Starlink indicators might be reverse-engineered to work like GPS—whether or not SpaceX likes it or not

In a non peer-reviewed paper that he has posted on his lab’s web site, Humphreys claims to have offered probably the most full characterization of Starlink’s indicators to this point. This data, he says, is step one towards growing a brand new international navigation know-how that might function independently of GPS or its European, Russian, and Chinese language equivalents. 

“The Starlink system sign is a carefully guarded secret,” says Humphreys. “Even in our early discussions, when SpaceX was being extra cooperative, they didn’t reveal any of the sign construction to us. We needed to begin from scratch, constructing principally somewhat radio telescope to snoop on their indicators.”

To get the challenge began, UT Austin acquired a Starlink terminal and used it to stream high-definition tennis movies of Rafael Nadal from YouTube, 24/7. This offered a continuing supply of Starlink indicators {that a} separate close by antenna may eavesdrop on.

Humphreys shortly realized that Starlink depends on a know-how known as orthogonal frequency-division multiplexing (OFDM). OFDM is an environment friendly technique of encoding digital transmissions, initially developed at Bell Labs within the Sixties and now utilized in Wi-Fi and 5G. “OFDM is all the fashion,” says Mark Psiaki, a GPS knowledgeable and aerospace professor at Virginia Tech. “It’s a method to pack probably the most bits per second right into a given bandwidth.” 

The UT Austin researchers didn’t attempt to break Starlink’s encryption or entry any person information coming down from satellites. As an alternative, they sought out synchronization sequences—predictable, repeating indicators beamed down by the satellites in orbit to assist receivers coordinate with them. Not solely did Humphreys discover such sequences, however “we have been pleasantly stunned to search out that they [had] extra synchronization sequences than is strictly required,” he says.

Every sequence additionally incorporates clues to the satellite tv for pc’s distance and velocity. With the Starlink satellites transmitting about 4 sequences each millisecond “that’s simply great for twin use of their system for positioning,” says Humphreys. 

If the terrestrial receiver has a good suggestion of the satellites’ actions—which SpaceX shares on-line to cut back the danger of orbital collisions—it will probably use the sequences’ regularity to work out which satellite tv for pc they got here from, after which calculate the gap to that satellite tv for pc. By repeating this course of for a number of satellites, a receiver can find itself to inside about 30 meters, says Humphreys.