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NASA NTRS2008

Smart Sensor Systems for Aerospace Applications: From Sensor Development to Application Testing

The application of Smart Sensor Systems for aerospace applications is a multidisciplinary process consisting of sensor element development, element integration into Smart Sensor hardware, and testing of the resulting sensor systems in application environments. This paper provides a cross-section of these activities for multiple aerospace applications illustrating the technology challenges involved. The development and application testing topics discussed are: 1) The broadening of sensitivity and operational range of silicon carbide (SiC) Schottky gas sensor elements; 2) Integration of fire detection sensor technology into a "Lick and Stick" Smart Sensor hardware platform for Crew Exploration Vehicle applications; 3) Extended testing for zirconia based oxygen sensors in the basic "Lick and Stick" platform for environmental monitoring applications. It is concluded that that both core sensor platform technology and a basic hardware platform can enhance the viability of implementing smart sensor systems in aerospace applications.

Hunter, G. W.↗
NASA NTRSDate not supplied

A Brief Overview of Relevant Silicon Carbide Electronics and Sensor Development for Long Duration Venus Surface Exploration

This presentation concentrates on the potential of long duration Venus surface missions, and the role of Silicon Carbide (SiC) electronics and sensor advancements in such exploration. For example, SiC integrated circuit (IC) electronics have matured to a state where a simple long-life scientific probe is feasible for extended Venus surface operations. These electronics have been demonstrated for more than a year at 500˚C, and 60 days in high-fidelity simulated Venus surface conditions [1-2]. Further, high temperature chemical sensing technology, including SiC-based gas sensors, integrated with SiC electronics can enable future exploration of the Venus surface atmosphere [3]. Continued maturation of these high temperature electronics and sensors has been part of the Long-Lived In-Situ Solar System Explorer (LLISSE) project to provide an operational system for in situ exploration of the Venus surface up to 60 days [4]. A key focus of this work includes increasing the complexity and decreasing the power consumption of the ICs which will pave the way to enhanced capabilities, such as long-duration Venus seismic measurements and other mission capabilities currently under development. This is in parallel to work expanding the capabilities of the sensor technology to provide science measurements on the Venus surface. This presentation will give an overview of possible extended duration Venus surface exploration and some of the SiC-based technologies that can enable this exploration.

high temperature Venus surface electronics sensors↗
NASA NTRS2016

New Approach to Characterize CO2 and CH4 Emissions over Sacramento, California Using an Airborne Aircraft Measurement

Emission fluxes of carbon dioxide (CO2) and methane (CH4) over Sacramento, California, USA, are estimated using an aircraft equipped with a cavity ring-down greenhouse gas sensor through the Alpha Jet Atmospheric eXperiment (AJAX). To better quantify the emission fluxes over the entire city and two small point sources within the area, we designed flights in a cylindrical pattern and computed the emission fluxes from 9 flights over all seasons using the Kriging method based on Gausss divergence theorem. The concentrations at the downwind side of Sacramento show somewhat persistent patterns among the 9 flights, but the magnitudes and locations of the fluxes vary depending on the individual weather conditions and seasonality on a given flight day. The net emission fluxes tend to be smaller in summer (July) than winter (November). Both trace gas mixing ratios as well as the wind speed and direction show high spatial variability both horizontally and vertically. The local maximum emission fluxes over a landfill and a rice field measured on July 29, 2015, were 2-3 times lower than the maximum measured over the entire city. These low emission fluxes suggest that not only the local source but also the transport of greenhouse gases due to diurnal and seasonal variation in winds have a strong effect on the CO2 and CH4 flux estimation of the both local emissions and city-size emissions. Our results highlight that the aircraft-based approach is effective and useful for capturing city-size emission fluxes and estimating the greenhouse gas emissions and its sources.

airborne↗
NASA NTRS2003

Method for Balancing Detector Output to a Desired Level of Balance at a Frequency

