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The Global Positioning System or GPS for short is the world’s first satellite radio-navigation system. It was developed by the United States Department of Defense under the name of NAVSTAR or Navigation Satellite Timing and Ranging. Research on timing and navigation by a satellite arrangement began in the 1960’s with the first operational GPS satellite launched in 1978. However it was not until April 27, 1995 that it became fully operational. Originally they were used primarily for troop navigation and positioning and for artillery fire. In the 1980’s the U.S. government by executive decree authorized its use by the civilian population.

The GPS System is made up of three main elements, Satellites, Earth Monitoring Stations and GPS Receivers. Presently there are 24 satellites circling the earth in 6 orbits. Each satellite circles the earth twice a day traveling at approximately 7000 miles per hour. At their highest point they orbit about 12,600 miles above the earth’s surface. At this height the signals from each satellite can be picked up over a large area of the earth’s surface. This is important since it offers at least four signals that can be picked up by your GPS receiver. The more signals used to pin point your location the more accurate your reported location will be. Working with the satellites are five monitoring stations located on earth. Four of these stations are unmanned and the fifth is a manned master station which is located in Colorado Springs, Colorado. The four unmanned stations constantly receive position data from the satellites and send it on to the master station. The information received by the master station is used to correct the position of the sat tiles and then sends that corrected information back to the satellites. All of this occurs so that the third element your GPS unit receives accurate data from the satellites it is receiving signals from at any particular moment. Your GPS unit then takes this information and reports to you by signal and screen information your exact location.

The signals sent from the GPS satellite system are low power radio signals. They are “line of sight” signals like your cell phone signals. This means they pass through clouds, glass and plastics but not through solid objects, such as buildings, in basements, caves, etc. Weather conditions also affect GPS signals, however not enough to affect the quality of the signal your GPS unit receives. Since GPS satellites cycle the earth, their signals can be picked up and used anywhere on earth. No fees or setup costs are needed to use the GPS satellite system.

Your GPS unit works by calculating the time it takes to receive a signal from each of at least three satellites comparing that to the reported location of each of those reporting satellites and then through triangulation techniques identifies its and your exact location at that moment.

It is possible by receiving signals from just three satellites to give your position by latitude and longitude and to report or track movement. However, when your GPS unit is able to receive signals from at least four satellites it can calculate your position in 3D. That is, it can report your position with latitude, a longitude and an altitude. With this information your unit will be able to report not only position and movement but it can report your speed, trip distance, distance to a destination, and more.

The accuracy of your GPS unit depends on its ability to quickly receive and hold onto, or lock on to, a GPS satellite’s signal. The ability to maintain a strong lock on that signal while your GPS unit is in dense foliage or urban settings with tall buildings and how it deals with weather factors such as snow and electrical storms depends on the features designed into your unit. Generally less expensive units will have accuracy’s averaging between 30 to 40 feet. Newer more expense GPS units pickup more satellite signal, retain them longer and increase accuracy down to just a few meters.