In October 1957, the first man-made earth satellite, Sputnik I, was successfully launched, and space-based navigation and positioning began.
Designed NNSS-TRANSIT in 1958, namely the satellite satellite system;
The system was officially launched in 1964;
In 1967, the system was decrypted for civilian use;
In 1973, the United States Department of Defense approved the development of GPS;
In the 1991 Gulf War, GPS was first used on a large scale for actual combat;
In 1994, GPS was completed and put into use;
In 2000, Clinton announced that GPS was canceling the implementation of SA (an artificial limitation of civil GPS accuracy).
GPS service strategy
Two GPS services:
SPS--standard positioning service, civil use, accuracy is about 100M;
PPS - precision positioning service, military and licensed private users, precision up to 10M.
Two Measures to Limit the Positioning Accuracy of Civil Use (Protecting National Interests from Being Infringed):
SA--choose usability, think that reduce the measurement accuracy of ordinary users, limit horizontal positioning accuracy 100M, vertical 157M (has been canceled on May 1, 2005);
AS - anti-spoofing.