GPS & Satellite Navigation
How 31 atomic clocks orbiting 20,180 kilometers above Earth in Medium Earth Orbit broadcast relativistic radio signals to calculate your exact position on the planet down to the meter.
Pieces in this series
How GPS Actually Knows Where You Are
Orbital atomic clocks, pseudorange trilateration, relativistic time dilation, and the four-satellite geometry equation
GPS does not track your phone from orbit or receive signals from your device. Your phone is a purely passive radio listener, capturing microscopic time-stamped radio pulses from at least four atomic-clock-equipped satellites in Medium Earth Orbit. By calculating the delay of each signal at the speed of light, applying Einstein’s Special and General Relativity corrections, and solving a system of four simultaneous sphere equations, your phone isolates its latitude, longitude, altitude, and local clock bias down to the meter.
Why GPS Sometimes Shows the Wrong Location
Ionospheric plasma delay, urban canyon multipath reflections, Dilution of Precision, and Assisted GPS
GPS accuracy does not degrade because satellites get confused. It falters because radio waves must travel through hundreds of kilometers of solar-charged ionospheric plasma, refract through humid tropospheric air, and bounce off glass and steel skyscraper facades. When reflected non-line-of-sight signals travel longer paths, or when visible satellites bunch together into cramped geometries, your phone’s pseudorange equations produce spatial error ellipsoids that pull your blue dot dozens of meters off course.