A milestone in telescope-mirror technology, completed recently by Air Force scientists here, is leading to lightweight, space-based telescopes much larger than NASA's Hubble Space Telescope.

Dr. Richard Carreras aligns, pressurizes and cleans a prototype thin-film membrane mirror. Reflected in the mirror are co-workers 2nd Lt. Ethan Holt, the film mirror project officer, and Nima Jamshidi, a Purdue University student employee. Credit: U.S. Air Force photo by Deb Mercurio

Rather than use a heavy, glass mirror, researchers at the Air Force Research Laboratory's directed energy directorate were able to produce a 1-meter-diameter (about 3.25-feet) mirror, made of a thin-film membrane material. This optical-quality polyimide mirror, about the thickness and flexibility of kitchen plastic wrap, was more than three times larger than the biggest membrane mirror previously possible.

The optical quality of the membrane material was exceptional, as judged by the uniformity of its thickness, which did not vary by more than an average of about one-millionth of an inch, according to officials.

Shifting from glass mirrors was necessary because of the limited cargo capacity of space shuttles and other rocket boosters. Replacing glass with thin-film meant that a mirror could be brought to space in a folded or rolled configuration and then unrolled or expanded like an umbrella once in space, officials said.

"Our goal is to produce a telescope mirror with a diameter of 10 meters, or nearly 33 feet," said 2nd Lt. Ethan Holt, the film mirror project officer in the directorate's surveillance technologies branch. "A surveillance telescope that size in orbit 124 miles over the earth would really improve our ability to image enemy and friendly assets and capabilities."

An artist concept shows a thin-film membrane mirror, at right, in a folded configuration so it can fit aboard a rocket and then opened in space as shown at left. Researchers at the Air Force Research Laboratory's directed energy directorate here have produced a 1-meter-diameter (about 3.25-feet), optical-quality membrane mirror. Their goal is to produce a lightweight 10-meter membrane mirror, which could be used as part of a space-based telescope. Credit: U.S. Air Force

"The larger the mirror, the greater its ability to see, or resolve, objects on the ground," said Dr. Richard Carreras, the branch's technical adviser. "For example, a 10-meter telescope in Los Angeles would be able to tell the difference between a basketball and a volleyball as far away as Washington, D.C."

Large space-based telescopes could also be used to focus the energy from lasers, another potential application for this technology, officials said.