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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Spacecraft radio scattering observations of the power spectrum of electron density fluctuations in the solar wind

Solar wind electron density power spectra in the solar equatorial region are inferred from observations of phase scintillations and spectral broadening made with the Viking, Helios, and Pioneer spacecraft. The heliocentric distance range covered is 2-215 solar radii and for some observations close to the sun the spectra extend to fluctuation frequencies as high as 100 Hz. For heliocentric distances of about 20 solar radii the equivalent spacecraft-measured one-dimensional density spectrum is well modeled by a single power law in the frequency range 0.0001-0.05 Hz. The flattening of the density spectrum within 20 solar radii is presumably associated with energy deposition in the near-sun region and acceleration of the solar wind.

Woo, R.↗
NASA NTRS1975

A linear feedback guidance law for an Aeromaneuvering Orbit-to-Orbit Shuttle

The sensitivity of the trajectory of an Aeromaneuvering Orbit-to-Orbit Shuttle (AMOOS) to unpredictable variations in atmospheric density is shown and a compensating guidance law is developed. The sensitivity was determined using a varying atmosphere model whose statistical properties matched those of actual atmosphere data. This study showed that a compensating guidance law is crucial to the feasibility of AMOOS. Using an optimal regulator approach, a linear feedback law for bank angle was developed and checked out with the atmosphere model. This law uses the altitude profile of the trajectory to control the amount of energy dissipated within the atmosphere.

Rehder, J. J.↗
NASA NTRS2001

Preliminary Study of Electron Emission for Use in the PIC Portion of MAFIA

This memorandum summarizes a study undertaken to apply the program MAFIA to the modeling of an electron gun in a traveling wave tube (TWT). The basic problem is to emit particles from the cathode in the proper manner. The electrons are emitted with the classical Maxwell-Boltzmann (M-B) energy distribution; and for a small patch of emitting surface; the distribution with angle obeys Lambert's law. This states that the current density drops off as the cosine of the angle from the normal. The motivation for the work is to extend the analysis beyond that which has been done using older codes. Some existing programs use the Child-Langmuir, or 3/2 power law, for the description of the gun. This means the current varies as the 3/2 power of the anode voltage. The proportionality constant is termed the perveance of the gun. This is limited, however, since the 3/2 variation is only an approximation. Also, if the cathode is near saturation, the 3/2 law definitely will not hold. In most of the older codes, the electron beam is decomposed into current tubes, which imply laminar flow in the beam; even though experiments show the flow to be turbulent. Also, the proper inclusion of noise in the beam is not possible. These older methods of calculation do, however, give reasonable values for parameters of the electron beam and the overall gun, and these values will be used as the starting point for a more precise particle-in-cell (PIC) calculation. To minimize the time needed for a given computer run, all beams will use the same number of particles in a simulation. This is accomplished by varying the mass and charge of the emitted particles (macroparticles) in a certain manner, to be consistent with the desired beam current.

Freeman, Jon C.↗
NASA NTRS1975

Long-term differential energy spectrum for solar-flare iron-group particles

A long-term solar-flare differential energy spectrum for iron-group nuclei from approximately 0.1 to approximately 600 MeV/amu is derived from track density profile measurements in sample 64455 and sample 68815. Measurements from uneroded surfaces were obtained from quench crystals of plagioclase in 64455, and a Kr-81/Kr method indicates that the exposure age of this sample is 2,010,000 yrs. The power laws which best fit the normalized track density data are reported; the energy spectrum consists of two power law curves smoothly joined together which in turn are smoothly connected to a modulated galactic cosmic-ray spectrum. Standard track production versus depth profiles can be used to determine solar-flare track exposure ages and erosion rates for lunar samples.

