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Global Positioning Satellite System (GPS)

Satellite Images of GPS

GPS is a space-based radio-positioning system nominally consisting of a minimum of 24-satellite constellation that provides navigation and timing information to military and civilian users worldwide. GPS satellites, in one of six medium earth orbits, circle the earth every 12 hours emitting continuous navigation signals on two different L-band frequencies, L1 and L2. In addition to the satellites, the system consists of a worldwide satellite control network and GPS receiver units that acquire the satellite's signals and translate them into precise position and timing information.

GPS provides the following:

  • 24-hour, worldwide service
  • Highly accurate, three-dimensional location information
  • Precision velocity and timing services
  • Accessibility to an unlimited number of global military, civilian, and commercial users

As a service to GPS users, the Department of Transportation established the "Navigation Information Service" (formerly "GPS Information Service") as a point of contact for civil GPS users. Operated and maintained by the United States Coast Guard, the NIS can be reached at (703) 313-5900, seven days a week, 24 hours a day, and at www.navcen.uscg.gov.

U.S. Space-Based Positioning, Navigation, and Timing Policy (DOT Responsibilities)

The national policy issued on December 8, 2004 established guidance and implementation actions for space-based positioning, navigation, and timing programs, augmentations, and activities for U.S. national and homeland security, civil, scientific, and commercial purposes. Per this policy, the Department of Transportation’s responsibilities are outlined below

The Secretary of Transportation shall:

  • Have lead responsibility for the development of requirements for civil applications from all United States Government civil Departments and Agencies;
  • Ensure, in cooperation with the Secretary of Defense and the Secretary of Homeland Security, the performance monitoring of U.S. civil space-based positioning, navigation, and timing services;
  • Consistent with the guidance in Section V of this policy, and in coordination with the Secretary of Commerce and the Secretary of State, facilitate: (1) foreign development of civil positioning, navigation, and timing services and systems based on the Global Positioning System; and (2) international participation in the development of civil applications for U.S. space-based positioning, navigation, and timing services;
  • Ensure, in coordination with the Secretary of Defense, that space-based positioning, navigation, and timing public safety services meet or exceed international performance standards, including but not limited to those used for these services in aviation and/or maritime applications;
  • In cooperation with other Departments and Agencies, promote the use of U.S. civil space-based positioning, navigation, and timing services and capabilities for transportation safety;
  • Represent the civil Departments and Agencies in the development, acquisition, management, and operations of the Global Positioning System;
  • Develop, acquire, operate, and maintain Global Positioning System space or terrestrial augmentations for civil transportation applications;
  • Ensure the earliest operational availability for modernized civil signals and services on the Global Positioning System and its augmentations, in coordination with the Secretary of Defense;
  • In coordination with the Secretary of Homeland Security, develop, acquire, operate, and maintain backup position, navigation, and timing capabilities that can support critical transportation, homeland security, and other critical civil and commercial infrastructure applications within the United States, in the event of a disruption of the Global Positioning System or other space-based positioning, navigation, and timing services, consistent with Homeland Security Presidential Directive-7, Critical Infrastructure Identification, Prioritization, and Protection, dated December 17, 2003; and
  • In cooperation with the Secretary of Defense, assess and assist, as appropriate, in the international acceptance for using the military positioning, navigation, and timing services of the Global Positioning System for operations in civil airspace.

Global Positioning System (GPS) Related Documents