Boosted Modal Survey Testing for Dynamic Qualification of Large Satellite Spacecraft

Large satellites, utilising the increased transport capabilities of the new European ARIANE-5 launcher, have been developed or are presently under development by the European Space Agency ESA. The enlarged size category of these spacecraft rises new challenges of test methods and facilities for mechanical verification and qualification. The limits of existing vibration facilities were partially exceeded by the mass and overturning moments of the test specimen, asking for new test facilities or appropriate test methods. As an alternative approach to the conventional sine vibration tests with lateral and axial base excitations, an attempt was made to simulate the base input by means of modal survey testing with tuned modal exciter forces. In the mechanical verification process of spacecraft structures, the modal survey test is required for modal identification and for validation of the respective mathematical model. The vibration level of the test is relatively low with moderate exciter forces. A high-level "boosted" modal survey test with large multi-point modal forces can be used as a backup solution for spacecraft mechanical qualification. The test method was applied by DLR to the large X-ray astronomy satellite XMM. The paper describes the fundamentals of the approach and gives an overview on the applied test performance including further applications. Emphasis is placed on the significance of non-linear behaviour, which has to be taken into account due to the large range of excitation levels