Constellations of low- orbiting satellites hold the key to today's flexible global telephone networks. These systems integrate satellite communications with existing land- line and cellular networks to provide truly global coverage from a mobile phone. This enables people in remote areas, even those on tiny Pacific islands or high in the Himalayas, to keep in touch with the rest of the world. Satellite system are the next logical step in the mobile- phone revolution that swept the world in the late 1990s. Iridium®  was the first system to offer a commercial service. It was conceived and developed by the US electronics company Motorola, and began operation on November 1998. The system was named after the 77th chemical element in the Periodic Table, as there were originally to be 77 satellites in the network. Other networks offering a similar service include Globalstar, which operates with the constellations of 48 satellites.


in the figure: Iridium satellite phones




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