Satellite Orbits (http://www.satcom.co.uk/article.asp?article=11) 
Satellite Orbits  
There is only one main force acting on a satellite when it is in orbit, and
that is the gravitational force exerted on the satellite by the Earth. This force is
constantly pulling the satellite towards the centre of the Earth.
There are many different types of orbits used for satellite telecommunications, the geostationary orbit described above is just one of them. Outlined below are the most commonly used satellite orbits. The orbits are sometimes described by their inclination  this is the angle between the orbital plane and the equatorial plane. 

Geostationary Orbit  
The most common orbit used for satellite communications is the geostationary orbit (GEO).
This is the orbit described above – the rotational period is equal to that of the Earth. The
orbit has zero inclination so is an equatorial orbit (located directly above the equator). The
satellite and the Earth move together so a GEO satellite appears as a fixed point in the sky
from the Earth. 

Low Earth Orbit/Medium Earth Orbit  
A low earth orbit (LEO), or medium earth orbit (MEO) describes
a satellite which circles close to the Earth. Generally, LEOs have altitudes of around 300 –
1000 km with low inclination angles, and MEOs have altitudes of around 10,000 km.
A special type of LEO is the Polar Orbit. This is a LEO with a high inclination angle (close to 90degrees). This means the satellite travels over the poles.


Elliptical Orbits  
A satellite in elliptical orbit follows an ovalshaped path. One part of the orbit is closest to the centre of Earth (perigee) and another part is farthest away (apogee). A satellite in this type of orbit generally has an inclination angle of 64 degrees and takes about 12 hours to circle the planet. This type of orbit covers regions of high latitude for a large fraction of its orbital period. 
Copyright 2002 Satcom Online (http://www.satcom.co.uk)
21/04/2018 01:20:45