Criteria for the Choice of Synchronous or Medium-Altitude System

The peculiar requirements of a military communications satellite system as distinguished from a commercial one are examined. The effects on the system of requiring the system to operate with transportable ground stations, to be jam resistant, and to degrade gracefully are discussed. The choice of orbit inclination and altitude along with the number of satellites is shown to be a function of booster payload capability, geometric coverage, and the communications power budget. The effect of altitude on Anti-Jamming is also considered. It is shown that the choice of a communications satellite system is critically dependent on the reliability of the booster mission, the possibility of multiple launching, and the mean time-to-failure of the satellite. A booster mission for a medium-altitude system is shown in detail, as is the injection and random dispersion of satellites into a common orbit. Typical communications link calculations are shown to demonstrate the effects of key parameters on performance. A short discussion of the dependence of performance to weather, especially for very low temperature receivers, is given. The growth of satellites from a spin to gravity gradient stabilization without serious changes in either dispenser or spacecraft is described. The implications of this growth to system performance are outlined. The paper is in general terms without reference to specific spacecraft or booster data or other information that is classified.