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At least 1,261 records · Page 70
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

The Micro-Arcsecond Metrology Testbed

The Micro-Arcsecond Metrology (MAM) testbed is a ground-based system of optical and electronic equipment for testing components, systems, and engineering concepts for the Space Interferometer Mission (SIM) and similar future missions, in which optical interferometers will be operated in outer space. In addition, the MAM testbed is of interest in its own right as a highly precise metrological system. The designs of the SIM interferometer and the MAM testbed reflect a requirement to measure both the position of the starlight central fringe and the change in the internal optical path of the interferometer with sufficient spatial resolution to generate astrometric data with angular resolution at the microarcsecond level. The internal path is to be measured by use of a small metrological laser beam of 1,319-nm wavelength, whereas the position of the starlight fringe is to be estimated by use of a charge-coupled-device (CCD) image detector sampling a large concentric annular beam. For the SIM to succeed, the optical path length determined from the interferometer fringes must be tracked by the metrological subsystem to within tens of picometers, through all operational motions of an interferometer delay line and siderostats. The purpose of the experiments performed on the MAM testbed is to demonstrate this agreement in a large-scale simulation that includes a substantial portion of the system in the planned configuration for operation in outer space. A major challenge in this endeavor is to align the metrological beam with the starlight beam in order to maintain consistency between the metrological and starlight subsystems at the system level. The MAM testbed includes an optical interferometer with a white light source, all major optical components of a stellar interferometer, and heterodyne metrological sensors. The aforementioned subsystems are installed in a large vacuum chamber in order to suppress atmospheric and thermal disturbances. The MAM is divided into two distinct subsystems: the test article (TA), which is the interferometer proper, and the inverse interferometer pseudo-star (IIPS), which synthesizes the light coming from a distant target star by providing spatially coherent wavefronts out of two mirrors, separated by the MAM baseline, that feed directly into two siderostats that are parts of the TA. The two feed mirrors of the IIPS are articulated (in translation and tilt) in order to simulate stars located at different orientations in space, while still illuminating the TA siderostats. The spectrum of the simulated starlight of the IIPS corresponds to that of a blackbody at a temperature of about 3,100 K.

Goullioud, Renaud↗
NASA NTRS2015

Iodine Satellite

This project is a collaborative effort to mature an iodine propulsion system while reducing risk and increasing fidelity of a technology demonstration mission concept. 1 The FY 2014 tasks include investments leveraged throughout NASA, from multiple mission directorates, as a partnership with NASA Glenn Research Center (GRC), a NASA Marshall Space Flight Center (MSFC) Technology Investment Project, and an Air Force partnership. Propulsion technology is often a critical enabling technology for space missions. NASA is investing in technologies to enable high value missions with very small and low-cost spacecraft, even CubeSats. However, these small spacecraft currently lack any appreciable propulsion capability. CubeSats are typically deployed and drift without any ability to transfer to higher value orbits, perform orbit maintenance, or deorbit. However, the iodine Hall system can allow the spacecraft to transfer into a higher value science orbit. The iodine satellite (iSAT) will be able to achieve a (Delta)V of >500 m/s with <1 kg of solid iodine propellant, which can be stored in an unpressurized benign state prior to launch. The iSAT propulsion system consists of the 200 W Hall thruster, solid iodine propellant tank, a power processing unit, and the necessary valves and tubing to route the iodine vapor. The propulsion system is led by GRC, with critical hardware provided by the Busek Co. The propellant tank begins with solid iodine unpressurized on the ground and in-flight before operations, which is then heated via tank heaters to a temperature at which solid iodine sublimates to iodine vapor. The vapor is then routed through tubing and custom valves to control mass flow to the thruster and cathode assembly. 2 The thruster then ionizes the vapor and accelerates it via magnetic and electrostatic fields, resulting in thrust with a specific impulse >1,300 s. The iSAT spacecraft, illustrated in figure 1, is currently a 12U CubeSat. The spacecraft chassis will be constructed from aluminum with a finish to prevent iodine-driven corrosion. The iSAT spacecraft includes full three-axis control using wheels, magnetic torque rods, inertial management unit, and a suite of sensors and optics. The spacecraft will leverage heat generated by spacecraft components and radiators for a passive thermal control system.