Blanford, G. E.↗
NASA NTRS1985

Experimental and analytical derivation of arc-heater scaling laws for simulating high-enthalpy environments for Aeroassisted Orbital Transfer Vehicle application

The computer code ARCFLO II was used as a guide to increase the performance of the Interaction Heating Facility at Ames Research Center. A closed-form scaling law relation was derived that provides an understanding of the factors that affect enthalpy in the constricted-arc heater. From a study of this scaling law, it is concluded that at constant pressure, enthalpy is proportional to current density raised to the 0.60 power for current densities from 80 to 150 A/sq cm. At constant current density, enthalpy is inversely proportional to pressure to the nth power, where n varies from 0.14 to 0.43, depending on the current density. Radiative heat losses are responsible for the falloff in performance at combinations of high current density and high pressure. An analytical, closed form scaling law based on a constant-temperature arc-core model agrees qualitatively with the scaling law deduced from ARCFLO II.

Winovich, W.↗
NASA NTRS1998

Electron Temperature and Density at High Latitude

The background electron temperature and density at altitudes between 1000 and 8000 km at invariant latitudes greater than 60 degrees have been determined from swept Langmuir probe measurements from the S3-3 satellite. These plasma parameters are determined by fitting the measured probe current-voltage relation to the expected theoretical response. Statistically acceptable fits are found for approx. 20% of all measurements and do not include measurements within the auroral density cavity. The results indicate that the density varies as an inverse power law with increasing altitude which has a typical value of 10 per cubic centimeters at 8000 km in altitude. The electron temperature shows a slight increase with altitude but is less than 5 eV for almost all measurements. These results suggest that the background plasma outside of auroral density cavities on high-latitude field lines below 8000 km is dominated by cold plasma of ionospheric origin which is at least an order of magnitude more dense than hotter magnetospheric components.

Kletzing, C. A.↗
DOE OSTI2021

A novel energy balance approach for a verifiable and accurate solution of radiation extinction in purely absorbing particle clouds

Here we consider the problem of radiation transport through purely absorbing particle clouds. The gold-standard solution of particle-resolved Monte Carlo ray-tracing method to this problem is computationally expensive and therefore solving the radiation transport equation (specifically, the Beer-Bouguer law (BB-law)) on a Eulerian mesh is often preferred. While the absorption coefficient in the real problem is infinite, the BB-law approximates it to be a finite number in the form of number density through a set of assumptions. For particle clouds that do not obey these assumptions, the BB-law predicts an incorrect exponential decay. Also, when the number density is computed using the nearest-neighbor approach, the BB-law solution diverges when the Eulerian mesh size becomes closer to or smaller than the particle size. This numerical divergence is due to the homogenization error. Although the filtering strategy for number density minimizes the homogenization error, it still converges to an incorrect exponential decay for particle clouds that break the BB-law constraints and the cost of the filtering is equivalent to that of the gold-standard solution. In this study, we develop a novel, highly accurate, verifiable and cost-effective solution to the radiation transport equation on a Eulerian domain using an energy balance approach where we derive an expression for the absorption coefficient as a function of particle and Eulerian mesh sizes. We apply our new method to Poisson and turbulent particle clouds that violate all the BB-law constraints and show that the solution is converging upon the mesh refinement, and eventually, we recover the same gold-standard solution for a much cheaper computational cost.

42 ENGINEERING↗
NASA NTRS2009

Development of Jet Noise Power Spectral Laws Using SHJAR Data

High quality jet noise spectral data measured at the Aeroacoustic Propulsion Laboratory at the NASA Glenn Research Center is used to examine a number of jet noise scaling laws. Configurations considered in the present study consist of convergent and convergent-divergent axisymmetric nozzles. Following the work of Viswanathan, velocity power factors are estimated using a least squares fit on spectral power density as a function of jet temperature and observer angle. The regression parameters are scrutinized for their uncertainty within the desired confidence margins. As an immediate application of the velocity power laws, spectral density in supersonic jets are decomposed into their respective components attributed to the jet mixing noise and broadband shock associated noise. Subsequent application of the least squares method on the shock power intensity shows that the latter also scales with some power of the shock parameter. A modified shock parameter is defined in order to reduce the dependency of the regression factors on the nozzle design point within the uncertainty margins of the least squares method.

