Types of satellites

Communication Electronics - Satellite Communication

1. TYPES OF SATELLITES Dr.R.Hepzi Pramila Devamani , Assistant Professor, Department of Physics, V.V.Vanniaperumal College for Women, Virudhunagar

2. Satellite A satellite is a moon, planet or machine that orbits a planet or star . In space, satellites move in certain specific paths. These paths are called as orbit. The orbit of a satellite decides its utility. Satellite orbits can be classified into three types : Synchronous orbit ( Geostationary orbit) Polar orbit Inclined orbit.

3. SYNCHRONOUS ORBIT If a satellite is placed in the synchronous orbit then it completes one revolution around the earth in exactly 24 hours. These satellites are at a height of about 36000km from the earth’s surface. The synchronous orbit which is parallel to the “ equator” is known as “equatorial” orbit or “geostationary” orbit Communication satellites are generally placed in such equatorial orbits. As the satellite revolution time around the earth is exactly equal to the time taken by earth for one rotation, the satellite appears to be stationary. Therefore such satellites are called as “geostationary” satellites. Three such geostationary satellites can establish communication over the entire earth.

4. DISADVANTAGES OF GEOSTATIONARY ORBITS Geostationary orbits have certain disadvantages. They are As this orbit is at 36,000km from earth, powerful rockets are required to launch a satellite in the orbit. The satellite placed in these orbits cannot establish communication in the polar region of the earth . These satellites require sophisticated devices on board to maintain them in the geosynchronous orbit. These satellite need higher power transmitter and more sensitive receivers due to heavy path loss.

5. POLAR ORBITS This orbit is a lower orbit at heights of 900 to 1000km from the earth. It passes over the north and the South Pole. This orbit is used to put the remote sensing satellites. This orbit is generally not used for normal communication purpose, however if a communication satellite is placed in the polar orbit, it can establish communication with the Polar Regions. Sometimes navigation satellite are also placed in polar orbit . There is only one geostationary orbit but at least theoretically there can be infinite number of polar orbits.

6. INCLINED ORBITS Inclined orbits are used by many countries for their domestic communication. Like polar orbit, these orbits can also be used to place the communication satellites which can establish communication with the polar regions. Inclined orbit is used for domestic communication in Russia as its geographical location is near the north pole of the earth.