Much of the western United States was put on notice earlier this year when the U.S. Air Force announced that it would be blocking GPS signals on its base south of Las Vegas, Nevada. The tactic—which occurred during an annual month-long military training exercise—could cause air traffic disruption and potentially require flight rerouting due to inconsistent GPS, the notice stated. While the Air Force would not confirm that the GPS disruption was a part of its yearly exercises, experts believe that the military is training its pilots to fly in conditions where GPS signals are inaccurate or nonexistent—a scenario that has become increasingly common.
Thirty-one satellites currently orbiting the earth transmit signals to civilian and military terrestrial receivers, essentially using time signals to run location-based devices and activities and syncing networks around the world. The satellites—called the GPS constellation—are owned by the United States and operated by the Air Force. Since 1978, the satellites have provided location, navigation, and timing capabilities to the military, and an unencrypted version became available for public use in the 1980s. Over the years, the signals from the GPS constellation have become critical for a variety of applications, including communications, precise time measurements, and critical infrastructure technologies—in addition to its military uses of navigation, target tracking, and missile guidance.
However, the signal—which is inherently weak—is susceptible to outside interference. Anything from space weather to malfunctioning machinery to malicious actors can cause problems with GPS, including blocking the signal—called jamming—and sending false signals, known as spoofing. Even small interferences can cause big headaches.
For example, a man who drove a company car purchased a GPS jammer to keep his boss from knowing his whereabouts, but when he passed near Newark airport in New Jersey, the jammer blocked signals from reaching the air traffic controller system. Although the sale and use of jammers is illegal in the United States, they can be purchased online for less than $50 and can successfully hide a vehicle's location.
In January 2016, a routine equipment switch caused a series of 13-microsecond timing errors in half of the GPS constellation satellites, which triggered about 12 hours of confusion for computers, networks, and timing devices around the world.
The U.S. government has referred to GPS as a single point of failure for critical infrastructure and, in 2004, called for the U.S. Department of Transportation to acquire a backup capability for GPS. However, an alternative has never come to fruition.
U.S. President Donald Trump reemphasized the need for redundancy by including a section in the 2018 National Defense Authorization Act that requires the U.S. Departments of Defense, Transportation, and Homeland Security to demonstrate a GPS backup capability within the next 18 months.
"We were concerned that the federal government was not doing all of the things it said it would do in order to protect GPS signals, which are being interfered with on a regular basis," says Dana Goward, the president of the Resilient Navigation and Timing Foundation (RNTF). He established the nonprofit in 2013 to protect, toughen, and augment GPS signals. "Since we started, over the last five years, GPS has been interfered with more and more," he notes.
Goward and other members of RNTF are also members of the National Space-Based Positioning, Navigation, and Timing (PNT) Advisory Board, which has existed since the call for a GPS backup capability was issued in 2004.
It's hard to tell exactly how big an impact a widespread GPS outage would have on critical infrastructure sectors around the world, but Goward notes that glitches such as the January 2016 blip can foreshadow what systems might be affected. "The implementation and use of GPS signals is so widely spread for so many different things it was never intended to be used for that it's really impossible to outline all the bad things that would happen and the sequence in which they would occur," he says. "But there are some things we do know."
Say a terrorist plants a high-powered GPS jammer hidden in a suitcase in the middle of a city. Transportation will probably be the first system visibly affected, which could quickly impact an entire metropolitan area, Goward says. Traffic lights will become desynchronized and GPS-based apps will no longer function, creating distracted and dangerous driving conditions. Airplanes and other forms of mass transportation will have to slow down or alter routes to stay in contact with people who can keep them on course. Package delivery routes as well as land, sea, and air-based supply chain operations will be disrupted. "All forms of transportation will be forced to carry less capacity in the area," Goward notes.
Countless systems that rely on GPS's perfectly synchronized timing—including data networks, financial activities, the electric grid, and other utilities—will slowly become out of sync, causing system failures.
"When the networks start to fall apart, it's hard to tell how much of a cascading failure you're going to see," Goward notes. "Networks depend on each other. It's really such a vast and hyper complex system, the structures of which are not known and may not be knowable."
