An advanced test strategy for boosted modal survey testing of non-linear space structures

Abstract

The dynamic qualification of today´s space structures is performed by means of driven base tests in order to simulate the dynamic loads during launch. This method is limited to structures which fit onto the shaker facility. For large and unwieldy structures an alternative approach can be utilized which applies modal forces for the qualification. This testing concept is called Modal Force Combination (MFC) technique and replaces the base acceleration by a set of forces acting directly in a selected number of structural points. Modal forces are patterns of single forces that are able to excite single resonances and which can be applied by movable electrodynamic shakers. An advanced test strategy for the MFC technique is presented in this article. The strategy applies narrow-banded swept sine excitation and considers structural non-linearities. In extension to MFC technique introduced up to now, a non-linear model which is identified from the narrow-banded swept sine runs on a low or intermediate level is used for the redefinition of the transients which are needed to achieve the next excitation level and finally the qualification of the structure. Since within the strategy single modes are used for the qualification the method is called boosted modal survey test on the flight model of the European Robotic Arm (ERA) are used to demonstrate the suitability of the concept. The pros and cons of the approach are discussed, recommendations concerning the application are given and the limitations are point out.