Communications satellites are commonly used for mobile phone signals, weather tracking, or broadcasting television programs. Communications satellites are artificial satellites that relay receive signals from an earth station and then re-transmits the signal to other earth stations.
Three types or Satellite orbits are:
- LEO : Low Earth Orbit
- MEO : Medium Earth Orbit
- GEO : Geostationary / Geosynchronous Earth Orbit
1. LEO : Low Earth Orbit
- LEO satellites are much closer to the earth than GEO satellites, ranging from 500 to 1,500 km above the surface.
- LEO satellites don’t stay in fixed position relative to the surface, and are only visible for 15 to 20 minutes each pass.
- A network of LEO satellites is necessary for GEO satellites to be useful.
Advantages of LEO : A LEO satellite’s proximity to earth compared to a GEO satellite gives it a better signal strength and less of a time delay, which makes it better for point to point communication. A LEO satellite’s smaller area of coverage is less of a waste of bandwidth.
Disadvantages of LEO : A network of LEO satellites is needed, which can be costly §LEO satellites have to compensate for Doppler shifts cause by their relative movement. Atmospheric drag effects LEO satellites, causing gradual orbital deterioration.
2. MEO : Medium Earth Orbit
- A MEO satellite is in orbit somewhere between 8,000 km and 18,000 km above the earth’s surface.
- MEO satellites are similar to LEO satellites in functionality.
- MEO satellites are visible for much longer periods of time than LEO satellites, usually between 2 to 8 hours.
- MEO satellites have a larger coverage area than LEO satellites.
Advantage of MEO : A MEO satellite’s longer duration of visibility and wider footprint means fewer satellites are needed in a MEO network than a LEO network.
Disadvantage of MEO : A MEO satellite’s distance gives it a longer time delay and weaker signal than a LEO satellite, though not as bad as a GEO satellite.
3. GEO : Geostationary / Geosynchronous Earth Orbit
- These satellites are in orbit 35,863 (36000) km above the earth’s surface along the equator.
- Objects in Geostationary orbit revolve around the earth at the same speed as the earth rotates.
- This means GEO satellites remain in the same position relative to the surface of earth.
Advantages of GEO : A GEO satellite’s distance from earth gives it a large coverage area, almost a fourth of the earth’s surface. GEO satellites have a 24 hour view of a particular area. These factors make it ideal for satellite broadcast and other multi-point applications.
Disadvantages of GEO : A GEO satellite’s distance also cause it to have both a comparatively weak signal and a time delay in the signal, which is bad for point to point communication. GEO satellites, centered above the equator, have difficulty broadcasting signals to near polar regions.