02 Jul 2025
Company Allvar working with NASA on NTE space telescope optics; other applications are possible.
A 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; planets beyond our solar system (exoplanets) that could support life. Over the past 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 of the light, and can detect various shifts in the light caused by gases in the planetary atmosphere.
To successfully detect habitable exoplanets, NASA’s future Habitable Worlds Observatory (HWO) will need a contrast ratio of one to one billion. This in turn 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 Allvar Alloys, College Station, TX, and Syracuse, NY, 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.
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 HWO.
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 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. For example, Allvar’s Alloy 30 exhibits a -30 ppm/°C coefficient of thermal expansion 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. In contrast, aluminum expands at +23 ppm/°C.
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.
Thermal stability ‘improved up to 200 times’
Calculations have indicated that integrating 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, and the nickel–iron alloy, Invar.
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 HWO. 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 change in the mirror’s shape across a 28K temperature change.
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.