The Inmarsat system is a satellite communication network.
It is used by ships, and also by other users. This Inmarsat system supports the GMDSS system and for that reason it is used a lot on SOLAS ships as well as on non-SOLAS ships.
Within the GMDSS system the Inmarsat system may be used for distress- alerting in sea area A3. Although areas A1 and A2 are not excluded from distress-alerting by Inmarsat, in these areas the GMDSS system offers better solutions for distress-alerting. It is also used for transmission of Maritime Safety Information (MSI) outside the coverage of a NAVTEX station.


The International Maritime Satellite Organization was founded on 16 July 1979.
At this time Inmarsat took over the Marisat-network from the American company Comsat.
From this moment on it was possible for ships at sea to communicate via satellite. In the beginning the system was only used by ships.
Now Inmarsat is offering a wide range off products/services also for airplanes and other landmobile users.
Apart from commercial activities, Inmarsat is committed to the IMO to ensure a 100% functioning communication network for Distress communication.

Satellite Propagation

The Inmarsat services will use 'direct wave' propagation (just like at the VHF 'Line of Sight'). There should always be a direct line of sight between the ship's Inmarsat antenna and the satellite used. For this reason the antennae should be fitted clear of the superstructure or other obstructions. Coverage for GMDSS purposes is considered reliable up to latitudes 70 degrees North and 70 degrees South (assuming not 'in shadow' of mountains, terrain or buildings), though service can often be accessed further North or South than the mentioned 70 degrees. The further you are from the equator, the lower the angle of sight from the antenna to the satellite, and the greater the possibility of losing sight of the satellite when near to land or other obstruction.

Satellite positions
Inmarsat satellites 36000 km above the earth

The picture above shows the position of the four Inmarsat satellites. These geo-stationary orbiting satellites are situated in fixed positions above the equator.
Last modified: Saturday, 25 April 2020, 7:50 PM