The satellites are celestial bodies that rotate around another celestial body, folowing it in his movement during the revolution. Their origin, they are divided into two categories: natural and artificial. In astronomy, natural satellites are defined as celestial bodies that executes a secondary rotational motion around a planet or a star. The best know Earth’s natural satellit is The Moon.
Although the two are close enough in size to be considered a system. Movement of most satellites is direct, from west to east and the same direction as the planets around which orbits. Only a few satellites of the major planets rotate in the opposite direction; they were likely captured in their gravitational field after a certain period of solar system formation.
For example, Pluto, which rotates around the Sun in an independent orbit satellite is believed to be a kick of Neptune. Recently, it has been discovered that, in turn, and Pluto has a moon. Artificial satellites are placed objects with a definite purpose in an orbit around a planet. Since the launch of the first artificial satellite in 1957, thousands of these worlds created by man were sent to orbit the Earth. Nowadays, they play and important role in the communications industry, in military strategy and scientific studies of the Earth and the Universe.
Some of the first satellites were designed to operate in passive mode. Instead of actively transmit radio signals, they serve only to reflect signals which were directed to them by the ground station worldwide. Nowadays, satellites used exclusively active operating systems, in which each of them carries its own transmission – reception equipment. Hundreds of communications satellites are curently in orbit. They receive signals from a ground station, amplify them, and retransmit them on a different frequency to other stations. The satellites use a range of frequencies measured in hertz, namely frequency band of about 6 GHz. The first active satellite, Score, launched in 19588 by the United States, was equipped with a recording device messages received during passage over a transmission station.
They were retransmitted when the satellite is above the reception station. Telstar 1, launched by American Telephone and Telegraph company in 1962, offering direct TV transmission between the US, Europe and Japan, and can also provide playback of several hundred radio stations. Another satellite, Echo 1, launched by the US in 1960, was constructed of aluminized plastic balloon with a diameter of 30m. In 1964, it was released Echo 2, which have a diameter of 41m. The ability of these systems was limited by the need for powerful transmitters and large antennas on the ground.
Satellites can be connected to a signal system which is called the phone number tracker that enables viewing from space.
Most first satellites included some communication equipment. NASA launched the first satellite phone and televission, AT & T’s Teslar 1, in 1962. US department of Defense launched Syncom 3 in 1964. It was the first satellite that had a geostationary orbit. Since 1957 over 300 satellites were launched communications.
The present offers audio – visual and data transmission. Weather satellites carries cameras and other instruments directed by the Earth’s atmosphere. They can provide warnings about unstable weather and contributes greatly to weather forecasting. NASA launched the first satellite TIROS 1 in 1960, which transmitted approximately 23,000 photographs of the Earth and atmosphere.