IMAGE CAPTION: [http://www.vs.afrl.af.mil/News/Images/06-03.jpg (108KB)] Photograph displaying the deployable optical telescope’s three, 60 centimeter, optical mirrors with the laser-based sensing system. (U.S. Air Force photo)
Space Vehicles Directorate’s research on the deployable optical telescope validates the placement of a large system in a standard launch vehicle to ultimately provide enhanced imagery to the joint warfighter
Positioning three delicate, circular mirrors to one one-thousandth of the width of a human hair consistently challenged scientists at the Space Vehicles Directorate, Kirtland Air Force Base, N.M., during their five-year study of the deployable optical telescope (DOT), a 1.5 meter (approximately 4.9 feet) in size demonstrator, which represents the future of foldable, larger aperture optics housed in existing launch vehicles.
One year ago, the research team, however, discovered a breakthrough for the complex experiment, which successfully ended last fall, and the technology advancement will eventually produce significantly improved tactical imagery supporting the joint warfighter 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 to getting it done because it might take too long, but we nailed it,” said Dr. Lawrence “Robbie” Robertson, chief, Dynamics and Controls Group, Space Vehicles Directorate, Air Force Research Laboratory. “We wanted to give the warfighter better tactical imagery.”
In 1995, a group of six researchers serving at the Space Vehicles Directorate desired to construct a larger telescope for the Air Force for applications in the cosmos, and within a few months, they had completed a conceptual design structure, conducted the required analysis, and initiated the building of a test bed for their vision. Serving as the experiment’s model, the National Aeronautics and Space Administration’s Hubble Telescope, launched in April 1990 from the Space Shuttle Discovery’s cargo bay, and with a projected mission duration of 20 years, measured 2.4 meters (8 feet) in diameter and resembled a large school bus. On the other hand, for cost effectiveness, project personnel began investigating the potential housing of a similar sized optical device in a standard launch vehicle by reducing the apparatus’ dimensions through structural folding.
During the test program’s first five years, a limited demonstrator, the precision deployable optical structure (PDOS), exhibited, primarily through software and structural evaluations, some of the intended technologies, but did not have true optical mirrors, a crucial element. The follow-up experiment, the 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. For example, 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 Space Vehicles Directorate provided the primary main structure. NASA also served as a key program partner.
“The DOT project pulled together the best and brightest in AFRL today. It really was an interdisciplinary team, and the project required one,” said Dr. Robertson. “Early on, we teamed with NASA because we realized that the DOT project was not going to require just AFRL, 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 other vibrations produced by a construction crew working several feet away from the 1.5 meter structure. Nevertheless, another major challenge, arranging the mirrors to the miniscule dimension of one one-thousandth thickness of a human hair for sharper resolution, tested the researchers’ resilience and patience. After four years of trial and error in folding and unfolding the three objects to the required placement specification, the program finally reached the target benchmark by employing 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.
While the DOT experiment occurred, NASA started work on the proposed successor to the Hubble, The James Webb Space Telescope, a projected 6.3 meter in-length folding optical device slated for operations early in the next decade. Technologies advanced by the DOT have already been transitioned to enhance the planned, high performance telescope.
“AFRL sees the DOT as technology complete and has been transitioned out to large aerospace companies to develop and use to build systems for the Air Force, NASA, and other potential customers,” said the Dynamics and Controls Group chief. “Academia was also involved with the DOT. We brought in professors from around the country to help with the pointing algorithms, and the result was a lot of new ideas and technologies for accurate positioning of structures/optics were spawned.”
For the DOT project team, the phrase “patience is bitter, but its fruit is sweet,” aptly describes the dedication, determination, and commitment displayed during the past 10 years. Mission accomplished.
