Right now, some 100 new-generation satellites are speeding overhead at an altitude of 1,200 kilometers. These mass-produced technological wonders are the satellite equivalents of Henry Ford's Model T. Today, satellite constellations are bringing voice communications services to the entire planet. Tomorrow, they will deliver a host of interactive, multimedia communications options on a global scale. A lmost all communications satellites used to orbit nearly 36,000 kilometers above the equator. A signal beamed up to the satellite from a ground station can be beamed back down to blanket millions of sites in one or several footprints.
Terminals are simpler and less costly, and antennas can fit on handheld phones.
But they are constantly spinning around the Earth, so it takes many of them to ensure global coverage. At the forefront of the new generation of constellations are the Globalstar and Iridium programs, which target a potential market of over 30 million subscribers for mobile telephone services. Iridium, backed by Motorola, launched commercial service last November. While Globalstar, Iridium and ICO all plan to offer similar services, each takes a different approach. Once a call from a Globalstar user has bounced off a satellite to the nearest local gateway, it is relayed to its final destination via existing telecom networks.