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Global Positioning System


    Global Positioning System (GPS) allows people to pinpoint their geographical location within a few hundred feet using satellites that transmit radio waves through the receiver.  The GPS is owned by the U.S. government and was first created for military purposes, but has been made available for public use around the world.  The U.S. government has a site that shows what a GPS is and how it is used in certain what applications.


    There are 24 satellites that orbit the earth (31 total counting the additional 7 that are not in orbit) in outer space that transmit one-way signals that give the user their location and time.  The GPS receiver translates longitude, latitude and altitude into a map and location on the screen of a device, such as a portable or in-dash navigation. 

    The GPS measures the location of the receiver by a process called trilateration.  Three satellites are identified by the receiver in order for the location to be detected.   Two spheres overlap each other and a ring is formed around that overlap.  This ring acts as an imaginary sphere and two positions are pinpointed to the location of the receiver on Earth.  The location in space is disregarded by the receiver, which leaves one location on Earth.  This is the geographical location of the person using the GPS device.  The receiver is able to track the person as he or she moves or drives from location to location until the on screen program is canceled or reset by the user. 


    One wouldn't think the GPS needs to be monitored constantly, but it is by the Schriever Air Force Base in Colorado Springs, CO.  Each satellite has a built-in clock.  The time on the satellites must be exact by the seconds with the time on Earth in order for the GPS to work correctly. 
Time in space runs a little faster than time on Earth due to that the gravitational pull on Earth is stronger.  If there is a time difference between the time on Earth and the satellites, the satellites can drift out of orbit about 10-12 kilometers a day, causing GPS devices to inaccurately pinpoint a user's location. Therefore, the Air Force Base must maintain the GPS and make any time corrections when needed.


    There are many devices that use GPS.  For instance, hand held devices for hikers, GPS watches, Smartphones, in-dash automobile navigation systems, and portable devices for automobiles.  Popular brands such as Garmin, Magellan and TomTom have made their way to the top of the market, each with their own competitive advantage by marketing to a certain audience and each having special features. United Parcel Service (UPS) also has delivery trucks equipped with GPS tracking device that helps accurate tracking of packages, utilizing more efficient online transaction processing of logistics. With GPS, other advance technology may branch out in the future from this advance, yet basic technology.

"How GPS Receivers Work" HowStuffWorks.Com
"How GPS Works" You Tube