Dankanich, John↗
NASA NTRS2020

Radiometric Degradation Curves for the ASTER VNIR Processing Using Vicarious and Lunar Calibrations

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) onboard Terra platform, which was launched in 1999, has three separate subsystems: a visible and near-infrared (VNIR) radiometer, a shortwave-infrared radiometer, and a thermal-infrared radiometer. The ASTER VNIR bands have been radiometrically corrected for approximately 14 years by the sensor degradation curves estimated from the onboard calibrator according to the original calibration plan. However, this calibration by the onboard calibrator encountered a problem; specifically, it is inconsistent with the results of vicarious calibration and cross calibration. Therefore, the ASTER VNIR processing was applied by the radiometric degradation curves calculated from the results of three calibration approaches, i.e., the onboard calibrator, the vicarious calibration, and the cross calibration since February 2014. Even though the current degradation curves were revised, the inter-band and lunar calibrations show some inconsistencies owing to the different traceability in the bands by different calibration approaches. In this study, the current degradation curves and their problems are explained, and the new curves that are derived from the vicarious calibration with lunar calibration are discussed. The new degradation curves that have the same traceability in the bands will be used for future ASTER VNIR processing.

ASTER; Vicarious calibration; Lunar calibration; R↗
NASA NTRS2004

SIM Narrow and wide angle astrometric demonstration on the MAM testbed.

The Space Interferometry Mission (SIM) requires fringe measurements to the level of picometers in order to produce astrometric data at the micro-arc-second level. To be more specific, it is necessary to measure both the position of the starlight central fringe and the change in the internal optical path of the interferometer to tens of picometers. The internal path is measured with a small heterodyne metrology beam, whereas the starlight fringe position is estimated with a CCD sampling a large concentric annular beam. One major challenge for SIM is to align the metrology beam with the starlight beam to keep the consistency between these two sensors at the system level while articulating the instrument optics over the field of regard. The Micro-Arcsecond Metrology testbed (MAM), developed at the Jet Propulsion Laboratory, features an optical interferometer with a white light source, all major optical components of a stellar interferometer and heterodyne metrology sensors. The setup is installed inside a large vacuum chamber in order to mitigate the atmospheric and thermal disturbances. Astrometric observations are simulated by articulating the optics over the 15 degrees field of regard to generate multiple artificial stars. Recent data show agreement between the metrology and starlight paths to 20pm in the narrow angle field and to 350pm in the full wide angle field of regard of SIM. This paper describes the MAM optical setup, the observation process, the current data and how the performance relates to SIM.

Catanzarite, Joseph H.↗
DOE OSTI2024

System and method for in situ inspection of defects in additively manufactured parts using high speed melt pool pyrometry

A system and method is disclosed for detecting anomalies in an additively manufactured part. An energy source generates a signal forming an optical beam for creating a melt pool in a layer of feedstock material being selectively fused to make a part in an additive manufacturing operation. A sensor is configured to receive a signal reflected from the melt pool. The reflected signal forms a thermal signal indicative of a temperature of the feedstock material at a known location on a layer of the feedstock material while the feedstock material is being fused at the known location. A controller receives and analyzes data relating to the received signal to determine if an anomaly exists at the known location.

