I thought the idea for GPS went back pretty much to Sputnik. People realized pretty quickly they could track it by timing its signals from a known location on E

I thought the idea for GPS went back pretty much to Sputnik. People realized pretty quickly they could track it by timing its signals from a known location on Earth and then also quickly realized you could reverse that and figure out where on Earth you are once you have enough timing signals from known locations in space. It just took a bit for the computers to get small enough and for us to put up the satellites.