Overview

The first satellites for communications use ECHO 1 and ECHO 2 were launched by the United States in 1960. They were little more than metallic balloons that simply reflected microwave signals from point A to point B. Although highly reliable, these passive satellites could not amplify the signals. Reception was often poor and the range of transmission limited. Ground stations had to track them across the sky and communication between two ground stations was only possible for a few hours a day when both had visibility with the satellite at the same time. Advances in technology gradually overcame this and other problems.

Over the years, satellites have come to play an increasingly important role in both domestic and international communications networks. They are able to bring voice, data, and video communications to areas of the world that are otherwise inaccessible using terrestrial lines. Present mobile services, such as cellular telephone, in practice have a very short radio propagation range, only a few kilometers, within which good service is available. Many expensive ground cell sites are needed to extend coverage over a wide area. Terrestrial mobile system operators are reluctant to expand coverage over areas that cannot provide a return on investment within a reasonable time. As a consequence, many rural areas are not served by cellular telephone. Where cellular service is available, the mobile telephone user may find that other global regions he or she visits do not use the same cellular standards as the home service. Such travelers often find...