How does GPS work?

TomTom Education


What is GPS?

GPS is the world’s first satellite navigation system. It was developed by the U.S. Government’s Department of Defense, who gave GPS its official name: the NAVSTAR system (Navigation Satellite Timing and Ranging).

GPS consists of 3 key elements:

• Satellites in space
• Monitoring Stations on Earth
• And last but not least, you and your GPS receiver.

The satellites
GPS has 24 satellites that circle Earth in six orbital paths, sending out radio signals from their position in high orbit, 12,600 miles/ 20,300 kilometres above our heads. Being so high, each satellite’s signal covers a large area of the earth’s surface and their orbits have been ‘choreographed’ so that your GPS receiver back on Earth is always getting signals from at least 4 satellites, the number you need to pinpoint your location.

The monitoring stations
There are 5 monitoring stations: the master station in Colorado Springs, USA and four unmanned stations. One on Hawaii, the other three in remote locations as close to the equator as possible: Ascension Island in the Mid Atlantic; Kwajalein in the Pacific and Diego Garcia Atoll in the Indian Ocean.

The 4 unmanned stations receive constant data from the satellites and forward it to the master control station, which ‘corrects’ the data and then sends corrected data back up to the GPS satellites.

GPS signals
Your GPS receiver picks up signals from GPS satellites to work out your location. The last, important step in the process is of course you making use of that information.

Each satellite transmits low power radio signals on different frequencies for different users. The signals travel by so-called ‘line of sight’. This means they pass through clouds, glass and plastic, but not usually through solid objects, such as buildings.


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