RIGIDIZATION STUDIES ON INFLATABLE SPACE STRUCTURES

Abstract

The inflatable structures are being used for space applications such as inflatable habitats, space antennas, inflatable solar sails, and many others due to their incomparable features like ultra-low mass, high packaging efficiency, and easy deployment. These structures lose their integrity after venting and must be rigidized to extend their functional life in space. The thesis focuses on rigidizing different components of an inflatable space antenna containing booms, a torus, and a doubly curved parabolic reflector using embedded shape memory alloys (SMA) wires between polyimide films. The thesis could be broadly divided into three sections: rigidization of booms, rigidization of toroidal structures, and rigidization of doubly curved parabolic reflectors. The study started by investigating the material properties and different phase transformation temperatures of Ni-Ti-based SMA wires through the uniaxial tensile and differential scanning calorimetry (DSC) tests to use the obtained data for numerical analysis as an input. Furthermore, the deployability analysis and restoring force generation under thermal loading are carried out for an SMA-based boom when the boom's degree of freedom is constrained to zero. The mechanical load transforms the boom into a stowed one, followed by thermal loading without releasing the deformation load, leading to the accumulation of restoring force in the bend region. The finite element analysis is performed on the COMSOL Multiphysics by incorporating the Lagodus material model for SMA wires. Moreover, the deployability test is conducted through experiments to demonstrate the load-lifting ability of thermally actuated booms. The study outcomes show that the SMA materials are applicable for space applications because of their controlled deployability with minimum efforts, encouraging the development of polyimide-SMA-based booms. Initially, the material properties of laminated polyimide films were found through the uniaxial tensile test, and a mathematical model was developed. The structural rigidity of polyimide-based booms is identified through numerical code under different inflation pressure intensities based on the per-unit deflection approach. The stiffness of the rigidized booms is further investigated and compared to experimental observations to identify the authenticity of the approach. Moreover, the parametric study helps to examine the impact of design and material parameters on the structure's rigidity on partial or complete inflation gas venting. The second segment of the thesis covers the rigidization of toroidal structures and their shape integrity after venting the inflation gas. An algorithm is developed to rigidize the torus using heat actuated embedded SMA wires between polyimide membranes. Initially, polyimide film-based torus is investigated for deployment, and corresponding inflation pressure is found numerically, followed by the experimental demonstration. The outcomes of polyimide film-based torus are utilized for SMA-based torus and got the deployment pressure. Since stowing, the mechanical force is applied and held in the folded configuration during thermal loading to find the restoring force, the parameter for regaining the initial shape. The experiments are also carried out to demonstrate the authenticity of the approach and verify the numerical outcomes. The third part explains the rigidization of the doubly curved parabolic reflector and its analysis. The algorithm for Kapton-based parabolic reflector generation is developed, and inflation pressure for its deployment is investigated. It is an input parameter in FE analysis to deploy the SMA-based reflector. The authenticity of the FE outcomes is verified through experimental demonstration under no inflation pressure scenario. The part is ended with the examine reflector's stiffness using 'per unit deflection.