Khavaran, Abbas↗
NASA NTRS2001

Resolving the Structure of Ionized Helium in the Intergalactic Medium with the Far Ultraviolet Spectroscopic Explorer

The neutral hydrogen and the ionized helium absorption in the spectra of high-redshift quasi-stellar objects (QSOs) are unique probes of structure in the universe at epochs intermediate between the earliest density fluctuations seen in the cosmic background radiation and the distribution of galaxies visible today. We present Far-Ultraviolet Spectroscopic Explorer (FUSE) observations of the line of sight to the QSO HE2347-4342 in the 1000-1187 angstrom band at a resolving power of 15,000. Above redshift z = 2.7, the IGM is largely opaque in He II Ly-alpha (304 angstroms). At lower redshifts, the optical depth gradually decreases to a mean value tau = 1 at z = 2.4. We resolve the He II Ly-alpha absorption as a discrete forest of absorption lines in the z = 2.3 - 2.7 redshift range. Approximately 50% of these spectral features have H I counterparts with column densities N(sub HI) > 10(exp 12.3)/sq cm visible in a Keck spectrum. These account for most of the observed opacity in He II Ly-alpha. The remainder have N(sub HI) < 10(exp 12.3)/sq cm, below the threshold for current observations. A short extrapolation of the power-law distribution of H I column densities to lower values can account for these new absorbers. The He II to H I column density ratio eta averages approximately 80, consistent with photoionization of the IGM by a hard ionizing spectrum resulting from the integrated light of quasars at high redshift, but there is considerable scatter. Values of eta > 100 in many locations indicate that there may be localized contributions from starbursts or heavily filtered QSO radiation.

Kriss, G. A.↗
NASA NTRS1987

Torsion as a source of expansion in a Bianchi type-I universe in the self-consistent Einstein-Cartan theory of a perfect fluid with spin density

It is shown that a generalized (or 'power law') inflationary phase arises naturally and inevitably in a simple (Bianchi type-I) anisotropic cosmological model in the self-consistent Einstein-Cartan gravitation theory with the improved stress-energy-momentum tensor with the spin density of Ray and Smalley (1982, 1983). This is made explicit by an analytical solution of the field equations of motion of the fluid variables. The inflation is caused by the angular kinetic energy density due to spin. The model further elucidates the relationship between fluid vorticity, the angular velocity of the inertially dragged tetrads, and the precession of the principal axes of the shear ellipsoid. Shear is not effective in damping the inflation.

Bradas, James C.↗
DOE OSTI2024

The physics of gain relevant to inertial fusion energy target designs

In inertial confinement fusion, pellets of deuterium tritium fuel are compressed and heated to the conditions where they undergo fusion and release energy. The target gain (ratio of energy released from the fusion reactions to the energy in the drive source) is a key parameter in determining the power flow and economics of an inertial fusion energy (IFE) power plant. In this study, the physics of gain is explored for laser-direct-drive targets with driver energy at the megajoule scale. This analysis is performed with the assumption of next-generation laser technologies that are expected to increase convergent drive pressures to over 200 Mbar. This is possible with the addition of bandwidth to the laser spectrum and by employing focal-spot zooming. Simple physics arguments are used to derive scaling laws that describe target gain as a function of laser energy, adiabat, ablation pressure, and implosion velocity. Scaling laws are found for the unablated mass, ablation pressure, areal density, implosion velocity, and in-flight aspect ratio. Furthermore, those scaling laws are then used to explore the design space for IFE targets.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1990

Equilibrium models of self-gravitating inviscid disks resulting from the collapse of rotating clouds

A method is presented for the construction of velocity and surface density profiles of infinitely thin, self-gravitating disks formed from the collapse of spherical clouds, under the condition that the angular momentum of each material parcel is conserved. Results are presented for initially uniformly rotating clouds with density distributions varying as R exp -n and n = 0, 1, 2. The resulting disk surface density distributions are well represented by power laws in the cylindrical radius over most of their extent. The form of the zeroth-order approximation provides a useful representation of the final surface density function near the center for all three cases, and for n = 2 this result holds throughout the disk. This result is not generally true for the velocity functions, however.

