into an overall sound level using weighting factors that account for time of day, frequency of occurrence, and duration of noise level. The first step is relatively easy. No data were presented in Ref. 2.8.2 as to the frequency distribution of the HLLV-generated noise, but since the information was based on an extrapolation of Saturn V data it can be assumed that the HLLV noise frequency spectrum will be similar to that of the Saturn as presented in Ref. 2.8.9. Thus, the conversion from absolute to A-weighted levels results in a reduction of approximately 30 dB (Ref. 2.8.9). The second conversion is not as straightforward as numerous methods are used to account for the other factors. Equivalent 24-hour weighted average, effective perceived noise level, and noise exposure forecasts are among some of the alternatives. Reference 2.8.9 uses the 24-hour weighted average for the space shuttle analysis and the 123-dB absolute sound level (measured at 6 km) is reduced to 95dB(A) for the frequency adjustment and further to 65dB(A) for the 24-hour weighted average (assuming a 1-minute duration and 60dB(A) background). This is compared to the 70dB(A) daytime guideline set by EPA and the 50dB(A) nighttime guideline. Considering that the overall sound pressure levels of the HLLV are estimated at about 7 dB over the Saturn V (Ref. 2.8.2) and that the frequency of launch is higher (as many as four per day as compared to one per day for the space shuttle), it appears that the EPA guidelines may be exceeded by the SPS launching program. More detailed system analysis will be required to verify this considering actual launch frequency and sound pressure levels. The problems of sonic booms result from the supersonic flight of the space vehicles during ascent and reentry. The effects of sonic booms come from their abruptness causing a startle response in humans and the intensity of the overpressure causing property damage. Table 2.6, compiled from Ref. 2.8.9, shows the effect of sonic booms from several studies. No information is available on SPS vehicle sonic boom generation but Ref. 2.8.3 gives some data on the space shuttle system. These are presented in Table 2.7. Considering the larger size of the SPS sysem components and the increased frequency of sonic boom occurence, it is evident that some problems will be encountred. An analysis of the SPS system sonic boom generation will be needed to evaluate the extent of these impacts.
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