All UK Sat Nav systems are based on a network of 24 GPS satellites launched by the U.S. Department of Defence originally for military use. The satellites orbit the earth twice a day transmitting signals that can be picked up by GPS receivers. Using triangulation, together with the signals from at least 3 satellites, the receiver can calculate the users exact position and display it on the unit’s electronic map.
Essentially it does this by comparing the time the signal was transmitted by the satellite with the time it was received. With 4 or more satellites in view, the receiver can determine the users 3D position (latitude, longitude and altitude) and calculate other information including speed, bearing, distance etc.
Here are some interesting facts about GPS satellites:
- The first GPS satellite was launched in 1978.
- GPS satellites are powered by solar energy.
- The satellites orbit approximately 12,000 miles above us at a speed of around 7,000 mph.
- Satellites last about 10 years and replacements are constantly being launched.
- GPS satellites weigh approximately 2,000 lbs and measure about 7 feet across with the solar panels extended.
- Transmitter power is less than 50watts.