Using Frequency to Find Position
The Transit system, initially designed to provide precise positioning for the Polaris submarine fleet, depended on noting changes in Doppler frequency shift.
During the 15 minutes it took a Transit satellite to pass from horizon to horizon, navigators on a ship or submarine measured the Doppler shift in the satellite’s radio transmissions to produce a fix of their position.
Mathematician Bill Guier and physicist George Weiffenbach told APL Research Center director Frank T. McClure about using Doppler tracking for Sputnik. McClure suggested that a navigator could use signals from a known satellite position to determine his location anywhere in the world. This idea became the basis for Transit.