A historical overview of military communications by satellites and a detailed description of current systems are provided. The capabilities of present systems are reviewed in relation to user requirements and threats. It is concluded that use of satellite communications by a large number of small-terminal users (aircraft, ships, submarines, and land mobiles) still requires major technological innovations to meet needs for a substantial increase in system capacity and performance improvements in a jamming environment. The next-generation systems of the 1990s are reviewed with emphasis placed on the discussion of extremely-high-frequency (EHF) systems. Architectural trends are investigated for the post-2000 era. Alternative directions for future systems development, such as the use of highly proliferated satellite constellations, are explored.>