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Three selected for national hypersonic centers
NASA's Mach 5+ X-43A, first flown on March 27, 2004
NASA’s Aeronautics Research Mission Directorate and the Air Force Research Laboratory’s Office of Scientific Research have tapped the University of Virginia in Charlottesville, Texas A&M University in College Station and Teledyne Scientific & Imaging LLC of Thousand Oaks, Calif. to be the nation’s hypersonic science centers.
The new centers will focus on Mach 5 aircraft using “air-breathing” propulsion. Of special interest to people in the ceramics field is that these centers will be spending a lot of time working on the materials and structures of such aircraft.
“NASA and the Air Force Research Laboratory have made a major commitment to advancing foundational hypersonic research and training the next generation of hypersonic researchers,” said James Pittman, principal investigator for the Hypersonics Project of NASA’s Fundamental Aeronautics Program at NASA’s Langley Research Center in Hampton, Va. “Our joint investment of $30 million over five years will support basic science and applied research that improves our understanding of hypersonic flight.”
Researchers hope to eventually create an engine that could propel aircraft to speeds exceeding 12 times the speed of sound.
Each center will have a different specialty. The UVA center will be the National Center for Hypersonic Combined Cycle Propulsion. Researchers from the University of Pittsburgh, George Washington University, Cornell University, Stanford University, Michigan State University, SUNY Buffalo, North Carolina State University, ATK GASL Inc. (Ronkonkoma, N.Y.), NIST and Boeing will join the UVA effort.
Teledyne Scientific & Imaging will be the National Hypersonic Science Center for Hypersonic Materials and Structures. Team members include researchers from the University of California, University of Colorado in Boulder, the University of Miami, Princeton University, Missouri University of Science and Technology, the University of California, Berkeley and the University of Texas.
Texas A&M’s project, the soon-to-be National Center for Hypersonic Laminar-Turbulent Transition will concentrate in boundary layer control research. It’s partners include researchers from the California Institute of Technology, the University of Arizona, the UCLA and Case Western Reserve University.
In the past, the work by NASA and the AFOSR sometimes overlapped. The announcement about establishing the three centers follows a review of each other’s technology portfolios.
“The Air Force Office of Scientific Research is very excited to continue our partnership with NASA,” said John Schmisseur, manager for the Air Force Office of Scientific Research’s Hypersonics and Turbulence Program. “The centers represent our first effort to sponsor research jointly.”
NASA and the AFOSR will each kick in approximately $15 million to fund the centers at the rate of about $2 million per year per center. The funding can be renewed for up to five years. NASA and AFOSR received more than 60 proposal before selecting UVA, Texas A&M and Teledyne.
Teledyne is clearly pleased with making the cut.
“For over three decades, Teledyne Scientific & Imaging has been a leader in the development of novel materials such as ultra-high performance ceramic composites, polymer composites, and multi-functional materials,” said Robert Mehrabian, chairman, president, and chief executive officer of Teledyne Technologies. “Teledyne is honored by our selection as a National Hypersonic Science Center from an extremely competitive group of respondents. This effort supports Teledyne’s strategy of leadership in areas of fundamental science and technology critical to the U.S. Government.”
According to its abstract, Teledyne says it will lead an effort to “[R]evolutionize the design of hypersonic vehicles by creating a new class of hybrid, hierarchical materials that achieve substantial breakthroughs in oxidation resistance, maximum useable temperature, and maximum supportable heat flux.”
The company says this will cover:
- Novel routes for combining different materials in tailored morphologies,
- New experimental methods that will enable the direct visualization of the mechanisms that control a material’s performance,
- Multi-scale probabilistic model formulations that can simulate mechanisms at all length scales with high fidelity,
- Novel methods of net-shape processing, and
- The combination of experiments and multi-scale models into a virtual test system that will transform the way in which materials are designed and qualified.
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Air Force cuts costs, boosts performance of aerospace mirrors
NASA's James Webb Space Telescope features mirror segments fabricated under MMD’s Advance Mirror System Demonstrator Program. (Credit: NASA/E. Given)
Air Force researchers are investigating ways to boost the performance of aerospace mirrors, while cutting in half the cost and time required to manufacture them. No wonder! It takes about two years and nearly one million dollars to produce a one-meter, lightweight glass aerospace mirror, according to the AF Research Lab’s Materials and Manufacturing Directorate. The MMD has responsibility for developing, producing and maintaining materials used in AF aircraft, missiles, rockets and ground-based military systems.
Aerospace mirrors are key components of everything from surveillance-and-reconnaissance systems to transformational communications networks, directed-energy technology, laser-radar devices and large, high-powered telescopes. Hence MMD’s concern with manufacturing these mirrors in the most efficient and cost-effective way. Until recently, “state-of-the-art” mirror manufacturing meant using monolithic glass. Appealing because of its ability to be bent into diverse shapes, precisely ground and “polished to an angstrom-level surface finish,” monolithic glass also possesses another important asset - a “coefficient of thermal expansion that can be chemically tailored to be near zero ppm/°C,” say MMD’s Lawrence Matson and Pete Meltzer Jr. This coefficient of thermal expansion “minimizes distortion of the optical surface caused by thermal excursions during service,” Matson and Meltzer explain. This advantage has enabled MMD to form mirrors with an areal density of about 15 kg/m2, an accomplishment that took place during MMD’s Advance Mirror System Demonstrator Program.