Forien, Jean-Baptiste↗
NASA NTRS2006

The Need for High Spatial Resolution Multispectral Thermal Remote Sensing Data In Urban Heat Island Research

Although the study of the Urban Heat Island (UHI) effect dates back to the early 1800's when Luke Howard discovered London s heat island, it has only been with the advent of thermal remote sensing systems that the extent, characteristics, and impacts of the UHI have become to be understood. Analysis of the UHI effect is important because above all, this phenomenon can directly influence the health and welfare of urban residents. For example, in 1995, over 700 people died in Chicago due to heat-related causes. UHI s are characterized by increased temperature in comparison to rural areas and mortality rates during a heat wave increase exponentially with the maximum temperature, an effect that is exacerbated by the UHI. Aside from the direct impacts of the UHI on temperature, UHI s can produce secondary effects on local meteorology, including altering local wind patterns, increased development of clouds and fog, and increasing rates of precipitation either over, or downwind, of cities. Because of the extreme heterogeneity of the urban surface, in combination with the sprawl associated with urban growth, thermal infrared (TIR) remote sensing data have become of significant importance in understanding how land cover and land use characteristics affect the development and intensification of the UHI. TIR satellite data have been used extensively to analyze the surface temperature regimes of cities to help observe and measure the impacts of surface temperatures across the urban landscape. However, the spatial scales at which satellite TIR data are collected are for the most part, coarse, with the finest readily available TIR data collected by the Landsat ETM+ sensor at 60m spatial resolution. For many years, we have collected high spatial resolution (10m) data using an airborne multispectral TIR sensor over a number of cities across the United States. These high resolution data have been used to develop an understanding of how discrete surfaces across the urban environment (e.g., rooftops, pavements) interact from a surface-lower atmosphere energy flux perspective, to force the development of the UHI. Moreover, the airborne TIR sensor we used in our UHI studies was a multispectral sensor that had six channels in the 8-12pm range. The advantages of collecting multispectral TIR data became readily evident as a valuable tool for better calculation of unique surface thermal energy responses for urban materials over the 8-12 micrometer region, and also for getting a better handle on surface emissivity characteristics for these discrete surfaces. In this presentation, we will provide evidence on the virtues of how high spatial resolution multispectral TIR data can provide for better analysis of the UHI that cannot now be attained via TIR data obtained from satellites. Furthermore, we wish to provide compelling evidence on why future TIR satellite sensors should collect data at fine spatial resolutions (e.g. less than or equal to 30m) to better allow for measurement of surface thermal energy fluxes from discrete urban surfaces, and to better understand how surface fluxes from different urban materials in cities around the world in different climatic regimes, affect development of the UHI characteristics.

Quattrochi, Dale A.↗
NASA NTRS2002

Power System for Venus Surface Exploration

A radioisotope power and cooling system is designed to provide electrical power for a probe operating on the surface of Venus. Most foreseeable electronics devices and sensors cannot operate at the 450 C ambient surface temperature of Venus. Because the mission duration is substantially long and the use of thermal mass to maintain an operable temperature range is likely impractical, some type of active refrigeration may be required to keep electronic components at a temperature below ambient. The fundamental cooling parameters are the cold sink temperature, the hot sink temperature, and the amount of heat to be removed. In this instance, it is anticipated that electronics would have a nominal operating temperature of 300 C. Due to the highly thermal convective nature of the high-density (90 bar CO2) atmosphere, the hot sink temperature was assumed to be 50 C, which provided a 500 C temperature of the cooler's heat rejecter to the ambient atmosphere. The majority of the heat load on the cooler is from the high temperature ambient surface environment on Venus, with a small contribution of heat generation from electronics and sensors. Both thermoelectric (RTG) and dynamic power conversion systems were analyzed, based on use of a standard isotope (General-purpose heat source, or GPHS) brick. For the radioisotope Stirling power converter configuration designed, the Sage model predicts a thermodynamic power output capacity of 478.1 watts, which slightly exceeds the required 469.1 watts. The hot sink temperature is 1200 C, and the cold sink temperature is 500 C. The required heat input is 1740 watts. This gives a thermodynamic efficiency of 27.48 %. It is estimated that the mechanical efficiency of the power converter design is on the order of 85 %, based on experimental measurements taken from 500-watt power class, laboratory-tested Stirling engines. The overall efficiency is calculated to be 23.36 %. The mass of the power converter is estimated at approximately 21.6 kg. Additional information is included in the original extended abstract.

