tions systems which transmit radio energy within and through the ionosphere may be severely affected and suffer possible performance degradation. Thus, it is necessary to assess accurately the potential for ionosphere modification resulting from SPS operation. Specific questions that must be answered are: • Is the SPS transmission sufficient to cause harmful interference to telecommunication systems? • Is the SPS transmission likely to give rise to interference effects that are not permissible by CCIR standards? • Will the SPS power-beam transmission cause deterioration to the SPS pilot-beam transmission? The results that follow from any effort to address these issues must provide quantitative information concerning effects on telecommunication systems caused by SPS-induced ionospheric modification. In Table 4.8 are listed selected telecommunications systems that could be adversely affected by ionospheric changes associated with SPS operation. These systems are provided only as an example of the type of changes that could occur, as the table is not meant to be all inclusive. It must be pointed out, however, that not all potential telecommunications impacts will be adverse. As mentioned, frequencies above HF are propagated through the ionosphere with speed less than that of free space. If SPS operation caused a substantial decrease in the ionospheric density, these waves would not be slowed down as much and conceivably an improvement in the performance of such systems could result. 4.2.2.2 Vehicle Effluent Effects The large launch vehicles and frequent surface-launch and near-earth orbit maneuver operations postulated to establish and maintain the SPS systems indicate a significant potential for transitory modification of regions of the ionosphere and magnetosphere because of effluent discharges. For SPS, the discharge rates and consequent ionospheric effects could exceed the F-layer density reductions noted following the Skylab launch. The limited data available from this previous launch indicate that the exhaust from heavy lift launch vehicle (HLLV) engines would cause large depletion areas in the ionospheric F-layer. Recombination and stabilization periods could extend for several hours, impacting communications systems that
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