Stable Method of Attaching Thin Films to Torsionally Compliant Space Structures

Author: Popov, George Arthur

Year: 2026

Degree: Dissertation (Ph.D.)

Advisor: Pellegrino, Sergio

Committee Members: Meiron, Daniel I.; Bhattacharya, Kaushik; Pellegrino, Sergio; Shaikeea, Angkur

Option: Aerospace Engineering; Space Engineering

Abstract

Ultralight space structures utilize composite structural elements supporting active thin films in order to achieve deployed configurations with lower areal densities. However, as these space structures get larger, they get increasingly less stiff, leaving them susceptible to adverse effects, such as torsional buckling. Simultaneously, this conflicts with the requirements that more ambitious space missions impose on the surface accuracy to make technologies like large phased arrays viable.

This thesis presents a novel method of continuously attaching thin films to deployable thin shell structures, allowing for materials with widely different coefficients of thermal expansion. It proposes a double s-spring border that exhibits a local post-buckling behavior and provides a tunable continuous edge attachment method that can maintain constant preload under large thermal strains. The mechanical behavior of the double s-spring under different mechanical loading conditions is studied both numerically and experimentally. Additionally, a reduced order model that greatly reduces the computational cost of optimizing double s-springs for various applications is presented.

In parallel, the torsional buckling of elastic composite frames is studied to understand the fundamental limits of attaching thin films without incurring torsional buckling. This study analytically calculates the critical prestress of torsionally soft square frames supporting an internal thin film. The study highlights the role of the attachment scheme, which has a very significant impact on the critical prestress. It is shown that the average of the compression load on a frame caused by a prestress is an invariant buckling load. The analytical calculation is verified via numerical finite element analyses and an experiment, which characterizes the post-buckling behavior of the torsionally soft frames as well. It is concluded that distributed edge attachments, such as the double s-spring, significantly increase the stability of space structures against torsional buckling. The findings for the torsionally soft square frames are validated against a high fidelity orthotropic material model in order to justify the assumptions made in the analytical study.

In the final section of the thesis, it is shown that the double s-spring continuous attachment scheme enables consistent deployment and compact packaging. The scheme is also shown to be versatile for additional applications, enabling novel deployment and folding schemes, such as a doubly-curved composite foldable toroid.