GPS (Global Positioning System)

What is GPS?

The global positioning system is a satellite-based navigation system made up of a network of satellites put into orbit by the U.S. Department of Defence. GPS was originally intended for military use, but in the 1980s the government made the system available for civilian use.

How does GPS work?

GPS satellites circle the earth in a very precise orbit and transmit a signal to the earth. Your GPS receiver works out how long it took for the signal to reach it from the satellite and this tells it how far away the satellite is. By comparing the signals from 3 satellites your receiver can calculate exactly where it is on Earth (using triangulation – ask your Maths teacher!)

GPS facts

• There are 24 satellites in the GPS system and they are orbiting the Earth at about 20,000 kilometres above us. The satellites are travelling at about 11,000 kilometres per hour.
• Small rocket boosters keep each satellite on the correct path.
• The satellites are powered by solar energy and have backup batteries on board to keep them running if there is a solar eclipse.
• A GPS satellite weighs approximately 900 kilograms and is about 5 metres across with its solar panels extended.
• Each satellite is built to last about 10 years and replacements are constantly being built and launched into orbit.