The Advantages of Satellite Communications

Satellites are like very tall transmitting towers.

Although it was proposed earlier, the first clear explanation of how satellites could change communications was by Aurthur C. Clark in 1945. He was the first to outline clearly how a few satellites in exactly the right orbits could allow us to send messages to anywhere on the planet. The amazing thing about this prediction was that it came 12 years before the first satellite was launched.

Coverage

Satellites are like very tall transmitting towers. If they are in orbit around the Earth at the equator and going at exactly the same speed that the Earth is rotating, they stay over the same position on the earth. At the speed that rockets need to go to escape the Earth's gravity, the height that satellites wind up in these Geosynchronous Earth Orbits (GEO) is 35,786 km. This is effectively a transmitting tower that is high enough to cover 1/3 of the Earth. Three of these satellites, placed equal distances around the equator, can broadcast to any place on Earth. These satellites can also broadcast to each other. The biggest advantage of satellite communications is that they make it possible to broadcast from any place on Earth to any other place on Earth.

Remote Areas

Satellites also make it possible to receive transmissions in remote areas of the earth. No big receivers or electrical infrastructure (or cable feed) is needed to receive satellite transmissions because all the energy is coming from the satellite. Energy for satellites is easy because solar power is much more efficient in space. There is no air, no clouds, no weather. Although the signal travels a long distance, most of the distance is through empty space and only a very small percentage is through the air. In land-based communications, all of the distance is through the air, which is a real problem during bad weather. Satellites can even switch frequencies to work around bad weather.

Military

The military uses GEO and Low Earth Orbit (LEO) satellites, the latter varying in height from 50 to a few thousand km. The advantage of LEO satellites is that they can take sharper pictures (because they are nearer the Earth) and, because they are not geosynchronous, cover the entire globe in a few hours. The ability of satellites to act as both communication channels and "eyes in the sky" make satellite communications especially valuable for military applications. You not only communicate with troops and superiors, you can see what the enemy is doing by having the satellite that is currently over enemy positions communicate directly with the satellite that is directly over you, perhaps relayed through other satellites.

References

• Intelsat: Satellite Basics
• Tpub: Satellite Communications
• DavidDarling: Communications Satellites

Resources

• ViaSat: Military Communications