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By NASA
5 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
The Swept Wing Flow Test model, known as SWiFT, with pressure sensitive paint applied, sports a pink glow under ultraviolet lights while tested during 2023 in a NASA wind tunnel at Langley Research Center in Virginia.NASA / Dave Bowman Many of us grew up using paint-by-number sets to create beautiful color pictures.
For years now, NASA engineers studying aircraft and rocket designs in wind tunnels have flipped that childhood pastime, using computers to generate images from “numbers-by-paint” – pressure sensitive paint (PSP), that is.
Now, advances in the use of high-speed cameras, supercomputers, and even more sensitive PSP have made this numbers-by-paint process 10,000 times faster while creating engineering visuals with 1,000 times higher resolution.
So, what’s the big difference exactly between the “old” capability in use at NASA for more than a decade and the “new?”
“The key is found by adding a single word in front of PSP, namely ‘unsteady’ pressure sensitive paint, or uPSP,” said E. Lara Lash, an aerospace engineer from NASA’s Ames Research Center in California’s Silicon Valley.
With PSP, NASA researchers study the large-scale effects of relatively smooth air flowing over the wings and body of aircraft. Now with uPSP, they are able to see in finer detail what happens when more turbulent air is present – faster and better than ever before.
In some cases with the new capability, researchers can get their hands on the wind tunnel data they’re looking for within 20 minutes. That’s quick enough to allow engineers to adjust their testing in real time.
Usually, researchers record wind tunnel data and then take it back to their labs to decipher days or weeks later. If they find they need more data, it can take additional weeks or even months to wait in line for another turn in the wind tunnel.
“The result of these improvements provides a data product that is immediately useful to aerodynamic engineers, structural engineers, or engineers from other disciplines,” Lash said.
Robert Pearce, NASA’s associate administrator for aeronautics, who recently saw a demonstration of uPSP-generated data displayed at Ames, hailed the new tool as a national asset that will be available to researchers all over the country.
“It’s a unique NASA innovation that isn’t offered anywhere else,” Pearce said. “It will help us maintain NASA’s world leadership in wind tunnel capabilities.”
A technician sprays unsteady pressure sensitive paint onto the surface of a small model of the Space Launch System in preparation for testing in a NASA wind tunnel.NASA / Dave Bowman How it Works
With both PSP and uPSP, a unique paint is applied to scale models of aircraft or rockets, which are mounted in wind tunnels equipped with specific types of lights and cameras.
When illuminated during tests, the paint’s color brightness changes depending on the levels of pressure the model experiences as currents of air rush by. Darker shades mean higher pressure; lighter shades mean lower pressure.
Cameras capture the brightness intensity and a supercomputer turns that information into a set of numbers representing pressure values, which are made available to engineers to study and glean what truths they can about the vehicle design’s structural integrity.
“Aerodynamic forces can vibrate different parts of the vehicle to different degrees,” Lash said. “Vibrations could damage what the vehicle is carrying or can even lead to the vehicle tearing itself apart. The data we get through this process can help us prevent that.”
Traditionally, pressure readings are taken using sensors connected to little plastic tubes strung through a model’s interior and poking up through small holes in key places, such as along the surface of a wing or the fuselage.
Each point provides a single pressure reading. Engineers must use mathematical models to estimate the pressure values between the individual sensors.
With PSP, there is no need to estimate the numbers. Because the paint covers the entire model, its brightness as seen by the cameras reveals the pressure values over the whole surface.
A four-percent scale model of the Space Launch System rocket is tested in 2017 using unsteady Pressure Sensitive Paint inside the 11-foot by 11-foot Unitary Plan Wind Tunnel at NASA’s Ames Research Center in California.NASA / Dominic Hart Making it Better
The introduction, testing, and availability of uPSP is the result of a successful five-year-long effort, begun in 2019, in which researchers challenged themselves to significantly improve the PSP’s capability with its associated cameras and computers.
The NASA team’s desire was to develop and demonstrate a better process of acquiring, processing, and visualizing data using a properly equipped wind tunnel and supercomputer, then make the tool available at NASA wind tunnels across the country.
The focus during a capability challenge was on NASA’s Unitary Plan Facility’s 11-foot transonic wind tunnel, which the team connected to the nearby NASA Advanced Supercomputing Facility, both located at Ames.
Inside the wind tunnel, a scale model of NASA’s Space Launch System rocket served as the primary test subject during the challenge period.
Now that the agency has completed its Artemis I uncrewed lunar flight test mission, researchers can match the flight-recorded data with the wind tunnel data to see how well reality and predictions compare.
With the capability challenge officially completed at the end of 2024, the uPSP team is planning to deploy it to other wind tunnels and engage with potential users with interests in aeronautics or spaceflight.
“This is a NASA capability that we have, not only for use within the agency, but one that we can offer industry, academia, and other government agencies to come in and do research using these new tools,” Lash said.
