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NASA NTRS1992

Decoupled predictions of radiative heating in air using a particle simulation method

A particle simulation technique with decoupled radiation is used to estimate the radiative emission along the stagnation streamline and the radiative heating at the stagnation point of a blunt-nosed vehicle entering the earth's atmosphere at hypersonic speed. The direct simulation Monte Carlo (DSMC) method is used to compute the fluid mechanics of the weakly ionized flow. The radiative emission is computed using the NEQAIR computer code with the radiation decoupled from the flowfield solution. It is concluded that the new models make it possible to decrease the predicted total radiative heating at the stagnation point of the vehicle by a factor of 15. A comparison of the DSMC approach with a continuum flow model shows that the total predicted radiative heating estimates agree within a factor of 2.

Boyd, Iain D.↗

NASA NTRS1997

Comparative Soot Diagnostics Experiment Looks at the Smoky World of Microgravity Combustion

From an economic standpoint, soot is one of the most important combustion intermediates and products. It is a major industrial product and is the dominant medium for radiant heat transport in most flames used to generate heat and power. The nonbuoyant structure of most flames of practical interest (turbulent flames) makes the understanding of soot processes in microgravity flames important to our ability to predict fire behavior on Earth. In addition, fires in spacecraft are considered a credible possibility. To respond to this risk, NASA has flown fire (or smoke) detectors on Skylab and the space shuttles and included them in the International Space Station design. The design of these detectors, however, was based entirely on normal gravity (1g) data. The detector used in the shuttle fleet is an ionization detector, whereas the system planned for the space station uses forward scattering of near-infrared light. The ionization detector, which is similar to smoke detectors used in homes, has a comparative advantage for submicron particulates. In fact, the space shuttle model uses a separation system that makes it blind to particles larger than a micron (believed to be dust). In the larger size range, the lightscattering detector is most sensitive. Without microgravity smoke data, the difference in the particle size sensitivities of the two detectors cannot be evaluated. As part of the Comparative Soot Diagnostics (CSD) experiment, these systems were tested to determine their response to particulates generated during long periods of low gravity. This experiment provided the first such measurements toward understanding soot processes on Earth and for designing and implementing improved spacecraft smoke detection systems. The objectives of CSD were to examine how particulates form from a variety of sources and to quantify the performance of several diagnostic techniques. The sources tested included four overheated materials (paper, silicone rubber, Teflon-coated (DuPont) wire, and Kapton-coated (DuPont) wires), each tested at three heating rates, and a candle tested at three air velocities. Paper, silicone rubber, and wire insulation, materials found in spacecraft crew cabins, were selected because of their different smoke properties. The candle yielded hydrocarbon soot typical of many 1g flames. Four diagnostic techniques were employed: thermophoretic sampling collected particulates for size analysis; laser light extinction measurements near the source tallied total particulate production; and laser light scattering and ionization detector measurements far from the particulate source provided data for evaluating the performance of smoke detection systems for these particulate sources.

Urban, David L.↗

NASA NTRS2000

Laser Lightcraft Performance

The purpose of this study is to establish the technical ground for modeling the physics of laser powered pulse detonation phenomenon. The principle of the laser power propulsion is that when high-powered laser is focused at a small area near the surface of a thruster, the intense energy causes the electrical breakdown of the working fluid (e.g. air) and forming high speed plasma (known as the inverse Bremsstrahlung, IB, effect). The intense heat and high pressure created in the plasma consequently causes the surrounding to heat up and expand until the thrust producing shock waves are formed. This complex process of gas ionization, increase in radiation absorption and the forming of plasma and shock waves will be investigated in the development of the present numerical model. In the first phase of this study, laser light focusing, radiation absorption and shock wave propagation over the entire pulsed cycle are modeled. The model geometry and test conditions of known benchmark experiments such as those in Myrabo's experiment will be employed in the numerical model validation simulations. The calculated performance data will be compared to the test data.

