IMO-recognised GMDSS satellite service using Iridium's low Earth orbit constellation, providing global coverage including polar Sea Area A4.
Iridium GMDSS is the satellite communication service provided by Iridium Communications Inc. that was formally recognised by the IMO Maritime Safety Committee as a GMDSS provider in 2018 under MSC Resolution MSC.434(98). Unlike Inmarsat's geostationary satellites, Iridium's 66-satellite low Earth orbit (LEO) constellation provides truly global coverage, extending to both polar regions and constituting a GMDSS-capable service for Sea Area A4 (polar waters above 70°N or below 70°S not covered by geostationary satellites).
The service supports distress alerting, urgency and safety calling, ship-to-shore and shore-to-ship communications, and the receipt of Maritime Safety Information. IMO Performance Standards for Iridium GMDSS Ship Earth Stations are set out in IMO Resolution MSC.434(98), adopted at MSC 98 (June 2017) and brought into force on 1 January 2020 following SOLAS Chapter IV amendments.
Iridium GMDSS equipment may be used in lieu of Inmarsat equipment for vessels operating in Sea Areas A3 and A4, providing shipowners with an alternative provider. The LEO architecture results in lower signal latency compared to geostationary systems, though the link-margin and antenna-design considerations differ. National administrations may accept Iridium GMDSS terminals under their respective flag-state approval processes.