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AFRL breakthrough furthers space optics

by Michael P. Kleiman
Air Force Research Laboratory Space Vehicles Directorate Public Affairs


1/24/2006 - KIRTLAND AIR FORCE BASE, N.M. (AFPN) -- Positioning three delicate, circular mirrors to one one-thousandth of the width of a human hair challenged scientists at the Air Force Research Laboratory’s space vehicles directorate here.

But, not anymore.

For five years they studied the deployable optical telescope, or DOT. The telescope represents the future of foldable, large aperture optics.

In 1995, six researchers at the directorate wanted to build a larger telescope for Air Force applications. Within a few months, they had completed a conceptual design structure, conducted the required analysis and began building a test bed for their vision.

The National Aeronautics and Space Administration's Hubble Telescope served as the experiment's model. Launched in April 1990 from the Space Shuttle Discovery, It measured 8 feet in diameter and resembled a large school bus. Project personnel began researching housing a similar-sized optical device in a standard launch vehicle by reducing the apparatus' dimensions to 4 feet 10 inches, through structural folding.

During the test program's first five years a limited demonstrator exhibited some of the intended technologies, but did not have true optical mirrors -- a crucial element of the project. The follow-up experiment, DOT, comprised a scale representation of the concepts developed by the six scientists five years earlier, and involved a collaboration between public and private industries.

Kodak constructed the three 60-centimeter mirrors, Shafer Corp. built the three-meter deployable secondary tower, Boeing-SVS, Inc. and CSA Engineering, Inc. integrated the demonstrator's components, as well as assembled its control systems, and the directorate provided the primary main structure. NASA also served as a key program partner.

"It really was an interdisciplinary team, and the project required one," said Dr. Lawrence Robertson, the chief of the dynamics and controls group in the space vehicles directorate. "Early on, we teamed with NASA because we realized that the DOT project was not going to require just (Air Force Research Laboratory,) but help from other federal government agencies to make it happen."

Because of the sensitivity of its three optical mirrors, the DOT resided in possibly the quietest confines in the country. To prevent minimal motion and vibration, the laboratory's floor consisted of bedrock with 50 feet of concrete poured on top. During the telescope's inaugural tests, the program added another control system to compensate for vibrations produced by a construction crew working several feet away from the 1.5 meter structure.

Arranging the mirrors to the miniscule dimension of one one-thousandth thickness of a human hair for sharper resolution proved challenging for researchers.

After four years of trial and error in folding and unfolding the three objects to the required placement specification, the program team finally reached the target benchmark.

Team members employed four optical sensors and 18 pointing devices, as well as a laser-based sensing system, which measured the position at about 10,000 times per second. For the remaining nine months of the $40 million DOT project, scientists continued to assess the correct location of the mirrors to ensure proper functioning in the space environment.

The DOT technology has been transitioned out to large aerospace companies to develop systems for the Air Force, NASA and other potential customers.

"Academia was also involved with the DOT. We brought in professors from around the country to help with the pointing algorithms. The result was a lot of new ideas and technologies for accurate positioning of structures (and) optics," Dr. Robertson said.

This breakthrough will eventually improve tactical imagery supporting joint warfighters on the battlefield.

"When all of us in the beginning saw what we had to do to get the DOT study completed, there were some doubts because it might take too long. But, we nailed it," Dr. Robertson said. "We wanted to give the warfighter better tactical imagery."

(Courtesy of Air Force Materiel Command News Service)



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