It is imprecise at best and incorrect at worst to say that Transit was a predecessor to GPS—the idea really did come from the Navy rather than from DARPA. To me, this would be akin to saying that Thomas Edison had a vital role in developing the iPod because his wax cylinder system was also capable of recording and playing back music.
Roger Easton, Jr., professor at the Center for Imaging Science at the Rochester Institute of Technology, points out that the early DARPA-funded system on which I based my contention, TRANSIT, used an entirely different technology for establishing the location of ground receivers than today’s GPS.
While TRANSIT was the first satellite positioning system (with launches beginning in 1959), its reliance on less-than-precise doppler shift measurements was rendered obsolete by later satellites using transmitted time signals for determining position. As Easton put it to me:
Not incidentally, Easton is the son of Roger Easton, Sr., one of the pioneering Naval Research Laboratory engineers behind the idea of using satellite time signals (as in today’s GPS) for navigation. In fact, Easton, Sr. holds a patent for the idea, “Navigation Using Satellites and Passive Ranging Techniques,” number 3789409, filed in 1970.
Thanks for the correction, Dr. Easton. I’ll be more nuanced in future statements (DARPA funded the first satellite navigation system, not GPS, along with the first small, lightweight GPS receivers, paving the way for wide use). I’ll also correct the next edition of the book.