A multi-gas sensor is provided which modulates a polarized light beam over a broadband of wavelengths between two alternating orthogonal polarization components. The two orthogonal polarization components of the polarization modulated beam are directed along two distinct optical paths. At least one optical path contains one or more spectral discrimination elements, with each spectral discrimination element having spectral absorption features of one or more gases of interest being measured. The two optical paths then intersect, and one orthogonal component of the intersected components is transmitted and the other orthogonal component is reflected. The combined polarization modulated beam is partitioned into one or more smaller spectral regions of interest where one or more gases of interest has an absorption band. The difference in intensity between the two orthogonal polarization components is then determined in each partitioned spectral region of interest as an indication of the spectral emission/absorption of the light beam by the gases of interest in the measurement path. The spectral emission/absorption is indicative of the concentration of the one or more gases of interest in the measurement path. More specifically, one embodiment of the present invention is a gas filter correlation radiometer which comprises a polarizer, a polarization modulator, a polarization beam splitter, a beam combiner, wavelength partitioning element, and detection element. The gases of interest are measured simultaneously and, further, can be measured independently or non-independently. Furthermore, optical or electronic element are provided to balance optical intensities between the two optical paths.

Sachse, Glenn W.↗
NASA NTRS2019

Quantification of CO2 and CH4 emissions over Sacramento, California, based on divergence theorem using aircraft measurements

Emission estimates of carbon dioxide (CO2) and methane (CH4) and the meteorological factors affecting them are investigated over Sacramento, California, using an aircraft equipped with a cavity ring-down greenhouse gas sensor as part of the Alpha Jet Atmospheric eXperiment (AJAX) project. To better constrain the emission fluxes, we designed flights in a cylindrical pattern and computed the emission fluxes from two flights using a kriging method and Gauss’s divergence theorem. Differences in wind treatment and assumptions about background concentrations affect the emission estimates by a factor of 1.5 to 7. The uncertainty is also impacted by meteorological conditions and distance from the emission sources. The vertical layer averaging affects the flux estimate, but the choice of raw wind or mass-balanced wind is more important than the thickness of the vertical averaging for massbalanced wind for both urban and local scales. The importance of vertical mass transfer for flux estimates is examined, and the difference in the total emission estimate with and without vertical mass transfer is found to be small, especially at the local scale. The total flux estimates accounting for the entire circumference are larger than those based solely on measurements made in the downwind region. This indicates that a closed-shape flight profile can better contain total emissions relative to a one-sided curtain flight because most cities have more than one point source and wind direction can change with time and altitude. To reduce the uncertainty of the emission estimate, it is important that the sampling strategy account not only for known source locations but also possible unidentified sources around the city. Our results highlight that aircraft-based measurements using a closed-shape flight pattern are an efficient and useful strategy for identifying emission sources and estimating local- and city-scale greenhouse gas emission fluxes.

Ju-Mee Ryoo↗
NASA NTRS1978

Rocket effluent size distributions made with a cascade quartz crystal microbalance

Airborne particulate size distribution measurements were made in the stabilized ground cloud from a Titan III C rocket just after launch from the Kennedy Space Center on May 12, 1977. The measurements were made from aboard a small twin engine aircraft instrumented with particle and gas sensors. The plume was followed for about 1 hour while making multiple passes through the cloud at varying altitudes. The results obtained with a ten-stage cascade quartz crystal microbalance impactor show that the mass concentration as a function of particle diameter is bimodal with the first maximum between 0.05 micrometers and 0.1 micrometers and the second maximum between 0.8 and 1.0 micrometer. Scanning electron microscope analysis were performed on the material collected and show distinctly different kinds of particles in the two modes.

Woods, D. C.↗
NASA NTRS1995

Experiments On Transparent Conductive Films For Spacecraft

Report describes experiments on thin, transparent, electrically conductive films made, variously, of indium tin oxide covered by magnesium fluoride (ITO/MgF2), aluminum-doped zinc oxide (AZO), or pure zinc oxide (ZnO). Films are candidates for application to such spacecraft components, including various optoelectronic devices and window surfaces that must be protected against buildup of static electric charge. On Earth, such films useful on heat mirrors, optoelectronic devices, gas sensors, and automotive and aircraft windows.

