GPS Development and GPS information.

North Pole Adventure Travel

      Timeline of GPS Development

• Late 1960s, concept development.
• Early 1970s, program funding and establishment of a Joint Program Office within the Department of Defense.
• December 1973, proposal for GPS approved by the Defense System Acquisition and Review Council (DSARC).
• Mid-1970s, ground testing of the GPS concept.
• February 22, 1978, launch of the first GPS satellite.
• 1989, Magellan Corporation introduces the first hand-held GPS receiver.
• 1991, detection and fix of a major a glitch that slowed progress.
• January 1991, military use of GPS in Operation Desert Storm in Iraq.
• December 1993, declaration of Initial Operational Capability (IOC) by the U.S. Secretary of Defense.
• May 2, 2000, SA is turned off by presidential directive; inexpensive civilian GPS receivers increase their horizontal accuracy from "no worse than" 100 meters to 15-25 meters.
• Oct 1, 2005 First Modernized GPS Satellite with improved accuracy

The Navstar Global Positioning System, or GPS for short, consists of three segments or components.

• A constellation of satellites ( currently 27 satellites ) orbiting about 20,000 km above the earth’s surface which transmit ranging signals on two frequencies in the microwave spectrum.

• A control segment which maintains GPS through a system of ground monitoring stations and satellite upload facilities.

• The user receivers – both civil and military.

Each satellite transmits a unique digital code sequence precisely timed by an atomic clock which is picked up by a GPS receiver’s antenna and matched with the same code sequence generated inside the receiver. By matching the signals, the receiver determines how long it takes the signals to travel from the satellite to the receiver. These timing measurements are converted to distances using the speed of light ( 300,000,000 meters per second or 186 miles per second or 6.18 micro seconds per mile )

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.