Environmental constraints in earth-space propagation

The advantages of utilizing space for telecommunications is well known in both the commercial and military arenas. A small complement of satellites at synchronous orbit, for example, may provide nearly global coverage and may be designed to support small disadvantaged customers as well as those characterized by large antenna structures and sophisticated acquisition and processing capabilities. Modern navigational and timing needs can also be satisfied through exploitation of space platforms and NAVSTAR/GPS is a system which exemplifies the utilization of space for those purposes. Applications of space in surveillance and kindred areas also exist and spaceborne instruments for monitoring the exoatmospheric environment and transmissions from the Sun abound. There is an obvious charm in the utilization of space for various purposes, however, most applications require the transmission of intelligence or data between space platforms and other space segments or a ground terminal. Thus the channel or the propagation path clearly becomes a part of the total system as a perturbation source. The nuisance value of the propagation path derives from the extent to which it does not duplicate free space at a specified frequency. This paper reviews the general utilization of space to introduce the importance of Earth-space radio propagation with special emphasis directed toward DoD mission areas. An outline of the basic properties of Earth-space RF propagation follows and finally an assessment of the major effects is given.