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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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By European Space Agency
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By NASA
Explore This Section Earth Earth Observer Editor’s Corner Feature Articles Meeting Summaries News Science in the News Calendars In Memoriam Announcements More Archives Conference Schedules Style Guide 8 min read
ICESat-2 Applications Team Hosts Satellite Bathymetry Workshop
Introduction
On September 15, 2018, the NASA Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) mission launched from Vandenberg Air Force Base and began its journey to provide spatially dense and fine precision global measurements of our Earth’s surface elevation. Now in Phase E of NASA’s project life cycle (where the mission is carried out, data is collected and analyzed, and the spacecraft is maintained) of the mission and with almost six years of data collection, the focus shifts to looking ahead to new applications and synergies that may be developed using data from ICESat-2’s one instrument: the Advanced Topographic Laster Altimetry System (ATLAS) – see Figure 1.
Figure 1. The ATLAS instrument onboard the ICESat-2 platform obtains data using a green, photon-counting lidar that is split into six beams. Figure credit: ICESat-2 Mission Team Satellite-derived bathymetry (SDB) is the process of mapping the seafloor using satellite imagery. The system uses light penetration and reflection in the water to make measurements and estimate variations in ocean floor depths. SDB provides several advantages over other techniques used to map the seafloor (e.g., cost-effectiveness, global coverage, and faster data acquisition). On the other hand, SDB can be limited by water clarity, spatial resolution of the remote sensing measurement, and accuracy, depending on the method and satellite platform/instrument. These limitations notwithstanding, SDB can be used in a wide variety of applications, e.g., coastal zone management, navigation and safety, marine habitat monitoring, and disaster response. ICESat-2 has become a major contributor to SDB, with over 2000 journal article references to this topic to date. Now is the time to think about the state-of-the-art and additional capabilities of SDB for the future.
To help stimulate such thinking, the NASA ICESat-2 applications team hosted a one-day workshop on March 17, 2025. The workshop focused on the principles and methods for SDB. Held in conjunction with the annual US-Hydro meeting on March 17–20, 2025 at the Wilmington Convention Center in Wilmington, NC, the meeting was hosted by the Hydrographic Society of America. During the workshop the applications team brought together SDB end-users, algorithm developers, operators, and decision makers to discuss the current state and future needs of satellite bathymetry for the community. The objective of this workshop was to provide a space to foster collaboration and conceptualization of SDB applications not yet exploited and to allow for networking to foster synergies and collaborations between different sectors.
Meeting Overview
The workshop provided an opportunity for members from government, academia, and private sectors to share their SDB research, applications, and data fusion activities to support decision making and policy support across a wide range of activities. Presenters highlighted SDB principles, methods, and tools for SDB, an introduction of the new ICESat-2 bathymetric data product (ATL24), which is now available through the National Snow and Ice Data Center (NSIDC). During the workshop, the ICESat-2 team delivered a live demonstration of a web service for science data processing. Toward the end of the day, the applications team opened an opportunity for attendees to gather and discuss various topics related to SDB. This portion of the meeting was also available to online participation via Webex Webinars, which broadened the discussion.
Meeting Goal
The workshop offered a set of plenary presentations and discussions. During the plenary talks, participants provided an overview of Earth observation and SDB principles, existing methods and tools, an introduction to the newest ICESat-2 bathymetry product ATL24, a demonstration of the use of the webservice SlideRule Earth, and opportunities for open discission, asking questions and developing collaborations.
Meeting and Summary Format
The agenda of the SDB workshop was intended to bring together SDB end-users, including ICESat-2 application developers, satellite operators, and decision makers from both government and non-governmental entities to discuss the current state and future needs of the community. The workshop consisted of six sessions that covered various topics of SDB. This report is organized according to the topical focus of the plenary presentations with a brief narrative summary of each presentation included. The discussions that followed were not recorded and are not included in the report. The last section of this report consists of conclusions and future steps. The online meeting agenda includes links to slide decks for many of the presentations.
Welcoming Remarks
Aimee Neeley [NASA’s Goddard Space Flight Center (GSFC)/Science Systems and Applications Inc. (SSAI)—ICESat-2 Mission Applications Lead] organized the workshop and served as the host for the event. She opened the day with a brief overview of workshop goals, logistics, and the agenda.
Overview of Principles of SDB
Ross Smith [TCarta—Senior Geospatial Scientist] provided an overview of the principles of space-based bathymetry, including the concepts, capabilities, limitations, and methods. Smith began by relaying the history of satellite-derived bathymetry, which began with a collaboration between NASA and Jacques Cousteau in 1975, in which Cousteau used Landsat 1 data, as well as in situ data, to calculate bathymetry to a depth of 22 m (72 ft) in the Bahamas. Smith then described the five broad methodologies and their basic concepts for deriving bathymetry from remote sensing: radar altimetry, bottom reflectance, wave kinematics, laser altimetry, and space-based photogrammetry – see Figure 2. He then introduced the broad methodologies, most commonly used satellite sensors, the capabilities and limitations of each sensor, and the role of ICESat-2 in satellite bathymetry.
Figure 2. Satellite platforms commonly used for SDB. Figure credit: Ross Smith Review of SDB Methods and Tools
In this grouping of plenary presentations, representatives from different organizations presented their methods and tools for creating satellite bathymetry products.
