Overview of multiple satellite communication networks

Recently interest in packet communications has stimulated an interest in constellations of low altitude satellites. Such a configuration would have less propagation delay and be cheaper to launch than satellites at higher or geosynchronous altitude. However, many more satellites are necessary at low altitude to achieve reasonable coverage of the earth and insure availability of the resource. Further, the geometry of such a constellation would be dynamic with communication links of short duration as the satellites speed past each other or a ground site. The most difficult design issue in these systems is a stable method of routing messages that will sustain a reasonable level of traffic. This paper explores the problems of routing and switching messages through a constellation of low altitude satellites and examines some of the related demands on technology. The dynamic nature of crosslinks, uplinks, and downlinks requires a very agile antenna system, and the volume of information for routing of traffic is overwhelming. Use of some type of facetted phased array antenna is advocated to solve the former problem, but the latter problem is more subtle. Since the volume of ephemeris and constellation data as well as the rate of update is unmanageable, schemes relying on some form of broadcast or random access may be considered. It is concluded that none of the known or examined approaches to routing and switching is completely satisfactory