How Does GPS Technology Work?

TheGPSStore.com Automotive Outdoor Marine Electronics How Does GPS Technology Work? A Start 1978- First satellite NAVTSAR The earliest GPS elements were developed in the 1950's, however the first satellite, called the NAVSTAR, launched in 1978. The system relies on a network of at least 24 and as many as 31 active satellites, travelling at about 7,000 miles per hour. 12,500 miles Altitude Satellites orbit around the earth at an altitude of about 12,500 miles, following a precise orbit and completing two revolutions around the earth in one day. Satellites transmit their signals to earth where GPS receivers harvest this information and apply triangulation to calculate the user's exact location. GPS satellites continuously broadcast satellite position and timing data via radio signals on two frequencies (L1 and L2). The radio signals travel at the speed of light (186,000 miles per second) and take approximately 6/100ths of a second to reach the earth. s are GPS is a line-of-sight instrument. The satellite orbits are assigned in such a way that at least six satellites are visible to ground antennas situated around the world. To calculate precise latitude and longitude, the GPS receiver must lock on to at least three satellites, called triangulation. 'z"Ri bx Triangulation is the mathematical modekused to find the distance of the GPS d, receiver from visible satellites. d, To find a three-dimensional location that includes latitude, longitude and alti- tude, the receiver must communicate with at least four satellites. GPS requires a precise time reference. The atomic clocks onboard each satellite were set to the Coordinated Universal Time or UTC in 1980. However, leap seconds and other anomalies have caused a lag and the current offset is about 14 seconds. offset- 14s End GPS Satellites are engineered to last at least 10 years, at which point a replacement satellite is sent to space, and the defunct satellite is sent into a graveyard orbit. Source: http://en.wikipedia.org/wiki/Global_Positioning System http://www.montana.edu/gps/understd.html http://www.faa.gov/about/office_org/headquarters_offices/a- to/service_units/techops/navservices/gnss/gps/howitworks/ http://geography.about.com/od/geographictechnology/a/gps.htm http://www.magazine.ordnancesurveyleisure.co.uk/magazine/ts- content/editorials/technology/2012/gps-facts-and-figures.html