| Global Positioning Systems |  |
The Global Positioning System (GPS) is a satellite-based navigation system comprised of a network of 24 satellites placed in orbit by the U.S. Department of Defense. Originally intended for military applications, it was made available for civilian use the 1980s. GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use triangulation to calculate the user's exact location. A GPS receiver calculates how far away a satellite is by comparing the time a signal was sent with the time it was received. New GPS receivers are, on average, accurate to within 15 meters.
