Effects of exhaust plasmas upon signal transmission to and from rocket-powered vehicles

This paper presents theoretical and experimental results for characterizing the signal transmission disturbances caused by the presence of rocket-exhaust plasmas in the propagation medium betwem a ground station and a rocket-powered vehicle. The object of this characterization is to provide quantitative data on the propagation effects of the exhaust plasma that are of critical importance in the design of space tele-instrumentation and communication systems. Basic propagation effects, including multipath and forward and back scatter are discussed, and important gross signal transmission parameters are defined and expressed. The general discussion of channel characteristics is followed by a presentation and discussion of typical results of measurements obtained from the Saturn test series. Three major effects of the presence of the exhaust plasma upon signal transmission are emphasized. These are the possibility of a large drop in received signal level, a significant reduction of coherence bandwidth caused by time-variant multipath, and an unusually high fading rate. The bearing of these effects upon the design and demodulation of signals for links that include a rocket-powered terminal or relay vehicle is discussed.