Landis, Geoffrey A.↗
NASA NTRS2010

Developing NDE Techniques for Large Cryogenic Tanks - Year 2 Report

The Shuttle Program requires very large cryogenic ground storage tanks in which to store liquid oxygen and hydrogen. The existing Launch Complex-39 Pad tanks, which will be passed onto future launch programs, are over 40 years old and have received minimal refurbishment and only external inspections over the years. The majority of the structure is inaccessible without a full system drain of cryogenic liquid and insulation in the annular region. It was previously thought that there was a limit to the number of temperature cycles that the tanks could handle due to possible insulation compaction before undergoing a costly and time consuming complete overhaul; therefore the tanks were not drained and performance issues with these tanks, specifically the Pad B LH2 tank, were accepted. There is a need and an opportunity, as the Shuttle program ends and work to upgrade the launch pad progresses, to develop innovative non-destructive evaluation (NDE) techniques to analyze the current tanks. Techniques are desired that can aid in determining the extent of refurbishment required to keep the tanks in service for another 20+ years. A non-destructive technique would also be a significant aid in acceptance testing of new and refurbished tanks, saving significant time and money, if corrective actions can be taken before cryogen is introduced to the systems. Year one of this project concentrated on analysis of the current tanks located at LC-39 while cryogen was present. Year two of this project concentrated on analysis of detectable thermal variations on the outer surface of the tanks as the cryogen was drained and the inner vessel warmed to ambient conditions. Two techniques have been deployed in the field to monitor the tank. The first consisted of a displacement sensor to monitor for any expansions at the base of the tank during warm-up that could indicate a compaction issue with the insulation. The second technique was continued thermal monitoring of the tank through and after warm up. The indications noted in the thermal images were compared to bore-scope images of the annular region taken once the tank was inert and warmed to ambient conditions. Similar thermal imaging was performed on a smaller tank where an insulation void was induced to compare the effectiveness of thermal imagining on a different tank geometry.

Arens, Ellen↗
DOE OSTI2024

Theoretical investigation of decoherence channels in athermal phonon sensors

The creation and evolution of nonequilibrium phonons is central in applications ranging from cosmological particle searches to decoherence processes in qubits. However, the fundamental understanding of decoherence pathways for athermal phonon distributions in solid-state systems remains an open question. Using first-principles calculations, we investigate the primary decay channels of athermal phonons in two technologically relevant semiconductors—Si and GaAs. We quantify the contributions of anharmonic, isotopic, and interfacial scattering in these materials. From this, we construct a model to estimate the thermal power in a readout scheme as a function of time. We discuss the implication of our results on noise limitations in current phonon sensor designs and strategies for improving coherence in next-generation phonon sensors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRSDate not supplied

Jpss-4 VIIRS Polarization Sensitivity Performance Comparison With Heritage VIIRS Sensors

The Joint Polar Satellite System 4 (JPSS-4) is the follow-on for the Suomi-National Polar-orbiting Partnership (S-NPP) and Joint Polar Satellite Systems 1-3 (JPSS-1, -2 and -3) missions. A primary sensor on both JPSS and S-NPP spacecrafts is the Visible-Infrared Imaging Radiometer Suite (VIIRS) that provides valuable weather and climate products to the user community. VIIRS covers the Reflective Solar Band (RSB) and Thermal Emissive Band (TEB) spectral regions and contains a Day Night Band (DNB) that uses Lunar illumination at night. VIIRS provides top-of-atmosphere radiance, reflectance, and brightness temperature within the Sensor Data Records (SDRs) that are used in sea surface temperature, cloud characterization, land surface properties and ocean color/chlorophyll Environmental Data Record (EDR) products. The SDR calibration is performed using unpolarized sources such as a Solar Diffuser (SD) for the RSBs or an On-Board Calibrator BlackBody (OBCBB) for the TEBs. Earth scenes with polarizing properties will create radiometric bias errors within the SDRs based on how sensitive VIIRS is to polarized illumination and must be corrected in some EDR algorithms. This paper will discuss the JPSS-4 VIIRS polarization characterization methodology, polarization sensitivity results and compare its performance to its predecessors S-NPP and JPSS-1 through -3 VIIRS.

