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Air Force Reservists in space-related career fields interested in volunteering to join the U.S. Space Force as Guardians serving in a part-time capacity can apply.
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By NASA
Advancing Single-Photon Sensing Image Sensors to Enable the Search for Life Beyond Earth
A NASA-sponsored team is advancing single-photon sensing Complementary Metal-Oxide-Semiconductor (CMOS) detector technology that will enable future NASA astrophysics space missions to search for life on other planets. As part of their detector maturation program, the team is characterizing sensors before, during, and after high-energy radiation exposure; developing novel readout modes to mitigate radiation-induced damage; and simulating a near-infrared CMOS pixel prototype capable of detecting individual photons.
Single-photon sensing and photon-number resolving CMOS image sensors: a 9.4 Mpixel sensor (left) and a 16.7 Mpixel sensor (right). Credit: CfD, RIT Are we alone in the universe? This age-old question has inspired scientific exploration for centuries. If life on other planets evolves similarly to life on Earth, it can imprint its presence in atmospheric spectral features known asbiosignatures. They include absorption and emission lines in the spectrum produced by oxygen, carbon dioxide, methane, and other molecules that could indicate conditions which can support life. A future NASA astrophysics mission, the Habitable Worlds Observatory (HWO), will seek to find biosignatures in the ultraviolet, optical, and near-infrared (NIR) spectra of exoplanet atmospheres to look for evidence that life may exist elsewhere in the universe.
HWO will need highly sensitive detector technology to detect these faint biosignatures on distant exoplanets. The Single-Photon Sensing Complementary Metal-Oxide-Semiconductor (SPSCMOS) image sensor is a promising technology for this application. These silicon-based sensors can detect and resolve individual optical-wavelength photons using a low-capacitance, high-gain floating diffusion sense node. They operate effectively over a broad temperature range, including at room temperature. They have near-zero read noise, are tolerant to radiation, and generate very little unwanted signalâsuch as dark current. When cooled to 250Â K, the dark current drops to just one electron every half-hour. If either the read noise or dark current is too high, the sensor will fail to detect the faint signals that biosignatures produce.
A research team at the Rochester Institute of Technology (RIT) Center for Detectors (CfD) is accelerating the readiness of these SPSCMOS sensors for use in space missions through detector technology maturation programs funded by NASAâs Strategic Astrophysics Technology and Early Stage Innovations solicitations. These development programs include several key goals:
Characterize critical detector performance metrics like dark current, quantum efficiency, and read noise before, during, and after exposure to high-energy radiation Develop new readout modes for these sensors to mitigate effects from short-term and long-term radiation damage Design a new NIR version of the sensor using Technology Computer-Aided Design (TCAD) software SPSCMOS sensors operate similarly to traditional CMOS image sensors but are optimized to detect individual photonsâan essential capability for ultra-sensitive space-based observations, such as measuring the gases in the atmospheres of exoplanets. Incoming photons enter the sensor and generate free charges (electrons) in the sensor material. These charges collect in a pixelâs storage well and eventually transfer to a low-capacitance component called the floating diffusion (FD) sense node where each free charge causes a large and resolved voltage shift. This voltage shift is then digitized to read the signal.
Experiments that measure sensor performance in a space relevant environment use a vacuum Dewar and a thermally-controlled mount to allow precise tuning of the sensors temperature. The Dewar enables testing at conditions that match the expected thermal environment of the HWO instrument, and can even cool the sensor and its on-chip circuits to temperatures colder than any prior testing reported for this detector family. These tests are critical for revealing performance limitations with respect to detector metrics like dark current, quantum efficiency, and read noise. As temperatures change, the electrical properties of on-chip circuits can also change, which affects the read out of charge in a pixel.
The two figures show results for SPSCMOS devices. The figure on the left shows a photon counting histogram with peaks that correspond to photon number. The figure on the right shows the dark current for a SPSCMOS device before and after exposure to 50 krad of 60 MeV protons. Credit: CfD, RIT The radiation-rich environment for HWO will cause temporary and permanent effects in the sensor. These effects can corrupt the signal measured in a pixel, interrupt sensor clocking and digital logic, and can cause cumulative damage that gradually degrades sensor performance. To mitigate the loss of detector sensitivity throughout a mission lifetime, the RIT team is developing new readout modes that are not available in commercial CMOS sensors. These custom modes sample the signal over time (a ârampâ acquisition) to enable the detection and removal of cosmic ray artifacts. In one mode, when the system identifies an artifact, it segments the signal ramp and selectively averages the segments to reconstruct the original signalâpreserving scientific data that would otherwise be lost. In addition, a real-time data acquisition system monitors the detectorâs power consumption, which may change from the accumulation of damage throughout a mission. The acquisition system records these shifts and communicates with the detector electronics to adjust voltages and maintain nominal operation. These radiation damage mitigation strategies will be evaluated during a number of test programs at ground-based radiation facilities. The tests will help identify unique failure mechanisms that impact SPSCMOS technology when it is exposed to radiation equivalent to the dose expected for HWO.
