Category: 7. Science

For over a decade, NASA’s Curiosity rover has been capturing images of Mars as scientists continue to study the planet’s structures and surface.

Curiosity’s goal as it travels across Mars is to look for unique signs of life, including signs of possible ancient life on the planet.

What is it?

A vast cloud of energetic particles surrounding a cluster of galaxies that existed around four billion years after the Big Bang could help scientists discover how the early universe took shape.

But was the halo of the massive cluster of galaxies — called SpARCS104922.6+564032.5, and located 9.9 billion light-years from Earth— built by erupting supermassive black holes or a cosmic particle accelerator?

Editor’s note: Those of you in the space community know that NASA Science is facing an immense budget cut. Dozens of missions have been cancelled and many missions that are still returning valuable data are being shut off – in many cases to save a few million dollars – a tiny fraction of what it took to mount the missions in the first place. This data will be lost. In the case of New Horizons, currently traversing the outer solar system, NASA is going to forfeit a third interstellar mission (after the twin Voyagers). This latest interstellar mission would be done with a healthy spacecraft outfitted with 21st century instrumentation. We could continue to expand America’s pre-eminent exploration of interstellar space until the middle of this century. And that lead will last unchallenged for a generation or more to come. But instead we are going to shut off this explorer – and many others – long before they cease to explore the unknown.

As NASA’s New Horizons spacecraft exits the Solar System bound for interstellar space, it has traveled so far that the nearest stars have shifted markedly from their positions seen from Earth.

We demonstrated this by imaging the Proxima Centauri and Wolf 359 fields from Earth and New Horizons on 2020 April 23, when the spacecraft was 47.1 au distant. The observed parallaxes for Proxima Centauri and Wolf 359 are 32.4″ and 15.7″, respectively.

These measurements are not of research grade, but directly seeing large stellar parallaxes between two widely separated simultaneous observers is vividly educational. Using the New Horizons positions of the two stars alone, referenced to the three-dimensional model of the solar neighborhood constructed from Gaia DR3 astrometry, further provides the spacecraft spatial position relative to nearby stars with 0.44 au accuracy.

The range to New Horizons from the Solar System barycenter is recovered to 0.27 au accuracy, and its angular direction to 0.4^∘ accuracy, when compared to the precise values from NASA Deep Space Network tracking. This is the first time optical stellar astrometry has been used to determine the three-dimensional location of a spacecraft with respect to nearby stars, and the first time any method of interstellar navigation has been demonstrated for a spacecraft on an interstellar trajectory.

We conclude that the best astrometric approach to navigating spacecraft on their departures to interstellar space is to use a single pair of the closest stars as references, rather than a large sample of more distant stars.

The location of New Horizons on 2020 April 23 as derived from the directions to Proxima Cen and Wolf 359 measured from the spacecraft. The view is from the ecliptic north pole; the vertical axis is at zero RA. Gray circles show the orbits of the outer planets. Line of position P passes through the Gaia 3-D location of Proxima Cen, in the direction measured from the spacecraft; the observations of Proxima Cen thus constrain the spacecraft to lie on line P. Similarly, observations of Wolf 359 constrain the spacecraft to lie on line of position W. The faint dotted lines show how much P and W would be displaced by a 1 ′′ change in line direction; the transverse displacement in au is just the distance to the star in pc (1.30 for P, 2.41 for W). The trajectory NH is the actual path of the spacecraft from launch in 2006 through 2023, marked with yearly tickmarks. The actual angular uncertainties are much less than the 1′′ indicated by the dotted lines. Line P is inclined ∼ 45^◦ from the ecliptic plane; line W and the NH trajectory are inclined less than 2^◦ from the ecliptic. — — astro-ph.IM

The Earth-based and New Horizons images of Proxima Centauri and its star field are shown side by side to demonstrate the large Earth-spacecraft parallax. Proxima Cen is the bright star near the center of the field. The field shown is 10′ × 10′ . North is at the top. The image pairs have been prepared to a common image scale, field, and orientation so that the parallax can also be recognized with stereo imaging. The top pair is positioned for “cross-eyed” viewing. Crossing your eyes to view the NH-based image with the left eye, and the Earth-based image with the right eye, will create the appearance of Proxima Cen floating in front of the background stars. The two images are swapped in position in the bottom row to allow for parallel viewing. In this case, the left eye views the left panel, and the right eye the right panel. Parallel viewing can also be done by mounting the images in a stereoscopic viewer. Our experience on the New Horizons team is that there is no clear preference between cross-eyed vs. parallel viewing. — astro-ph.IM

