Abstract
Accurate experimental estimation of modal damping ratios for large spacecraft structures prior to mission deployment is critical for reliable prediction of structural vibration levels. However, full-scale testing is often impractical due to laboratory spatial constraints, while scaled models fail to adequately capture nonlinear damping mechanisms. This paper proposes a novel modal-based hybrid simulation (MHS) method for estimating low-order nonlinear modal damping ratios of large periodic spacecraft structures. Using modal information as the coupling interface between the physical substructure and the full-structure numerical copy, the method delivers three core contributions. First, it eliminates the need for real-time closed-loop iteration, markedly reducing hardware requirements and experimental costs. Second, integrated with an energy-based theoretical framework, it enables accurate quantitative characterization of amplitude-dependent nonlinear damping characteristics. Third, adopting full-scale physical substructures fundamentally eliminates scale effects and extrapolation errors inherent in conventional scaled-model and piecewise extrapolation approaches. The effectiveness and robustness of the proposed method are systematically validated via numerical simulations, parameter sensitivity analyses, and hybrid experimental tests. Experimental results show an average relative error of 4.82% for the nonlinear first bending modal damping ratio, using a physical substructure of only one-fifth the total length against the full-structure benchmark. This work provides a reliable and efficient approach for ground-based experimental identification of low-order nonlinear modal damping in large periodic spacecraft structures.