INMARSAT 3 communications system requirements

INMARSAT-3 satellites needed to provide a capacity nearly 10 times that of INMARSAT-2 as well as sufficient usable bandwidth with the ability to meet evolving requirements and constraints over a lifetime of 13 years or more. These factors ensured that INMARSAT-3 satellites would have to use L-band spot beams while also giving flexibility in spot beam deployment, as well as considerable flexibility in EIRP and spectrum usage. The challenge in writing the INMARSAT-3 specification was to meet these requirements while allowing bidders to propose low risk designs using proven technologies, consistent with introduction of service by 1994. In developing the specification a number of trade-off studies were performed and the most important of these are described