How Starlink and Iridium could redefine navigation

GPS failures aren’t as rare as most people think. In deep forests, narrow canyons, or dense city centers, signals can vanish without warning. Global Navigation Satellite Systems (GNSS) like GPS, Galileo, and BeiDou operate on signals so faint that even trees or tall buildings can block them. They’re also vulnerable to jamming and spoofing, raising concerns about the reliability of systems that underpin everything from ride-hailing apps to air traffic control.

A study published in Satellite Navigation by researchers from the Aerospace Information Research Institute, Chinese Academy of Sciences, explores an intriguing alternative: using low-Earth orbit (LEO) satellites such as SpaceX’s Starlink and Iridium as backup navigation sources. What makes this idea stand out is that these satellites were never meant for navigation. They’re communication satellites, yet with the right engineering, their signals can double as unintentional navigation beacons.

Why look beyond GPS?

GNSS has been the gold standard for decades. But its weak signals make it fragile, especially in crowded cities or remote wilderness. Military strategists and civilian engineers alike have worried about what happens if GPS is jammed, hacked, or simply unavailable. That’s where Signals of Opportunity (SOPs) come in. Instead of building a new navigation system from scratch, scientists have started reusing signals that are already bouncing around us, from cell towers, Wi-Fi hotspots, TV broadcasts, and increasingly, massive constellations of satellites whizzing overhead. The big advantage of LEO satellites is their proximity and abundance. Unlike GPS satellites, which orbit 20,000 km above Earth, Starlink’s fleet cruises just 550 km up. That means stronger signals. And with over 6,000 Starlink satellites already in orbit and nearly 5,000 active, coverage is near-global and rapidly growing.

However, Starlink and Iridium weren’t built for navigation. Unlike GPS satellites, they don’t tell you when a signal left the satellite, or broadcast precise orbital data to the public. Without that information, figuring out your exact location becomes much trickier. The researchers tackled this challenge with a joint pseudo-range and Doppler positioning method. That may sound intimidating, but let’s break it down. Pseudo-range, which is the basic GPS trick, measures how long a signal takes to travel from a satellite to you. But since Starlink doesn’t tell you the send time, the researchers had to invent a clever workaround using synchronization sequences embedded in Starlink’s signals. Doppler shift instead, just like a passing ambulance changes pitch, satellites’ signals shift frequency depending on their relative motion. Measuring this Doppler effect provides clues about your position and velocity. By combining these two approaches, the team found a way to squeeze accurate location information out of “opportunistic” signals never meant for navigation.

The researchers used low-cost, wide-beam antennas, the same kind used in satellite TV dishes, to capture multiple Starlink signals at once. This is important because while specialized parabolic or phased-array antennas are powerful, they’re expensive and bulky. The goal here is accessibility: could an ordinary receiver help everyday devices like cars or drones navigate using Starlink? Since Starlink signals aren’t available in China, the team turned to Iridium NEXT satellites for part of their experiments. They used Iridium signals to extract pseudo-range measurements, and Starlink’s Doppler data for the rest. Think of it as blending ingredients from two different recipes to cook up something new.

The results were promising. In fact, using Starlink Doppler alone, they achieved 3.6 meters accuracy in 2D positioning and 6.2 meters in 3D positioning, an improvement of over 35% compared to existing methods. In a long-distance test with Iridium NEXT, the system managed 24 meters accuracy in 2D and 41 meters in 3D. Not perfect, but good enough for many applications.

The implications are huge. A backup navigation system based on LEO satellites could improve resilience. If GPS goes down, planes, ships, and smartphones wouldn’t be left blind. Also, this system could enhance urban navigation. Cities are notorious “GPS jungles,” where signals bounce off skyscrapers. Stronger LEO signals could cut through the noise. This approach would also lower costs: by using cheap wide-beam antennas instead of pricey phased arrays, this method could be widely adopted. Finally, alternative GPS systems would advance autonomy. Self-driving cars, delivery drones, and robotics all need hyper-reliable positioning. Multiple layers of navigation systems make that safer.

In other words, this isn’t just about redundancy. It’s about making location services more robust, affordable, and accessible.

We’re entering an era where the line between communication and navigation blurs. Just as your smartphone now serves as a camera, a wallet, and a ticket scanner, satellites built to beam internet might also guide planes, ships, and rescue workers. The work realized by the researchers behind the study is part of a growing movement to make navigation more resilient, democratic, and multi-layered. In the future, your phone or car might use a cocktail of signals, GPS, Starlink, Iridium, Wi-Fi, and 5G towers, to pin down your location with near-perfect reliability. So, hiking through dense woods, flying across continents, or navigating a blackout city, you may have to thank not just GPS, but also the satellites you once thought were only for streaming Netflix at sea.

If you want to learn more, read the original article titled "Joint pseudo-range and Doppler positioning method with LEO Satellites‘ signals of opportunity" on Satellite Navigation at http://dx.doi.org/10.1186/s43020-025-00163-y.