ONR Science & Technology Focus
               Oceanography       Space Sciences       Blow the Ballast!       Teachers' Corner   
Observing the Sky Solar System Satellites Navy Research Resources

The Navy & Satellites: Global Positioning System (GPS)

The Global Positioning System, better known as GPS, is a satellite-based radio navigation system developed and operated by the U.S. Department of Defense. GPS permits land, sea, and airborne users to determine their three dimensional position, velocity, and time, 24 hours a day in all weather, anywhere in the world.

How does GPS work?

The GPS Operational Constellation consists of 24 satellites that orbit the Earth in 12 hours.

  • GPS provides specially coded satellite signals that can be processed by a GPS receiver, which can compute position, velocity, and time.
  • Four GPS satellite signals are used to compute 4 dimensions of X, Y, Z (position), and time.


What is GPS used for?

  • GPS receivers are used for navigation, positioning, time dissemination, and research. The system is used by the military as well as civilians, including hikers, boaters, car drivers, and others who need to know their exact location.
  • Navigation in three dimensions is the primary function of GPS.
  • Navigation receivers are made for aircraft, ships, ground vehicles, and for hand carrying by individuals.
  • Since precise positioning is possible using GPS receivers, it can be used for surveying as well as for studying plate tectonics
  • Precision clocks on board the GPS satellites help us keep the most accurate time in the world!
  • Astronomical observatories, telecommunications, and laboratory standards can be set to precise time signals or controlled to accurate frequencies by special purpose GPS receivers.
  • Research projects have used GPS signals to measure atmospheric information.

The GPS system actually operates in two different ways.

  • U. S. and Allied military, certain U. S. Government agencies, and selected civilian users with cryptographic equipment (which can decipher coded information) and specially equipped receivers use the Precise Positioning System, or PPS.
  • Civilian users worldwide can use the Standard Position Service, or SPS, without charge or restrictions. Receivers capable of receiving and using the SPS signal can be bought by anyone, and some are even standard equipment in new cars.