Perez-Davis, Marla E.↗
NASA NTRS1995

Silicon Carbide-Based Hydrogen and Hydrocarbon Gas Detection

Hydrogen and hydrocarbon detection in aeronautical applications is important for reasons of safety and emissions control. The use of silicon carbide as a semiconductor in a metal-semiconductor or metal-insulator-semiconductor structure opens opportunities to measure hydrogen and hydrocarbons in high temperature environments beyond the capabilities of silicon-based devices. The purpose of this paper is to explore the response and stability of Pd-SiC Schottky diodes as gas sensors in the temperature range from 100 to 400 C. The effect of heat treating on the diode properties as measured at 100 C is explored. Subsequent operation at 400 C demonstrates the diodes' sensitivity to hydrogen and hydrocarbons. It is concluded that the Pd-SiC Schottky diode has potential as a hydrogen and hydrocarbon sensor over a wide range of temperatures but further studies are necessary to determine the diodes' long term stability.

Hunter, Gary W.↗
NASA NTRS1997

Space Environment Stability and Physical Properties of New Materials for Space Power and Commercial Applications

Useful and informative results were obtained on virtually all materials investigated. For example, the stability of ITO-based arc-proof transparent coatings was greatly improved by substitution of silicon oxide for magnesium fluoride as a dopant. Research on 'air-doped' ITO films has yielded new insight into their conduction mechanism which will help in further development of these coatings. Some air-doped films were found to be extremely pressure sensitive. This work may lead to improved, low-cost gas sensors and vacuum gauges. Work on another promising transparent arc-proof coating (titanium oxide) was initiated in collaboration with industry. Graphite oxide-like materials were synthesized and tested for possible use in high energy-density batteries and other applications. We also started a high-priority project to find the cause of unexpected environmental damage to the exterior of the Hubble Space Telescope (HST) discovered on a recent Shuttle mission. Materials were characterized before and after exposure to soft x-rays and other threats in ground-based simulators.

Hambourger, Paul D.↗
NASA NTRS1998

Temperature Dependence of Diffusion and Reaction at a Pd/SiC Contact

Schottky diodes of Palladium/SiC are good candidates for hydrogen and hydrocarbon gas sensors at elevated temperature. The detection sensibility of the diodes has been found heavily temperature dependent. In this work, emphasis has been put on the understanding of changes of physical and chemical properties of the Schottky diodes with variation of temperature. Schottky diodes were made by depositing ultra-thin palladium films onto silicon carbide substrates. The electrical and chemical properties of Pd/SiC Schottky contacts were studied by XPS and AES at different annealing temperatures. No significant change in the Schottky barrier height of the Pd/SiC contact was found in the temperature range of RT-400 C. However, both palladium diffused into SiC and silicon migrated into palladium thin film as well as onto surface were observed at room temperature. The formation of palladium compounds at the Pd/SiC interface was also observed. Both diffusion and reaction at the Pd/SiC interface became significant at 300 C and higher temperature. In addition, silicon oxide was found also at the interface of the Pd/SiC contact at high temperature. In this report, the mechanism of diffusion and reaction at the Pd/SiC interface will be discussed along with experimental approaches.

Shi, D.T.↗
NASA NTRS1998

"Un-annealed and Annealed Pd Ultra-Thin Film on SiC Characterized by Scanning Probe Microscopy and X-ray Photoelectron Spectroscopy"

Pd/SiC has been used as a hydrogen and a hydrocarbon gas sensor operated at high temperature. UHV (Ultra High Vacuum)-Scanning Tunneling Microscopy (STM), Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) techniques were applied to study the relationship between the morphology and chemical compositions for Pd ultra-thin films on SiC (less than 30 angstroms) at different annealing temperatures. Pd ultra-thin film on 6H-SiC was prepared by the RF sputtering method. The morphology from UHV-STM and AFM shows that the Pd thin film was well deposited on SiC substrate, and the Pd was partially aggregated to round shaped participates at an annealing temperature of 300 C. At 400 C, the amount of surface participates decreases, and some strap shape participates appear. From XPS, Pd2Si was formed on the surface after annealing at 300 C, and all Pd reacted with SiC to form Pd2Si after annealing at 400 C. The intensity of the XPS Pd peak decreases enormously at 400 C. The Pd film diffused into SiC, and the Schottky barrier height has almost no changes. The work shows the Pd sicilides/SiC have the same electronic properties with Pd/SiC, and explains why the Pd/SiC sensor still responds to hydrogen at high operating temperatures.

