Analytical and experimental characterization of gravity-induced deformations in subscale gossamer structures

The development of gossamer space structures such, as solar sails and sunshields presents many challenges due to their large size and extreme flexibility. The postdeployment structural geometry exhibited during ground testing may significantly depart from the in-space configuration due to the presence of gravity-induced deformations (gravity sag) of lightly preloaded membranes. This paper describes a study carried (out to characterize gravity sag in two subscale gossamer structures: a single quadrant square solar sail and a single membrane layer from a multilayer sunshield. An experimental study was carried out to measure the global surface profiles using photogrammetry, and nonlinear finite element analysis was used to predict the behavior of the test articles. Comparison of measured and predicted surface profiles shows that the finite element analysis qualitatively predicts deformed shapes comparable to those observed in the laboratory. Quantitatively, finite element analysis predictions for peak gravity-induced deformations in both test articles were on the order of 10% of measured values. Results from this study provide increased insight into gravity sag behavior in gossamer structures, and demonstrates the potential to analytically predict gravity-induced deformations to within reasonable accuracy.