of serious communications effects. In addition, strong local plasma heating frequently results in plasma turbulence, which contributes to scintillations of ground-to-satellite signals, including the uplink pilot beam. These striations can result from the self-focusing instability. 4.2.3.2 Vehicle Effluent Effects The details of the changes in the ionosphere resulting from launch vehicle effluents have been provided in Section 3 and need not be repeated here. * 4.2.4 State of Knowledge 4.2.4.1 Ionosphere Heating Considerable knowledge exists concerning the effects of large amounts of heating on the ionosphere. Most of the theoretical and experimental work has been directed to the "overdense case,” i.e., the case where the ionospheric density is sufficient to reflect the incident heating frequency. The modification of the ionosphere caused by intense heating resulting from the transmission of electromagnetic energy has been confined primarily to heating using frequencies below 2 MHz. In fact, hardly any experiments have been performed that attempt to heat the ionosphere at frequencies greater than HF. Likewise, most of the theoretical work undertaken has been directed toward the response of the ionosphere to high-powered HF radio waves that are reflected from the ionosphere. Thus, in order to arrive at this preliminary assessment, it has been necessary to rely heavily on theoretical extrapolation of results (Ref. 4.2.7) obtained from HF heating to frequencies corresponding to the satellite power system operation. The overdense heating experiments conducted at Platteville and Arecibo are well-documented in the literature. Both theory and experimental data are being investigated in order to resolve differences between observation and prediction. Very little has been done in the area of underdense heating from an experimental point of view.
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