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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Effect of hard X-rays on the emission lines of Seyfert galaxies and QSOs

Models of photoionized emission-line regions show that inclusion of a hard X-ray component in the ionizing continuum has relatively minor effects on most optical line intensities but helps to explain the strong O VI emission observed from QSOs. The optical-forbidden lines of NGC 4151 indicate roughly solar abundances ratios of N/O/Ne/Fe. The X-ray absorption arises largely in neutral portions of the emission-line clouds.

Shields, G. A.↗
NASA NTRS2011

Evaluation of Lightning Induced Effects in a Graphite Composite Fairing Structure

Defining the electromagnetic environment inside a graphite composite fairing due to near-by lightning strikes is of interest to spacecraft developers. This effort develops a transmission-line-matrix (TLM) model with a CST Microstripes to examine induced voltages. on interior wire loops in a composite fairing due to a simulated near-by lightning strike. A physical vehicle-like composite fairing test fixture is constructed to anchor a TLM model in the time domain and a FEKO method of moments model in the frequency domain. Results show that a typical graphite composite fairing provides adequate shielding resulting in a significant reduction in induced voltages on high impedance circuits despite minimal attenuation of peak magnetic fields propagating through space in near-by lightning strike conditions.

Trout, Dawn H.↗
DOE OSTI2022

Bioinspired synthesis of thermally stable and mechanically strong nanocomposite coatings

Abstract An innovative biomimetic method has been developed to synthesize layered nanocomposite coatings using silica and sugar-derived carbon to mimic the formation of a natural seashell structure. The layered nanocomposites are fabricated through alternate coatings of condensed silica and sugar. Sugar-derived carbon is a cost-effective material as well as environmentally friendly. Pyrolysis of sugar will form polycyclic aromatic carbon sheets, i.e., carbon black. The resulting final nanocomposite coatings can survive temperatures of more than 1150 °C and potentially up to 1650 °C. These coatings have strong mechanical properties, with hardness of more than 11 GPa and elastic modulus of 120 GPa, which are 80% greater than those of pure silica. The layered coatings have many applications, such as shielding in the form of mechanical barriers, body armor, and space debris shields. Graphical abstract

36 MATERIALS SCIENCE↗
NASA NTRS2009

Probabilistic Assessment of Radiation Risk for Astronauts in Space Missions

Accurate predictions of the health risks to astronauts from space radiation exposure are necessary for enabling future lunar and Mars missions. Space radiation consists of solar particle events (SPEs), comprised largely of medium energy protons, (less than 100 MeV); and galactic cosmic rays (GCR), which include protons and heavy ions of higher energies. While the expected frequency of SPEs is strongly influenced by the solar activity cycle, SPE occurrences themselves are random in nature. A solar modulation model has been developed for the temporal characterization of the GCR environment, which is represented by the deceleration potential, phi. The risk of radiation exposure from SPEs during extra-vehicular activities (EVAs) or in lightly shielded vehicles is a major concern for radiation protection, including determining the shielding and operational requirements for astronauts and hardware. To support the probabilistic risk assessment for EVAs, which would be up to 15% of crew time on lunar missions, we estimated the probability of SPE occurrence as a function of time within a solar cycle using a nonhomogeneous Poisson model to fit the historical database of measurements of protons with energy > 30 MeV, (phi)30. The resultant organ doses and dose equivalents, as well as effective whole body doses for acute and cancer risk estimations are analyzed for a conceptual habitat module and a lunar rover during defined space mission periods. This probabilistic approach to radiation risk assessment from SPE and GCR is in support of mission design and operational planning to manage radiation risks for space exploration.