Tod R. Lauer, David H. Munro, John R. Spencer, Marc W. Buie, Edward L. Gomez, Gregory S. Hennessy, Todd J. Henry, George H. Kaplan, John F. Kielkopf, Brian H. May, Joel W. Parker, Simon B. Porter, Eliot Halley Vrijmoet, Harold A. Weaver, Pontus Brandt, Kelsi N. Singer, S. Alan Stern, Anne. J. Verbiscer, Pedro Acosta, Nicolás Ariel Arias, Sergio Babino, Gustavo Enrique Ballan, Víctor Ángel Buso, Steven J. Conard, Daniel Das Airas, Giorgio Di Scala, César Fornari, Jossiel Fraire, Brian Nicolás Gerard, Federico González, Gerardo Goytea, Emilio Mora Guzmán, William Hanna, William C. Keel, Aldo Kleiman, Anselmo López, Jorge Gerardo Machuca, Leonardo Málaga, Claudio Martínez, Denis Martinez, Raúl Meliá, Marcelo Monópoli, Marc A. Murison, Leandro Emiliano Fernandez Pohle, Mariano Ribas, José Luis Ramón Sánchez, Sergio Scauso, Dirk Terrell, Thomas Traub, Pedro Oscar Valenti, Ángel Valenzuela, Ted von Hippel, Wen Ping Chen, Dennis Zambelis

Comments: Accepted for publication in the Astronomical Journal. The introduction includes a link to the Jupyter notebook and images used in the analysis
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2506.21666 [astro-ph.IM] (or arXiv:2506.21666v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2506.21666
Focus to learn more
Submission history
From: Tod R. Lauer
[v1] Thu, 26 Jun 2025 18:00:02 UTC (4,720 KB)
https://arxiv.org/abs/2506.21666

Astrobiology, Interstellar, Stellar Cartography,

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.

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 1/10^th 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.

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.

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).

NASA has extended recovery efforts for its stricken Lunar Trailblazer spacecraft to mid-July, but is warning that if the probe remains silent, the mission could end.

Contact with the small satellite was lost the day after its launch on February 26. Controllers were initially able to receive engineering data from the vehicle, but the telemetry indicated power system issues, and the spacecraft eventually fell silent.

The theory is that the spacecraft entered a low-power state, with its solar panels incorrectly oriented, thus generating insufficient power to charge its batteries.

Since then, the Lunar Trailblazer team has attempted to contact the probe. If control can be regained, the instruments are still functional, and the propulsion system is not frozen, there’s a chance that the spacecraft can be inserted into an elliptical orbit and complete its lunar science objectives – if not the mission as initially envisaged.

Ground-based optical and radio telescopes have been used to track the satellite’s position and rate of spin, and radio antennas belonging to various organizations worldwide have provided time to listen for a signal from the Lunar Trailblazer.

However, the further away it travels, the weaker its communication with Earth becomes, should it be re-established, to the point where controllers would be unable to command the probe or receive telemetry.

A few extra weeks were added to recovery efforts after updated models suggested that light conditions might be right for the probe to generate enough power for its batteries to reach an operational state and its radio to switch on. However, once those weeks are exhausted, NASA will have to consider its options, including ending the mission.

The Lunar Trailblazer is a 200 kg (440 lb) spacecraft designed to generate high-resolution maps of the Moon’s surface to determine the location of water, its abundance, form, and how it changes over time. It was supposed to orbit the Moon approximately 100 km (60 miles) from the surface.

The mission came out of NASA’s SIMPLEx (Small Innovative Missions for Planetary Exploration) competition, which was all about low-cost, high-risk missions that could ride share with primary payloads. SIMPLEx missions also have less stringent requirements for oversight and management. ®

New high‑pressure experiments show that the chemical recipe of Earth’s deep mantle has barely budged since our planet formed 4.5 billion years ago.

