Wrinkling Puts Light Mirrors in Doubt

Engineers may have to look elsewhere for lightweight mirrors for the next generation of space telescopes. A research team at the University of Arkansas in Fayetteville has determined that the polymer films proposed for large, inflatable mirrors cannot provide the necessary flatness because they suffer from too much wrinkling when they are folded.

The researchers used an optical micrometer to measure the wrinkles that were randomly produced in 0.3- and 0.5-mil polyimide films, ignoring creases, explained Bob Reynolds, an assistant professor of mechanical engineering who headed the project. They found that up to 80 percent of the wrinkles, some up to 2-mm deep, remained after 24 hours of tensile loading such as that produced during inflation.