Technical satellites, which are meant in this context, are used for communication and positioning tasks. They orbit the earth in elliptical orbits, with the point farthest from the earth in an elliptical orbit being apogee, and the point closest to the earth being perigee.
Satellites can be classified according to the altitude of their orbit, the power radiated, the coverage of the radiation cone, the footprint, and the satellite services. The altitude of the orbit is related to the communication type. Since very high orbit causes delays due to signal propagation time, the geostationary satellites, the Geostationary Earth Orbiters( GEO), can be used for telecommunications services and broadcast services such as the transmission of radio and television programs. These are telecommunications and communications satellites. Typical examples of GEO satellites are Astra, Inmarsat and Eutelsat.
The lower orbits are called Medium Earth Orbiter( MEO) and Low Earth Orbiter( LEO). Above the MEO satell ites orbit at about 20,000 km are the navigation satellites for the GPS system, Galileo and Glonass. Examples of MEO satellites are Odyssey and Ellipso. Below that, orbiting between 700 km and 1,500 km, are LEO satell ites for satellite-based mobile communications. Their low-Earth orbits give them the lowest delay times. Examples of LEO satellites are Iridium, Globalstar and Teledesic.
According to the power radiated, a distinction is made between low-power satellites, which have up to 30 W per transponder, medium-power satellites with a power between 30 W and 100 W, and high-power satellites with more than 100 W per transponder.
In addition to the satellites mentioned above, there are also HEO satellites, which have an elliptical orbit and whose closest point to Earth is below the orbit of LEO satellites and the farthest point to Earth is above GEO satellites. From the radiation, the footprint, which is determined by the beam, one distinguishes between global beam and spot beam.