Chen, Yen-Sen↗

NASA NTRS1995

Enhanced Low Dose Rate Effects in Bipolar Circuits: A New Hardness Assurance Problem for NASA

Many bipolar integrated circuits are much more susceptible to ionizing radiation at low dose rates than they are at high dose rates typically used for radiation parts testing. Since the low dose rate is equivalent to that seen in space, the standard lab test no longer can be considered conservative and has caused the Air Force to issue an alert. Although a reliable radiation hardness assurance test has not yet been designed, possible mechanisms for low dose rate enhancement and hardness assurance tests are discussed.

bipolar integrated circuits↗

NASA NTRS1971

Comparison of the energy response of an ionization spectrometer for pions and protons

An ionization spectrometer consisting of a sandwich of iron absorbers and plastic scintillation counters was used to measure the energy of pions and protons in the interval 10 to 1000 GeV. For the limited energy interval of 10 to 40 GeV, pions and protons were identified by an air cerenkov counter. Interactions in carbon were studied in a multiplate cloud chamber placed between the cerenkov counter and the spectrometer. Knowledge of these interactions were used in conjunction with a Monte Carlo simulation of the cascade process to study differences in the response of the spectrometer to pions and protons.

Jones, W. V.↗

NASA NTRS1992

Eleven-Species Thermochemical Model Of Air

SPECIES program computes thermodynamic and transport properties and equilibrium constants. Uses least-squares polynomial curve fits of most accurate data available to provide requested values more quickly than table-lookup methods. Subroutines computing transport coefficients and collision cross sections include additional code to correct for any electron pressure when working with ionic species. Species represented: diatomic nitrogen, diatomic oxygen, atomic nitrogen, atomic oxygen, nitric oxide, ionized nitric oxide, free electron, ionized atomic nitrogen, ionized atomic oxygen, ionized diatomic nitrogen, and ionized diatomic oxygen. Written in FORTRAN 77.

Thompson, Richard A.↗

NASA NTRS1988

The computation of radiation from nonequilibrium hypersonic flows

The results of the solution of the equations that describe a hypersonic ionized flow about an elliptically blunted cone are presented. The flow conditions correspond to those of the proposed Aeroassist Flight Experiment (AFE) vehicle at altitudes between the perigee at 78 km and the approximate limit of the continuum regime at 90 km. For the free-stream velocities of interest, about 9 km/sec, the flowfield is out of thermo-chemical equilibrium, electronically excited, ionized and radiating. The gas consists of eight-chemical species including free electrons. The thermal state of the gas is modeled with a translational-rotational temperature, four vibrational temperatures for the diatomic species and an electron-electronic temperature. The electronic excitation of molecules is included. The nonequilibrium air radiation from each fluid element is computed and the radiative heat flux at the body surface is determined. The stagnation point radiative heating result agrees with previous calculations.

Candler, Graham↗

NASA NTRSDate not supplied

Retrospectives: Current State of Knowledge on the Intersection of Spaceflight Stressors and Microbial Risks to Crew and Craft

