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 and super-yachts.

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

  1. Send or receive messages between an Inmarsat-C SES and a shore-based telex terminal, personal computer, fax machine or electronic mail service.
  2. 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:
  3. 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 (GMDSS).

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