Kim, Myung-Hee↗
NASA NTRS2009

Improving the Visible and Infrared Contrast Ratio of Microshutter Arrays

Three device improvements have been developed that dramatically enhance the contrast ratio of microshutters. The goal of a microshutter is to allow as much light through as possible when the shutters are in the open configuration, and preventing any light from passing through when they are in the closed position. The ratio of the transmitted light that is blocked is defined here as the contrast ratio. Three major components contribute to the improved performance of these microshutters: 1. The precise implementation of light shields, which protect the gap around the shutters so no light can leak through. It has been ascertained that without the light shield there would be a gap on the order of 1 percent of the shutter area, limiting the contrast to a maximum of 100. 2. The precise coating of the interior wall of each microshutter was improved with an insulator and metal using an angle deposition technique. The coating prevents any infrared light that finds an entrance on the surface of the microshutter cell from being emitted from a sidewall. Since silicon is in effect transparent to any light with a wavelength longer than .1 micrometer, these coatings are essential to blocking any stray signals when the shutters are closed. 3. A thin film of molybdenum nitride (MoN) was integrated onto the surface of the microshutter blade. This film provides the majority of light blockage over the microshutter and also ensures that the shutter can be operated over a wide temperature range by maintaining its flatness. These improvements were motivated by the requirements dictated by the James Webb Space Telescope NIRSpec instrument. The science goals of the NIRSpec require observing some of the very faintest objects in a given field of view that also may contain some very bright objects. To observe the faint objects, the light from the bright objects - which could be thousands of times brighter - must be completely blocked. If a closed microshutter is even slightly transmissive, a very bright object will still transmit a small signal, which can be larger than a signal from a very faint object transmitted through an open shutter. Since this situation can completely corrupt the results, it was necessary that the closed shutters be able to attenuate light by at least a factor of 2,000. There currently exist four flight-quality microshutter arrays that have been fully or are currently undergoing testing and the results support that the three improvements described above have successfully led to contrast levels greater than 50,000 in over 99 percent of the microshutters at an operating temperature of 35 K. Applications for these high-contrast microshutters are in the photomask generation and stepper equipment used to make integrated circuits and microelectromechanical (MEMS) devices. Since microshutters are a reconfigurable optical element, their versatility in these industries provides an improvement over printed masks and fixed projection alignment systems.

Jhabvala, Murzy↗
NASA NTRS2015

Experimental and Finite Element Modeling of Near-Threshold Fatigue Crack Growth for the K-Decreasing Test Method

The experimental methods to determine near-threshold fatigue crack growth rate data are prescribed in ASTM standard E647. To produce near-threshold data at a constant stress ratio (R), the applied stress-intensity factor (K) is decreased as the crack grows based on a specified K-gradient. Consequently, as the fatigue crack growth rate threshold is approached and the crack tip opening displacement decreases, remote crack wake contact may occur due to the plastically deformed crack wake surfaces and shield the growing crack tip resulting in a reduced crack tip driving force and non-representative crack growth rate data. If such data are used to life a component, the evaluation could yield highly non-conservative predictions. Although this anomalous behavior has been shown to be affected by K-gradient, starting K level, residual stresses, environmental assisted cracking, specimen geometry, and material type, the specifications within the standard to avoid this effect are limited to a maximum fatigue crack growth rate and a suggestion for the K-gradient value. This paper provides parallel experimental and computational simulations for the K-decreasing method for two materials (an aluminum alloy, AA 2024-T3 and a titanium alloy, Ti 6-2-2-2-2) to aid in establishing clear understanding of appropriate testing requirements. These simulations investigate the effect of K-gradient, the maximum value of stress-intensity factor applied, and material type. A material independent term is developed to guide in the selection of appropriate test conditions for most engineering alloys. With the use of such a term, near-threshold fatigue crack growth rate tests can be performed at accelerated rates, near-threshold data can be acquired in days instead of weeks without having to establish testing criteria through trial and error, and these data can be acquired for most engineering materials, even those that are produced in relatively small product forms.