The finding, drawn from crushed rock samples held at pressures rivaling those 1,800 miles down, reshapes ideas about how oxygen and metals move through our planet’s interior.

The research centers on bridgmanite, the most common mineral on Earth yet one that never reaches the surface.

After being squeezed until it glowed at 4,000 °F, the mineral kept almost the same ratio of ferric iron to total iron that scientists infer for early Earth, hinting at an enduring redox balance.

Lead author Fei Wang, Bavarian Research Institute of Experimental Geochemistry & Geophysics, and colleagues combined the lab data with thermodynamic models to track iron chemistry through the lower mantle.

Why Earth’s mantle matters

Geologists care about the lower mantle because it locks in the planet’s earliest history and influences how volcanoes feed the surface.

If its chemistry drifts over time, gases like carbon dioxide and water entering the atmosphere would shift too, altering climate and habitability.

Early models suggested that violent mixing during a global magma ocean phase might have reset the interior’s redox state.

Yet samples of ancient diamonds indicate the volatile mix inside Earth has matched today’s values since at least 2.7 billion years ago. Those diamonds act as time capsules, trapping mantle gases long before complex life emerged.

Bridgmanite under crushing pressure

In the new study, the team packed powdered silicates with tiny metal sensors, then drove them to 730,000 pounds per square inch inside a multi‑anvil press.

Temperature was held near 2,300 K so the crystals mirrored lower‑mantle conditions.

Despite equilibrium with metallic iron, bridgmanite still carried roughly 17 percent of its iron in the oxidized state, a figure almost identical across pressures from 400 to 1,000 miles depth.

Similar laser‑heated diamond‑anvil experiments last year reached the same conclusion, showing ferric‑iron ratios unchanged by pressure across the mid‑mantle.

The key variable turned out to be temperature: hotter crystals shed ferric iron, while cooler ones gain it.

That trend explains why Earth’s current lower mantle may sit near the threshold where metallic iron precipitates, matching seismic hints of scattered iron blobs.

Earth’s mantle in the early days

Thermodynamic modeling stitched the lab data into a planet‑wide picture, simulating how the Fe³⁺/ΣFe ratio evolved as the magma ocean cooled.

The results imply that only 0.2 weight percent of metallic iron separated into the core while the rest of the solid mantle held steady.

Such a small escape fits with earlier calculations showing that iron droplets wet grain boundaries and percolate downward quickly at near‑solidus temperatures.

Once the mantle fully crystallized, further oxidation stalled because the dominant substitution of Fe³⁺ and Al³⁺ in bridgmanite is remarkably pressure‑insensitive.

This built‑in stability means later plate recycling and plume activity simply stir existing chemistry rather than overhaul it.

As a result, the upper mantle’s oxygen level rose to present values through slow mixing instead of fresh inputs.

Stability over time

Observations outside the lab echo the model. Seismic studies find that the bulk sound speed of the mid‑mantle matches compositions with constant iron valence, leaving little room for dramatic chemical layering.

“These processes played a major role in the Earth being surrounded by an oxygen‑rich atmosphere,” said Dr. Catherine McCammon of the University of Bayreuth.

Volatile ratios in volcanic gases also line up with Archean samples, reinforcing the idea of a long‑lived interior equilibrium. 

Diamond data add another hint: helium, neon, and argon proportions trapped in 2.7‑billion‑year‑old stones mirror those in modern basalts.

“This was a surprising result. It means the volatile‑rich environment we see around us today is not a recent development,” noted Dr. Michael Broadley of University of Lorraine.

Plate tectonics and life on Earth

A chemically constant interior simplifies models of atmospheric evolution because surface reservoirs can be traced back to a fixed deep source.

It also suggests that catastrophic oxidation events were not required to set the stage for photosynthesis.

For plate tectonics, a stable redox budget means that slabs sinking today enter roughly the same environment as their ancient counterparts.

That constancy helps seismologists interpret deep‑Earth images without invoking hidden chemical layers.

Earth’s mantle still holds mysteries

Researchers now want to know whether small pockets of iron‑rich melt lurk near the core‑mantle boundary and how they affect heat flow.

Upcoming experiments that combine synchrotron X‑rays with electrical measurements aim to pin down the conductivity of iron‑bearing bridgmanite at even higher temperatures.

