Satellite
Satellites are man-made objects that are put into orbit around the earth to collect and/or relay information back to earth using radio waves.
Early satellites and many modern ones are repeaters for radio waves carrying telecommunication and television signals. Others have cameras to study weather patterns, crops and even create detailed maps. These satellites are designed to orbit on a slightly different track every orbit so as to cover the whole earth over a period of time. Other satellites, outside the earth’s atmosphere, have a clearer view to survey distant galaxies. Many satellites have geostationary orbits (36km above the equator), taking one day to orbit, whilst the earth turns in the same direction. These are used as beacons for satellite navigation (GPS, SATNAV) and satellite television.
Satellites are launched into space on rockets. Once the satellite reaches the correct position, it detaches from the rocket and is kept in orbit by the earth’s field of gravity.
Satellites derive their power from photovoltaic panels mounted on an array of wings that are deployed once the satellite is in orbit.
The first satellite, Sputnik 1, was launched by the Soviet Union in October 1957. Today over 5 000 satellites, from more than 40 countries, are orbiting the earth, half of which are no longer in use.
