Vibroacoustic loads on spacecraft antennae: analysis and test correlations

摘要

The acoustic load during launch is one of the dimensioning cases of spacecraft structures, especially demanding for large antenna reflectors. Current specifications rely on the diffuse field idealisation, while tests are actually performed in reverberating chambers, leading to discrepancies between predicted and measured responses. Most of these are due to the limited capabilities of analytical tools for industrial applications and the testing facilities, particularly when dealing with the modelling or control of the acoustic inputs. However, as shown in this paper, some sources of correlation errors are inappropriate signal processing methods, that do not take into account the physical nature of the loads and the fluid-structure coupling. In particular, digital filtering techniques applied to fine resolution power spectral densities are proposed, in order to better retain the effect of cavity modes, instead of the octave-fraction bands approach. This is of interest when analysing the low frequency range, in which the most important contributions to structural stresses usually appear, depending on the size in terms of pressure blocking, the structural impedance, the acceptance of eigen-mode shapes and the radiation coupling. Several industrial examples are studied, providing insight into typical results, the nature of the discrepancies and some possible solutions.