GPS Navigation Revolution
There are six orbital planes equally spaced (60 degrees
apart), and inclined at about fifty-five degrees with respect
to the equatorial plane. This constellation provides the
user with between five and eight satellites visible from any
point on the earth.
GPS is funded by and controlled by the U. S. Department of Defense
(DOD). While there are many thousands of civilian users of GPS
world-wide, the system was designed for- and is operated by the U. S.
Military. GPS works in any weather conditions, anywhere in the world, 24
hours a day. There are no subscription fees or setup charges to use GPS.
The GPS Satellite System
The 24 satellites that make up the GPS space
segment are orbiting the earth about 12,000
miles above us. They are constantly moving,
making two complete orbits in less than 24
hours. These satellites are travelling at speeds of
roughly 7,000 miles an hour.
GPS satellites are powered by solar energy.
They have backup batteries on board to keep
them running in the event of a solar eclipse, when
there's no solar power. Small rocket boosters on
each satellite keep them flying in the correct path.
Here are some other interesting facts about the
GPS satellites (also called NAVSTAR, the
official U.S. Department of Defense name for
* The first GPS satellite was launched in 1978.
* A full constellation of 24 satellites was achieved
* Each satellite is built to last about 10 years.
Replacements are constantly being built and
launched into orbit.
* A GPS satellite weighs approximately 2,000
pounds and is about 17 feet across with the
solar panels extended.
* Transmitter power is only 50 watts or less.
All about GPS!
The satellites orbit the same ground track (as the earth
turns beneath them) once each day. The orbit altitude is
such that the satellites repeat the same track and
configuration over any point approximately each 24 hours
(4 minutes earlier each day).
The Global Positioning System (GPS) is a worldwide
radio-navigation system formed from a constellation of 24
satellites and ground stations. GPS receivers are
becoming very economical, and are now available to
consumers as hand held devices in vehicles, and PCs.
The Global Positioning System uses these satellites as
reference points to calculate positions accurate to a
matter of meters. In fact, with the latest forms of GPS,
locations can be determined to within a centimeter of
|Click on a picture to learn about
these two inventors of GPS
Four GPS satellite signals are used to compute positions in three
dimensions and the time offset in the receiver clock. The GPS
Operational Constellation consists of 24 satellites that orbit the earth in 12
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