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Lab Achieves Mirror Technology Milestone

Photonics.com
Aug 2003
KIRTLAND AIR FORCE BASE, N.M., August 19 -- A milestone in telescope mirror technology achieved by Air Force scientists here recently is leading to large, lightweight, space-based telescopes many times larger than NASA's Hubble Space Telescope.



MIRROR MILESTONE: An artist concept shows a thin-film membrane mirror, at right, in a folded configuration so it can fit aboard a rocket and then be opened in space, as shown at left. Researchers at the Air Force Research Laboratory's Directed Energy Directorate here reached a milestone recently by producing a 1-meter-diameter (approximately 3 ? 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.
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 (approximately 3 ? feet) mirror made of a thin-film membrane material - a material closer in thickness and flexibility to plastic wrap. This optical-quality polyimide mirror was more than three times larger than the biggest membrane mirror that was previously possible.

In this case, the membrane material was also of exceptional optical quality as judged by the uniformity of its thickness, which didn't vary by more than an average of 25 nanometers or approximately one-millionths of an inch.



FILM CREW: Richard A. Carreras, technical advisor for the Surveillance Technologies Branch, aligns, pressurizes and cleans a prototype thin-film membrane mirror. Reflected in the mirror are coworkers Ethan D. Holt, film mirror project officer, and Nima Jamshidi, a Purdue University student employee. (US Air Force photo by Deb Mercurio)
Shifting from glass mirrors was necessary because of the limited cargo capacity of the Space Shuttle and other rocket boosters, the researchers said. But replacing glass with thin-film meant that a mirror could be transported to space in a folded or rolled configuration aboard a current rocket and then unrolled or expanded like an umbrella once in space.

According to 2nd Lt. Ethan D. Holt, the film mirror project officer in the directorate's surveillance technologies branch, "Our goal is to produce a telescope mirror with a diameter of 10 meters, or nearly 33 feet. 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."

"The larger the mirror, the greater its ability to see, or resolve, objects on the ground," said Richard A. Carreras, the branch's technical advisor. "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."



COMBINED EFFORT: Engineers at Air Force Research Laboratory's Directed Energy Directorate pose next to their accomplishment: a lightweight mirror for space telescopes. The mirror combines the benefits of advanced wavefront control and thin-film mirror technology. Left to right: Dennis Duneman, Jim Rotge, Mike Wilkes, Richard Carreras, Mark Gruneisen and Dan Marker. (US Air Force photo by Kimberly D. Smith)
Large space-based telescopes could also be used to focus the energy from lasers, another potential application for this technology.

Laboratory researchers said their accomplishment was made possible through the Small Business Innovation Research Program, through which they were able to work with SRS Technologies of Huntsville, Ala.

"SRS Technologies provided a unique processing capability," said Dan K. Marker, membrane mirror principle investigator. "Our collaboration led to them producing this thin-film product that was subsequently named CP1-DE. The 'DE' suffix was added to recognize the Directed Energy Directorate's role in its development."

Numerous commercial contractors, including Boeing Rocketdyne Technical Service (an in-house contractor), were involved in the project.

The laboratory's Directed Energy Directorate is the Air Force focal point for high-energy lasers, a variety of others directed energies and imaging technologies.

For more information, visit: www.de.afrl.af.mil/pa/



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