When you launch a constellation of 2,300 satellites into space, it’s not just internet and visual pollution that you can offer. Todd Humphreys, professor of aerospace engineering at University of Texas-Austinmanaged to set up a “GPS” system using Starlink signals — and the most curious thing: Elon Musk was against the proposal.
In 2020, Humphreys presented SpaceX with the project to make minor changes to the software, thus creating a satellite tracking system, serving as a “backup” for the GPS. The company’s engineers loved the idea, but Musk did not authorize the partnership.
Using Starlink as a GPS Needed Reverse Engineering
First of all, it must be explained that GPS is the name of a satellite navigation system technology. With its popularization, the acronym became associated with the technology itself. However, there are other satellite navigation services, such as Galileo (European Space Agency) and BeiDu (China’s National Space Administration).
The project presented by Todd Humphreys (whose research is funded by the United States Army) for SpaceX would take advantage of the thousands of satellites launched to create a navigation system independent of government services (GPS is owned by the US government).
According to Humphreys, SpaceX directors reported that Musk was against the idea because, in the billionaire’s words, “all other LEO communication networks [sigla em inglês para órbita terrestre baixa] went bankrupt”. As the saying goes, whoever pays for the band, chooses the music. And Humphreys decided to “make a remix”.
After Elon Musk’s refusal, the professor’s laboratory began the development of the navigation system using the Starlink network. Two years into the project, which used the technique of reverse engineering the signals from the satellite constellation, Humphreys’ team says they found the solution to use Starlink “as a GPS”.
Research had Starlink and Rafael Nadal terminal
In the article published in arXiv, still without peer review, it is explained that the signals sent from the constellation for the receivers to connect with the satellites can be the basis of a navigation system.
The research started with the acquisition of a Starlink terminal. With the service operating, the team streamed, via YouTube, high definition tennis videos Rafael Nadal. This formed a constant connection to Starlink and a second “gossip” antenna picked up the signals received by the terminal.
Humphreys and his team then looked for synchronization sequences, repeating signals that help receivers coordinate with satellites. The researchers found such signs—and better yet, SpaceX uses more sync sequences than recommended. Sequences provide data such as distance and speed of a satellite. In the case of Starlink, there are four sequences every millisecond (0.001 second)
According to Humphreys, the location system created by the Starlink terminal is accurate to within 30 meters. But if Elon Musk changes his mind and SpaceX provides more satellite position data, accuracy can go down to less than 1 meter — just like GPS.
With information: Technology Review