April 26, 2008
The GPS space segment made up of 24 satellites orbits the earth about 12,000 miles above us. They make two complete orbits in less than 24 hours and are constantly moving. They travel at speeds of roughly 7,000 miles an hour.
Powered primarily by solar energy, the GPS satellites have back-up batteries on board to keep them running when there is no solar power such as in a solar eclipse. They are kept flying in the right path by small rocket boosters on each satellite. Officially, the U.S. Department of Defense calls the GPS satellites NAVSTAR. Each satellite is built to last about 10 years while replacements are constantly being built and launched into orbit. It weighs approximately 2,000 pounds and is about 17 feet across with the solar panels extended. The GPS transmitter power is only 50 watts or less.
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