Satellites...............

           A satellite is like an object which is lyk a secondary planet which revolves about another planet.......


    satellites  are classified as.... 


       1. artificial satellites
       2. natural satellites.


1.artificial satellites


The world's first artificial satellite, the Sputnik 1, was 

launched by the Soviet Union  on October 4 in 1957.

 The first artificial satellite to orbit Earth.

Sputnik 1 helped to identify the density of high atmospheric layers through 

measurement of its orbital change and provided data on radio-signal distribution in the 

ionosphere. The unanticipated announcement of Sputnik 1's success precipitated the 

Sputnik crisis in the United States and ignited the so-called Space Race within the Cold 

War....

       Since then, thousands of satellites have been 

launched into orbit around the Earth; also some 

satellites, notably space stations, have been launched in 

parts and assembled in orbit. Artificial satellites originate 

from more than 50 countries and have used the satellite 

launching capabilities of ten nations. A few hundred 

satellites are currently operational, whereas thousands of 

unused satellites and satellite fragments orbit the Earth 

as space debris. A fewspace probes have been placed 

into orbit around other bodies and become artificial 

satellites to the Moon, Mercury, Venus, Mars, Jupiter, 

Saturn, and the Sun.

An animation depicting the orbits of GPS satellites in medium Earth orbit.

main uses.............

Satellites are used for a large number of purposes. 

Common types include military and civilian Earth 

observation satellites, communications satellites, 

navigation satellites, weather satellites, and research 

satellites. Space stations and human spacecraft in orbit 

are also satellites. Satellite orbits vary greatly, depending 

on the purpose of the satellite, and are classified in a 

number of ways. Well-known (overlapping) classes 

include low Earth orbit, polar orbit, and geostationary 

orbit.

Satellites are usually semi-independent computer-

controlled systems. Satellite subsystems attend many 

tasks, such as power generation, thermal control, 

telemetry, attitude control and orbit control.