Stemwedel, Sally W.↗
DOE OSTI2021

First Digit Oscillations

The frequency of the first digits of numbers drawn from an exponential probability density oscillate around the Benford frequencies. Analysis, simulations and empirical evidence show that datasets must have at least 10,000 entries for these oscillations to emerge from finite-sample noise. Anecdotal evidence from population data is provided.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

Dislocation Patterning in Deforming Crystals: Theory, Computational Predictions and Validation (Final Technical Report)

This project was awarded for an initial period of three years, followed by a no-cost extension for one year and a funded one-year renewal. During the first four years, the project focused on investigating the role of dislocation reactions and dislocation correlation in dislocation patterning in FCC metals. During the fifth year, the scope of research was expanded to investigate the effects of composition inhomogeneity on the mesoscale plastic response of Body-Centered Cubic (BCC) alloys. In addition to its impact on metal hardening during deformation, dislocation patterning provides the microstructure information required to understand phenomena like fracture and recrystallization in metals. The Continuum Dislocation Dynamics (CDD) framework was the methodology used during the first four years, followed by the use of Discrete Dislocation Dynamics (DDD) during the fifth year. CDD is a density-based formalism of dislocation dynamics in which the plastic deformation of crystals is predicted together with the mesoscale dislocation patterns by tracking the space-time evolution of dislocations as driven by the applied stress, short-range and long-range interactions of dislocations, and cross slip. CDD is a crystal mechanics approach in which the plastic constitutive part is replaced with the equations of dislocation dynamics, which is driven by the internal stress via a mobility laws, while the evolution of the density gives the eigenstrain required to update the internal stress itself. The governing equations are thus those of crystal mechanics cast as an eigenstrain problem and those of dislocation transport and reactions. Our investigations during the first four years were driven by the hypothesis that that dislocation patterning is triggered by spatiotemporal dislocation density and internal stress fluctuations, and that such fluctuations influence the collective dislocation dynamic through their effects on the short-range reaction rates and the collective dislocation mobility. This hypothesis was tested by modeling the influence of the dislocation reactions and dislocation correlations on collective dislocation dynamics. The main research components during the first four years were: 1) Reformulation of the CDD framework to integrate the dislocation correlations and dislocation reactions. 2) Simulation of the dislocation correlations and quantifying their contribution to the long-range stress of complex dislocation systems. 3) Computational implementation of the updated CDD model for FCC single crystals and development of an efficient CDD code. 4) Investigation of dislocation patterning in FCC crystals based on the updated CDD model. Some key findings from these investigations were: 1) The patterning of dislocations is initiated by cross slip and internal stress fluctuations, and the refinement of the pattern results from junction formation. 2) Patterning is more prominent under high stress. 3) The correlation stress was found to be a significant part of the mean field stress in continuum representations of dislocation dynamics. During the last year of the project, we have established a method for performing dislocation dynamics in inhomogeneous alloys and demonstrated the impact of composition inhomogeneity on the characteristics of initial yielding and dislocation character in BCC alloys. We also tested this method using an irradiated ferritic alloy in which the composition and dislocation loops effects are both present. In doing so, we have considered two aspects of the role of inhomogeneity, the creation of internal coherency stress due to the dependence of the lattice parameter on the local composition, and the dependence of the dislocation mobility on the local composition. These two aspects resulted in an unexpected behavior of the dislocation system, and, in turn, the yielding behavior of BCC alloys. Key findings include: 1) The composition inhomogeneity in BCC alloys alters the well-known role of screw dislocations by forcing a level of waviness on the average dislocation character, thus destroying the screw character dominance in the yielding observed in pure or homogeneous BCC metals. 2) In the case of irradiated alloys, while composition inhomogeneity by itself and dislocation loops by themselves result in some hardening, the superposition of the two mechanisms does not result in the sum of the two contributions via any known rule. The latter result contradicts the classical works related hardening via multiple mechanisms, which state that various hardening mechanisms can be added linearly or using some Pythagorean additive rule. We were able to rationalize this unexpected result by a closer loop at the origin of the hardening mechanisms themselves, which both involved long-range elastic interactions with dislocations. We reached the conclusion that the hardening resulting from the total stress associated with these two mechanisms (current work) differs from the sum of the effects of the individual stress fields (classical literature). We have also found a major flaw in the classical theory of spinodal hardening. The latter theory never considered the impact of composition undulation on the solute hardening. We have built a new general theory accounting for the effect of solute friction together with the composition undulations on the dislocation configuration at Critical Resolved Shear Stress (CRSS), which is yielding a new definition of the spinodal hardening and new different results. This work is the first to recognize the lack of the role of solute in spinodal hardening theory of alloys.

