Signals from SpaceX satellites used like GPS to pinpoint location on Earth

Engineering researchers have developed a method to use signals broadcast by Starlink Internet service satellites to accurately locate a position here on Earth, much like GPS does. This is the first time that the Starlink system has been used by researchers outside SpaceX for navigation.

Starlink satellites, sent into orbit by Elon Musk’s SpaceX, are designed to provide high-speed internet connections in remote locations around the world. The researchers used signals from six Starlink satellites to pinpoint a location on Earth with an accuracy of 8 meters.

Their findings, shared today (September 22, 2021) at the Institute of Navigation GNSS annual meeting in Saint-Louis, could be a promising alternative to GPS. Their results will be published in the next issue of the journal. IEEE Transactions on Aerospace and Electronic Systems.

The researchers didn’t need SpaceX’s help to use the satellite signals, and they stressed that they didn’t have access to the actual data sent from the satellites – only information related to location and location. satellite movement.

“We listened to the signal, then we designed sophisticated algorithms to locate our location, and we showed that it worked with great precision,” said Zak Kassas, director of the Center for Automated Vehicles Research with Multimodal Assured Navigation (CARMEN ), a multi-institution transportation hub housed at Ohio State University.

“And although Starlink was not designed for navigation purposes, we have shown that it is possible to learn parts of the system well enough to use it for navigation.

CARMEN is one of four recently awarded US Department of Transportation University Transportation Centers. Kassas is an assistant professor of electrical and computer engineering at Ohio State and an associate professor at the University of California at Irvine.

For this research, Kassas and his research team studied the Starlink system and analyzed the signals sent by the satellites. They developed an algorithm that could use signals from multiple satellites to locate a position on Earth. Then they set up an antenna on the UCI campus and tried to use the network to locate the antenna.

Using Starlink, they identified the location of the antenna about 7.7 meters away. GPS, by comparison, usually identifies the location of a device within 0.3 and 5 meters. The team used similar techniques with other constellations of low-earth orbiting satellites, but with less precision, locating locations around 23 meters away, Kassas said. The team also worked with the US Air Force to locate aircraft at high altitude; they were able to approach within 5 meters using terrestrial cellular signals, Kassas said.

SpaceX has some 1,700 low orbit satellites, which means they circle the planet about 1,200 km from the Earth’s surface. SpaceX plans to eventually launch more than 40,000 satellites.

Kassas said that as the Starlink constellation grows, the accuracy of his team’s navigation and geolocation technique with their signals will also increase.

Their discovery could allow the government or other agencies to use Starlink’s satellites as an alternative – and perhaps safer – navigation system to GPS, which powers nearly all navigation systems around the world, Kassas said. .

GPS has been in place for over 30 years and its signals are well known, akin to open source software, Kassas said. This is a boon for companies developing GPS receivers in smartphones, portable fitness devices, and vehicles, but it also makes the system vulnerable to attack. GPS satellites are also farther from Earth than low orbit systems, making their signals weaker and therefore more susceptible to interference.

Jamming attacks on GPS signals can suppress GPS signals completely, which is a growing problem for aviation. Identity theft attacks on GPS can manipulate where a given vehicle appears in systems designed to monitor locations and prevent vehicles from straddling routes; attacks can also take the path of a vehicle – for example, some attacks have overtaken military and civilian drones, maritime vessels and even Tesla’s autopilot.

The Starlink system appeals to navigation experts, Kassas said, because the signals, so far, have been private – SpaceX has not shared them with governments or researchers. Starlink satellites are closer to the Earth than GPS satellites, making their signals much stronger and less susceptible to interference.

“The big problem here is that we don’t listen to what is being sent from these satellites,” Kassas said. “We learned the signals just well enough to use them for navigation.”

The co-authors of the research were Joe Khalife and Mohammad Neinavaie from the University of California, Irivine.

This work was funded by the US Office of Naval Research, the US Department of Transportation, and the National Science Foundation.

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