The Global Positioning System
The Global Positioning System is a constellation of over 24 U.S. Government satellites providing PNT services to civilian and military users on a continuous, worldwide basis -- free of direct user charges. The system provides highly accurate location and time information to anyone equipped with a GPS receiver. GPS provides a precise, common location and time reference to an unlimited number of people in all weather, day and night, anywhere in the world.
For further information about how GPS works, please visit one of the following websites:
- Air Force Fact Sheet on GPS
- GPS Education Page at NOAA
- GPS Education Page at Federal Highway Administration
- GPS Education Page at Smithsonian Institution
- GPS Education Page at PBS
GPS Applications
GPS technology can be found in everything from cars and planes to cell phones and wristwatches. It is being used to improve productivity in areas as diverse as farming, mining, construction, surveying, taxicab management, and package delivery. It is enhancing public safety by preventing transportation accidents and by reducing the response times of ambulances, firefighters, and other emergency services. GPS is also furthering scientific aims such as weather forecasting, earthquake prediction, and environmental protection. Furthermore, the precise GPS time signal, derived from atomic clocks, is being applied to critical economic activities such as synchronizing communication networks, managing power grids, and authenticating electronic transactions.
Similar with the growth in civil and commercial applications, the PNT information provided by GPS remains critical to U.S. national security, and its applications are integrated into virtually every facet of U.S. military operations. U.S. and Allied military forces will continue to rely on GPS military services for PNT services.
For further information about how people are utilizing GPS around the world, visit one of the following websites:
GPS Modernization
The United States is committed to continuously upgrading the Global Positioning System to provide enhanced performance for the end user. In 2000, the United States ended the use of Selective Availability, which was an intentional degradation of civilian GPS service, thereby increasing civilian accuracy by an order of magnitude. In 2005, several monitoring stations were added to the GPS ground segment, enabling more accurate orbital information to be broadcast from the satellites.
Also in 2005, the United States fielded the first next-generation GPS satellite, featuring new civilian and military capabilities. In the future, the entire GPS constellation will transmit three new civilian signals in addition to the original signal, enabling significant enhancements in user accuracy, integrity, and reliability. For more information about GPS modernization, download the GPS modernization fact sheet (PDF).
GPS User Support
The United States provides GPS users with critical information on the status of the GPS constellation through several means.
- The broad civilian community is served by the U.S. Coast Guard Navigation Center (NAVCEN), which distributes GPS service updates and other user information via email and the web. NAVCEN is the appropriate contact point for civilians around the world to report user problems with the civilian GPS service. NAVCEN can track down whether these are due to local interference, user equipment problems, temporary coverage issues, satellite errors, or other causes.
- For those in the civilian aviation community, the FAA National Operations Control Center will issue a Notice to Airmen (NOTAM) whenever a GPS anomaly is detected that may affect air navigation safety.
- Finally, the military community is served by the GPS Operations Center, which monitors both the civilian and military GPS services and produces anomaly advisories and other information products about the GPS constellation.
Technical Information for Developers
The United States openly publishes all of the technical documentation needed to design civilian GPS user equipment. By putting such information into the public domain, the U.S. Government seeks to encourage widespread adoption and use of GPS as an international PNT standard.
The technical documentation includes the following materials: