4.1. PART 1: PRELIMINARY MEASURED DATA ANALYSIS 71
Figure 4.2: Linear SDOF system broadband random excitation (left) and response (right).
4.1.10 ILLUSTRATIVE EXAMPLE: ISPE MODAL TEST
In 2017, NASA/MSFC conducted a modal test on the Integrated Spacecraft and Payload Ele-
ment (ISPE), general overview (courtesy of NASA/MSFC) depicted in Figure 4.3.
Figure 4.3: ISPE test article overview.
e modal test sensor suite included four electrodynamic shakers (excitation forces) and
273 accelerometer channels (dynamic responses). Preliminary measured data analysis displays
for excitation “1” and response “1” are shown in Figure 4.4.
Both the spectrogram and autospectrum for the excitation indicate broadband frequency
content. e drop-off in the autospectrum above 90 Hz is the result of low-pass filtering of
measured data histories. e response spectrogram and autospectrum reveal the presence of
many peaks in the 15–90 Hz frequency band, suggesting the presence of many test article modes.
Gaussian probability density distribution for the response history suggests that the ISPE test
article exhibited linear MDOF system behavior in the 15–90 Hz frequency band.
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