The First GPS satellite was launched in 1978.
The Defense Department declared GPS fully operational in 1995.
When the system was first introduced miscalculations were
placed
in GPS transmissions to non-military receivers.
This function
was cancelled in May 2000.
The 24 Earth-orbiting satellites cost an estimated $12
billion
to build and launch.
Each satellite weighs 1,735 pounds.
It takes a satellite 12 hours to orbit the Earth once.
The Russians have a system similar to the U.S. that
is known as GlONASS. The Russian system is not
yet fully operational.
Low cost GPS receivers have an accuracy of 100 meters.