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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Propulsion Physics Using the Chameleon Density Model

To grow as a space faring race, future spaceflight systems will require a new theory of propulsion. Specifically one that does not require mass ejection without limiting the high thrust necessary to accelerate within or beyond our solar system and return within a normal work period or lifetime. The Chameleon Density Model (CDM) is one such model that could provide new paths in propulsion toward this end. The CDM is based on Chameleon Cosmology a dark matter theory; introduced by Khrouy and Weltman in 2004. Chameleon as it is hidden within known physics, where the Chameleon field represents a scalar field within and about an object; even in the vacuum. The CDM relates to density changes in the Chameleon field, where the density changes are related to matter accelerations within and about an object. These density changes in turn change how an object couples to its environment. Whereby, thrust is achieved by causing a differential in the environmental coupling about an object. As a demonstration to show that the CDM fits within known propulsion physics, this paper uses the model to estimate the thrust from a solid rocket motor. Under the CDM, a solid rocket constitutes a two body system, i.e., the changing density of the rocket and the changing density in the nozzle arising from the accelerated mass. Whereby, the interactions between these systems cause a differential coupling to the local gravity environment of the earth. It is shown that the resulting differential in coupling produces a calculated value for the thrust near equivalent to the conventional thrust model used in Sutton and Ross, Rocket Propulsion Elements. Even though imbedded in the equations are the Universe energy scale factor, the reduced Planck mass and the Planck length, which relates the large Universe scale to the subatomic scale.

Robertson, Glen A.↗
NASA NTRS1990

A gravitational test of wave reinforcement versus fluid density models

Spermatozoa, protozoa, and algae form macroscopic patterns somewhat analogous to thermally driven convection cells. These bioconvective patterns have attracted interest in the fluid dynamics community, but whether in all cases these waves were gravity driven was unknown. There are two conflicting theories, one gravity dependent (fluid density model), the other gravity independent (wave reinforcement theory). The primary objectives of the summer faculty fellows were to: (1) assist in sample collection (spermatozoa) and preparation for the KC-135 research airplane experiment; and (2) to collaborate on ground testing of bioconvective variables such as motility, concentration, morphology, etc., in relation to their macroscopic patterns. Results are very briefly given.

Johnson, Jacqueline Umstead↗
NASA NTRS1983

Sensitivity /comparison study between the Jacchia 1970, 1971, and 1977 upper atmospheric density models

The neutral upper atmospheric models for the Earth's thermosphere currently used in NASA-MSFC programs are the Jacchia 1970 (J70), 1971 (J71), and 1977 (J77). The Jacchia 1970 model (modified) is used in all MSFC orbital mechanics analyses. Since total density and its variations are the main environmental parameters of interest in orbital lifetime and attitude control studies, the total neutral density was selected for this analysis. This report presents the results of a parametric study of the total density (at 400 km altitude) as computed with three MSFC/Jacchia models. The sensitivity of each of the density models at the summer solstice to varying solar conditions (flux) and geomagnetic (index) values is discussed.

Johnson, D. L.↗
DOE OSTI2022

Composition-Based Density Model for High Level Waste Glasses

In this report, the Savannah River National Laboratory (SRNL) provides a first-principles model capable of predicting the density of high-level waste (HLW) glass based on the glass composition. The model relies on the additivity of the specific volume of bound glass oxides to obtain a quantitative evaluation of the approximate glass density.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

An Extensible High Energy Density Modeling Tool for Extreme Regimes

The overreaching goal of the project is to develop a simulation capability to model an entire High Energy Density (HED) target heated by an X-ray Free Electron Laser (XFEL) beam including the surrounding material with a focus on target material associated with subsequent shots. Our primary objective is to study target fratricide problems, where radiation/debris from the current shot degrade the target for subsequent shots. This work will have a large impact on research being conducted at HED facilities where the quality of data is directly related to the effective repetition rate of the driver, which is often limited by target fratricide problems. This project focuses on a stream of closely spaced droplet targets that are appropriate for new very high repetition rate sources such as the ~1 MHz LCLS-II upgraded XFEL. The capability of the PISALE (Pacific Island Structured-AMR with ALE) code is extended to model this class of problems. We summarize the capability and improvements made to the HED branch of the PISALE code. We discuss our simulations of target fratricide for small (5 micron) hydrogen droplets heated by an XFEL beam at SLAC. We also compare simulations of the initial dynamics of larger (50 micron) water droplets, heated by the same XFEL beam, with experimental data. We briefly discuss training, dissemination, and related activities associated with this project.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1987

