For a long time, Inmarsat satellite system was the only maritime mobile satellite service provider when Global Maritime Distress and Safety System (GMDSS) is concerned. This satellite system has different generations of its satellites providing a wide range of services and applications. In 2018, its services related to the GMDSS have migrated to a newer generation of satellites. This satellites’ services migration is systematically discussed and analysed in this paper in order to familiarize the readers with its effects on the safety of navigation. Furthermore, Inmarsat system announced a new service called Inmarsat Fleet Safety which will incorporate and provide all functional requirements for the GMDSS which are currently provided by Inmarsat-C and Inmarsat Fleet 77 terminals. However, in 2018 a new satellite system called Iridium has been recognized as a mobile satellite communication services provider in the GMDSS. Accordingly, this system and its capabilities are also introduced and briefly described in this paper. In addition, authors have discussed impacts of the introduction of the new satellite system as a service provider in the GMDSS and addressed several emphasized issues related to this GMDSS modernization.