Navigating the Future of Positioning, Navigation, and Timing
It is no secret that the Global Positioning System we rely on for everything from car navigation to military operations, cell phone service to banking, is highly vulnerable to outages—both unintentional and intentional. Ensuring future positioning, navigation, and timing services will likely depend on multiple strategies.
When the U.S. Air Force was tasked with the design of the NAVSTAR Global Positioning System (GPS) more than 40 years ago, the system was intended primarily “to deliver weapons precisely on target and to reverse the proliferation of navigation systems in the U.S. military,” according to Rick W. Sturdevant, Ph.D., deputy director of history for U.S. Air Force Space Command, in The Societal Impact of Spaceflight. Today, GPS is not only integral to military operations, it is also one of society’s most ubiquitous global utilities and has become essential to important functions like stock market exchanges and power grid management.
Such dependency brings great risk, and military agencies and experts in positioning, navigation, and timing (PNT) technologies are looking at numerous ways to address the challenge. “Like most things in the complex world we live in, there is not likely to be just one solution,” says L3Harris Vice President Pat Seamon.
Shoring Up GPS
According to Seamon, one of the strategies being pursued is improving GPS itself. “GPS signals were weak by design,” he advises. “The satellites are solar powered. To constantly produce and broadcast their signals requires balancing energy requirements for generating them, the equipment, and other resources needed to operate the GPS mission. That has meant some give and take when it comes to signal strength. Plus radio waves weaken as they come through the atmosphere. This all makes them very vulnerable to disruption.”
Anyone who has used a handheld GPS device knows how GPS signals can be blocked in areas flanked by tall buildings or covered with thick foliage. Of greater concern, though, is the use of jamming devices despite federal laws prohibiting their marketing and operation. As recently as May 2016, the Federal Communications Commission fined a Chinese company $34.9 million for illegally marketing and selling devices that jam signals like GPS to U.S. consumers.
As a result, expectations for the next generation of GPS satellites are improved signal strength and accuracy, “We now have the capability to deliver signals that are three times stronger than those from today’s satellites. This enables a location accuracy to 3 feet, compared to today’s 10-foot accuracy,” explains Seamon, whose team has been working to advance PNT technology since the program’s earliest days. “It also means overall better coverage in those urban canyons and forests.”
Another benefit of stronger signals is that they become more impervious to jamming. For military personnel, who use a different, more resilient signal, Seamon’s team has developed a signal that provides an eightfold increase in anti-jamming power.
A Better “Brain” for PNT Payloads
Advancements like these are the result of applying more than four decades of L3Harris PNT research and development, and even longer experience in radio frequency and satellite communications to build a better “brain” for global navigation satellite systems, states Senior PNT Systems Engineer James Phelan. “Today it’s important that missions can support spiral life-cycle development so that new technologies can be ‘gracefully’ incorporated,” Phelan says. “What we have come up with is a modular, fully redundant system that uses independent circuit cards for critical algorithms and data processing, command and control, maintenance, and telemetry functions.”
While GPS has been very successful, the time frame to add new signals has been about 10 years—an eon in today’s fast-paced world. According to Phelan, L3Harris’ research has led to the ability for military users to add new codes and signals. “A flexible code generation system can add resiliency to the system to adapt to changing needs and enable the military to respond to threats more quickly,” he adds.
Future PNT payloads are likely to become more digital—maybe even all-digital,” says Phelan. “And components like solid-state gallium nitride (GaN) transmitters could make a difference in signal efficiency size, weight, and power requirements.”
The recognized limitations and vulnerability of GPS signals and satellites have prompted military strategists to look for ways to augment their PNT capabilities. With the goal of protecting warfighters in contested environments, the U.S. Army has initiated the Assured PNT (A-PNT) program, a system of systems approach to provide innovative and robust terrestrial-based PNT solutions through use of mounted platforms; dismounted soldiers; anti-jam antennas; and pseudo-satellites, or pseudolites, small ground-based transceivers for broadcasting location information.
“Then there’s the issue of an alternative source for precise timing, which is critical for navigation, synchronizing operations, and timestamping,” comments L3Harris System Engineer Huascar Ascarrunz. “The sole dependence of society on GPS time for critical infrastructures was documented as a long-term national security risk in the 2011 National Risk Assessment.”
For this reason, L3Harris is investing research and development funds and engaging both the government and the Stanford University Center for PNT to demonstrate a backup timing system for the continental U.S., says Ascarrunz. “We envision a robust network that leverages multiple signals of opportunity—not all space-based and some already available, like NIST WWVB1—to provide accurate, available, and trusted time anywhere in the continental United States. You can validate your GPS time source by comparing it with information from this alternative system or switch over to it entirely in the absence of GPS,” he explains.
The Way Ahead
In the beginning, GPS’ spread spectrum modulation, its encryption, and the physical security of space protected the integrity of the signal and its source.” But in 2000, GPS was made more accurate for commercial users and went from being the domain of only a few to being open to many,” states Pat Seamon, citing both the threat of GPS signals being jammed and their vulnerability to being spoofed, or overridden by counterfeit GPS signals, as the result.
“We live in a world where threats can come from anywhere, where our adversaries are nimble—highly mobile and able to learn and adapt to changes quickly,” Seamon observes. “We require resilient solutions to the systems we rely on the most. Strengthening our PNT capabilities and having backup strategies are not just smart, they are essential to our future safety.”
1The National Institute of Standards and Technology (NIST) operates time signal radio station WWVB.
As published in the L3Harris Space and Intelligence Systems publication, Insights for a Better World, Ensuring Superiority in Space.