OVERVIEW The spaceflight environment has several unique stressors that affect the health of both the crew and the spacecraft. An area of continued, albeit incomplete, study is the interaction of these stressors on microbial populations inherent to both astronauts and spacecraft surfaces and systems. A primary concern is the potential for the spaceflight environment to perturb the phenotype of these populations towards negative outcomes for crew and craft. In order to effectively mitigate these potential risks, they must first be characterized. We performed a retrospective literature analysis to assess the current state of knowledge regarding the affects of ionizing radiation and elevated CO2 on relevant microbial populations. The results of these retrospectives will guide next steps in the decisions of what (if any) further studies should be pursued and to guide decisions of the need for countermeasures. STRESSORS Ionizing radiation. The health risk involved with increased exposure to cosmic radiation has been studied in crew for 35+ years, with human health and cancer risk being the main focus. However, space radiation could also affect both the resident microorganisms aboard the ISS and the normal, healthy astronaut microbiomes that are of direct concern for crew health. A retrospective review of over 250 publications was accomplished looking at the impact of cumulative ionizing radiation doses lower than 3 Gy (chronic or acute) on microbial populations. Elevated CO2. The health risk involved with elevated atmospheric CO2 in spacecraft, primarily focusing on human toxicological risks, is understudied. The current Spaceflight Maximum Allowance Concentration for 24-hour average CO2 is 0.4% (3 mm Hg), which is significantly higher than terrestrial levels (0.04%). Whether these elevated ambient CO2 levels aboard spacecraft influence the diversity and phenotypic responses of the resident microbial communities from both the spacecraft environment (air, surface, water) and crew members (gut, nasal, skin microbiomes) is not known. A retrospective review was accomplished looking at the impact of chronic CO2 exposure up to 0.7% (5 mm Hg) for up to 6 months and acute exposure up to 2.6% (20 mm Hg) for up to 24 hours. CONCLUSIONS: MICROBIOME OF THE BUILT ENVIRONMENT The microbiome of the built spacecraft environment has been sampled consistently over the course of human spaceflight and significant advancements have been made in identifying microbial populations on the ISS. The dominant source of microbes on spacecraft surfaces are human-derived. Once in the spacecraft built environment, the extreme environment selects for features that enhance survival. While efforts to understand potential antibiotic resistance and pathogenicity of ISS isolates is robust, there is little to no understanding of which spaceflight environmental stressors, to include ionizing radiation or elevated CO2, drive the evolutionary trajectory of spacecraft-associated microbial populations. CONCLUSIONS: MICROBE-HOST INTERACTIONS The host-microbiome field has emerged as an important factor in human health on Earth as well in spaceflight. The field is struggling with the complexity of the system under investigation as there is substantial taxonomic and functional heterogeneity in these communities, making it difficult to establish clear stimulus-response dynamics. Taxonomic characterization is the norm; however, the functional role of each community member is key to linking environmental perturbations to potential dysbiosis. For both ionizing radiation and elevated CO2, the likely target of the perturbation is the host tissue, not the microbes themselves.. Any resulting changes to the microbial community composition and/or function is likely a result of adapting to those changes in the host physiology. RECOMMENDATIONS Emphasize functional characterization as opposed to taxonomic characterization of microbial communities. Increase the number of investigations using chronic, spaceflight-relevant doses of ionizing radiation. MoBE studies should move away from observational studies towards predictive modeling of community dynamics. Continue to develop scale-down models, such as tissues-on-a-chip & defined microbial communities. Focus on the crew response to elevated CO2 over MoBE considerations. Assess how direct contact with the hypercapnic environment affects skin microbiome dynamics.

retrospective↗

NASA NTRSDate not supplied

Retrospectives: Intersection of Spaceflight Stressors and Microbial Risk to Crew and Craft