Preventing GPS glitches is a multifaceted challenge. The GPS satellites themselves are fairly resilient—they are replaced on a rotating basis depending on their estimated operational life. Still, mechanical glitches like the one that caused the January 2016 blip are possible. The signals transmitted from the satellites are even weaker than cosmic background noise, and Goward notes that even upgraded equipment won't substantially change the strength.
"The basic problem is fundamental physics," Goward says. "Satellites are 12,500 miles up in space and powered by solar panels and transmitting all the time—unlike other satellites that can store up their solar power, GPS satellites have to transmit all the time. They will always be really weak and easy to interfere with."
An inherent area of weakness is the equipment used to receive the GPS signal sent by the satellites—anything from cell phones to networks to military ground stations that encrypt the signal.
"Most GPS receivers in use right now are very vulnerable to jamming and spoofing," Goward notes. "The technology in terms of antennas and software is available to make them much less susceptible to jamming and spoofing, but it costs a little extra and users don't feel motivated to incorporate anti-jamming and spoofing technology into their receivers and systems, even when they involve and support critical infrastructure like phone and IT networks."
RNTF is working with the government to establish guidance or best practices to improve GPS receiver security.While a fix is relatively simple, Goward says he doubts most companies will make the upgrade unless they are told to do so or they experience a GPS-induced crisis. "We think that for critical infrastructure applications there's a government role there to advocate for, encourage, and perhaps require users to have the latest anti-jamming and spoofing technology."
Military-level encrypted GPS signals aren't exempt from jamming or spoofing, either. While the use of a secured ground system to control the broadcast of an encrypted signal, along with military-grade receivers, provides an inherent level of protection, it's not foolproof—and it only works when it's used properly.
"Because of the encryption, that makes military receivers as a practical matter more difficult to use, so we had seen any number of photographs of military folks in the field with GPS receivers they bought at Walmart strapped to their arms and using them instead of military receivers," Goward notes. Encrypted equipment tends to be stored under lock and key—and is usually unwieldy—making it more cumbersome to use.
It's suspected that the infamous straying of a U.S. naval ship into Iranian waters in 2016 was a result of the sailors using unencrypted receivers that allowed Iran to spoof the signal and direct them into the country's territory. And headlines were made when the movements of U.S. military personnel at several overseas bases could be tracked via a GPS-based fitness app—no jamming or spoofing required.
The U.S. Department of Defense (DoD) is in the middle of upgrading the military ground systems and replacing the current GPS constellation—which is near the end of its intended operational life—but the efforts have faced a series of setbacks. The new generation of satellites, called GPS III, are expected to provide a stronger signal that is more resistant to spoofing and jamming and will permit interoperability with other global navigation systems. But, according to the U.S. Government Accountability Office (GAO), the acquisition and timeline of deploying the new satellites has run into several roadblocks, delaying the launch of the new equipment.
For example, the first GPS III satellite built, which is slated to become operational in 2019, includes energy storage devices that had not been appropriately tested by the subcontractor. When the Air Force discovered the failure to test the equipment, it made the subcontractor remove the devices from the second and third satellites currently being built, but "decided to accept the first satellite and launch it 'as is' with the questionable capacitors installed," the GAO reports. The rest of the GPS III satellites are expected to be launched and operational—replacing the current devices—by 2021.
Three components of the upgrade—the new ground control systems, GPS III satellites, and contingency operations programs—are expected to face "numerous challenges" over the next 18 months, GAO notes. "If any of the three programs cannot resolve their challenges, the operation of the first GPS III satellite—and constellation sustainment—may be delayed."
Meanwhile, Goward and the RNTF are continuing to encourage the government to promote more secure GPS receiver technology and build a backup capability when—not if—the GPS signal fails.
"We are concerned that the federal government does not have a central point of accountability for protecting GPS," Goward explains. "It's possible that this lack of responsibility and governance will mean that nothing is going to happen until the nation has suffered substantial damage because of the failure to protect, toughen, and augment GPS."