Satellites Keep the World’s Clocks on Time. What if They Fail?

Standardized time is broadcast by satellite networks around the world, but their signals are vulnerable to interference—so the UK is building a more resilient system.

If you head southwest out of London, you might enter Teddington, a suburb with tree-lined avenues that sits on the banks of the river Thames. Here, in this innocuous neighborhood, you’ll find one of the United Kingdom’s more unusual security programs: the National Timing Centre (NTC), a government-led laboratory that is working to create a new, more resilient way for the country to measure time.

For decades, the UK, like almost every other country, has relied on global navigation satellite systems—signals from satellites orbiting in space—to tell the time accurately. These GNSS signals provide the foundation for mobile networks, energy grids, and the internet. They’re the source of the time on your smartphone, your laptop, and pretty much any other smart device that plays a part in your life. But there are growing fears that GNSS could be disrupted or fail—and with huge implications. A five-day disruption would cost the British economy an estimated £5.2 billion ($6.15 billion).

In 2017, an independent report commissioned by the British government declared that ignorance of the importance of precise time measurement, and the role of GNSS in providing it, was “especially acute.” It added that the vulnerability of the system, to both natural and intentional interference, was “poorly understood,” before recommending that the country take steps to increase the resilience of its accurate timing.

“Our dependency on time, an invisible utility, is rapidly increasing across our digital infrastructure,” says Leon Lobo, head of the NTC program. And yet despite this, the UK’s time is provided through a vulnerable system, he explains. This is why, in 2020, the NTC was set up.

Exactly how your phone and, say, a departures board in a train station both show you the same time might not be something you’ve thought about before—but here’s how this is achieved. GNSS signals are delivered through a constellation of satellites, with each satellite broadcasting coded messages stating which satellite it is, its location in space, and a stable time stamp that it generates on board through multiple atomic clocks, the gold standard of time measurement. These measure time by counting the oscillations of certain atoms, whose vibrations are highly consistent and stable, meaning that clocks relying on them barely drift. (NASA’s atomic clock, for example, will stay precise to the second for more than 10 million years.)

When a signal is received by a GNSS receiver, thousands of kilometers below, on earth, it’s able to calculate the distance to the satellite that sent it by measuring the time delay between the signal’s transmission and its receipt, because radio signals travel at a known speed. Provided the receiver is able to receive a signal from at least four satellites, it can calculate not only its position to meter-level accuracy but also the local time to fractions of a microsecond.

And because this data can be picked up by any device with a small chip-sized receiver, including a mobile phone or an in-car navigation system, GNSS is low-cost, beyond initially launching the satellites. More accurate systems can be deployed locally but, speaking generally, GNSS is able to deliver atomic clock accuracy on a global scale without the need for actual local atomic clocks. For this reason, it’s used by billions of people daily and is the backbone of a vast range of services that require accurate time or positioning, including emergency responders, aviation, and precision agriculture.

“Using GNSS is the least costly way of securing accurate time, because it’s free and you can do it absolutely anywhere,” says Gavin Schrock, a specialist in geomatics engineering. “If you want to set up a computer network in the middle of nowhere, you can quickly and easily secure precise time with GNSS.”

The time derived from GNSS can also be used to synchronize devices and systems across entire networks, allowing time to be kept much more consistently and accurately than with most local measures. Battery-powered, plug-in, and mechanical clocks will all drift from the true local time—and from each other—because of their individual physical properties, changes in temperature, and sometimes magnetic interference. Typical clocks can drift by more than an hour a year.

So instead, companies and services receive GNSS time, feed it into a local master clock, and then disseminate this downstream. Fixed and mobile telecommunications companies do this to provide time alignment between base stations. The energy grids that power our devices also rely on GNSS for time synchronization—measurements of power values across the grid must be continuously taken and time-stamped to optimize the flow of power through the network, which is only possible if the clocks agree. The financial services industry also relies on GNSS time-stamping to place all of its interactions in chronological order, for regulatory oversight.

According to the US Department of Homeland Security, the incapacitation or destruction of any one of the communications, energy, or financial sectors would have a “debilitating effect” on national economic security and on public health and safety. Given the interdependence of modern networks, GNSS is a single point of failure that could have implications across various other services and applications. It is a hidden reliance that touches almost every aspect of industrialized society.

