Computing advances continue to push the envelope for ever-smaller, ruggedized electronics that must thrive in extreme conditions, whether inside jet engines, nuclear reactors, geothermal wells deep in the Earth, or in one of the harshest environments: space.
Ozark Integrated Circuits, Inc. (Ozark IC)—an Arkansas-based company that makes semiconductors work in places where normal electronics do not—developed a powerful, temperature-resistant silicon carbide ultraviolet (UV) detector purpose-built for operation in hostile environments. The high responsivity of the detector, integrated as a smart sensing system called UV eXtreme Node (UV XNode™), eliminates the need for signal amplification, which is standard in current UV detectors, thus significantly reducing the cost of the technology.
The UV XNode™ could serve as a cost-efficient UV detector system for a wide variety of remote sensing applications with valuable Earth benefits, such as improved detection of ocean-based oil spills and early fire detection in remote areas. However, the UV XNode™ first needed to be validated in the harsh space environment—which includes exposure to extreme temperature cycling, unfiltered UV radiation, ionizing radiation, and atomic oxygen (highly reactive single-oxygen atoms).
To do this, Ozark IC sent the UV XNode™ to the International Space Station (ISS) for performance testing in low Earth orbit (LEO). For the investigation, sponsored by the ISS U.S. National Laboratory, three UV XNodes™ spent a year on the MISSE Flight Facility, a permanent in-orbit platform from Alpha Space Test and Research Alliance that is mounted externally on the space station.
According to Jim Holmes, chief technology officer of Ozark IC, the investigation was a success. The UV XNode™ performed exactly in space as it did on Earth, with only a slight burn noted on the detector from the extreme UV conditions. During the experiment, Ozark IC received so much in-orbit data that the team had to develop a new way to capture and analyze performance measurements, with the resulting data visualization software now a core assessment tool for the company. Additionally, data from the experiment was beneficial not only to Ozark IC but also to NASA scientists conducting their MISSE experiments.
“Testing on MISSE allowed us first to determine whether our detector works in the space environment,” Holmes said, “and second, advance the detector’s technology readiness level so we can begin commercializing the technology.”
Advancing the Technology
Known as the “rugged circuit specialists,” Ozark IC started working with silicon carbide “primarily because its semiconductor properties are very good for building high-temperature electronics and UV detectors,” Holmes said.
Although silicon (Si) is the most widely used crystalline semiconductor material for integrated circuits, it does not perform well for UV detection. High-energy UV photons damage Si crystals, affecting device reliability. However, this is not the case with silicon carbide (SiC), which has a higher energy threshold than Si alone and can better withstand damage from photons. This higher threshold also allows low-energy visible and infrared (VIS-IR) photons to pass through SiC without interacting, which is why SiC detectors are considered “VIS-IR blind” and SiC integrated circuits are transparent to white light.
Prior to Ozark IC’s ISS National Lab investigation, the UV XNode™ was at a NASA technology readiness level (TRL) of 6, meaning the detector had been validated on the ground but needed testing and validation in space to advance to TRL-9 and be considered “flight-proven.”
The MISSE Flight Facility on the ISS was an ideal platform to test the UV XNode™, said Holmes, because it enabled Ozark IC to do prolonged testing of the detector across the entire solar UV spectrum. While several government and commercial labs support VIS-IR radiation testing and characterization, very few terrestrial labs support testing in the solar UV spectrum, including UV-A, UV-B, UV-C, and vacuum UV.
“Reproducing the solar UV spectrum in the laboratory is difficult, dangerous, and expensive, especially for long-term endurance testing of UV detectors,” Holmes said. “The MISSE Flight Facility provided Ozark IC with unique, year-long access to the solar UV spectrum without atmospheric attenuation or variation.”
Leveraging the MISSE Flight Facility
Since 2001, MISSE has been used to test more than 4,000 materials, from lubricants and paints to fabrics and container seals. After securing the right to commercialize MISSE in 2015, Alpha Space upgraded its capabilities, and now the MISSE Flight Facility is increasingly being used to test complex technologies, systems, and components to assess performance in the extreme space environment, said Mark Shumbera, vice president of space services at Houston-based Alpha Space, which owns and operates the MISSE Flight Facility on the ISS.
For Ozark IC’s investigation, Alpha Space integrated the UV XNode™ modules into three MISSE carriers, running functional tests to ensure everything worked before turning them over to NASA to put on the launch vehicle. The MISSE-10 mission, which included Ozark IC’s modules, launched to the ISS on Northrop Grumman’s 10th Commercial Resupply Services (CRS) mission in late 2018.
Once the carriers containing Ozark IC’s modules arrived at the ISS, the robotic arm installed them on the MISSE Flight Facility in three orientations: ram (the forward direction of the ISS), wake (opposite to ram) and zenith (away from Earth). Each orientation offers different solar UV exposures and intensity profiles. MISSE provides time-stamped data, so the telemetry shows detection of the UV sunrise (ram), then the high-noon peak (zenith), and the finale of a UV sunset (wake).
“Ram also gets a lot of atomic oxygen, whereas wake gets very little,” Shumbera said, “and zenith gets the solar noon and faces deep space where you get minimized light.” These exposures provided Ozark IC with additional insight into the reliability of the UV XNode™ in the space environment.
