The natural or artificial satellites are bodies that orbit at a certain speed stably around other bodies with mass significantly greater. So the Earth is a natural satellite of the Sun and the Moon is a natural satellite of the Earth (and Sun).


                            (  SATELLIT ORBITS  )

 The artificial satellites are all those which man has placed in orbit around the Earth or other celestial bodies around the solar system with the many tasks already performed by various space agencies. The first artificial satellite was Sputnik 1 launched by the Soviet Union on October 4, 1957 , that performed the complete orbits around the Earth and a simple radio communication. Currently the largest artificial satellite of the Earth is the ISS (International Space Station) which is being assembled.

Probes differ from the satellites to the fact that they must first reach the heavenly bodies to be studied and then they became satellite in an orbit appropriate of the body. On January 2, 1959 the first automatic probe to the Moon, Lunik 1 , was launched by the Soviet Union.

                  Sputnik 1

                                                 USE OF SATELLITES

The uses of satellites can be: 1) Do different measurements on the surface and whether the atmosphere of the celestial body such as the European meteorological satellites Meteosat (the American Tiros launched on 1st April 1960 was the first meteorological). 2) In communication systems like radio 3) In navigation systems (GPS, GLONAS, Galileo) 4) Studies on the solar system, the Milky Way and deep space (Hubble telescope, XMM-Newton, Soho).

  In general, the satellites can collect: a) information from the survey done by its own sensors b) information and / or commands from ground stations ( uplink ) c) information and / or commands from other satellites or space crafts. These informations are gathered and processed for better transmit them to a ground station ( downlink ) or another satellite or vehicle. The operation of the satellites is controlled and monitored from ground station, said TT & C (Tracking, Telemetry and Comand) although they are generally provided with an autonomous control system self-sufficient. 

             Fucino Ground Station


                New Norcia - Australia

                TO PLACE IN ORBIT


The launching of satellites is done using the launchers (Ariane, Delta, Soyuz) and vehicles like the Space Shuttle, which carry and release the satellite (payload) upon reaching the preset orbit (the first carrier reaches the parking orbit  that has the Earth in perigee and in apogee the geostationary arrival  orbit, and then the vector releases the satellite that will ignite its engine called apogee to reach the right speed for the final journey  into the transfer orbit). To the left in the figure the satellite Aqua is transported within a protective capsule of the Delta rocket. 

         SATELLIT ORBITS   ) CSR*XSpace




The satellite is equipped with the apogee engine and a simple propulsion system whith nozzle for adjustments and corrections its orbits because over time it tends to slowly get closer to the Earth or do to other causes. So that it is provided with a fuel load sufficient for 10/15 years (average life of a satellite). We prefer not to supply a satellite in orbit after 10/15 years as uneconomical and no longer useful because the technology of that satellite  was been outdated. It's better to disintegrate the old satellite and replace it with a new more advanced. The electrical system consists of batteries, accumulators, generators with solar panels deployed to collect solar energy. The satellites use predominantly terrestrial solar panels. For the various types of communications are used for different antennas sizes and shapes and one or more transponders. Also the satellites and probes are equipped with all the dots necesarri for measurements characterizing its mission. The left figure shows the weather satellite Meteosat (ESA), which has placed solar panels all around, while under the probe Pioneer (NASA).

             Probe PIONER - NASA

          Block diagram of a transponder (CSR*XSpace)      SATELLIT ORBITS  )           


The transponder performs the task of receiver, amplifier, frequency converter, processor and transmitter signal. A satellite can be provided with one or more transponder. In the transponder are used different frequency communications to avoid interference. For example, the uplink communication by the ground station to the satellite  occurs at a frequency higher than the downlink of the satellite to a ground station (because the earth station can have a greater transmission power with respect to the satellite necessary to compensate for the greater loss of power which occurs at higher frequencies).

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