Researchers create their own GPS system by hacking Satellites
How many satellites revolve around the Earth? 2,787 satellites were operational as of December 31, 2020 according to the UCS (Union of Concerned Scientists) association, more than half of which were launched by the United States. Three quarters of the satellites in operation rotate in low orbit (between 500 and 2,000 km altitude), and are used for telecommunications systems, terrestrial imaging or meteorology.
By exploiting data from Starlink satellites, researchers have managed to locate themselves to within seven meters, all without any intervention from the satellite itself. Eventually, this system could make it possible to build a real autonomous navigation system, accessible to all and completely free.
Today, most of our geolocation applications are based on GPS or Galileo systems, which operate using satellites in medium orbit (between 20,000 and 35,000 kilometers). The latter send radio signals towards the Earth to report their position, and the receiver can thus determine its precise location by triangulation. Very expensive systems worth several billion euros. A team of researchers from the University of Ohio (United States) has just found a completely free way to access a geolocation service: hack into the constellation of Starlink satellites, which already has more than 1,700 satellites in low orbit.
Accuracy to within seven meters
It thus took only 13 minutes and six Starlink satellites for the researchers to locate to within 7.7 meters, without the knowledge of the operator. The researchers did not use the data from the satellites themselves, but the signal sent by them. When a satellite flies over the Earth, it sends out a radio signal intended for the receiver on the ground. The frequency of these radio waves is distorted by the Doppler effect, which causes the waves to lengthen or shorten depending on the distance (like radars that measure speed on roads). This offset is proportional to the speed of the satellite relative to the user. By recording several signals over a given period, this therefore makes it possible to determine the orbital parameters of the satellite.
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Using their own antenna installed on the campus roof, Zak Kassas and his colleagues captured electromagnetic waves from six Starlink satellites for 800 seconds (about 13 minutes), then fed the data to an algorithm that determined their geolocation at ground with an accuracy of seven to eight meters. It is certainly less good than the current satellite applications (Galileo offers for example an accuracy of four to five meters for the free version and up to 20 centimeters for the paid version), but it remains sufficient for a good number of uses, emphasize the researchers who presented their results at the annual meeting of the GNSS Navigation Institute in Saint-Louis. Working with the US Air Force, the team also identified the location of high-altitude aircraft to within five meters. Other constellations of satellites in low orbit have also been tested, but with less precision (around 23 meters).
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