Tech, ExplainedNetworking, infrastructure and security
Concept

LEO and GEO satellites

Near and fast, or far and fixed.

HOW IT WORKSA user's dish sendsdata to a satelliteA GEO satellite isfar away and fixed,so the delay isabout half a secondA LEO satellite isnear and moving, sothe delay is a fewtens of millisecondsThe dish keepsswitching from one LEOsatellite to the nextThe satellitepasses the data toa ground stationDistance decides the delay, and the number of satellites needed, so each kind suits a different use.HOW IT WORKSA user's dishsends data toa satelliteA GEOsatellite isfar away andfixed, sothe delay isabout halfa secondA LEOsatellite isnear andmoving, sothe delay isa few tens ofmillisecondsThe dishkeepsswitchingfrom one LEOsatellite tothe nextThe satellitepasses thedata to agroundstationDistance decides the delay, and the number of satellites needed, so each kind suits a different use.HOW IT WORKSA user's dish sends data to a satellite↓A GEO satellite is far away and fixed, sothe delay is about half a second↓A LEO satellite is near and moving, sothe delay is a few tens of milliseconds↓The dish keeps switching from one LEOsatellite to the next↓The satellite passes thedata to a ground stationDistance decides the delay, and the number of satellitesneeded, so each kind suits a different use.
A few GEO satellites stay fixed over one spot and cover a large area, while thousands of LEO satellites move across the sky and give faster links.
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LEO and GEO satellites are the two main kinds of communication satellite. LEO, low Earth orbit, satellites travel 500 to 1,200 km above the ground and move fast across the sky. They are used in their thousands. GEO, geostationary orbit, satellites sit about 36,000 km above the equator and stay fixed above one spot on the Earth.

Here is how they differ in general. A GEO satellite goes around the Earth once in 24 hours, in step with the Earth's turn, so it appears still in the sky. One satellite covers a very large area, so only a few are needed. But the signal has to travel a long way, which causes a delay of about half a second for a round trip. A LEO satellite is close, so the delay is only a few tens of milliseconds, but it crosses the sky in minutes. So many satellites are needed, and a dish on the ground must keep switching from one satellite to the next.

The delay matters for some uses and not for others. A half-second lag spoils voice calls, video calls and games, but it is fine for television and for loading web pages. A GEO satellite cannot be seen well from places near the poles, because it sits above the equator. LEO satellites fall out of orbit after some years and must be replaced, which is a continuing cost. GEO satellites last longer, about fifteen years, but each one is large and costly to launch.

Take, for example, a television channel sent to homes. It uses a GEO satellite, because a small dish pointed at one spot always receives it. Consider broadband for a remote village. A LEO network gives a faster and lower-delay link, with a small flat terminal that follows the satellites; see satellite terminals. Imagine a ship at sea or an aircraft. It can use either, as in ship-to-shore connectivity and in-flight connectivity.

The products are described in GEO satellite broadband, laser satellite links, satellite data relay and direct-to-device services. Satellites that photograph the Earth are covered in earth observation satellites.

How is it different from a mobile tower? A tower covers a few kilometres around it. A satellite covers a region the size of a country, but it is far away and costlier to use.

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Networking, infrastructure and security
Industrial tech and mobility
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