OVERVIEW The spaceflight environment has several unique stressors that affect the health of both the crew and the spacecraft. An area of continued, albeit incomplete, study is the interaction of these stressors on microbial populations inherent to both astronauts and spacecraft surfaces and systems. A primary concern is the potential for the spaceflight environment to perturb the phenotype of these populations towards negative outcomes for crew and craft. In order to effectively mitigate these potential risks, they must first be characterized. We performed a retrospective literature analysis to assess the current state of knowledge regarding the affects of ionizing radiation and elevated CO2 on relevant microbial populations. The results of these retrospectives will guide next steps in the decisions of what (if any) further studies should be pursued and to guide decisions of the need for countermeasures. STRESSORS Ionizing radiation. The health risk involved with increased exposure to cosmic radiation has been studied in crew for 35+ years, with human health and cancer risk being the main focus. However, space radiation could also affect both the resident microorganisms aboard the ISS and the normal, healthy astronaut microbiomes that are of direct concern for crew health. A retrospective review of over 250 publications was accomplished looking at the impact of cumulative ionizing radiation doses lower than 3 Gy (chronic or acute) on microbial populations. Elevated CO2. The health risk involved with elevated atmospheric CO2 in spacecraft, primarily focusing on human toxicological risks, is understudied. The current Spaceflight Maximum Allowance Concentration for 24-hour average CO2 is 0.4% (3 mm Hg), which is significantly higher than terrestrial levels (0.04%). Whether these elevated ambient CO2 levels aboard spacecraft influence the diversity and phenotypic responses of the resident microbial communities from both the spacecraft environment (air, surface, water) and crew members (gut, nasal,skin microbiomes) is not known. A retrospective review was accomplished looking at the impact of chronic CO2 exposure up to 0.7% (5 mm Hg) for up to 6 months and acute exposure up to 2.6% (20 mm Hg) for up to 24 hours. CONCLUSIONS: MICROBIOME OF THE BUILT ENVIRONMENT The microbiome of the built spacecraft environment has been sampled consistently over the course of human spaceflight and significant advancements have been made in identifying microbial populations on the ISS. The dominant source of microbes on spacecraft surfaces are human-derived. Once in the spacecraft built environment,the extreme environment selects for features that enhance survival. While efforts to understand potential antibiotic resistance and pathogenicity of ISS isolates is robust, there is little to no understanding of which spaceflight environmental stressors, to include ionizing radiation or elevated CO2, drive the evolutionary trajectory of spacecraft-associated microbial populations. CONCLUSIONS: MICROBE-HOST INTERACTIONS The host-microbiome field has emerged as an important factor in human health on Earth as well in spaceflight. The field is struggling with the complexity of the system under investigation as there is substantial taxonomic and functional heterogeneity in these communities, making it difficult to establish clear stimulus-response dynamics.Taxonomic characterization is the norm; however, the functional role of each community member is key to linking environmental perturbations to potential dysbiosis. For both ionizing radiation and elevated CO2, the likely target of the perturbation is the host tissue, not the microbes themselves.. Any resulting changes to the microbial community composition and/or function is likely a result of adapting to those changes in the host physiology. RECOMMENDATIONS Emphasize functional characterization as opposed to taxonomic characterization of microbial communities.Increase the number of investigations using chronic, spaceflight-relevant doses of ionizing radiation. MoBE studies should move away from observational studies towards predictive modeling of community dynamics. Continue to develop scale-down models, such as tissues-on-a-chip & defined microbial communities. Focus on the crew response to elevated CO2 over MoBE considerations. Assess how direct contact with the hypercapnic environment affects skin microbiome dynamics.

Countermeasures↗

NASA NTRS1984

Nighttime observations of thunderstorm electrical activity from a high altitude airplane

Photographs from a NASA U-2 airplane flying over nocturnal thunderstorms show frequent lightning activity in the upper part of the cloud. In some cases, unobscured segments of lightning channels 1 km or longer are visible in clear air around and above the cloud. Multiple images of lightning channels indicate multiple discharges in the same channel. Photographs taken through a diffraction grating show that the lightning has a spectrum similar to that observed in the lower troposphere. Lightning spectra obtained with a slitless line-scan spectrometer show strong singly ionized nitrogen emissions at 463.0 and 500.5 nm. Field changes measured with an electric field-change meter correlate with pulses measured with a photocell optical system. Optical signals corresponding to dart leader, return stroke, and continuing current events are readily distinguished in the scattered light emerging from the cloud surface. The variation of light intensity with time in lightning events is consistent with predicted modification of optical lightning signals by clouds. It appears that satellite based optical sensor measurements cannot provide reliable information on current rise times in return strokes. On the other hand, discrimination between cloud-to-ground and intracloud flashes and the counting of ground strokes is possible using the optical pulse pairs which have been identified with leader, return-stroke events in the cloud-to-ground flashes studied.

Brook, M.↗

NASA NTRS2017

Mass Spectra Deconvolution of Gaseous Mixtures Containing Volatile Organic Compounds

The Spacecraft Atmosphere Monitor (S.A.M.) analyzes all gaseous pollutants in the 1-150Th mass-to-charge range based on their positive-ion mass spectra. Of particular interest is the Trace Gas Analysis (TGA) mode of operation in which S.A.M detects minute amounts of volatile organic compounds (VOC). Pollutant component of the ambient air is sampled on demand in twenty full mass spectra per second. All spectra is accumulated in two-second intervals by an on-board Field Programmable Gate Arrays (FPGA) unit. Mass spectra represents the number of detected fragment ions in a given mass-to-charge ratio channel. Electron impact ionization of neutral molecules results in creation of numerous fragment ions and most of organic compounds will contribute several identical fragments. Despite the presence of these molecular isobars, we developed the deconvolution algorithm capable of identifying target species based on their characteristic fragmentation patterns. We investigate the efficiency of deconvolution algorithm as a function of mass resolution with which mass spectrum is acquired. Higher the mass resolution, better the chances are to distinguish between stereoisomers using their fragmentation propensities, but also results in higher data volumes to be processed by a set of small footprint software stacks hosted by an on-board computer. Finding the balance between deconvolution accuracy and generated data volume under time constrains and limited computing resources is the main topic of this study.