Yet there has been little consideration about what happens when GNSS fails. With satellites, there’s the possibility of geomagnetic storms and space debris, which could stop their signal or even disable them entirely. “There are quite a wide range of reasons why GNSS signals might be unavailable, and this can create significant harm,” says Ulrich Kohn, a telecommunications expert.

Because the signals satellites send are weak, all GNSS-enabled services are also susceptible to jamming, where the signal becomes lost among interference. The range and scale of this problem is growing as jamming equipment becomes more available. Anyone from criminals looking to evade electronic-tag monitoring to van drivers looking to conceal unauthorized stops might consider using a jammer.

Cheap trucker jammers are available for less than $100, but because they’re manufactured so poorly, they’re more disruptive than they’re designed to be. In 2009, on board the British vessel Galatea—a boat responsible for, among other things, maintaining the country’s lighthouses—a jammer with less than one-thousandth of the power of a mobile phone caused the vessel’s electronic charts to show false positions, leading the autopilot to steer the ship quietly off course.

Another growing concern is spoofing, where false signals are sent to the receiver from a ground station, resulting in misleading information being passed into systems. As with jamming, there’s a risk that spoofing can be used by hackers and rogue nation-states, but it’s more dangerous because it’s harder to detect a false signal than one that’s lost.

Since the 2014 annexation of Crimea, Russia has reportedly been blocking the GNSS signals beamed down to Ukraine, cutting the country off from position, navigation, and time services. Then, in 2017, 20 vessels in the Black Sea reported that their GNSS signals had been spoofed to indicate they were more than 32 kilometers inland, prompting reports that Russia was testing a new type of electronic warfare.

“The risk [of GNSS outages] is bigger now, because of the geopolitical situation, which gives certain national actors a certain interest in disturbing GNSS,” Kohn explains. “So, if you have a critical application—meaning critical in the sense of national interest—I am doubtful that only relying on GNSS is a good answer.”

The NTC’s solution for the UK is to set up an independent service that can serve as an alternative. The system comprises a network of atomic clocks housed at four secure facilities across the country, including Teddington. These will generate a perfectly stable pulse, precisely a second long. This service will be known as Resilient Enhanced Time Scale Infrastructure (RETSI), and it’ll be available even if one of the sites fails. “The route to creating resilience is through diversity, each with different failure modes, rather than relying on one solution,” Lobo says.

From RETSI, the NTC will directly administer a local time that is just as accurate as the time currently delivered by GNSS. It’ll be disseminated to key services through radio signals, satellite constellations, and fiber cables.

And because of its better reliability, the expectation is that RETSI will be “the source or heartbeat of a system of systems, or the core of the onion as it were,” Lobo says. Organizations that rely on resilient timing—banks, telecommunications companies, defense companies, as well as those that serve them—may switch to this system, but it’ll also accelerate innovation in new technologies, enabling companies to deliver new products and services. For instance, precise and robust timekeeping will be the foundation for technologies like smart grids, smart cities, and connected autonomous vehicles of the future.

“You have a good internet, and you can put distributed applications on it. You have a good timing network, and you can put distributed timing applications on top of it,” says Schrock. “When you have a good backbone like this, it allows companies to better serve their customers.”

None of this is to say that what the NTC is doing is wholly unique, because there are other places in the world with comparable mesh networks of atomic clocks. Mostly, though, these exist at a local or even laboratory scale where GNSS isn’t reliable enough. For instance, Japan relies on a network of synchronized time centers because of the risk of earthquakes. There are similar networks in China, the US, and other countries, but those are “rarely promoted outside of the precise timing community and industry,” Schrock says.

The hope is that RETSI will launch in 2024, with basic free access available over the internet and the most highly assured, extreme accuracy offered over fiber cable. With the growing demand for increasingly precise time across various industries, Lobo believes that this could be the beginning of a major change in how we understand precision timing.

“We see time in the future as a true utility,” he says. “Like power, water, and gas, it’ll be available at a wall, so you can use it with full trust and confidence, for all your applications.”

Satellites Keep the World’s Clocks on Time. What if They Fail?

(May require free registration to view)