What is a Geostationary Orbit?

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Sep 15, 2022

An earth-centered orbit with an altitude of about 35,7867 km above the surface of the earth is called a Geostationary Earth Orbit (GEO). The geostationary orbit is located directly above the earth's equator with zero eccentricity and inclination. A satellite in a geostationary orbit seems to be stationary when seen from the surface of the earth, as it moves in the direction of Earth’s rotation with the same speed as the rotation of the earth. The satellites in the GEO mostly are used for telecommunication, television, and meteorological purposes as they are expected continuously transmit to the antenna on the earth’s surface, without the need for changing the direction of the antenna.

The time taken by a satellite in a GEO orbit is 23 hours, 56 minutes, and 4 seconds which indicates the speed of the satellite is the same as the rate at which the earth rotates i.e 1000 mph (1,670 kmph). This speed which is required for a satellite to maintain its orbit around the earth is known as orbital velocity

If the satellite’s orbital velocity is higher than the optimal value, it faces the risk of flying out of orbit and into space, rendering the satellite out of bounds. Additionally, if the orbital velocity is kept too low, the satellite will be pulled back to earth due to gravity causing it to crash and burn. Hence, if the correct orbital velocity is maintained the gravity of the earth balances the inertia of the satellite, pulling it down to the earth’s surface just enough to enable the satellite to traverse in its intended orbit. At higher altitudes, the speed required to keep a satellite in orbit changes. 

An individual GEO satellite can provide much larger coverage of the earth when compared to LEO & MEO satellites. GEO orbits can be used to provide global coverage by placing just 3 satellites in GEO orbits. Satellite tracking is not required as the GEO satellite’s orbital velocity is equal to the earth's rotational period. 

A GEO satellite can be powered by solar panels for around 22 hours per day of its orbit and can be powered by a battery for the remainder of the time. This is possible because GEO satellites spend less time in the shadow of the earth, and as the distance from the earth increases, the time spent in the earth’s shadow decreases which enables the GEO satellites to be powered primarily by solar. 

Most commercial and military communication satellites operate at GEO. Satellites in the geostationary orbit are allocated a single slot above the earth’s equator by ITU (International Telecommunication Union).  These Slots are a Ring above the earth’s equator, which is used by a GEO satellite to traverse around the earth. There are limited slots that are available in the GEO orbit, which indicates that only a limited number of satellites can be operational in the geostationary orbit. The ITU Allocates only a single & specific Slot for a country’s GEO Satellite because of the disturbing RF interference of other functioning GEO satellites of different countries.

Key parameters of GEO:

Parameters

GEO Attributes

The altitude of GEO From Earth

35,7867 km

Orbital Velocity for a satellite in GEO

1000 mph (1,670 kph)

Orbits Completed in a Day for a Satellite

1 Orbit per day

Satellites Needed

3 for Global Coverage

Satellite Life

More than 15 years

Propagation Loss

High

Visibility of Satellite

Always

Transmission Delay

>200 ms