| Summary: | Spacecraft inside a fairing of the launch vehicle is exposed to the severe acoustic environment during the lift-off and flight stages. Since the early days of spacecraft development, diffuse acoustic field is one of the critical design consideration of spacecraft structure because all the structural modes are excited equally by mutually uncorrelated plane waves from all incident angles, in the considered frequency range. However, there is some discussion about the difference of acoustic environment between fairing internal acoustics during launch and theoretical diffuse acoustic field for design. In previous researches, it has been discussed about the acoustic field during launch mainly focused on sound pressure level, while the effect to the random vibration of spacecraft structure from the difference of acoustic environment between fairing internal and diffuse field has not been much discussed, because it is difficult to asses the detail of the acoustic field due to limitations of the number of microphone located in the field. This provides the motivation for the present work in order to analyze the vibroacoustic data for spacecraft structures by using the normalized cross power spectrum density, which means spatial correlation of acoustic pressure. This paper concerned with the approach to estimate real value of the normalized cross power spectrum density using the least square approximation polynomial based on the Monte Carlo simulation, and calculate joint acceptance which is based on the estimated value. The approach is applied to the different environment between fairing internal acoustics and theoretical diffuse acoustic field, and is compared the normalized cross power spectrum density and the effect to the spacecraft structure from the difference based on joint acceptance theory.
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