The wake- and zenith-facing MISSE carriers with Ozark IC’s modules returned to Earth on SpaceX CRS-20 in the spring of 2020. And in January 2021, the last module in the ram-facing carrier came back on SpaceX CRS-21. This module benefited from an extended stay in LEO because materials flying in the same MISSE carrier required additional time in orbit.
Managing the Data Overload
Ozark IC investigators sought testing in space through the ISS National Lab to generate new data in a challenging environment, but they did not count on the data overload that their detectors experienced almost immediately. The three UV XNode™ modules, each processing four UV detector channels, yielded 12 channels that collected one data set every second. Additional data streams for the voltage-sun input vector were also captured as the station orbited the Earth and changed its angle to the sun. The sensor’s location at the time of data acquisition was acquired using NASA’s open API, allowing the team to correlate altitude, velocity, and position with the UV data.
Thousands of detector data points, bundled into data packets, were transmitted from MISSE, via the ISS, to the ground and then sent to Ozark IC from NASA in near real-time. All in all, Ozark IC received 2.7 million data packets throughout the investigation. Alpha Space supported Ozark IC in the initial data management process, making sure the company was receiving data around the clock, but a data overload soon became apparent. “We were drowning in data,” said Holmes, noting that the company quickly realized a spreadsheet would not keep up with the constant updates.
With help from Alpha Space, NASA, and other partners, Ozark IC developed a real-time dashboard called OzIC.Lab, based in part on the open observability platform Grafana. This data visualization tool converted data into real-time performance information that was then correlated to ISS status (such as velocity, altitude, latitude, longitude, and solar heating). The dashboard included multiple views: a live feed from ISS on the upper right, UV response measurements from the UV XNode™ modules on the left, the voltage and current from the UV XNode™ modules in the middle, and location data at the bottom right showing if the ISS was in daylight or darkness.
By design, information was constantly updating—allowing data analysts to “decode on the fly with each query of the database,” and making it easy to drill down and view a lot of detailed information, said Holmes. Data received from the ISS along with the UV response from the detectors gave Ozark IC investigators a comprehensive picture. The team was able to correlate the detector measurements with ISS status and confirm the data were correct.
“Ozark IC has now implemented the dashboard as a crucial company-wide tool,” said Case Kirk, Ozark IC software engineer and one of seven core team members who developed the detector system. The dashboard remotely monitors and controls experiments and serves as a data visualization tool not only for internal use but also for customers to monitor Ozark IC’s products in action.
Providing Far-Reaching Value
Ozark IC was not the only one to find value in the in-orbit performance testing of the UV XNode™. The timestamps of the MISSE data enabled Ozark IC to merge ISS latitude, longitude, and altitude with every measurement, and putting this information into a searchable database has garnered the interest of NASA scientists.
Kim de Groh, senior materials research engineer in NASA Glenn Research Center’s Environmental Effects and Coatings Branch, hopes to use Ozark IC’s detector readings to determine UV radiation exposure for the 43 samples she and her research collaborators flew on the MISSE-10 mission.
“When I fly MISSE experiments, I need to know the solar exposure to make meaningful experiment conclusions,” said de Groh.
Active UV sensors that generate real-time solar exposure data from the same location as the exposed materials and devices enable the conversion of the data to equivalent sun hours (ESH). Such sensors are ideal, explained de Groh, as they provide exposure information that can be difficult to model—such as shadowing effects on the surface of the MISSE Flight Facility from ISS components like the solar arrays. On MISSE-10, she tested materials for space structures, new shielding material for spacesuits and spacecraft, and fiber composites for use in spacecraft structural components such as antennas and space telescope parts.
“Without ESH data, my flight results cannot be correlated with spacecraft materials durability,” de Groh said. “We need to know exactly how much solar UV radiation our MISSE samples were exposed to so we can correlate damage to UV exposure. This provides information needed for designing durable spacecraft.”
Furthermore, according to Shumbera, the UV XNode™ detector “appears to have performed extremely well, and Alpha Space certainly will evaluate Ozark IC’s sensor for possible use on MISSE.”
Applications in Space and on Earth
After withstanding a year of continuous exposure to the solar UV spectrum without degrading, the UV XNode™ is now space-proven and poised for use in numerous space-based applications. Holmes credits the company’s ISS National Lab investigation with enabling the UV XNode™ to achieve a TRL of 9, the final and highest level of readiness signaling that the technology is ready for commercialization.
Ozark IC plans to further miniaturize its UV detector technology and fly a pixelated detector array, potentially for UV imaging and UV spectrometer remote sensing applications. In the future, the UV XNode™ may also have applications in space exploration missions, such as rovers on the surface of Venus.
Back on Earth, jet and diesel engine makers may also see value in Ozark IC’s SiC technology. UV light is a by-product of combustion processes such as charge-compression ignition in diesel engines, fuel efficiency jet engines, and gas-powered generation systems. The XNode™ could have valuable applications in monitoring engine health and real-time fuel analysis.
The ISS serves as a powerful test bed in LEO, and the time on Alpha Space’s MISSE Flight Facility allowed Ozark IC to prove its UV XNode™ worked in space while advancing the detector’s TRL. “This really was a good result,” Holmes said. “It validated the robustness of the UV XNode™ and our ability to fly this technology again in the future.”