Communications satellites are often in geostationary orbit, but what is geostationary orbit.

This orbit follows the earth’s rotation.

The direction of travel is from west to east, at the same rotational speed as the earth.

Rotating in synchronisation with the earth means the satellite is always above the same geographic area.

Being above the same geographic area has advantages for communications satellites.

A popular use for geostationary, or geosynchronous satellites, is satellite television.

Satellite television dishes on peoples houses point in one fixed direction.

If the satellite did not rotate exactly with the earth, then you would lose signal.

The reason you would lose signal is that the dish on the house would not be pointing at the satellite due to its relative position to the house changing.

Footprints

The geographical area that a satellite signal covers is called its coverage footprint.

Footprint size does not have to be related to the distance of the satellite from the earth surface.

The orbit is at a distance of approximately 35,000 km from earth.

Footprint size can cover multiple countries, or a single one, from this same orbit.

Satellite antenna beam design achieves this.

Reasons for limiting footprint

Maximum footprint coverage is not always desirable.

Reasons for this can be both commercial and political.

For example, a television broadcaster may not want viewers from neighbouring countries.

This could be due to copyright reasons.

Published by Craig Miles

Craig Miles

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