Darrach, M.↗

NASA NTRS1985

Sub-luminal pulses from cosmic ray air showers

Some of the signals produced by air showers in scintillators possess a distinctive feature, a sub-luminal pulse (SLP) following the normal one with a time delay of approximately 1.5 r/c. The average amplitude of the SLP corresponds to an energy deposit of about 50 MeV, three times as much as is deposited in a typical scintillator by vertical minimum ionizing muons. The SLP account for approximately 5% of the energy deposited in the atmosphere by IR showers with energy 10 to the 10th power GeV at impact parameters 1 km. Assuming that these pulses are due to neutrons travelling with a speed slightly less than c, they provide a unique means of estimating E sub h, the energy deposited by slow hadrons, in showers of this very high energy. On the other hand, if not allowed for properly, these pulses are liable to cause errors in estimating the impact parameters of large showers from pulse width observations.

Linsley, J.↗

NASA NTRS2001

SMOKE: Characterization of Smoke Particulate for Spacecraft Fire Detection

'Smoke' is a flight definition investigation whose purpose is to characterize the smoke particulate from microgravity smoke sources to enable improved design of future space-craft smoke detectors. In the earliest missions (Mercury, Gemini and Apollo), the crew quarters were so cramped that it was considered reasonable that the astronauts would rapidly detect any fire. The Skylab module, however, included approximately 30 UV-sensing fire detectors. The Space Shuttle Orbiter has nine particle-ionization smoke detectors in the mid-deck and flight deck. The detectors for the US segments of the International Space Station (ISS) are laser-diode, forward-scattering, smoke detectors. Current plans for the ISS call for two detectors in the open area of the module, and detectors in racks that have cooling air-flow. Due to the complete absence of microgravity data, all three of these detector systems were designed based upon 1-g test data and experience. As planned mission durations and complexity increase and the volume of spacecraft increases, the need for and importance of effective, crew-independent, fire detection will grow significantly, necessitating more research into microgravity fire phenomena. In 1997 the Comparative Soot Diagnostics Experiment (CSD) flew in the Orbiter Middeck as a Glovebox payload. The CSD experiment was designed to produce small quantities of smoke from several sources to obtain particulate samples and to determine the response of the ISS and Orbiter smoke detectors to these sources. Marked differences in the performance of the detectors compared to their behavior in 1-g were observed. In extreme cases, the detector used in the orbiter was completely blind to easily visible smoke from sources that were readily detected in 1-g. It is hypothesized but as yet unverified that this performance difference was due to enhanced growth of liquid smoke droplets in low-g. These CSD results clearly demonstrate that spacecraft smoke detector design cannot be based on 1-g experience.

Urban, D. L.↗

NASA NTRS1989

Monte Carlo simulation of reentry plasmas

Attention is given to the treatment of ionization and plasma effects in the direct simulation Monte Carlo method. The requirements for accurate modeling of reentry plasmas are discussed along with the difficulties these requirements present. The current method for modeling such plasmas is reviewed and an alternative method is presented. Both methods are applied to the flow of a 10 km/s shock wave in air at 0.1 torr; a flowfield directly relevant to the projected aeroassisted orbital transfer vehicle. The results are compared and the differences between the methods are discussed.

