Low Earth Orbits (LEO) and geostationary orbit (GEO) are some of the classifications of orbital altitude. The altitude of LEO is approximately 1000 KM, or commonly above the atmosphere but just below the first Van Allen radiation belt. GEO lie at a unique altitude of 35786 KM. Geostationary are the most common orbit used for communication satellites (NASA, 2014). A brief description of geostationary orbit is that the period of rotation is equal to rotational period of the Earth. Geostationary orbit has zero inclination meaning that it is an equatorial orbit positioned directly above the equator (Elbert, 2008). They appear in the sky as if they are fixed because they move together with the Earth. On the other hand, Low Earth Orbit (LEO) communication satellites are satellites that circle near to the earth. They possess altitudes of approximately 300 and 1000 KM. In addition, they have low inclination angles. The Polar Orbit is one of the special type of LEO (NASA, 2014). LEOs are characterized by high inclination angles which is almost 90 degrees is meaning that they travel over the Earth’s poles.
The advantage of geostationary orbits satellites is that they do not require any tracking from the ground station on the earth. This is because geostationary satellites appear at fixed positions above the sky. At the same time, geostationary orbit satellites can also give continues functionalities and operation within the area of the satellite’s visibility. Several satellites for communication such as those transmitting TV signals travel in geostationary orbits (NASA, 2014). The disadvantage of geostationary orbit satellites is that because of their long distance from the Earth, geostationary orbit satellites possess an estimated delay signal of about 0.24 seconds to achieve a complete path of send and receive. This might raise problems with telecommunication equipment and services such as telephone devices and also data transmission services (Elbert, 2008). Furthermore, since geostationary orbit satellites lie along the equatorial orbit, the increase in the difference of latitude or longitude decreases the angle of elevation between the earth station and the satellite. This can affect and be problematic to mobile phone communications especially because of the low angles of elevation of the orbit satellites (Pierucci, 2002).
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Low Earth Orbit communication satellites have an advantage of capturing a detailed image of the Surface of the Earth because of them being close to the Earth. This is because they travel in a highly inclined LEO so that they can be able to sense remotely and also provide remote weather sensing information (Dean, 2009). A communication satellite located in the Polar orbit will travel over the Earth’s every region so that it can give a global coverage of the information required (Elbert, 2008). Unlike a geostationary orbit communication satellite, which is merely directly to ground stations along the equator, a satellite in Polar orbit will sometimes look overhead. This makes it possible for communication to take place in urban locations where there are large obstacles which include tall buildings blocking the satellite’s signal transmission path. In addition, LEO provide a very small transmission delay (Dean, 2009). They provide an easier way of achieving high levels of frequency re-use and also are easier to operate to low-gain ground antennas. However, LEO orbit communication satellites have disadvantage that they for them to be continually operational, they need a constellation or a large number is satellites to build and operate (Pierucci, 2002). They also have a minimal coverage of areas as compared to geostationary orbit communication satellites. In addition, a tracking wide beam or narrow beam is required to track the satellites since their movement is relative to the Earth.
- Dean, T. (2009). Network guide to networks. Cengage Learning
- Elbert, B. (2008). Introduction to Satellite Communication. Artech House.
- NASA. (2014). Three classes of Orbit. Retrieved 9 November 2014, from http://earthobservatory.nasa.gov/Features/OrbitsCatalog/page2.php
- Pierucci, L. (2002). Satellite Personal Communications for Future-generation Systems: Final Report: Cost 252 Action. Springer Science & Business Media
