How GPS Works

Timing signals from orbit

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• GPS measures distance from signal travel time: $d = c\,\Delta t$.
• A 1 μs clock error means 300 m of distance error.
• Four satellites solve for position and the receiver’s clock error.
• Relativity shifts the satellite clocks by 38 μs per day, which must be corrected.

Steps

1. Distance from time
2. A tiny timing error
3. Solve for the clock error
4. From orbit
5. How many satellites?
6. Without relativity