Check out the following information from the Office of Space Commercialization, on it’s Satellite Navigation page. There are a lot of good links and information about satellite GPS navigation.
The use of satellites for positioning, navigation, and timing (PNT) has grown dramatically since the U.S. Government authorized civilian access to the Global Positioning System (GPS) in 1983. Thanks to the long-standing U.S. policy of making GPS freely available to the entire world, as well as a track record of highly dependable service, GPS has evolved from a neat gadget into a ubiquitous technology that is now fundamental to the global information infrastructure.
GPS is a constellation of over 24 U.S. government satellites providing PNT services to an unlimited number of civilian and military users on a continuous, worldwide basis — free of direct user charges. Using the time and position data transmitted by the satellites, a GPS receiver can calculate its location on or above the surface of the Earth within a few meters. When used with an augmentation system, a receiver can attain much higher GPS accuracy — within centimeters, or even millimeters.
Today, GPS technology is in everything from cars and airplanes to Read the rest of this entry →