36 MATERIALS SCIENCE↗
NASA NTRS2002

XTE J1908+094

Goddard Space Flight Center reports the serendipitous discovery of a new x-ray transient, XTE J1908+094, in RXTE (Rossi X-ray Timing Explorer) PCA (Proportional Counter Array) observations of the soft-gamma-ray repeater SGR 1900+14, triggered following the burst activity on Feb. 17-18 (GCN 1253). These observations failed to detect the 5.2-s SGR pulsations, pointing towards a possible new source as the origin of the high x-ray flux. An RXTE PCA scan of the region around SGR 1900+14 on Feb. 21 was consistent with emission only from known sources (and no new sources). However, the scans required SGR 1900+14 to be 20 times brighter than its quiescent flux level (GCN 1256). A Director's Discretionary Time Chandra observation on Mar. 11 showed that the SGR was quiescent and did not reveal any new source within the Chandra ACIS (Advanced CCD (charge coupled device) Imaging Spectrometer) field-of-view. A subsequent RXTE PCA scan on Mar. 17, taken in combination with the first scan, required that a new source be included in the fit. The best-fit position is R.A. 19h 08m 50s, Decl. = +9 22 deg .5 (equinox J2000.0; estimated 2 deg systematic error radius), or approximately 24 deg away from the SGR source. The source spectrum (2-30 kev) can be best fit with a power-law function including photoelectric absorption (column density N_h = 2.3 x 10(exp 22), photon index = 1.55). Iron line emission is present, but may be due to the Galactic ridge. Between Feb. 19 and Mar. 17, the source flux (2-10 keV) has risen from 26 to 64 mCrab. The power spectrum is flat between 1 mHz and 0.1 Hz, falling approximately as 1/f**0.5 up to 1 Hz. At 1 Hz is seen a broad quasiperiodic oscillation peak and a break to a 1/f**2 power law, which continues to 4 Hz. The fractional rms (root mean square) amplitude from 1 mHz to 4 Hz is 43 percent. No coherent pulsations are seen between 0.001 and 1024 Hz. The authors conclude that XTE J1908+094 is a new blackhole candidate.

Woods, P. M.↗
NASA NTRSDate not supplied

Battery Cell-to-Pack Scaling Laws for Electric Aircraft

Battery pack gravimetric energy density is one of the most important, yet often miss-estimated design parameters for sizing all-electric aircraft. Proper accounting for thermal, structural, and operational safety margins are frequently lost when extrapolating performance from the cell level to the aircraft level. This paper summarizes the relevant engineering and certification details needed to better account for the penalties associated when assembling battery packs. The relationship between the cell and pack energy density is not linear, as is often assumed. Furthermore, the relationship varies depending on pack requirements, cell chemistry, and architecture. Parametric, high-fidelity models are used to determine optimal battery pack sizes over a range of conditions to better quantify technology scaling effects.

