Time to Find Your Way
All scenes › Chapter 1 How Does Your Phone Know?
The satellites circling Earth
About 30 satellites, 20,200 km up, twice around Earth a day
View in 3DThe satellites circling Earth
About 30 GPS satellites do the broadcasting. They circle about 20,200 km up, roughly 1.6 times Earth’s width. Each one flies at about 13,900 km per hour and goes around Earth twice a day. They are spread across six orbits, so from anywhere on the ground several of them are always in the sky. So what can a single broadcast tell you?
Why?If the satellites all followed one track, only the ground right under it would see them. Splitting them across six tilted orbits covers the whole planet evenly. To find your position, you need to see several satellites at the same time.
Learn moreThe 30 satellites on screen copy the real GPS layout (the height, and six orbits tilted 55° from the equator), but they are not the real satellites or their real positions. The satellite models are drawn huge so you can see them; a real one is only a few meters across, even with its wings open. Their motion is also sped up a lot.
- How high GPS satellites fly
- About 20,200 km
textbook formulas
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Wikipedia: GPS satellite blocks
More in the series
Orbits, distances and clock differences are calculated with textbook formulas (Kepler’s laws and simple forms of special and general relativity). The 30 satellites follow the real GPS layout but are not the real satellites or positions. In the 3D view, the satellite models are drawn huge and radio waves move far slower than in real life.