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.
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