Overview of Form Stiffened Thin Film Shell Characteristic Behavior

This paper provides an overview of the basic behavior of doubly curved form stiffened thin film shells. Such shells, which can be fabricated in a variety of manners, are perceived to have advantages relative to other methods of realizing extremely light weight apertures. Some of these advantages include 1) system mass/areal density advantages (i.e. does not require transmissive canopy and pressurization systems/make up gas, tensioning support structure/toroid), 2) compatibility with foldless roll stowage techniques, 3) deterministic, passive, self-deployment and rigidization with no need for external power or curing, 4) compatibility with methods to realize precision surfaces (good surface roughness, improving global surface figure, high inherent dynamic stiffness, compatibility with active boundary control), and 5) scalability to large diameter apertures. Various experimental hardware is shown to illustrate the range of sizes (0.1 to 0.75 m) and prescriptions (F#’s of 0.25 to ≈2) that have been demonstrated to date. Representative surface roughness (20 nm rms over 25 to 50 mm diameter sample sizes) and global surface figure measurements (sub-10’s to 100’s of microns RMS over 0.1 to 0.5m diameter apertures), and demonstration of small scale optically powered surfaces are discussed. The advantages of the foldless roll stowage approach are reviewed and experimental results of passive self deployment of roll stowed form stiffened shell are shown. Typical response to environmental loads, buckling onset, basic scalability for application in space environment (10’s of meters), and structural dynamic behavior trends are discussed as-well. Finally, representative results from the use of active boundary control to influence and correct surface figure are shown. The combination of above characteristics are believed to make discretely mounted form stiffened shells attractive solutions for a range of terrestrial and space applications including solar concentrators (for a variety of mission uses), precision apertures, and even non-precision surfaces that are traditionally realized from tensioned membrane flats (such as solar sails, thin film solar array substrates, sun shields, etc.).