Comparison of different methods of modal test on a spacecraft representative structure

FLECS, designed and manufactured by ESTEC, represents a typical modular spacecraft in terms of mass properties and modal density. The structure is well suited as a test item for the validation of dynamic identification methods and was, therefore, selected for the comparison of the following test methods: the phase resonance method with appropriate excitation (for every eigenmode, an exciter force distribution is found which compensates the damping forces of the structure); the mode separation method with excitation at various locations on the structure, with complex exponential; and a driven-base method with unidirectional base excitation. Since the structural damping level of FLECS is low compared to actual fully equipped satellite structures, the modal identification methods were also applied to a configuration of FLECS with supplemental non-proportional viscous damping. For this purpose, dampers were manufactured and integrated into the FLECS structure. This paper describes briefly the experience in applying the methods and compares the results.