GPS Development and GPS information.

    Timeline of GPS Development

Measuring distances to four or more satellites simultaneously and knowing the exact locations of the satellites (included in the signals transmitted by the satellites), the receiver can determine its latitude, longitude, and height while at the same time synchronizing its clock with the GPS time standard which also makes the receiver a precise time piece.

Determining a position from measurements of distances is known as triangulation (not triangulation, which involves the measurement of angles)  GPS receivers receive satellite signals, they do not transmit or bounce signals off the satellites. GPS Systems are a passive, receive-only system, GPS Systems can support an unlimited number of users, both military and civilian.

GPS system provides a 24 hour per day global coverage. GPS systems are an all-weather system which is not affected by rain, snow, fog, or sand storms.

GPS systems are a dual-use system being used by both civil and military, and is controlled by a joint civilian / military executive board of the U.S. government. The system is maintained by the U.S. Air Force on behalf of all users.

Civil GPS receivers access the C/A-code (coarse / acquisition code) transmitted on the L1 frequency (1575.42 MHz). Military receivers, in addition, use the encrypted P-code (precise or precision code) which is transmitted on both L1 and the L2 frequency (1227.60 MHz). Some military receivers can access the P-code directly rather than acquiring the C/A-code first and then transferring to the P-code giving them a faster acquisition time and a greater accuracy than civilian GPS receivers.