Communications satellite

Communications satellites (also messages or communications satellites ) are unmanned artificial satellite orbiting the Earth and provide information transfers in certain areas of the earth's surface. They orbit the Earth mostly as geostationary satellites to, for example, the transmission of television and radio programs ( see also Satellite TV ), satellite communications, digital data transmission or voice traffic allow. Among the most entertaining of government and commercial sources satellites also find the amateur radio satellites.

General

Some of the first communication satellite experimental work passively, that is, there were large metallized balloon which have been illuminated by strong radio transmitters and the radio waves reflected. Later generations of communications satellites are actively working transponders on board the satellite to receive the signal from the ground station, and send it via directional antennas at a particular area of the ground back. The geographic area where the satellite signal is to be received, is called illumination zone. In communications satellites with weak transmission devices the signal is again received by earth stations and fed into the telecommunications network. The broadcasts are then transferred either terrestrial or fed into the broadband cable network. Earth stations for cable television call themselves cable headends.

Modern communications satellites have transponders whose transmitters are so powerful that they can be received by the consumer directly. For a good quality signal, a quasi- sight connection is required to the satellite. A signal attenuation through walls, houses or heavy rain hampered the reception to impossibility.

Some communications satellites have additional functions. You can transmit correction signals for satellite navigation, for example.

The communications satellites orbiting the earth on circular or elliptical orbits. The most important type of communication satellites are satellites which orbit the earth in a geostationary orbit, ie seen from earth always the same location are ( synchronous satellite). With three rotated by 120 ° synchronous satellites can be any place to achieve the polar regions on Earth. For the polar regions one uses satellites in Molniya orbits with high orbital inclination relative to the equator.

History

The first communications satellite was called SCORE and was launched on 18 December 1958 in the United States. He was able to pass messages directly without any delay or took while flying over a ground station a message on tape and played it on another ground station again. However SCORE worked only 13 days.

However, the lack of a back channel was for normal message transmission ( telephone, etc. ) is not portable. In addition, the operating time was too low. Therefore, the first passive communications satellite Echo 1 was launched on August 12, 1960. He was a balloon having a reflective metal surface. 1 reflected echo, the signals sent to it a ground station to another further while it was able to use it at the same time to allow a signal reflected to the first ground station to another frequency.

When they later realized, however, that using only active satellites effective information transmission is possible, had to be invested in this technology. On July 10, 1962, finally became the first television satellite, called Telstar sent into space. This has already allowed a television transmission between Japan, the U.S. and Europe.

On February 14, 1963 Syncom 1 was sent as a first communications satellite in geostationary orbit. Since, however, he refused his service, he was replaced on 26 July 1963 Syncom 2. He was the first so-called synchronous satellite with terrestrial telephone transport and telecommunications.

The first commercial geostationary communications satellite was Intelsat I, also called " Early Bird ". This started from April 6, 1965 by Cape Kennedy into space.

Europe did not begin until about the middle of the 1970s with the launch of communications satellites. The first two were called Symphony 1 Symphony and 2 and were started on 19 December 1974 and 27 August 1975. They arose out of a collaboration between France and Germany.

In 2009, should also be a communications satellite to be sent on their way to another planet with the launch of the Mars Telecommunications Orbiter for the first time. He should, through the increase of the transmission capacity between the Mars probes and the earth, the exploration of Mars. But the mission was canceled by NASA for budget reasons in July 2005.