Responsive Communications missions typically require “persistent communications,” i.e., repeat coverage that lasts for an extended period or the entire day. LEO orbits cannot provide this coverage without a large number of satellites and GEO satellites are typically large and expensive, with a long development time. The solution has traditionally been thought of as moderate altitude elliptical orbits, such as Magic or Cobra orbits. However, recent IR&D work by Microcosm suggests that this may be the wrong answer. This paper compares moderate altitude elliptical and circular orbits in terms of coverage, coverage flexibility, constellation size, ASAT vulnerability, the environment, impact on spacecraft design, and overall system cost. The conclusion reached is that circular MEO orbits are a better choice than elliptical MEO orbits for supplementary or persistent communications.
Wertz, J. 5th AIAA Responsive Space Conference, Los Angeles, CA. April 23–26, 2007.