1. Low Earth Orbit (LEO):
Definitions vary. According to some, LEO includes orbits having apogees (high points) and perigees (low points) between about 100 km and 1500 km. Others extend that range up to 2000 or 3000 km. The majority of all satellites, as well as the Space Shuttle and International Space Station, operate from LEO.
The low Earth orbit for communications has more in common with terrestrial Land Mobile Radio communication networks than conventional Geo-stationary satellite communication system.
A special type of LEO is the Polar Orbit. This is a LEO with a high inclination angle (close to 90 degrees). This means the satellite travels over the poles.
2. Medium Earth Orbit (MEO):
An orbit that is intermediate in altitude between that of low Earth Orbit (LEO) and geostationary orbit (GSO) at 35,900 km.
The orbital periods of MEO satellites range from about 2 to 12 hours. A fleet of several MEO satellites, with orbits properly, coordinated, can provide global wireless communication coverage. A global coverage fleet of MEO satellites can have fewer members than a global coverage fleet of LEO satellites.
3. Geostationary Orbit (GSO):
The most common orbit used for satellite communication is the Geostationary Earth Orbit (GEO). This is the orbit at an altitude of 35,784 km that lies in the plane of Earth's equator and the rotation period is equal to that of the earth. The satellite and the earth move together so a GEO satellite appears as a fixed point in the sky form the Earth.
The advantages of such an orbit are that no tracking is required from the ground station since the satellite appears at a fixed position in the sky. The satellite can also provide continuous operation in the area of visibility of the satellite. Many communication satellites travel in GSO, including those that relay TV signal into our homes.
However, due to their distance from Earth GEO satellites have a signal delay of around 0.24 seconds for the complete send and receive path.
Read more: Indian Space Research Organisation