Learn GPS

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.

Hand-held GPS Receiver

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 GPS):

* The first GPS satellite was launched in 1978.
* A full constellation of 24 satellites was achieved in
1994.
* 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.

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 hours.

Demo One 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).

GPS provides coded satellite
signals that can be processed
in a GPS receiver, enabling
the receiver to compute
position, velocity and time.

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 accuracy.