Smith, Stephen W.↗
DOE OSTI2025

Accelerating Hamiltonian Monte Carlo for Bayesian inference in neural networks and neural operators

Hamiltonian Monte Carlo (HMC) is a powerful and accurate method to sample from the posterior distribution in Bayesian inference. However, HMC techniques are computationally demanding for Bayesian neural networks due to the high dimensionality of the network’s parameter space and the non-convexity of their posterior distributions. Therefore, various approximation techniques, such as variational inference (VI) or stochastic gradient MCMC, are often employed to infer the posterior distribution of the network parameters. Such approximations introduce inaccuracies in the inferred distributions, resulting in unreliable uncertainty estimates. In this work, we propose a hybrid approach that combines inexpensive VI and accurate HMC methods to efficiently and accurately quantify uncertainties in neural networks and neural operators. The proposed approach leverages an initial VI training on the full network. We examine the influence of individual parameters on the prediction uncertainty, which shows that a large proportion of the parameters do not contribute substantially to uncertainty in the network predictions. This information is then used to significantly reduce the dimension of the parameter space, and HMC is performed only for the subset of network parameters that strongly influence prediction uncertainties. This yields a framework for accelerating the full batch HMC for posterior inference in neural networks. We demonstrate the efficiency and accuracy of the proposed framework on deep neural networks and operator networks, showing that inference can be performed for large networks with tens to hundreds of thousands of parameters. Finally, we show that this method can effectively learn surrogates for complex physical systems by modeling the operator that maps from upstream conditions to wall-pressure data on a cone in hypersonic flow.

Bayesian inference↗
DOE OSTI2024

Momentum informed muon scattering tomography for monitoring spent nuclear fuels in dry storage cask

Development of an effective monitoring method for spent nuclear fuel (SNF) in a dry storage cask (DSC) is important to meet the increasing demand for dry storage investigations. The DSC investigation should provide information about the quantity of stored SNF, and quality assurance of materials should be possible without opening the cask. However, traditional nondestructive examination (NDE) methods such as x-rays are difficult to deploy for DSC investigation because a typical DSC is intentionally designed to shield against radiation. To address this challenge, cosmic ray muons (CRMs) are used as an alternative NDE radiation probe because they can easily penetrate an entire DSC system; however, a wide application of muons is often hindered due to the naturally low CRM flux (~10 4 muons/m 2 /min). This paper introduces a newly proposed imaging algorithm, momentum-informed muon scattering tomography (MMST) , and presents how a limitation of the current muon scattering tomography technique has been addressed by measuring muon momentum. To demonstrate its functionality, a commercial DSC with 24 pressurized light water reactor fuel assemblies (FAs) and the MMST system were designed in GEANT4. Three noticeable improvements were observed for MMST system as a DSC investigation tool: (1) a signal stabilization, (2) an enhanced capability to differentiate various materials, and (3) statistically increased precision to identify and locate missing FAs. The results show that MMST improves the investigation accuracy from 79 to 98% when one FA is missing and 51% to 88% when one-half FA is missing. The advancement of the NDE technique using CRM for DSC verification is expected to resolve long-standing problems in increasing demand for DSC inspections and nuclear security.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1974

Results from cascade thrust reverser noise and suppression experiments

Results from experimental work on model scale cascade reversers with cold airflow are presented. Sound power level directivity and spectral characteristics for cascade reversers are reported. Effect of cascade exit area ratio, vane profile shape, and emission arc are discussed. Model equivalent diameters varied from 3 to 5 inches, pressure ratios range from 1.15 to 3.0. Depending on the reverser type, acoustic power was proportional to the 4 1/2 to 6th power of ideal jet velocity. Reverser noise peaked at higher frequency and was more omnidirectional than nozzle-alone jet noise. Appreciable reduction in sideline noise was obtained from plane shields. Airfoil-vaned cascades were the most aerodynamically efficient and least noisy reversers. Scaling of cascade reverser data to example aircraft engines showed all cascades above the 95 PNdB sideline goal from STOL aircraft. However, the airfoil-vaned reverser has a good potential for meeting this goal for high-bypass (low pressure ratio) exhausts.

Gutierrez, O. A.↗
NASA NTRS1974

Results from cascade thrust reverser noise and suppression experiments

Results from experimental work on model scale cascade reversers with cold airflow are presented. Sound power levels, directivity, and spectral characteristics for cascade reversers are reported. Effect of cascade exit area ratio, vane profile shape, and emission arc are discussed. Model equivalent diameters varied from 3 to 5 inches; pressure ratios ranged from 1.15 to 3.0. Depending on the reverser type, acoustic power was proportional to the 4.5- to 6-th power of ideal jet velocity. Reverser noise peaked at higher frequency and was more omnidirectional than nozzle-alone jet noise. Appreciable reduction in sideline noise was obtained from plane shields.

