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TOBIAS: Tethered Observatory for Balloon-based Imaging and Atmospheric Sampling
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By European Space Agency
The second of the Meteosat Third Generation (MTG) satellites and the first instrument for the Copernicus Sentinel-4 mission are fully integrated and, having completed their functional and environmental tests, they are now ready to embark on their journey to the US for launch this summer.
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By NASA
5 min read
Ultra-low-noise Infrared Detectors for Exoplanet Imaging
A linear-mode avalanche photodiode array in the test dewar. The detector is the dark square in the center. Michael Bottom, University of Hawai’i One of the ultimate goals in astrophysics is the discovery of Earth-like planets that are capable of hosting life. While thousands of planets have been discovered around other stars, the vast majority of these detections have been made via indirect methods, that is, by detecting the effect of the planet on the star’s light, rather than detecting the planet’s light directly. For example, when a planet passes in front of its host star, the brightness of the star decreases slightly.
However, indirect methods do not allow for characterization of the planet itself, including its temperature, pressure, gravity, and atmospheric composition. Planetary atmospheres may include “biosignature” gases like oxygen, water vapor, carbon dioxide, etc., which are known to be key ingredients needed to support life as we know it. As such, direct imaging of a planet and characterization of its atmosphere are key to understanding its potential habitability.
But the technical challenges involved in imaging Earth-like extrasolar planets are extreme. First such planets are detected only by observing light they reflect from their parent star, and so they typically appear fainter than the stars they orbit by factors of about 10 billion. Furthermore, at the cosmic distances involved, the planets appear right next to the stars. A popular expression is that exoplanet imaging is like trying to detect a firefly three feet from a searchlight from a distance of 300 miles.
Tremendous effort has gone into developing starlight suppression technologies to block the bright glare of the star, but detecting the light of the planet is challenging in its own right, as planets are incredibly faint. One way to quantify the faintness of planetary light is to understand the photon flux rate. A photon is an indivisible particle of light, that is, the minimum detectable amount of light. On a sunny day, approximately 10 thousand trillion photons enter your eye every second. The rate of photons entering your eye from an Earth-like exoplanet around a nearby star would be around 10 to 100 per year. Telescopes with large mirrors can help collect as much of this light as possible, but ultra-sensitive detectors are also needed, particularly for infrared light, where the biosignature gases have their strongest effects. Unfortunately, state-of-the-art infrared detectors are far too noisy to detect the low level of light emitted from exoplanets.
With support from NASA’s Astrophysics Division and industrial partners, researchers at the University of Hawai’i are developing a promising detector technology to meet these stringent sensitivity requirements. These detectors, known as avalanche photodiode arrays, are constructed out of the same semiconductor material as conventional infrared sensors. However, these new sensors employ an extra “avalanche” layer that takes the signal from a single photon and multiplies it, much like an avalanche can start with a single snowball and quickly grow it to the size of a boulder. This signal amplification occurs before any noise from the detector is introduced, so the effective noise is proportionally reduced. However, at high avalanche levels, photodiodes start to behave badly, with noise exponentially increasing, which negates any benefits of the signal amplification. Late University of Hawai’i faculty member Donald Hall, who was a key figure in driving technology for infrared astronomy, realized the potential use of avalanche photodiodes for ultra-low-noise infrared astronomy with some modifications to the material properties.
University of Hawai’i team members with cryogenic dewar used to test the sensors. From left to right, Angelu Ramos, Michael Bottom, Shane Jacobson, Charles-Antoine Claveau. Michael Bottom, University of Hawai’i The most recent sensors benefit from a new design including a graded semiconductor bandgap that allows for excellent noise performance at moderate amplification, a mesa pixel geometry to reduce electronic crosstalk, and a read-out integrated circuit to allow for short readout times. “It was actually challenging figuring out just how sensitive these detectors are,” said Michael Bottom, associate professor at the University of Hawai’i and lead of development effort. “Our ‘light-tight’ test chamber, which was designed to evaluate the infrared sensors on the James Webb Space Telescope, was supposed to be completely dark. But when we put these avalanche photodiodes in the chamber, we started seeing light leaks at the level of a photon an hour, which you would never be able to detect using the previous generation of sensors.”
The new designs have a format of one megapixel, more than ten times larger than the previous iteration of sensors, and circuitry that allows for tracking and subtracting any electronic drifts. Additionally, the pixel size and control electronics are such that these new sensors could be drop-in replacements for the most common infrared sensors used on the ground, which would give new capabilities to existing instruments.
Image of the Palomar-2 globular cluster located in the constellation of Auriga, taken with the linear-mode avalanche photodiode arrays, taken from the first on-sky testing of the sensors using the University of Hawai’i’s 2.2 meter telescope. Michael Bottom, University of Hawai’i Last year, the team took the first on-sky images from the detectors, using the University of Hawai’i’s 2.2-meter telescope. “It was impressive to see the avalanche process on sky. When we turned up the gain, we could see more stars appear,” said Guillaume Huber, a graduate student working on the project. “The on-sky demonstration was important to prove the detectors could perform well in an operational environment,” added Michael Bottom.
