Global Positioning System (GPS)

GPS satellites circle the Earth twice a day in a precise orbit. Each satellite transmits a unique signal and orbital parameters that allow GPS devices to decode and compute the precise location of the satellite. GPS receivers use this information and trilateration to calculate a user’s exact location.


The 31 satellites that currently make up the GPS space segment are orbiting the Earth about 12,000 miles above us. These satellites are constantly moving, making two complete orbits in less than 24 hours. They travel at speeds of roughly 7,000 miles per hour. Small rocket boosters keep each satellite flying on the correct path.

Why are rocket boosters needed?

I assume because the satellites get closer and closer to the earth. I remember seeing something about the ISS for it to stay on orbit.

Here are some other interesting facts about the GPS satellites:

  • The first GPS satellite was launched in 1978
  • A full constellation of 24 satellites was achieved in 1994
  • Each satellite is built to last about 10 years. Replacements are constantly being built and launched into orbit
  • GPS satellites are powered by solar energy, but they have backup batteries on board in case of a solar eclipse
  • Transmitter power is only 50 watts or less
  • GPS is currently deploying Block III, it’s third-generation satellite