Description of the Inmarsat Systems
The Inmarsat-A system
This was the first Inmarsat system introduced into commercial operation in 1982
and now providing two-way telephone, telex, fax, elctronic mail (E-mail) and
other forms of data communications, including high-speed data at 56 and 64 kb/sec.
The large size and weight of the Inmarsat-A antenna has meant that units
have generally been fitted on larger ships such as oil tankers, trading vessels
The Inmarsat-C system
The Inmarsat-C system was introduced in 1991 to compliment Inmarsat-A by providing
low-cost global communications on a small termina, suitable for fitting on all
vessels, large and small. Its small size make sit especially suitable for smaller
vessels, such as yachts, fishing vessels or supply craft.
The Inmarsat-C system does not proved voice communications, but does provide
a means of sending text mesages or data to and from an SES using stor-and-forward
messaging. This technique requires the user (at either end) to prepare the
message/data on their end terminal, then transmit it via the Inmarsat-C satellite
system to the receiving end. Thereafter a delay of a few m inutes, the message/data
may be printed, viewed and/or stored.
Some of the Inmarsat-C communications services are listed
- Send or receive messages between an Inmarsat-C SES and a shore-based telex
terminal, personal computer, fax machine or electronic mail service.
- The Enhanced Group Call (EGC) services, which enable authorized shore-based
Information Providers to send information to selected groups of SESs. Two
EGC services available are:
- SafetyNET which is used to broadcast Maritime Safety Information (MSI)
- FleetNET used typically by companies to send commercial information
confidentially to ships belong to their fleet.
- The distress alerting and messaging capability of an Inmarsat-C SES which
may be used to send a distress alert or message with top prioirty to a Rescue
Coordination Centre (RCC)
The Inmarsat-C system is part of the GMDSS
The global communications capability of the Inmarsat-C system, combined with
its MSI broadcasting and distress alerting capabilities has resulted in the
Inmarsat-C system being accepted by the International Maritime Organization
(IMO as meeting the requirements of the Global Maritime Distress & Safety System
The Inmarsat-M system
The Inmarsat-M system was introduced in December, 1992 to compliment the existing
services by providing global telephone communications on an SES which is inexpensive
and compact in size. An Inmarsat-M terminal is smaller and lighter than and
Inmarsat-A terminal making it suitable for smaller vessels such as yachts, and
fishing vessels, as well as larger vessels such as cruise liners, and trading
vessels. The services possible on an Inmarsat-M terminal include two-way global
telephone, fax and computer data communications.
The Inmarsat-B system
Inmarsat-B is intended as the successor to Inmarsat-A providing its services
at generally lower charges than Inmarsat-A although the two systems will co-exist
for many years.
The inmarsat-B system introduced in 1994, uses digital technology to provide
high quality telephone, fax, telex and ata communications, with the antenna
size and weight approximately the same as that of Inmarsat-A