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Satellite Phone Services:
There are several different types of satellite phone service, with one of the more important differences being whether the satellite phone service uses 'low earth orbit' (LEO) satellites or geosynchronous (also called geostationary) satellites.
Geosynchronous
Geosynchronous satellites are at a fixed height of about 22,300 miles above the earth's surface. At this height, the satellite rotates freely around the earth at the same speed as the earth is rotating, so the satellite appears to stay fixed in the same spot in the sky.
Geosynchronous satellites are located directly above the equator, and - in theory if not in practice - one satellite can cover just over one third of the earth's surface. However, it is common for such satellites to have directional antennas, limiting the areas they provide service to, and saving precious satellite power in the process.
Low Earth Orbit (LEO)
LEO satellites are in lower orbits. This means they don't appear as stationary, but instead are moving relative to the earth's surface. The height of a LEO satellite can be pretty much anything - the International Space Station is a mere 215 miles up, Iridium satellites are at about 485 miles, Globalstar satellites are at about 880 miles, and GPS satellites are at about 11,000 miles altitude.
Although there's no exact point where the atmosphere stops and space starts, by convention, 'space' is considered to start at a 100 km (62 mile) altitude.
LEO orbits can be polar - with the satellites circling around each pole (as in the illustration above) or any other type of orbit. Polar orbiting satellites clearly fly over the entire world over time, whereas non-polar orbiting satellites don't reach to the very highest and lowest reaches of the earth (the Arctic and Antarctic regions).
The lower orbit a satellite has, the less of the earth's surface it covers, and so the more satellites that are needed to provide global coverage
The major telecommunication satellite constellations are: Globalstar, Inmarsat, and Iridium. As an example Globalstar has 48 satellites and Iridium has 66 that orbit the earth. Satellite phone systems are expensive to build and far less competitive than conventional mobile systems, so there are only a few providers from which to choose. Satellite phones are used in remote locations where normal "wired" telephones or cellular coverage is not available or in otherwise civilized locations when these communication infrastructures have been temporarily or permanently rendered inoperable (due to civil disturbance or earthquake for example).
There is no single phone that works everywhere except a satellite phone and although they are hand-held they don't work indoors. Satellite phones use incredible technology to provide global coverage at reasonably low costs. However, there are a few basic laws of physics that they cannot break. Satellite phones need a clear line of sight view of the satellite. Performance can also be affected by poor weather and use is generally restricted to outdoors (though they will sometimes work through glass or canvas). For Iridium, this means the phone (or at least the phone's antenna) must be outside with a reasonably unobstructed view of most of the sky. Iridium phones use a non-directional antenna - which means it does not have to be pointed in any particular direction.
Satellite Phone Working ............. |
