The Syrian airfield prepare for reception of military aircraft of China
The latest news about fast emergence in borders of Syria of navy of China encouraged Syrians and res[...]
The System
GPS has three parts, or segments. They are the Space Segment, the Control Segment, and the User Segment.
Satellites form the Space Segment. GPS satellites are divided into six groups of four. Each group is in a different orbit. The satellites orbit at a height of 12,600 miles (about 20,270 kilometers). At this height, they take 12 hours to circle Earth, so they go around the world twice in one day. The satellites travel at a speed of
О The satellites in the GPS occupy six orbital planes 60 degrees apart, all tilted at 55 degrees to the equator. Receivers on Earth determine their positions by picking up signals from four satellites.
ATOMIC CLOCKS
Each GPS satellite carries three or four atomic clocks, depending on which type of satellite it is. Amazingly, the clocks carried by GPS satellites are accurate to about 1 second in 300,000 years! Only one atomic clock is used at a time; the others are there as backups. If a clock fails for any reason, a backup takes its place.
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about 7,000 miles per hour (11,260 kilometers per hour). Electric power for the clocks, onboard computer, and radio equipment is generated by solar panels. As the satellites orbit Earth, their solar panels turn automatically to face the Sun, while the radio antennae keep pointing at Earth.
The Control Segment on Earth runs the system. Monitor stations check the orbit, position, and clock time of every satellite and send all the information to the Master Control Station at a U. S. Air Force base in Colorado. This information is compared with the information transmitted by the satellites, and any errors are corrected.
The User Segment includes all the GPS receivers that use the system. The receiver gets three pieces of information from the satellites: a code that identifies each satellite and two packets of data called ephemeris data and almanac data. Ephemeris data tell a receiver where each satellite should be. Almanac data tell the receiver the date, time, and whether or not the satellite is working correctly.