Geostationary satellites whose velocity relative to Earth is zero. These satellites remain stationary concerning the Earth at a height of about 42300 km from the surface of Earth. These are used for global TV transmissions and other telecommunication purposes.

            As Earth also completes its one rotation about its axis in 24 hours, hence, these communication satellites appear to be stationary concerning Earth. It is due to this reason that the orbit of such a satellite is called geostationary orbit.

Dish antennas sending and receiving the signals from them have fixed directions depending upon their location on the Earth.

 

Uses of geostationary satellites:

Such satellites are useful for the following purposes.

1. Worldwide communication      2. Weather observations

3.  Navigation                              4. Other military uses

Note:  Three geostationary satellites can cover the whole earth.

 

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Geostationary satellite:

The height of a geostationary satellite is about 42,300 km from the surface of the Earth. Its velocity concerning Earth is zero.

 

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Global Positioning System (GPS):

The Global Positioning System (GPS) is a satellite navigation system. It helps us to find the exact position of an object anywhere on the land, on the sea, or in the air. GPS consists of 24 Earth satellites. These satellites revolve around the Earth twice a day with a speed of $3.87 \: kms^{-1}$