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,
- 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
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.