Carlson, Ann B.↗

NASA NTRS1971

Design and Performance of a Gas Chromatograph for Automatic Monitoring of Pollutants in Ambient Air

In recent years, interest in air pollution constituents has focused on carbon monoxide and hydrocarbons as prime components of polluted air. Instrumental methods have been developed, and commercial instruments for continuous monitoring of these components have been available for a number of years. For the measurement of carbon monoxide, non-dispersive infrared spectroscopy has been the accepted tool, in spite of its marginal sensitivity at low parts-per-million levels. For continuously monitoring total hydrocarbons, the hydrogen flame ionization analyzer has been widely accepted as the preferred method. The inadequacy of this latter method became evident when it was concluded that methane is non-reactive and cannot be considered a contaminant even though present at over 1 ppm in the earth's atmosphere. Hence, the need for measuring methane separately became apparent as a means of measuring the reactive and potentially harmful non-methane hydrocarbons fraction. A gas chromatographic method for the measurement of methane and total hydrocarbons which met these requirements has been developed. In this technique, methane was separated on conventional gas chromatographic columns and detected by a hydrogen flame ionization detector (FID) while the total hydrocarbons were obtained by introducing a second sample directly into the FID without separating the various components. The reactive, or non-methane hydrocarbons, were determined by difference. Carbon monoxide was also measured after converting to methane over a heated catalyst to render it detectable by the FID. The development of this method made it possible to perform these measurements with a sensitivity of as much as 1 ppm full scale and a minimum detectability of 20 ppb. Incorporating this technique, criteria were developed by APCO for a second generation continuous automatic instrument for atmospheric monitoring stations.

Villalobos, R.↗

NASA NTRS2016

Thermochemistry of Strong Air Plasmas for Hypervelocity Earth Entry of Asteroids

The specific heat, enthalpy and free energy of nitrogen and oxygen are calculated for pressures between 1 and 100 bars and temperatures between 10,000 and 100,000 degrees Kelvin. The data are presented in a form suitable for input into computational fluid dynamics computer codes. This range of temperature and pressure are typical of the conditions expected in the bow shock layer of a meteor or small asteroid entering Earth's atmosphere. The extent of double and triple ionization of nitrogen and oxygen atoms under these conditions will be estimated.

Ionization Energy Depression↗

NASA NTRS1993

Micromachined Electron-Tunneling Infrared Detectors

Pneumatic/thermal infrared detectors based partly on Golay-cell concept, but smaller and less fragile. Include containers filled with air or other gas trapped behind diaphragms. Infrared radiation heats sensors, causing gas to expand. Resulting deflections of diaphragms measured by displacement sensors based on principle of electron-tunneling transducers of scanning tunneling microscopes. Exceed sensitivity of all other miniature, uncooled infrared sensors presently available. Expected to include low consumption of power, broadband sensitivity, room-temperature operation, and invulnerability to ionizing radiation.

Kenny, Thomas W.↗

NASA NTRS2015

Multifunctional Electroactive Nanocomposites Based on Piezoelectric Boron Nitride Nanotubes

Space exploration missions require sensors and devices capable of stable operation in harsh environments such as those that include high thermal fluctuation, atomic oxygen, and high-energy ionizing radiation. However, conventional or state-of-the-art electroactive materials like lead zirconate titanate, poly(vinylidene fluoride), and carbon nanotube (CNT)-doped polyimides have limitations on use in those extreme applications. Theoretical studies have shown that boron nitride nanotubes (BNNTs) have strength-to-weight ratios comparable to those of CNTs, excellent high-temperature stability (to 800 C in air), large electroactive characteristics, and excellent neutron radiation shielding capability. In this study, we demonstrated the experimental electroactive characteristics of BNNTs in novel multifunctional electroactive nanocomposites. Upon application of an external electric field, the 2 wt % BNNT/polyimide composite was found to exhibit electroactive strain composed of a superposition of linear piezoelectric and nonlinear electrostrictive components. When the BNNTs were aligned by stretching the 2 wt % BNNT/polyimide composite, electroactive characteristics increased by about 460% compared to the nonstretched sample. An all-nanotube actuator consisting of a BNNT buckypaper layer between two single-walled carbon nanotube buck-paper electrode layers was found to have much larger electroactive properties. The additional neutron radiation shielding properties and ultraviolet/visible/near-infrared optical properties of the BNNT composites make them excellent candidates for use in the extreme environments of space missions. utilizing the unique characteristics of BNNTs.

Kang, Jin Ho↗