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Modal vibration tests in conjunction with finite-element analysis were used to characterize a generic dynamic model. The model consisted of five substructures to simulate the multibody, low-frequency nature of large space structures. Static tests were used to refine the substructure analytical models prior to full assemblage analysis. The effects of a cable suspension system were analyzed using a prestressed vibration analysis. Coupling between a cable suspension mode and model bending mode was found to be influenced by the distance from the model center of gravity to the cable-to-model attachment location. A damping characterization method using noncontacting exciters was used to measure the amplitude-dependent damping. Frequency and damping measurements in ambient air and at near-vacuum conditions were made. Ambient air decreased vibration frequencies by an average 3.1% and increased the modal damping by an average 28% in the generic model. NomenclatureC/C C = critical damping ratio /! = fundamental frequency, Hz g = acceleration due to gravity / = model rotational inertia ti = suspension cable length £ 2 = distance from model center of gravity to cable-tomodel attachment location m -vibration cycle number M = model mass X Q = initial vibration amplitude X m = vibration amplitude of the rath cycle 0JJ0J = cable rotation and rotational acceleration (Fig. 13) $2962 =m°d el rotation and rotational acceleration (Fig. 13)

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