Newtonian physics is just an approximation of Relativity. At slow speeds, Einstein’s special relativity equations of motion are approximated by Newton’s equations. You don’t need Einstein’s equations for GPS, but they would make it more accurate. Relativity has been proven mathematically, and empirically, time and time again. Newton can get you to the moon, work on GPS, and is find in our every day life, but it gives the wrong answers at higher speeds. One day we will have a solar system positioning system and it will require relativity to be accurate.
find=fine ooops.