Satellite Networks:
A New International Distress System

In February of 1999, the satellite-based Global Maritime Distress Satellite System (GMDSS) replaced the old SOS system. For a century, marine distress calls were sent by the Radio Officer, in International Morse Code, on the 500 KC frequency.

The GMDSS is a group of systems, controlled through a single console, providing ships with communications, navigational information and distress signaling. Three satellite networks provide long-distance voice, telex, data, video and fax. Two services offer information on weather, ice, and hazardous sea conditions. GMDSS also retains direct medium and high-frequency radio capability.

GMDSS has an automatic distress system on the "INMARSAT C" satellite network. A "Search and Rescue Transponder" deploys manually or automatically if the ship sinks. With all its backups, total failure of the GMDSS system is unlikely, but the complexity of the system makes it prone to false emergency signals.

RO Bobbie Khan at the GMDSS console of the MV Global Mariner, in 1999. The set is isolated at the back end of the bridge.


The Emergency Position Indicating Radio Beacon (EPIRB) is a small radio transmitter which sends an automatic distress call via satellite to a land station, allowing rescuers to locate the vessel or life raft at sea. This ACR Category I 406 MHz model EPIRB is designed to float free and to automatically begin sending a signal. It will work anywhere in the world.

Above, GMDSS at work. A sinking ship can send a distress signal by microwave satellite relay to a land station, by medium-frequency radio to a nearby vessel, or by high-frequency radio to a shore station. Illustration by Amy Hosa.