The Global Positioning System (GPS) is a space based Global Navigation Satellite System (GNSS) that provides a Position, Navigation and Timing (PNT) service, which operates 24 hours a day, seven days a week, in all types of weather. It is available anywhere on Earth where there is an unobstructed line of sight to four or more GPS satellites.
GPS is maintained by the United States government and is freely accessible by anyone with a GPS receiver. The US have committed to providing continuous, reliable, space-based PNT services through GPS. The first GPS satellites were launched in 1978 and their original purpose was to provide a precise navigation system for the US military. In 1983, US President Reagan declared that GPS would be freely available for civilian use to help increase navigation accuracy in vital transportation.
By 1995, GPS was fully operational but the highest quality signals were reserved for military use, and the civilian accuracy was deliberately limited. This process is known as selective availability (SA). This limited the applications and number of potential users. In 2000, US President Clinton announced that SA would be switched off, which opened up the full potential of GPS to the civil community. This allowed the development of the mass market utility we know today, including car navigation systems and location-based services for smartphones.
By 2004, the rapidly growing GPS consumer market and adoption of PNT across many sectors of the economy including banking, energy, transport, mining and agriculture prompted US President Bush to create the National Executive Committee for Space Based Positioning, Navigation and Timing. This dual civil-military body coordinates U.S. federal Departments and agencies on matters concerning GPS and related systems.
Throughout its history, GPS has been constantly upgraded. In 2005 the first modernised GPS satellite was launched with new signals for both military and civilian users. The third generation of GPS satellites is due to be launched from 2014 onwards, which will guarantee increasingly accurate and reliable service for many years to come.
For more information, visit the United States of America's Government Website GPS.gov.