Introduction - If you have any usage issues, please Google them yourself
Not the fifties, the former Soviet Union launched the mankind s first artificial Earth satellite, the U.S. scientists in their follow-up study, found the phenomenon of Doppler shift, and led to use of the principle of Doppler satellite navigation and positioning system TRANSIT completed, in the military and civilian achieved a great success, is the history of navigation and positioning of the first leap. In order to improve the accuracy of satellite positioning, the United States since 1973 to build the Global Positioning System GPS