About Artificial Satellites
A satellite is an artificial object which has been intentionally placed into orbit.
Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as Earth’s Moon.
In 1957 the Soviet Union launched the world’s first artificial satellite, Sputnik 1.
Since then, about 6,600 satellites from more than 40 countries have been launched.
According to a 2013 estimate, 3,600 remained in orbit.
Of those, about 1,000 were operational; while the rest have lived out their useful lives and became space debris.
Approximately 500 operational satellites are in low-Earth orbit, 50 are in medium-Earth orbit (at 20,000 km), and the rest are in geostationary orbit (at 36,000 km).
A few large satellites have been launched in parts and assembled in orbit.
Over a dozen space probes have been placed into orbit around other bodies and become artificial satellites to the Moon, Mercury, Venus, Mars, Jupiter, Saturn, a few asteroids,and the Sun.
Satellites are used for many purposes.
Common types include military and civilian Earth observation satellites, communications satellites, navigation satellites, weather satellites, and space telescopes.
Space stations and human spacecraft in orbit are also satellites. Satellite orbits vary greatly,depending on the purpose of the satellite, and are classified in a number of ways.
Well-known (overlapping) classes include low Earth orbit, polar orbit, and geostationary orbit.-justplay
A launch vehicle is a rocket that throws a satellite into orbit.
Usually it lifts off from a launch pad on land.
Some are launched at sea from a submarine or a mobile maritime platform, or aboard a plane (see air launch to orbit).
Satellites are usually semi-independent computer-controlled systems. Satellite subsystems attend many tasks, such as power generation, thermal control, telemetry, attitude control and orbit control.
The first artificial satellite was Sputnik 1, launched by the
Soviet Union on October 4, 1957, and initiating the Soviet Sputnik program, with Sergei Korolev as chief designer (there is a crater on the lunar far side which bears his name).
This in turn triggered the Space Race between the Soviet Union and the United States.
Sputnik 1 helped to identify the density of high atmospheric layers through measurement of its orbital change and provided data on radio-signal distribution in the ionosphere.
The unanticipated announcement of Sputnik 1’s success precipitated the Sputnik crisis in the United States and ignited the so-called Space Race within the Cold War.
Sputnik 2 was launched on November 3, 1957 and carried the first living passenger into orbit, a dog named Laika.
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