The spacecraft revolved around the earth about its prescribed orbits are known as artificial satellites.
To revolve round the earth, the artificial satellites must be in dynamic equilibrium in centrifugal force and gravitational pull. For dynamic equilibrium, the satellite is placed at a certain height with a certain velocity. For example, to keep a satellite at a height 1600 km above the earth surface it must require a velocity about 7 × 103 ms-1. To provide the necessary velocity to the artificial satellite, a multi-stage rocket is used.
