Reduction of Overtesting During Base-Drive Random Vibration Tests for the Euclid Spacecraft Hardware

Abstract eng:
The purpose of random vibration testing is generally to verify strength and structural life by introducing random vibration through the mechanical interface. Typical applications are electrical components, instruments and small spacecraft for which acoustic testing is ineffective. The base-drive vibration test is conducted with the test item sitting on a moving platform that is driven by a shaker which introduces vibration typically up to 2000 Hz in three single-axis tests. The base-drive configuration is commonly employed to achieve test levels comparable to the launch environment. This conventional approach to testing has been known for decades to potentially overtest the test article at its own resonance frequencies. For this reason “notching” (i.e. reduction) of the specified input spectrum is often necessary. Notching on the input spectrum can be considered as far as it does not “jeopardise” the aim of the test, for example the qualification of the test specimen. As a consequence, one of the main issues for the structural engineer is to define a minimum threshold for the input notching. Special attention is paid to the “phenomenology” of secondary notching, which is related to level reduction on critical areas inside the test specimen. This paper provides some guidelines for assessing the notched profile in random vibration testing. In particular the importance and the benefits of performing a vibro-acoustic analysis of the complete spacecraft is illustrated with an example. The paper is based on some author’s contributions to the ECSS Spacecraft Mechanical Loads Analysis Handbook [1], and his experiences with the a number of European Space Agency projects. A critical investigation of the overall approach from the definition of the test specification to the quantification of the notching is shortly presented. The guidelines should be used in the frame of the Euclid spacecraft hardware verification when base-drive random vibration testing will be performed to show compliance to the random vibration and vibro-acoustic environment requirements.

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