Comment by linzhangrun

In principle it's actually easy to imagine: the speed of light is known, the orbital positions are known, the time differences give distances, and then it's just trilateration with three spheres. The idea isn't complicated. Engineering-level precision that’s hard to imagine: light can circle the Earth seven times in one second, so tiny deviations make a world of difference — the atomic clocks on GPS even have to account for relativistic effects. So cool!