The amount of refraction depends directly on the ionospheric electron density and is a function of the frequency of the electromagnetic wave sent into the ionosphere, the electron collision frequencies, and the strength of the geomagnetic field. The electron density can be sufficiently great to cause the incident EM wave to be totally reflected and returned to the earth’s surface. This property in fact permits long distance high frequency radio propagation systems to operate. The ionosphere therefore must be considered an integral part of such systems. At higher frequencies radio waves travel directly through the ionosphere with speeds slightly below that of light. Thus the waves arrive at reception points with travel times that are larger in the presence of the ionosphere. The travel time is related to the total number of electrons encountered along the propagation path. Changes in the ionosphere, whether due to natural or artificial causes, give rise to changes in the performance of electromagnetic sensitive systems (i.e., telecommunication systems) whose energy is propagated within and through the ionosphere. Any change in the ionosphere potentially can change the performance of an ionosphere-dependent telecommunication system. In addition, small-scale (meters to kilometers) irregularities in the ionospheric electron density can give rise to fading and scintillation of signals that pass through the irregularity region. This could result in loss of information associated with changes in amplitude and phase of the radio wave. The purpose of this section is to describe the impact of potential changes in the ionosphere that will result from the operation of the satellite power system microwave power transmitting system. These changes can evolve directly from heating of the ionsophere by the SPS power beam and also indirectly from the effluent material associated with the launch vehicles needed to place an operational SPS into geostationary orbit. 4.2.2 Methodology 4.2.2.1 Ionosphere Heating Because of the large amount of power transmitted (greater than 5 GW) to the earth that is associated with each SPS, it is possible that substantial modification of the earth’s ionosphere will result from direct heating of the ionosphere. If, in fact, this turns out to be the case, .then telecommunica-
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