Battery Electric Aircraft↗
NASA NTRS2002

Global Summary MGS TES Data and Mars-Gram Validation

Mars Global Reference Atmospheric Model (Mars-GRAM 2001) is an engineering-level Mars atmosphere model widely used for many Mars mission applications. From 0-80 km, it is based on NASA Ames Mars General Circulation Model (MGCM), while above 80 km it is based on University of Arizona Mars Thermospheric General Circulation Model. Mars-GRAM 2001 and MGCM use surface topograph$ from Mars Global Surveyor Mars Orbiting Laser Altimeter (MOLA). Validation studies are described comparing Mars-GRAM with a global summary data set of Mars Global Surveyor Thermal Emission Spectrometer (TES) data. TES averages and standard deviations were assembled from binned TES data which covered surface to approx. 40 km, over more than a full Mars year (February, 1999 - June, 2001, just before start of a Mars global dust storm). TES data were binned in 10-by-10 degree latitude-longitude bins (i.e. 36 longitude bins by 19 latitude bins), 12 seasonal bins (based on 30 degree increments of Ls angle). Bin averages and standard deviations were assembled at 23 data levels (temperature at 21 pressure levels, plus surface temperature and surface pressure). Two time-of day bins were used: local time near 2 or 14 hours local time). Two dust optical depth bins wereused: infrared optical depth either less than or greater than 0.25 (which corresponds to visible optical depth either less than or greater than about 0.5). For interests in aerocapture and precision entry and landing, comparisons focused on atmospheric density. TES densities versus height were computed from TES temperature versus pressure, using assumptions of perfect gas law and hydrostatics. Mars-GRAM validation studies used density ratio (TES/Mars-GRAM) evaluated at data bin center points in space and time. Observed average TES/Mars-GRAM density ratios were generally 1+/-0.05, except at high altitudes (15-30 km, depending on season) and high latitudes (> 45 deg N), or at most altitudes in the southern hemisphere at Ls approx. 90 and 180deg). Compared to TES averages for a given latitude and season, TES data had average density standard deviation about the mean of approx. 65-10.5% (varying with height) for all data, or approx. 5-12%, depending on time of day and dust optical depth. Average standard deviation of TES/Mars-GRAM density ratio was 8.9% for local time 2 hours and 7.1% for local time 14 hours. Thus standard deviation of observed TES/Mars-GRAM density ratio, evaluated at matching positions and times, is about the same as the standard deviation of TES data about the TES mean value at a given position and season.

Justus, C.↗
NASA NTRS2007

X-ray Properties of an Unbiased Hard X-ray Detected Sample of AGN

The SWIFT gamma ray observatory's Burst Alert Telescope (BAT) has detected a sample of active galactic nuclei (AGN) based solely on their hard X-ray flux (14-195keV). In this paper, we present for the first time XMM-Newton X-ray spectra for 22 BAT AGXs with no previously analyzed X-ray spectra. If our sources are a representative sample of the BAT AGN, as we claim, our results present for the first time global X-ray properties of an unbiased towards absorption (n(sub H) < 3 x 10(exp 25)/sq cm), local (< z >= 0.03), AGN sample. We find 9/22 low absorption (n(sub H) < 10(exp 23)/sq cm), simple power law model sources, where 4 of these sources have a statistically significant soft component. Among these sources, we find the presence of a warm absorber statistically significant for only one Seyfert 1 source, contrasting with the ASCA results of Reynolds (1997) and George et al. (1998), who find signatures of warm absorption in half or more of their Seyfert 1 samples at similar redshifts. Additionally, the remaining sources (13122) have more complex spectra, well-fit by an absorbed power law at E > 2.0 keV. Five of the complex sources (NGC 612, ESO 362-G018, MRK 417, ESO 506-G027, and NGC 6860) are classified as Compton-thick candidates. Further, we find four more sources (SWIFT J0641.3+3257, SWIFT J0911.2+4533, SWIFT J1200.8+0650, and NGC 4992) with properties consistent with the hidden/buried AGN reported by Ueda et al. (2007). Finally, we include a comparison of the XMM EPIC spectra with available SWIFT X-ray Telescope (XRT) observations. From these comparisons, we find 6/16 sources with varying column densities, 6/16 sources with varying power law indices, and 13/16 sources with varying fluxes, over periods of hours to months. Flux and power law index are correlated for objects where both parameters vary.

Winter, Lisa M.↗