or three more across Britain and Ireland would let receivers there work out position, too. There would be no need for new masts; existing radio transmitters could be used. George Shaw at the General Lighthouse Authority says such a system would cost less than 拢10 million.

The only trouble is that one of eLoran鈥檚 biggest strengths could also be its biggest weakness. The long wavelength makes compact spoofing devices hard to build, but so are receivers that would be small enough to fit into mobile technology like smartphones. 鈥淵ou鈥檙e taking a 3000-metre wavelength and trying to stuff it into a small antenna,鈥� says Charles Schue, CEO of , a company that makes Loran receivers. This is why the firm is focusing on receivers for maritime and aviation applications for the moment 鈥� though Schue is confident that receivers will shrink and fit into portable devices like phones over time.

There is another backup technology that has no need to trim antenna size. A US company called has developed a way to deliver time and position using a system of communications satellites called Iridium. 鈥淚t turns out the Iridium clocks are pretty good,鈥� says Satelles president Gregory Gutt. The firm monitors and constantly corrects them from the ground. The receivers also gain information from the frequency shifts as the 66 Iridium satellites move relative to the receiver. These two tricks mean the Satelles system can provide locations to within about 20 metres and timing accurate to within 100 nanoseconds.

The Iridium signals are about 1000 times stronger than those of GPS, making them harder to jam. And spoofing the signal would be very difficult because the satellites cover Earth with 3000 separate beams, each encrypted with changing keys. As the wavelength used is small, it would also be relatively easy to put receivers in phones and other mass-market devices.

Yet the fact that the Satelles system is based in space may be a pretty serious flaw. 鈥淵ou want to be able to drive there rather than take a space shuttle to do upgrades,鈥� says Goward. But with the stakes so high, perhaps we want both Satelles and eLoran out there, ready to step in and keep us from getting lost in space and time.

This article appeared in print under the headline 鈥淭owers of strength鈥