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Global Positioning System and How it Works

1/24/2013 7:54:59 AM | by Anonymous

Global Positioning Systems

The Global Positioning System (GPS) is a navigation system which is satellite-based that was initially designed for the U.S. military. The U.S. military name for the Global Positioning System is NAVSTAR. However in current times, the number of civilian GPS users now exceeds the military users and there are various commercial markets which have emerged. This navigation system provides location and time information in all weather conditions, anywhere or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites.


GPS satellites circle the earth twice a day in a very precise orbit and transits signal information to earth. GPS receivers utilize this information and use the triangulation method to calculate a user’s exact location. The GPS receiver will compare the time the satellite transmitted a signal with the time it was received. The difference in time will tell the GPS receiver the distance of length the satellite is. Currently, with distance measurements from several satellites, the user’s position can be determined by the user and display it on the unit’s electronic map. A GPS has to be locked on to the signal of at least three satellites to calculate a track movement and the user’s 2D position (latitude and longitude). Once a user’s location has been found, other information, such as distance, speed, bearing, trip, track, sunrise and sunset time, distance to destination and more can be calculated by the GPS unit.


There had been at least 24 GPS satellites roaming about earth. In 1989, the first of those 24 satellites was sent up. The first full constellation of satellites was set up in 1994. Today, however, there might be as many satellites as 30, including some spares circling about. The orbits are spread about so that no matter where you are located on Earth, you will have at least six of them in your line of sight. As previously mentioned, in order to get an accurate position reading, your GPS receiver would have to combine the signals from at least four satellites although in some special cases just three are enough. Every twelve hours, a GPS satellite goes around the world once. The satellites travel 12,500 miles above us at roughly 7000 miles per hour. They are equipped with small boosters so they can adjust their path when needed.


How did the common folk get to know about GPS when it was only made known to the United States military? Well, GPS was made public knowledge due to a tragedy. In 1983, a navigation error caused Korean Air Lines flight 007 to enter Soviet airspace and be shot down, killing all 269 passengers. Then President of the United States Ronald Regan subsequently ordered the United States military to make the Global Positioning System to be available for civilian use once it was finished, so that in the future similar incidents could be avoided.


GPS is not just utilized for navigation purposes. It also can be used to get a very exact time stamp. Multiple atomic clocks are usually found on every GPS satellite and time is included in the signal it sends out. These signals help a GPS receiver determine the current time within 1000 billionths of a second. These signals are used for one, to synchronize base stations in cell phone networks. The clocks on these satellites, though accurate they may be, are still subject to Einstein’s theory of relativity, which means the time of these clocks on the satellites will slowly start to deviate from those on earth. This is adjusted from control signals from the Earth.


The Global Positioning System is constantly a work in progress. It is continuously being upgraded and new satellites are being launched. This means that precisions will keep improving which in turn will make the system increasingly powerful. There are also several other Global Navigation Satellite Systems in existence or in the making. The European Union for one is working on a system named Galileo and China is planning for a system named Compass. Systems that also offer regional coverage today include China’s Beidou or Japan’s QZSS.

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