GPS

      GPS means Global Positioning System and it was developed by the U.S. government in the 1960's with the intention to use it during military missions. The space segment, the control segment and the user segment are the GPS' three segments. The space segment refers to a constellation of more than 24 operating satellites which are connected at all time with each GPS receiver, calculating its position and time information. 

      The control segment is formed by monitors and control stations which are located on Earth. This segment maintains the satellites in their orbits and adjust their clock. Without this segment, the GPS satellites would be "lost" in the sapace.

                                                                                         

      The space and control segment are developed and controlled by the United States Air Force. Therefore, The U.S. government is responsible for the export of some civivian receivers.

      Finally, the GPS receivers are in the user segment. These equipments receive the signals from the GPS satellites, after that, they are able to calculate the user's position.

      The United States intend to expand the GPS program, creating a second civil signal that will support the civilian service and help some safety-of-life applications.

      With a GPS receiver, people can go wherever they want, even if they don't know the place or destination. Because of that, it is known as one of the most important inventions in the last 50 years.