During this program, MMD was able to achieve a 50 percent reduction in mirror weight and fabrication costs compared with those required for construction of the Hubble Space Telescope. Today, however, it appears MMD researches have maxed-out the benefits of monolithic glass. It’s unlikely any more weight or cost reductions can be squeezed from monolithic glass because its structure offers low-elastic modulus, strength and fracture toughness,” say Matson and Meltzer. “Continued lightweighting would result in very fragile structures that would be difficult to polish and would fail catastrophically with a single handling mishap or during launch.” And, so, like fickle fans abandoning an aging superstar, AF researchers are abandoning monolithic glass in favor of new material up-and-comers.
To date, the most promising of these have been ceramic, metal and polymer hybrids and composite materials produced in one of two ways - by using either replicated nanolaminate foil technology pioneered by government labs or by sol-polymer-spinning technology. In either case, Matson and Meltzer say CTE matching is mandatory for success. “Both of these approaches require materials that are CTE-matched in order to obtain and keep the correct contour and smoothness of the optical surface during fabrication and operation,” they advise, indicating MMD’s focus on finding new foil chemistries with CTEs in the zero to 3ppm/°C range. MMD researchers also have discovered that replicated nanolaminate hybrid/composite mirror systems require “CTE-tailored bonding agents” to connect the replicated foil to unpolished structural substrates. To solve this problem, MMD researchers are creating “nanosized, negative CTE particles that can be uniformly dispersed in potential bonding medium, such as organic and inorganic polymers, aero gels and glass sols [and] could also be used to spin an optical surface of visible quality onto unpolished structural substrates,” the researchers said. The two have found they must use nano-sized powders to assure “uniform dispersion and to minimize print-through distortions on the optical surface.” With material solutions in the works, the MMD research team is now turning its attention to finding uniform, stress-free, reflective coatings and dielectric stacks for large mirror systems. It believes the result will be lighter, better, cheaper and faster-to-make aerospace mirrors suitable for any DOD or NASA application.
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Learning from lizards how to improve dry adhesives
Change in vertically-aligned multi-walled carbon nanotubes during adhesion measurements.
What can a team of highly trained researchers from four different U.S. universities learn from the feet of a gecko lizard? According to the researchers, how to improve carbon nanotube-based material so that, for the first time, it demonstrates “directionally varied (anisotropic) adhesive force” and gripping power nearly three times the level of existing nanotube dry adhesives.
The team - comprised of researchers from the University of Dayton, the Georgia Institute of Technology, the Air Force Research Lab and the University of Akron - describes its achievement in a paper published in the Oct. 10 edition of Science magazine.
As Science reports, the team believes their advance could lead to solder-free connections between electronic devices, longer-lasting adhesives for use in outer space and a broad range of other important applications.
In the article, team members explain that a gecko’s ability to scale vertical walls is due to atomic-scale van der Waals interactions that occur naturally in the microscopic hairs on the lizard’s toes.
These hairs - actually minute setae - give the gecko resistance to perpendicular shear force, enabling it to grab vertical surfaces with surprising strength. The setae also allow the gecko to easily release its strong hold.
By manipulating carbon nanotubes to simulate and intensify the anisotropic adhesive forces at work in gecko hairs, the team has created a carbon nanotube dry adhesive that is “ten times better than a real gecko at resisting perpendicular shear forces.”
According to team member Zhong Lin Wang, a Regents Professor in Georgia Tech’s School of Material Science and Engineering, the newly developed adhesive’s performance depends on the use of “rationally designed multi-walled carbon nanotubes formed into arrays with curly entangled tops.”
Wang likens the tangled tops to a “jungle of vines” that replicates the structure of a gecko’s foot, down to its “branching hairs of different diameters.”
These tangled tops become aligned with a surface when pressed against it, significantly increasing the contact area between the tops and the surface, Wang says.
Wang says, “When lifted off the surface in a direction parallel to the main body of nanotubes, only the [nanotube] tips remain in contact [with the surface], minimizing the forces of attraction.” He claims this “allows us to truly mimic what the gecko does naturally.”
Wang explains that, “When you have line contact along [a surface], you have van der Waals forces acting along the entire length of the nanotubes but, when you have a point contact, the van der Waals forces act only at the tip of the nanotubes.”
As the Science article reports, the researchers have tested their new adhesive’s grip on a number of surfaces, including glass, polymer, Teflon and rough sand paper. Wang says they found it measured up to 100 newtons per square centimeter in the shear direction and only 10 newtons per square centimeter in the normal direction. The team’s conclusion, he says, is that resistance to shear increases with nanotube length, while resistance to normal force is independent of tube length.
Funded by NSF, the project is led by the University of Dayton’s Liming Dai, the Wright Brothers Institute Endowed Chair in the UD’s School of Engineering. The research team also includes the UD’s Liangti Qu, Morley Stone from the Air Force Research Lab and Zhenhai Xia from the University of Akron.
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