Custom acquisition electronics (left) that will control the sensors during radiation tests, and an image captured using this system (right). Credit: CfD, RIT While existing SPSCMOS sensors are limited to detecting visible light due to their silicon-based design, the RIT team is developing the worldâs first NIR single-photon photodiode based on the architecture used in the optical sensors. The photodiode design starts as a simulation in TCAD software to model the optical and electrical properties of the low-capacitance CMOS architecture. The model simulates light-sensitive circuits using both silicon and Mercury Cadmium Telluride (HgCdTe or MCT) material to determine how well the pixel would measure photo-generated charge if a semiconductor foundry physically fabricated it. It has 2D and 3D device structures that convert light into electrical charge, and circuits to control charge transfer and signal readout with virtual probes that can measure current flow and electric potential. These simulations help to evaluate the key mechanisms like the conversion of light into electrons, storing and transferring the electrons, and the output voltage of the photodiode sampling circuit.
In addition to laboratory testing, the project includes performance evaluations at a ground-based telescope. These tests allow the sensor to observe astronomical targets that cannot be fully replicated in lab. Star fields and diffuse nebulae challenge the detectorâs full signal chain under real sky backgrounds with faint flux levels, field-dependent aberrations, and varying seeing conditions. These observations help identify performance limitations that may not be apparent in controlled laboratory measurements.
In January 2025, a team of researchers led by PhD student Edwin Alexani used an SPSCMOS-based camera at the C.E.K. Mees Observatory in Ontario County, New York. They observed star cluster M36 to evaluate the sensorâs photometric precision, and the Bubble Nebula in a narrow-band H-alpha filter. The measured dark current and read noise were consistent with laboratory results.
The team observed photometric reference stars to estimate the quantum efficiency (QE) or the ability for the detector to convert photons into signal. The calculated QE agreed with laboratory measurements, despite differences in calibration methods.
The team also observed the satellite STARLINK-32727 as it passed through the telescopeâs field of view and measured negligible persistent chargeâresidual signal that can remain in detector pixels after exposure to a bright source. Although the satellite briefly produced a bright streak across several pixels due to reflected sunlight, the average latent charge in affected pixels was only 0.03 eâ/pix â well below both the sky-background and sensorâs read noise.
Images captured at the C.E.K. Mees Observatory. Left: The color image shows M36 in the Johnson color filters B (blue), V (green), and R (red) bands (left). Right: Edwin Alexani and the SPSCMOS camera (right). Credit: : CfD, RIT As NASA advances and matures the HWO mission, SPSCMOS technology promises to be a game-changer for exoplanet and general astrophysics research. These sensors will enhance our ability to detect and analyze distant worlds, bringing us one step closer to answering one of humanityâs most profound questions: are we alone?
For additional details, see the entry for this project on NASA TechPort.
Project Lead(s): Dr. Donald F. Figer, Future Photon Initiative and Center for Detectors, Rochester Institute of Technology (RIT), supported by engineer Justin Gallagher and a team of students.
Sponsoring Organization(s): NASA Astrophysics Division, Strategic Astrophysics Technology (SAT) Program and NASA Space Technology Mission Directorate (STMD), Early Stage Innovations (ESI) Program
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Last Updated Sep 02, 2025 Related Terms
Astrophysics Science-enabling Technology Space Technology Mission Directorate Technology Highlights Explore More
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By NASA
NASA science and American industry have worked hand-in-hand for more than 60 years, transforming novel technologies created with NASA research into commercial products like cochlear implants, memory-foam mattresses, and more. Now, a NASA-funded device for probing the interior of storm systems has been made a key component of commercial weather satellites.
The novel atmospheric sounder was originally developed for NASAâs TROPICS (short for Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of SmallSats), which launched in 2023. Boston-based weather technology company Tomorrow.io integrated the same instrument design into some of its satellites.
NASAâs TROPICS instrument. TROPICS pioneered a novel, compact atmospheric sound now flying aboard a fleet of commercial small satellites created by the weather technology company Tomorrow.io.Credit: Blue Canyon Technologies Atmospheric sounders allow researchers to gather data describing humidity, temperature, and wind speed â important factors for weather forecasting and atmospheric analysis. From low-Earth orbit, these devices help make air travel safer, shipping more efficient, and severe weather warnings more reliable.
