Inmarsat's primary satellite constellation consists of four Inmarsat-3 satellites in geostationary orbit. Between them, the main ("global") beams in the satellites provide overlapping coverage on the complete surface area from the Earth apart in the poles. So, thanks to Inmarsat, it is becoming possible to extend the reach of terrestrial wired and cell networks to nearly anyplace on Earth.

A geostationary satellite follows a circular orbit in the plane in the Equator in a height of 35,600km, to ensure it seems to hover over a chosen point on the Earth's surface. Three these kinds of satellites are sufficient to cover most from the globe, and cellular customers hardly ever must switch from a single satellite to a different. Other cellular satellite television techniques use bigger numbers of satellites in lower, non-geostationary orbits. In the user's stage of view, they move across the sky at a comparatively large speed, frequently requiring a switch from a single satellite to yet another in mid-communication and also risking the opportunity of an interrupted call.

A call from an Inmarsat cellular terminal goes directly towards the satellite overhead, which routes it back down to some gateway around the ground named a land earth station (LES). From there the call is passed into the public mobile phone network.

The Inmarsat-3 satellites are backed up by a fifth Inmarsat-3 and 4 previous-generation Inmarsat-2s, also in geostationary orbit.

An important advantage with the Inmarsat-3s above their predecessors is their potential to produce an amount of spot-beams too as solitary substantial international beams. Spot-beams concentrate extra energy in areas of higher demand at the same time as which makes it feasible to provide standard providers to smaller, simpler terminals.

Inmarasat is usually a consortium of leading international telecommunications organizations originally established in 1991. The Inmarasat technique is designed to offer substantial good quality satellite-based services to a broad selection of customers, which includes:

* Voice calling * Brief Messaging Support (SMS) * Roaming * Positioning * Facsimile * Information transmission