Lu, W. J.↗
NASA NTRS1994

Effects of Increased CO2 Level on the Well-Being, Growth and Renal Function of Rats

On the Space Shuttle the mean CO2 levels have been 0.3% which is ten times normal air, while there have been extended periods with mean levels of 0.7% and peak concentrations of 2%. On the Space Station the projected mean concentration of CO2 is 0.7% and not to exceed 1.0%. To ensure that high level of CO2 does not compromise the integrity of the science on the Space Station, the effects of chronic exposure to high levels of CO2 were investigated. Following 7 days of cage adaptation animals exposed to 2% CO2 for 30 days were compared to control (ambient air) animals and the effects on the well-being, growth and renal function analyzed. Ten male rats per group were placed in individual metabolic cages which allowed monitoring of daily food and water consumption, as well as feces and urine to be collected. Cages were placed in a plexiglass chamber with internal environment controlled by a computer in conjunction with gas sensors. The elevated CO2 was held constant at 2.0 +/- 0.03% and the O2 at 20.9 +/- 0.15%. Body weight and food and water intake were measured daily for the first ten days of exposure and then every three to four days for the remaining three weeks. Urine was measured for pH, CO2 (as an indicator for bicarbonate) and ammonia (as an indicator for ammonium). During 2% CO2 exposure, animal growth, weight, food and water consumption were within normal ranges suggesting that their well-being was not affected. Urine pH decreased from 7.12 to 6.77 over the first 6 days of exposure and increased the following 24 days returning to pre-exposure levels. Urine NH4+ increased 68% the first 6 days then dropped to and remained at 29% higher than pre-exposure level. Urine bicarbonate concentration did not change the first 6 days, but significantly increased by day 30. These results of chronic exposure to 2% C02 are consistent with renal compensation for respiratory acidosis which may impact science conducted on the Space Shuttle or the Space Station if CO2 levels reach 2%.

Lang, C.↗
NASA NTRS2004

Atmospheric Trace Gas Abundances and Stable Isotope Ratios via IR-LIF

We propose to develop new technologies with support provided by PIDDP that will enable the in situ measurements of abundances and stable isotope ratios in important radiatively and biogenically active gases such as carbon dioxide, carbon monoxide, water, methane, nitrous oxide, and hydrogen sulfide to very high precision (0.1 per mil or better for the isotopic ratios, for example). Such measurements, impossible at present, could provide pivotal new constraints on the global (bio)geochemical budgets of these critical species, and could also be used to examine the dynamics of atmospheric transport on Mars, Titan, and other solar system bodies. We believe the combination of solid state light sources with imaging of the IR laser induced fluorescence (IR-LIF) via newly available detector arrays will make such in situ measurements possible for the first time. Even under ambient terrestrial conditions, the LIF yield from vibrational excitation of species such as water and carbon dioxide should produce emission measures well in excess of ten billion photons/sec from samples volumes of order 1 c.c. These count rates can, in principle, yield detection limits into the sub-ppt range that are required for the in situ isotopic study of atmospheric trace gases. While promising, such technologies are relatively immature, but developing rapidly, and there are a great many uncertainties regarding their applicability to in situ IR-LIF planetary studies. We therefore feel PIDDP support will be critical to developing these new tools, and propose a three-year program to combine microchip near-IR lasers with low background detection axes and state-of-the-art HgCdTe detectors developed for astronomical spectroscopy to investigate the sensitivity of IR-LIF under realistic planetary conditions, to optimize the optical pumping and filtering schemes for important species, and to apply the spectrometer to the non-destructive measurement of stable isotopes in a variety of test samples. These studies form the necessary precursors to the development of compact, lightweight stable isotope/trace gas sensors for future planetary missions.

