On December 9 th 2009, the International Space Station (ISS) 2A solar array mast experienced prolonged longeron shadowing during a Soyuz undocking. Analytical reconstruction of induced thermal and dynamic structural loads showed an exceedance of the mast buckling limit. Possible structural damage to the solar array mast could have occurred during this event. A Low fidelity video survey of the 2A mast showed no obvious damage of the mast longerons or battens. The decision was made to conduct an on-orbit dynamic test of the 2A array on December 18 th , 2009. The test included thruster pluming on the array while photogrammetry data was recorded. The test was similar to other Dedicated Thruster Firings (DTFs) that were performed to measure structural frequency and damping of a solar array. Results of the DTF indicated lower frequency mast modes than model predictions, thus leading to speculation of mast damage.A detailed nonlinear analysis was performed on the 2A array model to assess possible solutions to modal differences. The setup of the parametric nonlinear trade study included the use of a detailed array model and the reduced mass and stiffness matrices of the entire ISS being applied to the array interface. The study revealed that the array attachment structure is nonlinear and thus was the source of error in the model prediction of mast modes. In addition, a detailed study was performed to determine mast mode sensitivity to mast longeron damage. This sensitivity study was performed to assess if the ISS program has sufficient instrumentation for mast damage detection.

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The ISS Microgravity Integrated Performance Team has initiated a program of on-orbit testing and analysis to characterize the ISS quasi-steady and vibratory microgravity environment. A comparison of on-orbit quasi-steady data to model results from the Space Station Multi-Rigid Body simulator shows the model to be 30% conservative if baseline model inputs are used. This value improves to approximately 4% with realtime inputs, indicating that the model is a good approximation. Data for the peak magnitude of the quasi-steady vector show good agreement between the measured and model results if the measured data are filtered to remove one-time peaks and other highfrequency content. For characterization of the vibratory environment, a Station Development Test Objective has been initiated to characterize microgravity environment disturbers from crew exercise equipment and other disturbers.