David Moyer↗
NASA NTRS2015

Radiation Budget Instrument (RBI) for JPSS-2

Radiation Budget Instrument (RBI) will be one of five instruments flying aboard the JPSS-2 spacecraft, a polar-orbiting sun-synchronous satellite in Low Earth Orbit. RBI is a passive remote sensing instrument that will follow the successful legacy of the Clouds and Earth's Radiant Energy System (CERES) instruments to make measurement of Earth's short and longwave radiation budget. The goal of RBI is to provide an independent measurement of the broadband reflected solar radiance and Earth's emitted thermal radiance by using three spectral bands (Shortwave, Longwave, and Total) that will have the same overlapped point spread function (PSF) footprint on Earth. To ensure precise NIST-traceable calibration in space the RBI sensor is designed to use a visible calibration target (VCT), a solar calibration target (SCT), and an infrared calibration target (ICT) containing phase change cells (PCC) to enable on-board temperature calibration. The VCT is a thermally controlled integrating sphere with space grade Spectralon covering the inner surface. Two sides of the sphere will have fiber-coupled laser diodes in the UV to IR wavelength region. An electrical substitution radiometer on the integrating sphere will monitor the long term stability of the sources and the possible degradation of the Spectralon in space. In addition the radiometric calibration operations will use the Spectralon diffusers of the SCT to provide accurate measurements of Solar degradation. All those stable on-orbit references will ensure that calibration stability is maintained over the RBI sensor lifetime. For the preflight calibration the RBI will view five calibration sources - two integrating spheres and three CrIS (Cross-track Infrared Sounder ) -like blackbodies whose outputs will be validated with NIST calibration approach. Thermopile are the selected detectors for the RBI. The sensor has a requirement to perform lunar calibration in addition to solar calibration in space in a way similar to CERES instruments approach. To monitor climate change and to get stable and traceable results, it is critical to assure stable calibration over instrument lifetime.

Georgieva, Elena↗
NASA NTRSDate not supplied

Bakeout Workshop

Spacecraft hardware thermal vacuum exposures and bakeouts have been used for years to reduce molecular outgassing to limit contamination to critical optics and sensors on-ground and in orbit. This presentation will discuss lessons learned and vacuum procedural techniques to make the most of your vacuum time. Quartz Crystal Microbalances (QCMs) and Residue Gas Analyzers (RGA) are 2 devices that help track molecular outgassing and examples will be shown on how to use them for your analytical benefit.

Outgassing thermal vacuum QCM RGA↗
DOE OSTI2021

Chemiresistor sensor based on ion-imprinted polymer (IIP)-functionalized rGO for Cd(II) ions in water