Blake, Geoffrey A.↗
NASA NTRS2002

Near-infrared diode laser based spectroscopic detection of ammonia: a comparative study of photoacoustic and direct optical absorption methods

A photoacoustic spectroscopic (PAS) and a direct optical absorption spectroscopic (OAS) gas sensor, both using continuous-wave room-temperature diode lasers operating at 1531.8 nm, were compared on the basis of ammonia detection. Excellent linear correlation between the detector signals of the two systems was found. Although the physical properties and the mode of operation of both sensors were significantly different, their performances were found to be remarkably similar, with a sub-ppm level minimum detectable concentration of ammonia and a fast response time in the range of a few minutes.

NASA Discipline Life Sciences Technologies↗
NASA NTRS2001

Spectroscopic detection of biological NO with a quantum cascade laser

Two configurations of a continuous wave quantum cascade distributed feedback laser-based gas sensor for the detection of NO at a parts per billion (ppb) concentration level, typical of biomedical applications, have been investigated. The laser was operated at liquid nitrogen temperature near lambda = 5.2 microns. In the first configuration, a 100 m optical path length multi-pass cell was employed to enhance the NO absorption. In the second configuration, a technique based on cavity-enhanced spectroscopy (CES) was utilized, with an effective path length of 670 m. Both sensors enabled simultaneous analysis of NO and CO2 concentrations in exhaled air. The minimum detectable NO concentration was found to be 3 ppb with a multi-pass cell and 16 ppb when using CES. The two techniques are compared, and potential future developments are discussed.

NASA Discipline Environmental Health↗
NASA NTRS2004

Silicon Carbide Schottky Barrier Diode

This chapter reviews the status of SiC Schottky barrier diode development. The fundamental of Schottky barrier diodes is first provided, followed by the review of high-voltage SiC Schottky barrier diodes, junction-barrier Schottky diodes, and merged-pin-Schottky diodes. The development history is reviewed ad the key performance parameters are discussed. Applications of SiC SBDs in power electronic circuits as well as other areas such as gas sensors, microwave and UV detections are also presented, followed by discussion of remaining challenges.

Zhao, Jian H.↗
NASA NTRS1996

Transparent, Conductive Coatings Developed for Arc-Proof Solar Arrays

Transparent, conductive thin-film coatings have many potential applications where a surface must be able to dissipate electrical charges without sacrificing its optical properties. Such applications include automotive and aircraft windows, heat mirrors, optoelectronic devices, gas sensors, and solar cell array surfaces for space applications. Many spacecraft missions require that solar cell array surfaces dissipate charges in order to avoid damage such as electronic upsets, formation of pinholes in the protective coatings on solar array blankets, and contamination due to deposition of sputtered products. In tests at the NASA Lewis Research Center, mixed thin-films of sputter-deposited indium tin oxide (ITO) and magnesium fluoride (MgF2) that could be tailored to the desired sheet resistivity, showed transmittance values of greater than 90 percent. The samples evaluated were composed of mixed, thin-film ITO/MgF2 coatings, with a nominal thickness of 650 angstroms, deposited onto glass substrates. Preliminary results indicated that these coatings were durable to vacuum ultraviolet radiation and atomic oxygen. These coatings show promise for use on solar array surfaces in polar low-Earth-orbit environments, where a sheet resistivity of less than 10(exp 8)/square is required, and in geosynchronous orbit environments, where a resistivity of less than 10(exp 9)/square is required.

Source record↗
NASA NTRS2007

NASA Dryden Flight Research Center C-17 Research Overview

A general overview of NASA Dryden Flight Research Center's C-17 Aircraft is presented. The topics include: 1) 2006 Activities PHM Instrumentation Refurbishment; 2) Acoustic and Vibration Sensors; 3) Gas Path Sensors; 4) NASA Instrumentation System Racks; 5) NASA C-17 Simulator; 6) Current Activities; 7) Future Work; 8) Lawn Dart ; 9) Weight Tub; and 10) Parachute Test Vehicle.

Miller, Chris↗