GEO, LEO, and MEO Satellites: Types and Functions

Satellites play a crucial role in various aspects of modern technology and communication. They come in different types, each designed to serve specific applications such as communication, weather forecasting, navigation, and Earth observation.

Understanding the different satellite types and their functions helps us appreciate the immense impact these devices have on global connectivity, scientific research, and disaster management.

Geostationary (GEO), Low Earth Orbit (LEO), and Medium Earth Orbit (MEO) satellites have been deployed to serve these space requirements. Artificial satellites are mainly called communication satellites, which are categorized based on coverage, service type, and their usage.

Coverage varies based on the beamwidth of the antenna on the satellite and can be global, regional, or national. Service types are FSS (Fixed Service Satellite), BSS (Broadcast Service Satellite), and MSS (Mobile Service Satellite). Usage of the satellite can be either for military or commercial purposes.

The Moon is a natural satellite that orbits around the Earth. Similarly, Mars has two tiny natural satellites. The satellites made by human beings are known as artificial satellites such as CubeSat, INSAT, Sputnik, and so on.

Satellite Repeater

In order to use a satellite for communication or relay/repeater applications, a ground station (Earth station) needs to track the satellite as it revolves above the Earth for a short duration, depending on the orbit it is placed in.

There will be no communication when the satellite disappears and moves to the other side of the visible area of the Earth station antenna.

One solution to this problem is to launch a satellite in a long elliptical orbit, and a second solution is to have a Geosynchronous satellite at a distance of about 35,860 km. The same is explained below.

Geostationary (GEO) Satellite

A Geostationary satellite is the most common type of satellite and is more popular today. It is located in a geostationary circular orbit above the Earth at about 35,860 km. The GEO satellite’s angular speed is the same as that of the Earth, so it remains at the same position on the equator even if the Earth moves/rotates.

Hence, a GEO satellite is ideal for providing continuous service 24 hours a day.

Function: This allows them to maintain a constant view of a specific region on the Earth’s surface.

Advantages of GEO Satellite:

• Tracking of the satellite from Earth is easy.
• As the satellite is stationary, Doppler frequency change can be avoided between the satellite and antenna on the Earth.
• About three satellites separated by 120 degrees can cover the entire region of the Earth except for the north/south poles.

Disadvantages of GEO Satellite:

• The signal becomes weak after traveling such a long distance.
• The delay is more, about 120 ms from Earth to the satellite. It will be about 240 ms for a double-hop system, i.e., from the Earth to the satellite and back to the Earth.
• Some regions, such as the polar region and north and south hemispheres, are poorly served.

Low Earth Orbit (LEO) Satellite

Function: A LEO satellite is located at about 500 to 1500 km altitude. This type of satellite is visible for about 20 minutes from a fixed location on Earth. The orbit period is about 1.5-2 hours. Coverage diameter is approximately 8000 km.

Advantages of LEO Satellite:

• The signal power is good enough for Earth terminals.
• The round trip delay is also less (about 20 ms) due to its location at a lesser altitude than GEO satellites.

Disadvantages of LEO Satellite:

• This LEO satellite system requires many such satellites to provide 24-hour service on Earth.
• Atmospheric drag is significant, resulting in gradual orbital deterioration.

Medium Earth Orbit (MEO) Satellite

Function: A MEO satellite is located at an altitude of about 5000 to 12000 km above Earth. The orbit period is about 6 hours. Coverage diameter is approximately 10000-15000 km. Round trip delay is about 50 ms. It provides a balance between coverage and latency.

Advantages of MEO Satellite:

• This system of satellites requires much fewer handoffs compared to LEO satellites.
• The maximum visible time from Earth is about a few hours.

Disadvantages of MEO Satellite:

• Propagation delay is more compared to LEO satellites.
• Power required is also more than LEO satellites.

Conclusion

The diverse types of satellites, each with specialized functions, form the backbone of our global communication, navigation, and observation systems. From enabling instant communication across continents to predicting weather patterns and monitoring environmental changes, satellites have become indispensable tools for technological advancement and societal development.

By exploring satellite types and their functions, we gain insight into how these technologies continue to shape our world.

Active satellite: It has its own transmitting and receiving antennas. It amplifies the signal received from the Earth station or ground station and retransmits the amplified signal back to Earth.

Passive satellite: The passive satellite is a reflector that receives the signal from the transmitting Earth station and scatters the signal in all directions.