GPS DEVICES HOME PAGE
For a very complete, thorough overview and explanation of our present day GPS system, see the GPS page at Wikipedia.org. This article offers both a simple introduction to our GPS system, as well as a more technical in depth explanation of how this system works. Thanks to a combination of luck, vision, science, and hard work, we have this excellent navigational tool available for all to use. Unfortunately, we no longer can use the excuse that we got lost, or that the map was inaccurate!!
The official name for the GPS system is NAVSTAR. As this system was originally designed for military use, the Department of Defense named the system. The earliest of the NAVSTAR GPS satellites was placed in orbit in 1978.
The NAVSTAR Global Positioning System (GPS) is a constellation of orbiting satellites that provides navigation data to military and civilian users all over the world. The system is operated and controlled by members of the 50th Space Wing located at Falcon Air Force Base, Colorado as a space-based global radio navigation system which is operated by the U.S. Air Force.
Two GPS services are provided. The Precise Positioning Service (PPS) provides full system accuracy primarily to U.S. and allied military users. The Standard Positioning Service (SPS) provides an accurate positioning capability for civil users throughout the world.
The GPS has three major segments: space, control, and user. The GPS Space Segment is composed of 24 satellites in six orbital planes. The satellites operate in circular 20,200 km (10,900 nm) orbits at an inclination angle of 55 degrees and with approximately a 12-hour period. A minimum of four satellites must be visible to a user in order to compute a three-dimensional position solution.
The GPS Control Segment has five monitor stations and three ground antennas with uplink capabilities. The monitor stations track all satellites in view. The information from the monitor stations is processed at the Master Control Station (MCS) to determine satellite clock and orbit states and to update the navigation message of each satellite. This updated information is transmitted to the satellites via the ground antennas.
The GPS User Segment consists of a variety of receiver types to provide positioning, velocity, and precise timing to the user.