Iridium satellites and updates from Inmarsat are expanding the coverage and usability of the GMDSS
The Global Maritime Distress and Safety System (GMDSS) is simple, but effective. For decades, UK-based Inmarsat has been the sole provider, and the system has leaped from one successive generation of satellites to the next, such as the Inmarsat-4 (I-4) fleet of satellites that was launched into geosynchronous orbit between 2005 and 2013. The latest satellite, Inmarsat-5 (I-5) – also known as Global Xpress was launched from 2013 to 2019. It offers high-throughput data services on Ku-Band with lower volume, but high reliability, and Ka-Band with higher volume but intermittent reliability.
Both I-4 and I-5 satellites are geosynchronous constellations, with each craft covering a swath of the planet’s surface area. High above the equator, the satellites move at a speed matching the Earth’s rotation, always in the same position in the sky. The impression from the ground is as though they are hovering over its surface.
These satellites have provided surprisingly good coverage at the poles; Earth, after all, is not in fact a perfect sphere, but is more rotund around the middle. However, at a certain point, the Arctic weather and simple geometry get in the way; ‘Sea Area A4’ – the rather innocuous term for the two most inhospitable environments on Earth – has not been afforded consistent GMDSS coverage.
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