Types of communications satellite
Satellites have become an basic piece of today’s technology. They are used for various purposes, from offering long distance telephone connections, the direct broadcasting of television and radio broadcasts, and obtaining geological information about the weather or other facilities.
To get to the technology we have today, we needed a tremendous amount of research and investment in satellite communications when the idea was first proposed by Arthur C. Clarke in a 1945 article in the journal Wireless World. Since then electronic circuits have been developed which enable all functions of satellites and vehicles able to put these satellites orbit in space, sometimes weighing more than a ton. These two elements have required huge investments.
At the time of Clarke’s article, most advanced V2 rockets were made by the Germans, who had no intention at all to launch satellites in outer space. For satellites themselves had developed their own methods of power with control systems enabling them very precise positioning. Satellites must be very reliable because it can not be repaired once they launch. Nowadays these problems are already under control, and satellites are able to offer a long and reliable service.
Every day thousands of international calls are made. They are made usually by satellite. For use in communications of this kind, the satellite operates as a repeater. Its height from the Earth causes the transmission of signals to be able to make much greater distances than line-of-sight. A ground station transmits the signal, consisting of several phone calls to satellite.
This is called the uplink (uplink) and is generally a frequency of 6GHz. The satellite receives the signal and sends it back. This is generally done on a frequency of 4 GHz, on what is called downlink (downlink). It must be on a different frequency to avoid interference between the two signals. If transmission occurs with the same frequency of the received signal, the signal transmitted from the satellite receiver overloads, preventing uplink.
One of the latest developments in the applications of satellites is cell phone tracker System. Although originally conceived as a military system, it has become increasingly used in commercial applications. One of the advantages is that the system has full coverage of the entire planet with an accuracy of 100 m section and 40 m civilian access to military section. The system consists of 24 satellites placed in a low earth orbit. They transmit the low frequency microwave and receivers captures transmissions. A minimum of four satellites are received simultaneously to give a correct position and, from the information received, the receiver is able to calculate longitude, latitude and altitude. Each satellite is maintained in a very precise orbit. On board satellite has an atomic clock accurate to have a good time. This time information is transmitted from each satellite signal. Thus, it is possibly the receiver to calculate each length of road from various satellites to the receiver. The time required to get signal from the satellite to the receiver is proportional to the length of road, which can be calculated Since propagation velocity is known. This information is used in calculations by the processor of the handset to give its position on Earth.
Satellites orbiting Earth may provide data on Earth map, its size and shape and can study the dynamics of the oceans and the atmosphere. Scientists also use satellites to explore the Sun, Moon, planets, comets, stars and galaxies. The Hubble Space Telescope is an observatory launched in 1990. Some general science satellites orbiting celestial bodies other than Earth. One of the most familiar applications is forecast meteorological satellites that can throw an “eagle’s” on formations forecast from great heights above the Earth. It provides an overview meteorologists much better about development and forecast the movement formations. Satellites may also, use for geological exploration. They can analyze most of the landmass, providing information about the status of crops, woods etc. Often they can detect the appearance or the spread of plant diseases, in a manner which would not otherwise be possible. If they can detect geological exploration of mineral reserves in formations seen from outer space.
Military needs are at the origin of creation first observation satellites since 1959 the Cold War between the US and USSR, called “spy satellites”. They allow observation of military enemies in hard to reach areas.