Satellites

Satellites

Communication satellites

Communication satellites are artificial satellites that provide a worldwide linkup of radio and television transmissions and telephone service; such satellites avoid the limitations that were previously experienced by ground based facilities due to the curvature of the earth. The first communications satellite was NASA's Echo 1; it was uninstrumented inflatable sphere that reflected radio signals passively back to earth. Afterwards, satellites like NASA's Relay satellites and the American Telephone and Telegraph (AT&T) Company's Telstar satellites, were equipped with electronic devices for receiving, amplifying, and rebroadcasting signals to earth. The US. launching (1963) of The first synchronous-orbit satellite (Syncom 1) was launched in 1963 by the US and it paved the way for the formation of the International Telecommunications Satellite Organization, whose successive series of Intelsat geostationary satellites have steadily lowered the cost of transoceanic communications. Domestic communications satellites, also geostationary, have been launched by many nations, including Canada, Russia, and Indonesia, and by several private U.S. companies. The U.S. and NATO have also developed military satellite systems.

Navigation satellite

These are other types of satellites that are designed specially to aid navigation at sea, in the air, and on land, for example a navigator can locate the exact position of his ship and calculate his way he has to go. Two major navigational satellite systems have been launched into orbit, both by the U.S. A total of 24 NAVSTAR satellites are used. Precise to within a few feet for military uses and about 300 ft (90 m) for non-military uses, the GPS can also be used for non-navigation purposes, such as surveying, tracking migrating animals, and plotting the crop yields of small sections of farmland.

Satellite, artificial

Rocket-launched satellites are bodies placed into orbit around the earth or, occasionally, another celestial bodies launched by man. A satellite in circular orbit at an altitude of 22,300 mi (35,880 km) has a period of exactly 24 hr, the time it takes the earth to rotate once on its axis; such an orbit is called synchronous. A satellite is known to be geostationary if the satellite is launched in such a way that it appears to be motionless, i.e. it orbits around the earth at the same speed as the earth’s rotation. The U.S to survey the earth’s resources by means of special television cameras and radiometric scanners has also launched several Landsat remote-imaging satellites. Russia and other nations have also launched such satellites; the French SPOT satellite provides higher-resolution photographs of the earth.

Reconnaissance satellites

These types of satellites are used by a country to provide intelligence information on the military activities of foreign countries. There are four major types. Early-warning satellites that detect enemy missile launchings; nuclear-explosion detection satellites that are designed to detect and identify nuclear explosions in space and photo-surveillance satellites to provide photographs of enemy military activities. These satellites can also be

divided into two other categories, namely close-look satellites which provide high resolution photographs that are returned to earth via a re-entry capsule and area survey satellites which provide lower resolution photographs that are transmitted to earth via radio. Afterwards satellites were designed to combine these two functions. Other satellites use radar to provide images of enemy activity when there is cloud cover or it is dark. Electronic-reconnaissance (ferret) satellites are able to pickup and record radio and radar transmissions while passing over a foreign country. Two countries that have being launching a lot of reconnaissance satellites since 1960 are the U.S and Russia (former U.S.S.R).

Weather satellites

Weather satellites (or artificial satellites) are used for the gathering of data on a global basis for improvement of weather forecasting. They usually provide information about cloud cover, storm location, temperature and heat balance in the earth's atmosphere. They are sometimes also used as instruments to locate ships and aircraft and track the movement of marine life and pollution. The first experimental weather satellite was Tiros 1, launched by the U.S. in 1960. Russia, India, Japan, and the European Space Agency also operate weather satellites.

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