is a possibility for inadvertent weather modification by the SPS rocket effluents in the troposphere and because cumulative effects would be possible, continuing monitoring of rocket-exhaust ground clouds is needed. Simulations (using computer models) of inadvertent weather modification by HLLV launches under various meteorological conditions are also required to improve the assessment. Carbon dioxide emissions due to rocket launches would be expected to have no detectable effect in the stratosphere and mesosphere. However, water vapor concentrations could be increased by SPS-related rocket-exhaust emissions. The change in the total (globally averaged) ozone layer due to SPS spaceflights would be expected to be undetectable, as would the effects of nitrogen oxides. The presence of a 0.05% sulfur impurity in the fuel is not considered likely to have any impact, and a similar conclusion may be reached regarding other fuel impurities. Corridor-effect calculations are important to an improved assessment of the SPS perturbations of the composition of the stratosphere and mesosphere. The globally averaged effect, on the earth's surface, of the anticipated composition perturbation in the stratosphere and mesosphere would be negligible. Reliable assessments of general climatic effects due to SPS perturbations must await model predictions of altitude and latitude dependence. It is probable that transient clouds at stratosphere and mesosphere altitudes would be induced in the vicinity of the launch site but they would not be expected to have a detectable impact on anything el se. The lowest layers of the ionosphere (the D- and E-regions) could be affected by both rocket launches and spacecraft reentry. The effluents from these space operations include water vapor, hydrogen gas, and thermal energy during launch, and ablated materials, oxides of nitrogen, and thermal energy during reentry. These effluents would modify the composition and properties of the ionosphere and might influence climate, satellite-based surveillance systems, radio communications, navigation systems, microwave propagation (SPS power-beam stability) and magnetospheric processes. While the likelihood of altering the electron and ion composition seems to be fairly high, the magnitude of the impacts is uncertain. The effects of nitrogen oxides formed during reentry and the effects of ablated materials do not appear to be important at this time. Calculations have shown that injection of water and carbon dioxide into the F-region of the ionosphere results in both plasma reduction (electron-ion recombination) and enhanced airglow (visible and IR emissions from excited molecules). These predictions have been verified both inadvertently during the Skylab launch and deliberately during the Lagopedo experiments. Plasma reductions can result in interference with radio communications and navigation systems. Enhanced airglow, while not a serious matter at ground level, can contribute to the noise level of satellite-based surveillance systems.
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