Systems engineering trades for the IRIDIUM(R) constellation

The customer imperative has driven the system design for the IRIDIUM(R) constellation and ground support infrastructure. Although the goal of the system is to provide global, mobile telephone service, the two principal drivers for the trade studies are 16-dB link margin and commercial success, The systems engineering and constellation architecture trade studies that determined the design of the IRIDIUM telecommunications system were comprehensive and are continuously evaluated, The complexity of the total system drove the engineers to critical evaluations of major factors such as complexity of payload, size/weight of spacecraft, altitude of constellation, size of individual beams, space environment (radiation belts), size of telephone (pocket size), quality of voice/data, number of telephone calls, type of commercial launch vehicles, number of satellites, orbits and inclination of orbits, number of gateways, crosslink types, and type of modulation. The complexity of the decisions and how they trade off to one of the two basic principles of customer satisfaction, 16-dB link margin and commercial success, is discussed.