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  • 77 to 66 The Iridium Improvement

    Paper ID



    • Kenneth M. Peterson
    • Peter A. Swan


    Motorola's Satellite Communications






    The maturation of an engineering project is exciting and unpredictable. Since the IRIDIUM1 System is a global concept with critical factors varying from satellite size to phone service viability in small countries, the engineering and programmatic trade spaces are enormous. IRIDIUM System Trades were made while adhering to the goal of providing commercial, low density, portable telephone service via handheld, mobile, or transportable user units, employing low-profile antennas to millions of users throughout the world. Major factors such as spacecraft size and weight dominated the trades, with issues such as solar sail sizes critical. The original constellation was named after the element Iridium with the atomic number of 77. As the program matured, trade studies and a design review were conducted in which all aspects of the design were subject to reconsideration. It is a tribute to the early designers that the architecture of the resulting constellation was so similar to the original concept of 77 satellites. The final configuration of 66 satellites — 11 satellites in 6 planes — resulted from key parametric trade studies which addressed link margin and phased array antenna beam sizes. Each of these critical parameters was evaluated to ensure proper priorities. The customer satisfaction requirement for a design with the highest possible quality service led to the architecture redesign and system level improvement.