Hybrid Acoustically Layred Foam (HALF) foam for improved low frequency acoustic mitigation for launch fairings

摘要

Launch vehicles produce high levels of acoustic energy and vibration loads that can severely damage satellites during launch. Because of these high loads, the satellite structure is much more robust than it needs to be for on-orbit operations. Traditionally, acoustic foam is used for acoustic mitigation; however, it is ineffective at frequencies below 500 Hz. For this reason we investigated three different modified acoustic foam concepts consisting of a thin metal foil, a semi-rigid spacer, and a melamine foam substrate to improve the low frequency acoustic performance of the melamine foam. The goal of the Hybrid Acoustically Layered Foil (HALF) Foam concept was to excite bending waves within the plane of the foil to cause inter-particle interactions thus increasing the transmission loss of the foam. To determine the performance of the system, a transmission loss tube was constructed, and the normal incidence transmission loss for each sample was measured. The tests confirm the excitation of bending waves at the target frequency of 500 Hz and a significant increase, on the order of 8 dB, in the transmission loss.