MODAL SURVEY TESTING OF ESA ISPR RACKS FOR ISS

摘要

Structural mathematical model predictions (naturalfrequencies, mode shapes) can show deviations from thereal dynamic characteristics of the hardware in thecomplete frequency range of interest and are thereforenot suitable for accurate flight load predictions, even incase of best practice modelling. Therefore experimentalvalidation of modal characteristics of the hardware is afundamental step in the structural verification for spaceflight systems.Modal survey tests shall be used to verify the FiniteElement Models (FEM) of the integrated hardware, asrequested and used for the Design Loads Assessment(DLA) and the Verification/Coupled Load Analysis(VLA/CLA) of the launcher system.The payloads shall demonstrate compliance with therequired quality of the mathematical models and theconstraints on dynamic de-coupling between modes ofthe payload and the modes of the launcher. This is ofgreat concern for those payloads launched on the Shuttlefor the International Space Station (ISS).The International Standard Payload Racks (ISPR's) arewithin this payload group. Seven of the ISPR's fromESA have already undergone Modal Survey Testing.This paper gives an overview of the applicable testrequirements and the test process for these racks. Itpresents the resulting experimental dynamiccharacteristics.All these racks are based on a common rack framestructure developed by Ishikawajima-Harima HeavyIndustries, Japan. Then each rack integrator furnishesthe rack with scientific equipment using customizedsupport and structural elements. The paper studies howthe specific design choices in the integration influencethe dynamic behaviour of the final integrated rack.The paper also reviews the analysis/test correlationrequirements that call for a Finite Element Modelreproducing the experimental modal parameters with acertain acceptable error. The results of the correlationfor the ESA payload racks are provided.Finally the paper outlines the lessons learned in thecomplete testing process from the prediction analysesand selection of locations for accelerometers andexciters to the actual testing execution and theanalysis/test correlation.