NASA’s Aerosciences Evaluation and Test Capabilities portfolio office, an organization managed under the agency’s Aeronautics Research Mission Directorate, oversaw the development of the uPSP capability.
Watch this uPSP Video
About the Author
Jim Banke
Managing Editor/Senior WriterJim Banke is a veteran aviation and aerospace communicator with more than 40 years of experience as a writer, producer, consultant, and project manager based at Cape Canaveral, Florida. He is part of NASA Aeronautics' Strategic Communications Team and is Managing Editor for the Aeronautics topic on the NASA website.
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Last Updated Jul 03, 2025 EditorJim BankeContactJim Bankejim.banke@nasa.gov Related Terms
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By NASA
7 min read
A New Alloy is Enabling Ultra-Stable Structures Needed for Exoplanet Discovery
A unique new material that shrinks when it is heated and expands when it is cooled could help enable the ultra-stable space telescopes that future NASA missions require to search for habitable worlds.
Advancements in material technologies are needed to meet the science needs of the next great observatories. These observatories will strive to find, identify, and study exoplanets and their ability to support life. Credit: NASA JPL One of the goals of NASA’s Astrophysics Division is to determine whether we are alone in the universe. NASA’s astrophysics missions seek to answer this question by identifying planets beyond our solar system (exoplanets) that could support life. Over the last two decades, scientists have developed ways to detect atmospheres on exoplanets by closely observing stars through advanced telescopes. As light passes through a planet’s atmosphere or is reflected or emitted from a planet’s surface, telescopes can measure the intensity and spectra (i.e., “color”) of the light, and can detect various shifts in the light caused by gases in the planetary atmosphere. By analyzing these patterns, scientists can determine the types of gasses in the exoplanet’s atmosphere.
Decoding these shifts is no easy task because the exoplanets appear very near their host stars when we observe them, and the starlight is one billion times brighter than the light from an Earth-size exoplanet. To successfully detect habitable exoplanets, NASA’s future Habitable Worlds Observatory will need a contrast ratio of one to one billion (1:1,000,000,000).
Achieving this extreme contrast ratio will require a telescope that is 1,000 times more stable than state-of-the-art space-based observatories like NASA’s James Webb Space Telescope and its forthcoming Nancy Grace Roman Space Telescope. New sensors, system architectures, and materials must be integrated and work in concert for future mission success. A team from the company ALLVAR is collaborating with NASA’s Marshall Space Flight Center and NASA’s Jet Propulsion Laboratory to demonstrate how integration of a new material with unique negative thermal expansion characteristics can help enable ultra-stable telescope structures.
Material stability has always been a limiting factor for observing celestial phenomena. For decades, scientists and engineers have been working to overcome challenges such as micro-creep, thermal expansion, and moisture expansion that detrimentally affect telescope stability. The materials currently used for telescope mirrors and struts have drastically improved the dimensional stability of the great observatories like Webb and Roman, but as indicated in the Decadal Survey on Astronomy and Astrophysics 2020 developed by the National Academies of Sciences, Engineering, and Medicine, they still fall short of the 10 picometer level stability over several hours that will be required for the Habitable Worlds Observatory. For perspective, 10 picometers is roughly 1/10th the diameter of an atom.
NASA’s Nancy Grace Roman Space Telescope sits atop the support structure and instrument payloads. The long black struts holding the telescope’s secondary mirror will contribute roughly 30% of the wave front error while the larger support structure underneath the primary mirror will contribute another 30%.
Credit: NASA/Chris Gunn
Funding from NASA and other sources has enabled this material to transition from the laboratory to the commercial scale. ALLVAR received NASA Small Business Innovative Research (SBIR) funding to scale and integrate a new alloy material into telescope structure demonstrations for potential use on future NASA missions like the Habitable Worlds Observatory. This alloy shrinks when heated and expands when cooled—a property known as negative thermal expansion (NTE). For example, ALLVAR Alloy 30 exhibits a -30 ppm/°C coefficient of thermal expansion (CTE) at room temperature. This means that a 1-meter long piece of this NTE alloy will shrink 0.003 mm for every 1 °C increase in temperature. For comparison, aluminum expands at +23 ppm/°C.
While other materials expand while heated and contract when cooled, ALLVAR Alloy 30 exhibits a negative thermal expansion, which can compensate for the thermal expansion mismatch of other materials. The thermal strain versus temperature is shown for 6061 Aluminum, A286 Stainless Steel, Titanium 6Al-4V, Invar 36, and ALLVAR Alloy 30.
Because it shrinks when other materials expand, ALLVAR Alloy 30 can be used to strategically compensate for the expansion and contraction of other materials. The alloy’s unique NTE property and lack of moisture expansion could enable optic designers to address the stability needs of future telescope structures. Calculations have indicated that integrating ALLVAR Alloy 30 into certain telescope designs could improve thermal stability up to 200 times compared to only using traditional materials like aluminum, titanium, Carbon Fiber Reinforced Polymers (CFRPs), and the nickel–iron alloy, Invar.