Another open issue is how water cycles through Earth’s deep mantle without altering its oxidation state, a puzzle that links deep‑Earth chemistry to ocean volumes over geologic time.

Answers will refine our picture of a planet that, deep inside, appears to have kept the same recipe since birth.

The study is published in Nature Geoscience.

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Launched on Aug. 12, 2005, NASA’s Mars Reconnaissance Orbiter has been operating for nearly 20 years of operations. By rolling up to 30° mid-flight, it’s been able to aim its instruments at specific surface targets, capturing detailed images of landing zones, craters, and more.

After nearly 20 years in operation, NASA’s Mars Reconnaissance Orbiter (MRO) is still going strong. It’s now performing new rolling maneuvers to enhance its scientific capabilities, allowing it to gather even more data as it continues circling Mars.

New computer models suggested that the Mars Reconnaissance Orbiter (MRO) could get better radar data if it rolled farther than usual. So, NASA gave it a try, letting MRO flip almost upside down with a 120° roll. This bold move helps the orbiter look deeper underground, searching for things like liquid or frozen water.

But pulling off this trick isn’t easy. MRO has five scientific instruments, and they don’t all point the same way. So when the orbiter turns to help one tool look at a specific spot, the others may not get the best view. It’s like turning your head to focus on one thing while the rest of your senses look somewhere else.

Every time NASA’s Mars orbiter rolls to aim its instruments, it’s not a random move. It’s carefully planned weeks. Teams coordinate who gets to collect data and when, like scheduling time on a shared telescope.

To make it all happen, an onboard algorithm thinks. It checks where MRO is over Mars and commands it to roll so the right instrument points at the right spot. At the same time, it tells the spacecraft’s solar panels to follow the Sun and its antenna to stay linked with Earth, so it doesn’t lose power or contact.

For super-sized rolls, like the new 120° flips, it takes extra planning to keep everything safe. But it’s worth it. These big moves let MRO’s SHARAD radar look even deeper beneath the Martian surface, searching for clues like underground water.

Ideally, MRO’s radar tool, called SHARAD, would always point straight down to scan below Mars’ surface. But because of limited space and the need to avoid messing with other instruments, SHARAD was tucked onto the space-facing edge of the spacecraft.

In that spot, it still works, but not as well. When MRO rolls, it shifts its body out of the way, giving SHARAD a much better line of sight. This simple tilt makes a big difference, letting the radar see deeper underground and gather clearer data.

Ice trails on Mars: MRO captures ice-flow patterns

SHARAD can look over a mile below the Martian surface. It helps scientists tell the difference between rock, sand, and ice, especially water ice, which could be useful for future astronauts to dig up and turn into rocket fuel or drinking water.

But SHARAD couldn’t reach everywhere. Some parts of Mars remained just out of view.

So, in 2023, the team tried something bold: they rotated the spacecraft a full 120 degrees, flipping SHARAD’s antenna directly toward the planet. This new move gave the radar a clearer line of sight, and it worked. The signal became up to 10 times stronger, letting scientists see much deeper underground and gather better data about Mars’ hidden layers.

When NASA’s Mars orbiter does a giant 120° roll, it can’t point its antenna at Earth or its solar panels at the Sun. That’s because those parts can’t twist far enough without risking damage. So, during these rolls, the panels are parked to avoid hitting the spacecraft, and the orbiter runs on battery power alone.

That’s why each big role needs careful planning to make sure there’s enough energy to pull it off safely.

Because of the complexity, the team only does one or two of these big rolls per year. But engineers are working on ways to make the process smoother so they can do it more often.

As MRO nears its 20th year in space, it’s still pushing boundaries. These bold new moves are helping scientists learn even more about Mars, proving that this veteran spacecraft still has plenty of discoveries left in its orbit.

Journal Reference

1. Nathaniel E. Putzig, Gareth A. Morgan, Matthew R. Perry, Bruce A. Campbell, et al. SHARAD Illuminates Deeper Martian Subsurface Structures with a Boost from Very Large Rolls of the MRO Spacecraft. The Planetary Science Journal. DOI 10.3847/PSJ/addbe1

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.

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 1/10^th 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.

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.

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).