According to the research team, while the current sensors are a major step forward, the megapixel format is still too small for many science applications, particularly those involving spectroscopy. Further tasks include improving detector uniformity and decreasing persistence. The next generation of sensors will be four times larger, meeting the size requirements for the Habitable Worlds Observatory, NASA’s next envisioned flagship mission, with the goals of imaging and characterizing Earth-like exoplanets.
Project Lead: Dr. Michael Bottom, University of Hawai’i
Sponsoring Organization: NASA Strategic Astrophysics Technology (SAT) Program
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Last Updated Feb 18, 2025 Related Terms
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By NASA
NASA’s Nancy Grace Roman Space Telescope team has successfully integrated the mission’s deployable aperture cover — a visor-like sunshade that will help prevent unwanted light from entering the telescope — to the outer barrel assembly, another structure designed to shield the telescope from stray light in addition to keeping it at a stable temperature.
Technicians at NASA’s Goddard Space Flight Center in Greenbelt, Md., recently integrated the deployable aperture cover to the outer barrel assembly for the agency’s Nancy Grace Roman Space Telescope.NASA/Chris Gunn “It’s been incredible to see these major components go from computer models to building and now integrating them,” said Sheri Thorn, an aerospace engineer working on Roman’s sunshade at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Since it’s all coming together at Goddard, we get a front row seat to the process. We’ve seen it mature, kind of like watching a child grow up, and it’s a really gratifying experience.”
The sunshade functions like a heavy-duty version of blackout curtains you might use to keep your room extra dark. It will make Roman more sensitive to faint light from across the universe, helping astronomers see dimmer and farther objects. Made of two layers of reinforced thermal blankets, the sunshade is designed to remain folded during launch and deploy after Roman is in space. Three booms will spring upward when triggered electronically, raising the sunshade like a page in a pop-up book.
In this photo, technician Brenda Estavia is installing the innermost layer of the sunshade onto the deployable aperture cover structure of NASA’s Nancy Grace Roman Space Telescope. NASA/Jolearra Tshiteya The sunshade blanket has an inner and outer layer separated by about an inch, much like a double-paned window. “We’re prepared for micrometeoroid impacts that could occur in space, so the blanket is heavily fortified,” said Brian Simpson, Roman’s deployable aperture cover lead at NASA Goddard. “One layer is even reinforced with Kevlar, the same thing that lines bulletproof vests. By placing some space in between the layers we reduce the risk that light would leak in, because it’s unlikely that the light would pass through both layers at the exact same points where the holes were.”
Over the course of a few hours, technicians meticulously joined the sunshade to the outer barrel assembly — both Goddard-designed components — in the largest clean room at NASA Goddard. The outer barrel assembly will help keep the telescope at a stable temperature and, like the sunshade, help shield the telescope from stray light and micrometeoroid impacts. It’s fitted with heaters to help ensure the telescope’s mirrors won’t experience wide temperature swings, which make materials expand and contract.
“Roman is made up of a lot of separate components that come together after years of design and fabrication,” said Laurence Madison, a mechanical engineer at NASA Goddard. “The deployable aperture cover and outer barrel assembly were built at the same time, and up until the integration the two teams mainly used reference drawings to make sure everything would fit together as they should. So the successful integration was both a proud moment and a relief!”
This photo shows the deployable aperture cover for NASA’s Nancy Grace Roman Space Telescope as seen through the outer barrel assembly. Both components will help shield the telescope from stray light, improving Roman’s sensitivity to faint light from across the universe.NASA/Chris Gunn Both the sunshade and outer barrel assembly have been extensively tested individually, but now that they’re connected engineers are assessing them again. Following the integration, the team tested the sunshade deployment.
“Since the sunshade was designed to deploy in space, the system isn’t actually strong enough to deploy itself in Earth’s gravity,” said Matthew Neuman, a mechanical engineer working on Roman’s sunshade at NASA Goddard. “So we used a gravity negation system to offset its weight and verified that everything works as expected.”
Next, the components will undergo thermal vacuum testing together to ensure they will function as planned in the temperature and pressure environment of space. Then they’ll move to a shake test to assess their performance during the extreme vibrations they’ll experience during launch.
Technicians will join Roman’s solar panels to the outer barrel assembly and sunshade this spring, and then integrate them with the rest of the observatory by the end of the year.
The mission has now passed a milestone called Key Decision Point-D, marking the official transition from the fabrication stage that culminated in the delivery of major components to the phase involving assembly, integration, testing, and launch. The Roman observatory remains on track for completion by fall 2026 and launch no later than May 2027.
To virtually tour an interactive version of the telescope, visit:
https://roman.gsfc.nasa.gov/interactive/
By Ashley Balzer
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Media contact:
Claire Andreoli
NASA’s Goddard Space Flight Center, Greenbelt, Md.
