Experiments have demonstrated the feasibility of inflatable reflectors with very low system aerial densities of the order of 1 kg/m². Diverse applications include radio and optical communications, telescopes, and the concentration of sunlight for power generation. The same technology can be used for structural beams in single or multiple layers with excellent rigidity. Development work thus far has focused on potential uses in outer space, but inflatable rigidized structural elements are suitable for terrestrial applications where large lightweight surfaces and structures are needed.

A Stainless Steel Membrane is stretched across a circular boundary and pressurized to deform it into a curved mirror.

The basic concept of an inflatable reflector is simple: stretch a membrane beyond its elastic limit by using a combined mechanical tensioning and pressure. The shape the resulting surface takes is a good approximation to an ellipse with higher order correction terms. The shape can be modified by changing the boundary, the pressure, or the membrane material. A change in area of approximately 1 percent is required to plastically deform the membrane into the desired shape. After forming, the pressure is released with the resulting surface being a self-supporting membrane reflector. For imaging applications, the aberrations induced by the membrane reflector could be compensated for by secondary and tertiary optics. The design problem is to choose the membrane material and boundary conditions to obtain the desired reflector shape.

The figure shows an experimental apparatus on which a stainless steel membrane is stretched across a circular boundary and pressurized. The result is a smooth, rigid, self-supporting curved reflector surface of a quality suitable for use as a mirror in the far-infrared or submillimeter wavelengths (measured surface 8 micrometers root-mean square [RMS] over the central 40 cm of the membrane). The global surface figure can be adjusted by changing the pressure, the stretching forces, or the boundary over which the membrane is stretched.

This work was done by Neville Marzwell of Caltech and Mark Dragovan of the Fermi Institute, University of Chicago, for NASA's Jet Propulsion Laboratory. NPO-20359

Topics:
Electronic equipment Exteriors Ferrous metals Imaging and visualization Lightweight materials Metals Mirrors Optics Physical Sciences Pressure Radio equipment Steel Sun and solar Telescopes
This Brief includes a Technical Support Package (TSP).
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Inflatable membrane reflectors for multiple-purpose applications

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    NASA Tech Briefs Magazine

    This article first appeared in the May, 1999 issue of NASA Tech Briefs Magazine (Vol. 23 No. 5).

    Read more articles from the archives here.

    Overview

    The document presents a technical support package from NASA's Jet Propulsion Laboratory (JPL) detailing the development and applications of inflatable mirrors designed for multiple purposes. Invented by Mark W. Dragovan and Neville I. Marzwell, this innovative technology addresses the need for large, lightweight mirrors and light collectors essential for astronomical and communication applications.

    The core concept revolves around the use of inflatable reflectors with low system aerial densities, approximately 1 kg/m². These reflectors can be utilized in various fields, including radio and optical communications, telescopes, and solar power generation. The technology allows for the creation of structural beams that exhibit excellent rigidity, making it suitable for both space and terrestrial applications.

    The process involves stretching a membrane beyond its elastic limit using mechanical tensioning and pressure, resulting in a surface that closely approximates an ellipse. The shape of the reflector can be modified by adjusting the boundary conditions, pressure, or the material of the membrane. A critical aspect of the design is achieving a change in area of about 1 percent to plastically deform the membrane into the desired shape. Once formed, the pressure is released, leaving a self-supporting membrane reflector that can be used as a mirror, particularly effective in the far-infrared or submillimeter wavelengths.

    The document emphasizes the importance of careful design and modeling to achieve precise surfaces. The use of a stainless steel membrane, which is stretched and pressurized, results in a smooth, rigid surface of optical quality. The local root-mean-square (RMS) surface quality is noted to be around 8 micrometers over a central area of 40 cm, indicating high precision suitable for imaging applications. Additionally, any aberrations caused by the membrane can be corrected using secondary and tertiary optics.

    Overall, this NASA report highlights the potential of inflatable mirrors to revolutionize optical engineering by providing a lightweight, cost-effective alternative to traditional glass mirrors, which are often heavy and fragile. The technology's adaptability for various applications positions it as a significant advancement in the field of optics and space exploration.