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MAN MADE MOONS

 

   A small body circling around a big heavenly body is known as sattellite.  Natural satellites are moons.  Our earth has only one moon, where as Jupiter has 69 moons, saturn has 53, Uranus has 27 ,.... Man has made many artificial sattellites and put them into orbits.
     Any satellites has four main parts. 1. Solar power system 2. Control for its attitude. 3. Transmitter and Reciever 4. A payload to collect information such as camera or particle detector.
    The space is said be above 100 km from earth's surface.  A rocket carries satellites and launch it in its orbit.  The rocket must have more than 11.2 km/second speed.  Then only it can escape the earth's gravitational pull, else it will fall back.  That velocity is called 'escape velocity'.  Then the satellite must be given proper push (force, velocity) by the rocket in the orbit.  That orbital velocity is about 8 km/second.  If the speed is more, the satellite will go away from the earth.  If it is less, it will spiral down to the earth.
     Today size of computers and hardware have shrunken.  Hence we are able to make small satellites called 'cubesats'.  Companies and Universities frequently launch cubesats to do science.

SOME HISTORY
     Russia launched first satellite Sputnik I in 1957.  It is just a hollow metal sphere of about half meter width, with radio transmitter inside.  On 4 October 1957, it started circling the earth and the space age was born.  In Sputnik II , a female dog 'Laika' was put and sent.  The satellite has been equipped with poisoned food which would 'euthanize' Laika after 10 days, but she had died just 6 hours into the flight from stress and over heating.
     The Americans were woken up by the adventures of Russians and formed NASA.  They begun to send 'explorer' satellites.  It mainly replaced spy-planes.  And the space -race has begun.  The international space station ISS is the biggest satellite orbiting the earth.  It took 10 years to build and 15 nations contributed towards it.  It is expected function up to 2024.  Periodic supply and exchange of men, material, food is done.
     Satellite is the important invention of the mankind.  One good example of use of the satellite is GPS- Geo positioning system.  It is a group of satellites which pinpoints a location on the earth.  It is used everywhere from uber, swiggy app to flight and ship navigation.

FOOT NOTE: If a satellite is put at a height of 36000 km, its rotation speed will synchronize with that of the earth and the satellite will appear to be in fixed location above the earth.  Then it can be used by a particular country for communication purposes. 
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