Global Positioning System
Various radio navigation systems have been in use since the middle 20th century. In the 1960s, experiments put the radio transmitters in satellites. A new system, at first called Navstar, was designed in the 1970s by the United States Air Force. It became GPS and was only used by the U.S. military. In 1983 President Ronald Reagan made an order to allow anyone to use the system, though it was yet too small to be very useful. The highest precision signal was encrypted and only the armed forces were allowed to use it, but in the 1990s it was temporarily decrypted and this was made permanent at the turn of the century.