DYNAMIC CHARACTERIZATION OF AN INFLATABLE CONCENTRATOR FOR SOLAR THERMAL PROPULSION
An inflatable structural system that is a technology demonstrator for solar thermal propulsion and other applications is characterized for structural dynamic behavior both experimentally and computationally. The inflatable structure is a pressurized assembly developed for use in orbit to support a Fresnel lens or inflatable lenticular element for focusing sunlight into a solar thermal rocket engine. When the engine temperature reaches a pre-set level, the propellant is injected into the engine, absorbs heat from an exchanger, and is expanded through the nozzle to produce thrust. The inflatable structure is a passively adaptive system in that a regulator and relief valve are utilized to maintain pressure within design limits during the full range of orbital conditions. Modeling and test activities are complicated by the fact that the polyimide film material used for construction of the inflatable is nonlinear, with modulus varying as a function of frequency, temperature, and level of excitation. Modal vibration testing and finite element modeling are described in detail in this paper. The test database is used for validation and modification of the model. This work is highly significant because of the current interest in inflatable structures for space application, and because of the difficulty in accurately modeling such systems.
Modal testing of an inflated thin film polyimide torus structure
An experimental investigation into the dynamics of an inflated thin film polyimide torus has been performed. This paper describes an effort to define modal test procedures for extremely lightweight, flexible inflated structures. An impact hammer was modified to excite the global modes of the structure, while avoiding local excitation. Coherence measurements are examined to describe the nonlinearity in the structure. Nonlinearities include shell wrinkling and material nonlinearities such as film modulus variations with frequency and temperature. The baseline goal for the modal test is to determine the first six bending modes of the structure.
Structural Considerations of Inflatable Reentry Vehicles
The state of the design art for inflated structures applicable to reentry vehicles is discussed. Included are material properties, calculations of buckling and collapse loads, and calculations of deflections and vibration frequencies. A new theory for the analysis of inflated plates is presented and compared with experiment.