ST8 Ultraflex-175 Solar Array-Deployed Dynamics Analytical Modeling and Comparison to Validation Criteria

The UltraFlex-175 is a 5.5-meter diameter deployable accordion fanfold flexible blanket solar array. In the deployed configuration, it radially tensions ultra-lightweight triangular membrane sections to form a shallow umbrella-shaped structure. A comprehensive program of model development and validation by hardware testing was performed to demonstrate Technology Readiness Level (TRL) 6. This paper addresses the deployed dynamics modeling portion of this effort tested in vacuum and air. Due to the sensitivity to the internal stresses within the tensioned membrane on deployed transient response, a multistep modeling process was employed. The first step required the use of a nonlinear finite element model to obtain static pre-stress conditions. Next, the pre-stress conditions were used in the linear finite element modal and transient analyses. The modeling techniques employed agree well with ground tests. Having validated the modeling procedure, the same model was then used to predict the natural frequencies of the array in space. Finally, closedform equations were derived to predict the in-space deployed dynamics for a wide range of possible array sizes.