The hexapod assembly with six ALLVAR Alloy struts was measured for long-term stability. The stability of the individual struts and the hexapod assembly were measured using interferometry at the University of Florida’s Institute for High Energy Physics and Astrophysics. The struts were found to have a length noise well below the proposed target for the success criteria for the project. Credit: (left) ALLVAR and (right) Simon F. Barke, Ph.D. To demonstrate that negative thermal expansion alloys can enable ultra-stable structures, the ALLVAR team developed a hexapod structure to separate two mirrors made of a commercially available glass ceramic material with ultra-low thermal expansion properties. Invar was bonded to the mirrors and flexures made of Ti6Al4V—a titanium alloy commonly used in aerospace applications—were attached to the Invar. To compensate for the positive CTEs of the Invar and Ti6Al4V components, an NTE ALLVAR Alloy 30 tube was used between the Ti6Al4V flexures to create the struts separating the two mirrors. The natural positive thermal expansion of the Invar and Ti6Al4V components is offset by the negative thermal expansion of the NTE alloy struts, resulting in a structure with an effective zero thermal expansion.
The stability of the structure was evaluated at the University of Florida Institute for High Energy Physics and Astrophysics. The hexapod structure exhibited stability well below the 100 pm/√Hz target and achieved 11 pm/√Hz. This first iteration is close to the 10 pm stability required for the future Habitable Worlds Observatory. A paper and presentation made at the August 2021 Society of Photo-Optical Instrumentation Engineers conference provides details about this analysis.
Furthermore, a series of tests run by NASA Marshall showed that the ultra-stable struts were able to achieve a near-zero thermal expansion that matched the mirrors in the above analysis. This result translates into less than a 5 nm root mean square (rms) change in the mirror’s shape across a 28K temperature change.
The ALLVAR enabled Ultra-Stable Hexapod Assembly undergoing Interferometric Testing between 293K and 265K (right). On the left, the Root Mean Square (RMS) changes in the mirror’s surface shape are visually represented. The three roughly circular red areas are caused by the thermal expansion mismatch of the invar bonding pads with the ZERODUR mirror, while the blue and green sections show little to no changes caused by thermal expansion. The surface diagram shows a less than 5 nanometer RMS change in mirror figure. Credit: NASA’s X-Ray and Cryogenic Facility [XRCF] Beyond ultra-stable structures, the NTE alloy technology has enabled enhanced passive thermal switch performance and has been used to remove the detrimental effects of temperature changes on bolted joints and infrared optics. These applications could impact technologies used in other NASA missions. For example, these new alloys have been integrated into the cryogenic sub-assembly of Roman’s coronagraph technology demonstration. The addition of NTE washers enabled the use of pyrolytic graphite thermal straps for more efficient heat transfer. ALLVAR Alloy 30 is also being used in a high-performance passive thermal switch incorporated into the UC Berkeley Space Science Laboratory’s Lunar Surface Electromagnetics Experiment-Night (LuSEE Night) project aboard Firefly Aerospace’s Blue Ghost Mission 2, which will be delivered to the Moon through NASA’s CLPS (Commercial Lunar Payload Services) initiative. The NTE alloys enabled smaller thermal switch size and greater on-off heat conduction ratios for LuSEE Night.
Through another recent NASA SBIR effort, the ALLVAR team worked with NASA’s Jet Propulsion Laboratory to develop detailed datasets of ALLVAR Alloy 30 material properties. These large datasets include statistically significant material properties such as strength, elastic modulus, fatigue, and thermal conductivity. The team also collected information about less common properties like micro-creep and micro-yield. With these properties characterized, ALLVAR Alloy 30 has cleared a major hurdle towards space-material qualification.
As a spinoff of this NASA-funded work, the team is developing a new alloy with tunable thermal expansion properties that can match other materials or even achieve zero CTE. Thermal expansion mismatch causes dimensional stability and force-load issues that can impact fields such as nuclear engineering, quantum computing, aerospace and defense, optics, fundamental physics, and medical imaging. The potential uses for this new material will likely extend far beyond astronomy. For example, ALLVAR developed washers and spacers, are now commercially available to maintain consistent preloads across extreme temperature ranges in both space and terrestrial environments. These washers and spacers excel at counteracting the thermal expansion and contraction of other materials, ensuring stability for demanding applications.
For additional details, see the entry for this project on NASA TechPort.
Project Lead: Dr. James A. Monroe, ALLVAR
The following NASA organizations sponsored this effort: NASA Astrophysics Division, NASA SBIR Program funded by the Space Technology Mission Directorate (STMD).
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Last Updated Jul 01, 2025 Related Terms
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