This experiment was not capable of generating any effects which might accompany continuous heating of the lower ionosphere. The discrepancy between experimental results and theoretical predictions indicates that the physical mechanisms of ionospheric heating and cooling need to be studied in greater detail. Areas for further research needed to understand ionospheric heating as it applies to SPS include: study of the role of nonMaxwellian electron energy distributions in ohmic heating, electron cooling interactions, and incoherent scatter interpretation, consideration of the role of thermal conduction within small beams (or on edges of large beams) in the collision- dominated lower ionosphere; a search for additional cooling mechanisms or improved estimates of accepted mechanisms; and a detail study of the frequency scaling of ohmic heating in the ionosphere. These first results cast doubt that thermal runaway will occur at 15-25 mW/cm^ as predicted earlier. Thermal self-focusing and the creation of plasma striations, however, are likely to occur for SPS energy densities. The spatial extent of these effects away from the immediate vicinity of the power beam cannot be assessed at this time, and must await experimental and theoretical verification. Likewise, the details of potential impact on telecommunications systems must await further work. 4.2.6.2 Vehicle Effluent Effects The initial modeling predictions of F-layer depletion, and the Skylab and limited military missile data indicate that communications services using F-layer support could experience outage periods and subsequent marginal signal periods, with the ionosphere upper layer "hole" extending about 1000-1500 km around the trajectory depending on the actual launching scenarios. Specific service impacts need to be identified by the F-layer characteristic predictions from two-dimensional model parameter analysis, and the physical property and communication link testing to be accomplished with the space shuttle launches.
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