This paper presents the results of an experimental research program to develop a novel type of assembly‐level vibration test. The design of a multimodal test fixture, which simulates the high‐frequency (100–2000 Hz) dynamic characteristics of aMARINERspacecraft structure, is described. Data obtained in research vibration tests with an electronic assembly mounted in the multimodal fixture indicate that the novel testing technique results in a more realistic and more uniform high‐frequency vibration environment than conventional tests utilizing rigid fixtures. The paper presents guidelines for designing multimodal fixtures and discusses means of utilizing these fixtures in future spacecraft assembly‐level vibration test programs.