301-286-1940
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Last Updated Feb 12, 2025 EditorAshley BalzerContactAshley Balzerashley.m.balzer@nasa.govLocationGoddard Space Flight Center Related Terms
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By NASA
3 min read
NASA Solar Observatory Sees Coronal Loops Flicker Before Big Flares
For decades, scientists have tried in vain to accurately predict solar flares — intense bursts of light on the Sun that can send a flurry of charged particles into the solar system. Now, using NASA’s Solar Dynamics Observatory, one team has identified flickering loops in the solar atmosphere, or corona, that seem to signal when the Sun is about to unleash a large flare.
These warning signs could help NASA and other stakeholders protect astronauts as well as technology both in space and on the ground from hazardous space weather.
NASA’s Solar Dynamics Observatory captured this image of coronal loops above an active region on the Sun in mid-January 2012. The image was taken in the 171 angstrom wavelength of extreme ultraviolet light. NASA/Solar Dynamics Observatory Led by heliophysicist Emily Mason of Predictive Sciences Inc. in San Diego, California, the team studied arch-like structures called coronal loops along the edge of the Sun. Coronal loops rise from magnetically driven active regions on the Sun, where solar flares also originate.
The team looked at coronal loops near 50 strong solar flares, analyzing how their brightness in extreme ultraviolet light varied in the hours before a flare compared to loops above non-flaring regions. Like flashing warning lights, the loops above flaring regions varied much more than those above non-flaring regions.
“We found that some of the extreme ultraviolet light above active regions flickers erratically for a few hours before a solar flare,” Mason explained. “The results are really important for understanding flares and may improve our ability to predict dangerous space weather.”
Published in the Astrophysical Journal Letters in December 2024 and presented on Jan. 15, 2025, at a press conference during the 245th meeting of the American Astronomical Society, the results also hint that the flickering reaches a peak earlier for stronger flares. However, the team says more observations are needed to confirm this link.
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The four panels in this movie show brightness changes in coronal loops in four different wavelengths of extreme ultraviolet light (131, 171, 193, and 304 angstroms) before a solar flare in December 2011. The images were taken by the Atmospheric Imaging Assembly (AIA) on NASA’s Solar Dynamics Observatory and processed to reveal flickering in the coronal loops. NASA/Solar Dynamics Observatory/JHelioviewer/E. Mason Other researchers have tried to predict solar flares by examining magnetic fields on the Sun, or by looking for consistent trends in other coronal loop features. However, Mason and her colleagues believe that measuring the brightness variations in coronal loops could provide more precise warnings than those methods — signaling oncoming flares 2 to 6 hours ahead of time with 60 to 80 percent accuracy.
“A lot of the predictive schemes that have been developed are still predicting the likelihood of flares in a given time period and not necessarily exact timing,” said team member Seth Garland of the Air Force Institute of Technology at Wright-Patterson Air Force Base in Ohio.
Each solar flare is like a snowflake — every single flare is unique.
Kara kniezewski
Air Force Institute of Technology
“The Sun’s corona is a dynamic environment, and each solar flare is like a snowflake — every single flare is unique,” said team member Kara Kniezewski, a graduate student at the Air Force Institute of Technology and lead author of the paper. “We find that searching for periods of ‘chaotic’ behavior in the coronal loop emission, rather than specific trends, provide a much more consistent metric and may also correlate with how strong a flare will be.”
The scientists hope their findings about coronal loops can eventually be used to help keep astronauts, spacecraft, electrical grids, and other assets safe from the harmful radiation that accompanies solar flares. For example, an automated system could look for brightness changes in coronal loops in real-time images from the Solar Dynamics Observatory and issue alerts.
“Previous work by other researchers reports some interesting prediction metrics,” said co-author Vadim Uritsky of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the Catholic University of Washington in D.C. “We could build on this and come up with a well-tested and, ideally, simpler indicator ready for the leap from research to operations.”
By Vanessa Thomas
NASA’s Goddard Space Flight Center, Greenbelt, Md.
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Last Updated Jan 15, 2025 Related Terms
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By NASA
NASA/Steve Freeman On Oct. 22, 2024, the latest iteration of an atmospheric probe developed by researchers at NASA’s Armstrong Flight Research Center in Edwards, California, successfully completed a test flight. Building on NASA 1960s research on lifting body aircraft, which use the aircraft’s shape for lift instead of wings, the concept could offer future scientists a potentially better and more economical way to collect data on other planets. Testing demonstrated the shape of the probe works.
The atmospheric probe flew after release from a quad-rotor remotely piloted aircraft above Rogers Dry Lake, a flight area adjacent to NASA Armstrong. “I’m ecstatic,” said John Bodylski, atmospheric probe principal investigator at NASA Armstrong. “It was completely stable in flight. We will be looking at releasing it from a higher altitude to keep it flying longer and demonstrate more maneuvers.”
See more photos from the test flight.
Image credit: Steve Freeman
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