Gretchen Imahori [National Oceanic and Atmospheric Administration’s (NOAA) National Geodetic Survey, Remote Sensing Division] presented the NOAA SatBathy (beta v2.2.3) Tool Update. During this presentation, Imahori provided an overview of the NOAA SatBathy desktop tool, example imagery, updates to the latest version, and the implementation plan for ATL24. The next session included more details about ATL24.
Minsu Kim [United States Geological Survey (USGS), Earth Resource and Observation Center (EROS)/ Kellogg, Brown & Root (KBR)—Chief Scientist] presented the talk Satellite Derived Bathymetry (SDB) Using OLI/MSI Based-On Physics-Based Algorithm. He provided an overview of an SDB method based on atmospheric and oceanic optical properties. Kim also shared examples of imagery from the SDB product – see Figure 3.
Figure 3. Three-dimensional renderings of the ocean south of Key West, FL created by adding SDB Digital Elevation Model (physics-based) to a Landsat Operational Land Imager (OLI) scene [top] and a Sentinel-2 Multispectral Imager (MSI) scene [bottom]. Figure credit: Minsu Kim Edward Albada [Earth Observation and Environmental Services GmbH (EOMAP)—Principal] presented the talk Satellite Lidar Bathymetry and EoappTM SLB-Online. The company EOMAP provides various services, including SDB, habitat mapping. For context, Albada provided an overview of EoappTM SDB-Online, a cloud-based software for creating SDB. (EoappTM SDB-online is one of several Eoapp apps and is based on the ICESat-2 photon data product (ATL03). Albada also provided example use cases from Eoapp – see Figure 4.
Figure 4.A display of the Marquesas Keys (part of the Florida Keys) using satellite lidar bathymetry data from the Eoapp SLB-Online tool from EOMAP. Figure credit: Edward Albada Monica Palaseanu-Lovejoy [USGS GMEG—Research Geographer] presented on a Satellite Triangulated Sea Depth (SaTSeaD): Bathymetry Module for NASA Ames Stereo Pipeline (ASP). She provided an overview of the shallow water bathymetry SaTSeaD module, a photogrammetric method for mapping bathymetry. Palaseanu-Lovejoy presented error statistics and validation procedures. She also shared case study results from Key West, FL; Cocos Lagoon, Guam; and Cabo Rojo, Puerto Rico – see Figure 5.
Figure 5. Photogrammetric bathymetry map of Cabo Roja, Puerto Rico displayed using the SatSeaD Satellite Triangulated Sea Depth (SaTSeaD): Bathymetry Module for NASA Ames Stereo Pipeline (ASP) module. Figure credit: Monica Palaseanu-Lovejoy Ross Smith presented a presentation on TCarta’s Trident Tools: Approachable SDB|Familiar Environment. During this presentation, Smith provided an overview of the Trident Tools Geoprocessing Toolbox deployed in Esri’s ArcPro. Smith described several use cases for the toolbox in Abu Dhabi, United Arab Emirates; Lucayan Archipelago, Bahamas; and the Red Sea.
Michael Jasinski [GSFC—Research Hydrologist] presented on The ICESat-2 Inland Water Along Track Algorithm (ATL13). He provided an overview of the ICESat-2 data product ATL13 an inland water product that is distributed by NSIDC. Jasinski described the functionality of the ATL13 semi-empirical algorithm and proceeded to provide examples of its applications with lakes and shallow coastal waters – see Figure 6.
Figure 6. A graphic of the network of lakes and rivers in North America that are measured by ICESat-2. Figure credit: Michael Jasinski ATL24 Data Product Update
Christopher Parrish [Oregon State University, School of Civil and Construction Engineering—Professor] presented on ATL24: A New Global ICESat-2 Bathymetric Data Product. Parrish provided an overview of the recently released ATL24 product and described the ATL24 workflow, uncertainty analysis, and applications in shallow coastal waters. Parrish included a case study where ATL24 data were used for bathymetric mapping of Kiriwina Island, Papua New Guinea – see Figure 7.
Figure 7. ATL24 data observed for Kiriwina Island, Papua New Guinea. Figure credit: Christopher Parrish SlideRule Demo
J. P. Swinski [GSFC—Computer Engineer] presented SlideRule Earth: Enabling Rapid, Scalable, Open Science. Swinski explained that SlideRule Earth is a public web service that provides access to on-demand processing and visualization of ICESat-2 data. SlideRule can be used to process a subset of ICESat-2 data products, including ATL24 – see Figure 8.
Figure 8. ATL24 data observed for Sanibel, FL as viewed on the SlideRule Earth public web client. Figure credit: SlideRule Earth SDB Accuracy
Kim Lowell [University of New Hampshire—Data Analytics Research Scientist and Affiliate Professor] presented on SDB Accuracy Assessment and Improvement Talking Points. During this presentation, Lowell provided examples of accuracy assessments and uncertainty through the comparison of ground measurement of coastal bathymetry to those modeled from satellite data.
Conclusion
The ICESat-2 Satellite Bathymetry workshop fostered discussion and collaboration around the topic of SDB methods. The plenary speakers presented the state-of-the-art methods used by different sectors and organizations, including government and private entities. With the release of ATL24, ICESat-2’s new bathymetry product, it was prudent to have a conversation about new and upcoming capabilities for all methods and measurements of satellite bathymetry. Both in-person and online participants were provided with the opportunity to learn, ask questions, and discuss potential applications in their own research. The ICESat-2 applications team hopes to host more events to ensure the growth of this field to maximize the capabilities of ICESat-2 and other Earth Observing systems.
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Last Updated Jun 05, 2025 Related Terms
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