The orbit of an artificial satellite depends on several factors: the speed, the launching angle, friction from the Earth's atmosphere and the gravity of the Earth and other bodies.


For near-earth orbits, just outside the appreciable atmosphere, the satellite must attain a velocity of about 7.9km/sec in a horizontal direction. Failure to do so means that it returns to earth.

If, on the other hand, the satellite is released from its carrier rocket with excess speed it will assume an elliptical orbit, losing speed as it climbs to the zenith, and speeding up again as it swings back to its lowest point.

If the speed of projection is greater than 11.2km/sec, the satellite will escape from the earth, having overcome its gravitational pull.

Achieving escape velocity does not mean the satellite is free of the Earth's gravitational influence.

With power shut off, it will gradually lose speed due to the restraining influence of gravity; but it will always have enough momentum to continue moving away from the earth.

If it is properly directed, it can be sent on a journey to another planet when its future path will be dominated by the gravitational field of the sun.


In order for the satellite to remain in a particular orbit around the Earth, the launch angle must be such that the plane of the orbit passes exactly through the earth's centre.

The possible orbits are characterized by their angle in relation to the equator.

If the launch angle is at 90 degrees to the plane of the equator, that is, in a north-south direction, the satellite will pass directly over the poles.

This orbit is especially suitable for meteorological (weather) satellites, as a satellite in such an orbit circles round the earth every 2 hours.

Therefore, in one day, 12 different segments of this planet can be observed. Together, these make up the entire surface of the earth, because the earth com¬pletes one revolution under the satellite's orbit within twenty-four hours.


Although the Earth's atmosphere is very thin at great heights, it still creates friction. After a long time, this causes the satellite to spiral back into the atmosphere.

In the process, the more distant point of the orbit (apogee) contracts so that the original elliptical orbit even¬tually becomes more circular.

The time the satellite takes to complete an orbit also changes, - the speed varying in relation to shape, position and mass of the satellite. Eventually the effect of air drag becomes so great that the satellite burns up in the denser atmosphere.