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The geo-stationary Inmarsat-satellites

Inmarsat operates four geo-stationary satellites which cover about 97% of the earth's surface. Only the polar caps cannot be reached due to the low elevation angles (<5o). The Inmarsat satellites serve mainly as voice (Inmarsat A/B/M) and data communication (Inmarsat C/D). Since 1996 newly launched satellites are equipped additionally with transponders with GPS-similar signals to increase redundancy in modern navigations systems.

In addition to commercial communication channels there are also transponders for emergency calls installed in Inmarsat satellites (Inmarsat-E). The 1,6-GHz-EPIRBs operate via these transponders. The picture below shows the satellite coverage.

The globale satellite coverage

Picture published with kind permission of Inmarsat (London).

Only one satellite is required for satisfactory operation and three of the four satellites can be reached from Europe at any time. This guarantees that a distress call is forwarded without delay and minimizes the probability of data loss during transmission.

Many more informations are available at the Inmarsat homepage.

The table gives an overview on satellite availability .

  Atlantic West  Atlantic East Indian Ocean Pacific Ocean
Inmarsat-3 F4 
54 o West
Inmarsat-3 F2 
15.5 o West
Inmarsat-3 F1 
64 o East
Inmarsat-3 F3 
178 o East
Redundant-Satellit in hot-standby
Inmarsat-2 F2 
55 o West
Inmarsat-2 F4 
17 o West 
Inmarsat-2 F3 
65 o East
Inmarsat-2 F1 
175 o East
Example of an LES in England
Antennas in Goonhilly The picture shows LES Goonhilly in England and was kindly provided by  Chris Wortham.