Researchers Find Way to Use Starlink Signals As Alternative to GPS

The US Global Positioning System (GPS) is a crucial tool for navigation, but what happens if the satellites go down or face jamming attempts? New research shows SpaceX’s satellite internet service Starlink could operate as a viable alternative, whether the company likes it or not.

The research(Opens in a new window) comes from a team at the University of Texas at Austin’s Radionavigation Laboratory. They reverse-engineered the signals sent from the thousands of Starlink satellites in orbit to show how they can be used for positioning purposes. 

The research “could form the basis of a useful navigation system” to rival the US GPS and other equivalent positioning systems from China, Russia, and India, MIT Technology Review reports(Opens in a new window).

The current Starlink satellite network
(Credit: satellitemap.space)

Professor Todd Humphrey from the University of Texas’s Radionavigation Lab, asked SpaceX about using Starlink as a global navigation satellite system akin to GPS. The US Army has been funding Humphrey’s research, and was looking for a backup to the US GPS system, which currently operates 31 active satellites at about 12,500 miles above the planet, MIT Technology Review notes.

In contrast, Starlink already operates over 3,000 satellites, which orbit Earth around 340 miles above the surface, resulting in stronger signal coverage. However, SpaceX CEO Elon Musk reportedly declined to help Humphrey over fears it’d create a distraction for his company.

Despite the rejection, Humphrey’s team went ahead with their research and managed to analyze the signal structure for Starlink downlink beams in the 10.7 to 12.7GHz band. “We further identified four synchronization sequences that can be used to passively exploit Starlink signals for pseudorange-based positioning, navigation, and timing (PNT), and explicitly evaluated two of these,” his team wrote in their non-peer reviewed paper(Opens in a new window).  

Starlink can be used as a GPS-like system since the satellites are routinely beaming signals to Earth’s surface. Hence, a receiver on the ground can analyze these signals, and calculate the distance from a Starlink satellite, to pinpoint its location on the planet.

According to MIT Technology Review, Humphrey’s team used the Starlink satellites to locate a receiver within about 30 meters. That still isn’t as accurate as GPS, which can locate a device, such as a smartphone, within 5 meters or less. But if SpaceX were to cooperate with Humphrey, the accuracy of the Starlink-powered positions system could improve to less than a meter.

A team at the Ohio State University has also been researching how to use Starlink as a GPS alternative, without SpaceX’s cooperation. In September 2021, the team found(Opens in a new window) a way to do so with an accuracy of about 7.7 meters. “We eavesdropped on the signal, and then we designed sophisticated algorithms to pinpoint our location, and we showed that it works with great accuracy,” said Zak Kassas, a professor on the team.