Future large aperture infrared space telescopes such as the Next Generation Space Telescope will require lightweight, deployable sunshields to enable passive radiative cooling to cryogenic operating temperatures. In addition to the requirement for a high performance thermal design, mechanical and structural requirements are also demanding due to constraints on mass and volume. NASA has supported several technology development efforts to reduce risks in the area of sunshield structures, including: system packaging and deployment, film management, materials characterization, modeling tools for thin-film membranes, and ground test capabilities for characterizing structural performance. This paper discusses recent progress in sunshield structures technology development relating to post-deployment structural performance. First, improved approaches for analyzing partially wrinkled, thin-film membrane structures will be discussed. Next, new techniques for static and dynamic testing of ultra-lightweight structures will be described. Finally, analytical and experimental results from two recent studies will be described: (a) dynamic characterization of a 1/10th scale sunshield model and (b) static shape characterization of a 1/20th scale sunshield membrane layer. Results from these studies will provide valuable resources for use in design of sunshields for future space telescopes.