How did the Doppler shift observed from Sputnik 1 lead to satellite navigation ideas?

When scientists tracked Sputnik 1 in 1957, they discovered that the satellite’s orbit could be precisely plotted by analyzing the Doppler effect in its transmitted signals relative to a fixed location on Earth.1

This observation led to the realization that the process could be reversed: if the orbits of satellites were known with high precision, a receiver on the ground could determine its own location by measuring the magnitude and rate of change of the Doppler shift in signals received from those satellites. This insight was instrumental in the development of early satellite-based navigation systems, such as the U.S. Navy’s Transit system in the 1960s, which utilized Doppler-shift measurements to provide positioning for ships and submarines. While modern systems like the Global Positioning System (GPS) primarily rely on signal travel time and atomic clocks for positioning, they still utilize instantaneous Doppler-shift measurements to calculate accurate velocity components.21