https://www.technologyreview.com/2022/10/21/1062001/spacex-starlink-signals-reverse-engineered-gps/Todd Humphreys’s offer to SpaceX was simple. With a few software tweaks, its rapidly growing Starlink constellation could also offer precise position, navigation, and timing. The US Army, which funds Humphreys’s work at the University of Texas at Austin, wanted a backup to its venerable, and vulnerable, GPS system. Could Starlink fill that role?
Here's a link that was in the article, right to the PDF of the paper that Humphreys has published (but, not peer-reviewed and published) on his UTexas page:
https://radionavlab.ae.utexas.edu/wp-content/uploads/2022/10/starlink-structure.pdfI haven't looked into in depth yet myself. Not being steeped in the snobbery of academia, the "non peer-reviewed" aspect doesn't raise questions. To me, this means it's much more like... oh, a technical paper published by an engineer with the SAE.
Boy it'd be nice to have open hardware, and open code to piggyback on the Starlink comms/sync signals to use as an ersatz GPS system, without needing Starlink gear or a subscription itself.
I'm hoping that more develops from this, and it'll result in somewhat easy to build hardware, and readily available code to make it work, and then integrate elsewhere.