Using Starlink as GPS… without permission from SpaceX?

Researchers at the University of Texas at Austin claim in a preprinted paper (not peer-reviewed) to have successfully reverse-engineered Starlink satellite signals.

MIT Technology Review explains that Todd Humphreys and his colleagues suggested in 2020 that SpaceX try to fit an alternative to GPS if the geolocation system had a problem. Some corporate executives were interested, but Elon Musk himself reportedly declined. The researchers nevertheless persisted and ventured into a reverse-engineering operation.

After purchasing a simple Starlink terminal and launching the streaming of high-definition YouTube videos (videos of Rafael Nadal according to MIT Technology Review), they realized that these signals were based on the Orthogonal Frequency Division multiplexing (OFDM) technique used by both Wi-Fi and mobile networks (3G, 4G, 5G).

Without trying to break the cipher, they focused on possible synchronization sequences. Bingo! And these sequences provide information about the satellite’s speed and distance. Combined with those on the satellites’ movements, shared publicly by SpaceX to reduce the risk of collision, this data makes it possible to determine the receiver’s position within 30 meters, according to the researchers.

They estimate that they can reach less than a meter of precision if SpaceX communicates more precise data to them.

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