Gutierrez, O. A.↗
NASA NTRS1982

Electrostatic disturbance forces on a 3-axis drag-free sensor

The electrostatic analysis of a multiple-capacitance 3-axis drag-free sensor is presented in this paper. The instrument consists of a proof-mass (a dense metallic ball) floating freely inside a spherical cavity enclosed by the sensor plates and the shield. Since the ball and the cavity are not necessarily concentric, the problem in three-dimensional potential theory for electrostatics is solved by the method of boundary perturbations and specifically in terms of spherical harmonics. The capacitance outputs of the instrument and the electrostatic forces acting on the system are derived as non-linear functions of the ball position, ball charge and the sensor plate potentials. The instrument sensitivity and cross-coupling effects are discussed. The analysis may also be useful for electrostatic gyros and suspensions.

Hagstrom, T.↗
NASA NTRSDate not supplied

Identifying Neutron Irradiation in Space to Mitigate Bio-Medical Effects

One of the primary challenges to interplanetary human travel is mitigation of radiation expo-sure. As fast transit with LENR driven or conventional nuclear electric (NEP) or thermal propulsion (NTP) may be imminent, time and level of radiation exposure composingALARA (As Low as Rea-sonably Achievable) must be ascertained rapidly and precisely. Since acute physiological effects are difficult to detect, and chronic effects on crew health are delayed and potentially trans-generational, improved detection technologies will be game-changing and an essential element of the crew health monitoring and environmental protection toolkit.Secondary Galactic Cosmic Ray (GCR) induced neutrons are an additional hazard.

space medicine↗
NASA NTRSDate not supplied

Effects of Background Pressure and Electrical Configuration on the Velocity Field of the HERMeS Hall Thruster

A Laser-Induced Fluorescence test was performed during risk reduction testing on the HERMeS Hall thruster. This article focuses on the portion of the test to study trends in the ion acceleration characteristics with varying anode mass flow rate, background pressure, and electrical configuration. The acceleration zone of the HERMeS Hall thruster was observed to move upstream as the anode mass flow rate decreased and upstream as the background pressure increased. Examination of the characteristics of the ions near the pole covers suggested the possibility that thruster was no longer magnetically shielded at the extreme conditions of very low anode mass flow rate and high background pressure. The acceleration zone was also observed to move slightly upstream when the thruster body was floated as opposed to cathode-tied and did not move appreciably when the thruster body was grounded to the vacuum facility. Characteristics of the ions bombarding the pole covers did not vary across the tested electrical configurations.

Electric Propulsion↗
DOE OSTI2025

Extending the Nuclide Inventory Validation Basis for High-Burnup Fuel with New Radiochemical Assay Data

Efforts are underway at Oak Ridge National Laboratory to improve the nuclide inventory validation basis for spent nuclear fuel at high burnups. Recently conducted radiochemical assay experiments provided new measurement data for nine samples of fuel irradiated in a pressurized water reactor, with estimated sample burnups in the 30 to 70 GWd/t range. This type of destructive assay data is essential for validating computational methods, tools, and nuclear data applied in nuclear safety analyses and for improving our understanding of the bias and uncertainty in code predictions. The measurement data include key actinides and fission products that span a gamut of needs and interests for nuclear science and engineering applications in criticality safety, reactor physics, nuclide inventory, decay heat, and radiation shielding. The SCALE 6.3 code system with ENDF/B-VII.1 cross-section libraries was used to simulate the irradiation histories of the measured fuel samples. The calculated nuclide concentrations are compared to corresponding measurement data. The significance of the comparisons is discussed, emphasizing how the addition of the new measurement data fills gaps in the validation basis at high burnups and contributes to the decrease in bias and uncertainty for predicted nuclide concentrations. The discussion addresses the effect of the sample burnup used in the simulation—which is based on reactor operator records or on calibration to measured data for burnup indicator fission products—on the validation results.

