What is geostationary satellite?

A satellite that appears to be stationary in the sky is said to be in ‘geostationary’ orbit. It is launched in such a manner that it orbits the earth directly over its equator at a height of 36,000 kms. At that height, its orbital speed is such that it completes one orbit in 24 hours. Since the earth also completes one rotation around its axis in 24 hours, the satellite appears stationary in the sky from earth.

The advantage of this is that ground based communication antennas can remain ‘fixed’ pointing to the satellite and need not be turned to follow the satellite in the sky.

For communication, geostationary satellites have on board transponders which receive signals from ground antennas, amplify them and send these back to be received by satellite dish antennas on ground. Power is provided on board by solar panels.