This study reports the design and development of a novel chemiresistor (CR) sensor using ion imprinted polymer (IIP)-functionalized reduced graphene oxide (rGO) [IIP/rGO-CR] for cadmium ions (Cd(II)) determination in water. The sensor consisted of a CR transducer made of rGO channel bridging source and drain electrodes prepared by self-assembly and thermal reduction of graphene oxide (GO) on Au interdigitated electrodes chip fabricated on Si/SiO 2 substrate. The IIP was then grafted on rGO using surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization with polyethylenimine (PEI) and methylacrylic acid (MAA) as dual functional monomers and Cd(II) ions as template through UV light-initiated copolymerization. The IIP functionalized on rGO acted as an effective recognition element that modulated the resistance of rGO-CR upon binding of Cd(II), enabling Cd(II) detection at ppb level in aqueous solutions. The prepared IIP/rGO-CR sensor worked effectively in the linear range of 2~200ppb and achieved a limit of detection (LOD) of 0.83 ppb, which is lower than the World Health Organization guidelines of 3ppb for drinking water quality. The developed sensor of IIP/rGO-CR showed a high selectivity against a variety of trace and heavy metal ions found in water and good stability for up to 60 days when stored at room temperature for Cd(II) determination in water. Further, the sensor was successfully applied to analyzing Cd(II) spiked in tap, lake and river waters with a 94.5%–113.5% recovery, demonstrating a high degree of accuracy even in complex water samples. Finally, our results illustrated that the CR sensor of IIP functionalized rGO provides a potential platform for sensitive, robust and low-cost environmental analysis of Cd(II) in water.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2020

Controlled Environmental Effects on Creep Test Data of Woven Fabric Webbings for Inflatable Space Modules

eveloping technologies for proposed lunar and Mars space exploration missions. Enhanced habitation sy g studied as potential habitats due to their inherent low mass and small launch volume. One goal of inflatable module research is quantification of the safe-life and end-of-life creep-strain spectrum. Full-scale pressurized inflatable modules are large, costly, and difficult to experimentally study. Therefore, material subcomponents are often studied as an alternative. An experimental thermally controlled long-term creep study of VectranTM webbings for application to inflatable modules is presented. Vectran fibers have high strength and low creep properties. High strength webbing materials are desirable for the load bearing restraint layer of inflatable modules because they are strong, flexible, and lightweight. Characterization of the creep behavior, safe-life, and end-of- life of webbing specimens will help quantify comparable life properties for inflatable modules. Several experimental multiple-year creep studies of webbing specimens in uncontrolled thermal environments have been conducted at NASA Langley Research Center. Experimental data obtained exhibits the classic creep-strain curve due to load, coupled with unique sinusoidal variation due to variation in temperature and humidity over daily and annual time periods. Results also have indicated that specimens fail within a year if the applied load is greater than 50 percent of the rated load. The primary goal of this study is to eliminate thermal effects from the creep data for a group of webbing specimens, and to allow uncontrolled thermal effects to influence the creep data of a second group of webbing specimens. Comparison of both sets of data will define how temperature influences creep data. A unique creep test facility was fabricated to facilitate the generation and comparison of the two sets of data. The facility consists of five creep test stands with an integrated heating and cooling system, and four creep test stands exposed to external environmental or ambient conditions. The facility contains displacement, temperature, humidity, and load sensors. Test specimens consist of one- inch wide, 48-inch long Vectran webbings rated at 12,500 pounds-per-inch. Experimental thermally controlled creep-strain data has been generated for two groups of webbing specimens. Applied load for all test stands was above 9000 lbs and greater than 50 percent of the rated load. Temperatures varied between 58˚F and 83˚F for the four test stands exposed to ambient conditions. Associated creep data exhibited the classic creep- strain profiles. The temperature was set to 72˚F for the five test stands in the controlled temperature environment. Creep data for tests with temperature control also exhibited the classic strain profiles. Data indicated that if the load is greater n thermal effects do not manifest. Therefore, creep tests with loads less than 50 percent of the rated load are planned for in the near future.

Kenner, Winfred S.↗
NASA NTRS1983

Ablative thermal protection systems

The procedures used to establish the TPS (thermal protection system) design of the SRB (solid rocket booster) element of the Space Shuttle vehicle are discussed. A final evaluation of the adequacy of this design will be made from data obtained from the first five Shuttle flights. Temperature sensors installed at selected locations on the SRB structure covered by the TPS give information as a function of time throughout the flight. Anomalies are to be investigated and computer design thermal models adjusted if required. In addition, the actual TPS ablator material loss is to be measured after each flight and compared with analytically determined losses. The analytical methods of predicting ablator performance are surveyed.