Nuclide inventory↗
NASA NTRS1984

Radiating dipole model of interference induced in spacecraft circuitry by surface discharges

Spacecraft in geosynchronous orbit can be charged electrically to high voltages by interaction with the space plasma. Differential charging of spacecraft surfaces leads to arc and blowoff discharging. The discharges are thought to upset interior, computer-level circuitry. In addition to capacitive or electrostatic effects, significant inductive and less significant radiative effects of these discharges exist and can be modeled in a dipole approximation. Flight measurements suggest source frequencies of 5 to 50 MHz. Laboratory tests indicate source current strengths of several amperes. Electrical and magnetic fields at distances of many centimeters from such sources can be as large as tens of volts per meter and meter squared, respectively. Estimates of field attenuation by spacecraft walls and structures suggest that interior fields may be appreciable if electromagnetic shielding is much thinner than about 0.025 mm (1 mil). Pickup of such fields by wires and cables interconnecting circuit components could be a source of interference signals of several volts amplitude.

Metz, R. N.↗
NASA NTRS1991

Analytic potential in a linear radio-frequency quadrupole trap with cylindrical electrodes

An analytical expression is derived for a radio-frequency ion trap of novel configuration consisting of a four-sectored hollow cylinder enclosed between two end caps. The cylindrical geometry of the sectored trap provides shielding against the buildup of charge and also makes it possible to calculate the potential within the trap by solving Laplace's equation for given boundary conditions. Equations are presented for calculating the time-averaged potential generated by the RF fields, the end-cap potential, and the potential arising from the application of a dc bias on two of the four electrode sectors. It is shown that, near the ends of this trap, the effective potential arising from the RF fields acts to propel ions out of the trap and that the addition of a dc bias on two neighboring sectors generates an inhomogeneous field in the trap which produces a force on the ions along the trap's long axis in a direction dependent on the sign of the bias.

Melbourne, R. K.↗
NASA NTRS2005

Nanomaterials Work at NASA-Johnson Space Center

Nanomaterials activities at NASA-Johnson Space Center focus on single wall carbon nanotube production, characterization and their applications for aerospace. Nanotubes are produced by arc and laser methods and the growth process is monitored by in-situ diagnostics using time resolved passive emission and laser induced fluorescence of the active species. Parametric study of both these processes are conducted to monitor the effect of production parameters including temperature, buffer gas, flow rate, pressure, laser fluence and arc current. Characterization of the nanotube material is performed using the NASA-JSC protocol developed by combining analytical techniques of SEM, TEM, UV-VIS-NIR absorption, Raman, and TGA. Efforts at JSC over the past five years in composites have centered on structural polymernanotube systems. Recent activities broadened this focus to multifunctional materials, supercapacitors, fuel cells, regenerable CO2 absorbers, electromagnetic shielding, radiation dosimetry and thermal management systems of interest for human space flight. Preliminary tests indicate improvement of performance in most of these applications because of the large surface area as well as high conductivity exhibited by SWCNTs.

Arepalli, Sivaram↗
NASA NTRS1977

Preliminary design study of a baseline MIUS

Results of a conceptual design study to establish a baseline design for a modular integrated utility system (MIUS) are presented. The system concept developed a basis for evaluating possible projects to demonstrate an MIUS. For the baseline study, climate conditions for the Washington, D.C., area were used. The baseline design is for a high density apartment complex of 496 dwelling units with a planned full occupancy of approximately 1200 residents. Environmental considerations and regulations for the MIUS installation are discussed. Detailed cost data for the baseline MIUS are given together with those for design and operating variations under climate conditions typified by Las Vegas, Nevada, Houston, Texas, and Minneapolis, Minnesota. In addition, results of an investigation of size variation effects, for 300 and 1000 unit apartment complexes, are presented. Only conceptual aspects of the design are discussed. Results regarding energy savings and costs are intended only as trend information and for use in relative comparisons. Alternate heating, ventilation, and air conditioning concepts are considered in the appendix.

Wolfer, B. M.↗