Navigational satellites were one of the early applications of artificial earth satellites. Very early in the space age, researchers realized that satellites could be put on orbits to permit ships, aircraft, or other vehicles to exactly determine their locations. Global positioning systems (GPS) make of navigation satellites. The GPS constellation system was first established by the US military to support of their forces. But it is now in widespread in public and commercial applications.
The navigation equipment generally consists of a sensitive radio receiver, an accurate frequency reference, and an accurate clock. The idea of using satellites for navigation began with the launch of Sputnik 1 on October 4, 1957. Satellite navigation systems allow small electronic devices to determine their location.
Navigation satellites were developed in the late 1950's. They are of great help to transportation companies, especially for transportation over water and through the air. Navigation satellite systems help pilots and ship navigators locate their positions and many related information.
Navigation satellite systems have a wide variety of civilian uses also. They are used for to measure distances, for instance, between buildings. They are also used to make accurate maps of remote areas of earth.
GPS Navstar satellites operate at altitudes of 10,000 to 20,000 kilometers. In global positioning satellite system (GPS) 24 Navstar satellites are used to determine position. Each satellite broadcasts time and position messages continuously. GPS is the only fully functional satellite navigation system. The former Soviet Union established a positioning system equivalent to the Navstar, called the global orbiting navigation satellite system (GLONASS). GLONASS uses the same number of satellites as in Navstar. They use 24 to 27 satellites that orbit in three different planes. The first GLONASS satellites were launched into orbit in 1982.
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