Vaniman, J.↗
DOE OSTI2023

Fiber Optic Temperature Sensor System Using Air-Filled Fabry–Pérot Cavity with Variable Pressure

We report a high-resolution fiber optic temperature sensor system based on an air-filled Fabry–Pérot (FP) cavity, whose spectral fringes shift due to a precise pressure variation in the cavity. The absolute temperature can be deduced from the spectral shift and the pressure variation. For fabrication, a fused-silica tube is spliced with a single-mode fiber at one end and a side-hole fiber at the other to form the FP cavity. The pressure in the cavity can be changed by passing air through the side-hole fiber, causing the spectral shift. We analyzed the effect of sensor wavelength resolution and pressure fluctuation on the temperature measurement resolution. A computer-controlled pressure system and sensor interrogation system were developed with miniaturized instruments for the system operation. Experimental results show that the sensor had a high wavelength resolution (<0.2 pm) with minimal pressure fluctuation (~0.015 kPa), resulting in high-resolution (±0.32 ℃) temperature measurement. It shows good stability from the thermal cycle testing with the maximum testing temperature reaching 800 ℃.

47 OTHER INSTRUMENTATION↗
NASA NTRS1996

Design and Laboratory Validation of a Capacitive Sensor for Measuring the Recession of Thin-Layered Ablator

Flight vehicles are typically instrumented with subsurface thermocouples to estimate heat transfer at the surface using inverse analysis procedures. If the vehicle has an ablating heat shield, however, temperature time histories from subsurface thermocouples no longer provide enough information to estimate heat flux at the surface. In this situation, the geometry changes and thermal energy leaves the surface in the form of ablation products. The ablation rate is required to estimate heat transfer to the surface. A new concept for a capacitive sensor has been developed to measure ablator depth using the ablator's dielectric effect on a capacitor's fringe region. Relying on the capacitor's fringe region enables the gage to be flush mounted in the vehicle's permanent structure and not intrude into the ablative heat shield applied over the gage. This sensor's design allows nonintrusive measurement of the thickness of dielectric materials, in particular, the recession rates of low-temperature ablators applied in thin (0.020 to 0.060 in. (0.05 to 0.15 mm)) layers. Twenty capacitive gages with 13 different sensing element geometries were designed, fabricated, and tested. A two-dimensional finite-element analysis was performed on several candidate geometries. Calibration procedures using ablator-simulating shims are described. A one-to-one correspondence between system output and dielectric material thickness was observed out to a thickness of 0.055 in. (1.4 mm) for a material with a permittivity about three times that of air or vacuum. A novel method of monitoring the change in sensor capacitance was developed. This technical memorandum suggests further improvements in gage design and fabrication techniques.

Gregory K Noffz↗
DOE OSTI2020

Thermal and radiation response of 4H–SiC Schottky diodes with direct-write electrical contacts

In this work, a high-sensitivity 4H–SiC temperature sensor and an alpha detector have been fabricated using additively printed metal contacts. The surface morphology and electrical conductivity of the printed electrodes were established prior to Schottky diode development. 4H–SiC Schottky diodes with direct-write printed silver contacts on the 5 μ m-thick epilayer on 4H–SiC were characterized electrically in terms of the forward and reverse current–voltage and high-frequency capacitance–voltage characteristics. Furthermore, the turn-on voltage of the Schottky diodes, as established from the forward current–voltage characteristics measured up to a temperature of 400 °C, showed a linear temperature dependence. Schottky diodes with direct-write printed Ag electrodes were able to measure alpha particles emitted from Americium-241. The high temperature and radiation response of the Schottky diodes show their suitability for multi-modal sensor fusion on the 4H–SiC platform for harsh environment applications.

42 ENGINEERING↗