Novel tools for Observing Storm Systems
In the early 2000s, meteorologists and atmospheric chemists were eager to find a new science tool that could peer deep inside storm systems and do so multiple times a day. At the same time, CubeSat constellations (groupings of satellites each no larger than a shoebox) were emerging as promising, low-cost platforms for increasing the frequency with which individual sensors could pass over fast-changing storms, which improves the accuracy of weather models.
The challenge was to create an instrument small enough to fit aboard a satellite the size of a toaster, yet powerful enough to observe the innermost mechanisms of storm development. Preparing these technologies required years of careful development that was primarily supported by NASAâs Earth Science Division.
William Blackwell and his team at MIT Lincoln Laboratory in Cambridge, Massachusetts, accepted this challenge and set out to miniaturize vital components of atmospheric sounders. âThese were instruments the size of a washing machine, flying on platforms the size of a school bus,â said Blackwell, the principal investigator for TROPICS. âHow in the world could we shrink them down to the size of a coffee mug?â
With a 2010 award from NASAâs Earth Science Technology Office (ESTO), Blackwellâs team created an ultra-compact microwave receiver, a component that can sense the microwave radiation within the interior of storms.
The Lincoln Lab receiver weighed about a pound and took up less space than a hockey puck. This innovation paved the way for a complete atmospheric sounder instrument small enough to fly aboard a CubeSat. âThe hardest part was figuring out how to make a compact back-end to this radiometer,â Blackwell said. âSo without ESTO, this would not have happened. That initial grant was critical.â
In 2023, that atmospheric sounder was sent into space aboard four TROPICS CubeSats, which have been collecting torrents of data on the interior of severe storms around the world.
Transition to Industry
By the time TROPICS launched, Tomorrow.io developers knew they wanted Blackwellâs microwave receiver technology aboard their own fleet of commercial weather satellites. âWe looked at two or three different options, and TROPICS was the most capable instrument of those we looked at,â said Joe Munchak, a senior atmospheric data scientist at Tomorrow.io.
In 2022, the company worked with Blackwell to adapt his teamâs design into a CubeSat platform about twice the size of the one used for TROPICS. A bigger platform, Blackwell explained, meant they could bolster the sensorâs capabilities.
âWhen we first started conceptualizing this, the 3-unit CubeSat was the only game in town. Now weâre using a 6-unit CubeSat, so we have room for onboard calibration,â which improves the accuracy and reliability of gathered data, Blackwell said.
Tomorrow.ioâs first atmospheric sounders, Tomorrow-S1 and Tomorrow-S2, launched in 2024. By the end of 2025, the company plans to have a full constellation of atmospheric sounders in orbit. The company also has two radar instruments that were launched in 2023 and were influenced by NASAâs RainCube instrument â the first CubeSat equipped with an active precipitation radar.
More CubeSats leads to more accurate weather data because there are more opportunities each day â revisits â to collect data. âWith a fleet size of 18, we can easily get our revisit rate down to under an hour, maybe even 40 to 45 minutes in most places. It has a huge impact on short-term forecasts,â Munchak said.
Having access to an atmospheric sounder that had already flown in space and had more than 10 years of testing was extremely useful as Tomorrow.io planned its fleet. âIt would not have been possible to do this nearly as quickly or nearly as affordably had NASA not paved the way,â said Jennifer Splaingard, Tomorrow.ioâs senior vice president for space and sensors.
A Cycle of Innovation
The relationship between NASA and industry is symbiotic. NASA and its grantees can drive innovation and test new tools, equipping American businesses with novel technologies they may otherwise be unable to develop on their own. In exchange, NASA gains access to low-cost data sets that can supplement information gathered through its larger science missions.
Tomorrow.io was among eight companies selected by NASAâs Commercial SmallSat Data Acquisition (CSDA) program in September 2024 to equip NASA with data that will help improve weather forecasting models. âIt really is a success story of technology transfer. Itâs that sweet spot, where the government partners with tech companies to really take an idea, a proven concept, and run with it,â Splaingard said.
By Gage Taylor
NASAâs Goddard Space Flight Center, Greenbelt, Md.
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Last Updated Sep 02, 2025 Related Terms
Earth Hurricanes & Typhoons TROPICS (Time-Resolved Observations of Precipitation Structure and Storm Intensity with a Constellation of Smallsats) View the full article
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