NORAD/SPACECMD comments concerning the atmospheric density models

Recent models do not produce more accurate neutral densities (although they require more computer time), regardless of the level of solar activity. This implies that there has been no measurable improvement of the calculation of neutral density since the early 60s. With known solar flux and geomagnetic activity (Ap) inputs, the density evaluation needs improvement. For highly eccentric orbits which span low to high altitude, the accuracy generated which has an altitude limitation of 1000 km remains comparable with those obtained by more recent models. This implies that either the density at 1000 km and above is insignificant or that the values provided by the recent models at high altitudes may not be reliable or both. Prediction accuracies obtained through the use of precision data from the Defense Mapping Agency are generally comparable to those obtained by using operational sensor data. This implies that the prediction accuracy problem is not necessarily caused by less accurate observations. The definition of the mean solar flux F10.7 is not universal.

Liu, Joseph J. F.↗
NASA NTRS1982

Remanent magnetization and three-dimensional density model of the Kentucky anomaly region

Existing software was modified to handle 3-D density and magnetization models of the Kentucky body and is being tested. Gravity and magnetic anomaly data sets are ready for use. A preliminary block model is under construction using the 1:1,000,000 maps. An x-y grid to overlay the 1:2,500,000 Albers maps and keyed to the 1:1,000,000 scale block models was created. Software was developed to generate a smoothed MAGSAT data set over this grid; this is to be input to an inversion program for generating the regional magnetization map. The regional scale 1:2,500,000 map mosaic is being digitized using previous magnetization models, the U.S. magnetic anomaly map, and regional tectonic maps as a guide.

Source record↗
NASA NTRS1973

Effect of energetic oxygen atoms on neutral density models.

The dissociative recombination of O2(+) and NO(+) in the F region results in the production of atomic oxygen and atomic nitrogen with substantially greater kinetic energy than the ambient atoms. In the exosphere these energetic atoms have long free paths. They can ascend to altitudes of several thousand kilometers and can travel horizontally to distances of the order of the earth's radius. The distribution of energetic oxygen atoms is derived by means of models of the ion and neutral densities for quiet and disturbed solar conditions. A distribution technique is used to study the motion of the atoms in the collision-dominated region. Ballistic trajectories are calculated in the spherical gravitational field of the earth. The present calculations show that the number densities of energetic oxygen atoms predominate over the ambient atomic oxygen densities above 1000 km under quiet solar conditions and above 1600 km under disturbed solar conditions.

Rohrbaugh, R. P.↗
NASA NTRS1980

Time-dependent lunar density models

Simple models of the geochemical and geophysical evolution of the moon were constructed with the particular aim of investigating the mass density distribution within the moon as a function of time. The strongly inverted (densest material on top) density distribution resulting from fractional crystallization of the lunar magma ocean was found to rearrange itself into a highly stable stratification. Density stratification due to compositional variation dominated gravitational stability; thus, thermally driven convection was found to be suppressed in regions with relaxed (rearranged so as to minimize the gravitational potential energy) compositional density variation. The suppression of convection as a heat transfer process results in considerable modification of thermal evolution. The models produced sufficient density segregation from magma oceans of a few hundred km thickness, such that relaxation to the most stable rearrangement yielded a polar moment of inertia approximating that measured for the present-day moon. Thus, lunar models matching moment-of-inertia constraints but lacking a metallic core are motivated.

Herbert, F.↗
NASA NTRS2010

Enceladus Plume Density Modeling and Reconstruction for Cassini Attitude Control System

In 2005, Cassini detected jets composed mostly of water, spouting from a set of nearly parallel rifts in the crust of Enceladus, an icy moon of Saturn. During an Enceladus flyby, either reaction wheels or attitude control thrusters on the Cassini spacecraft are used to overcome the external torque imparted on Cassini due to Enceladus plume or jets, as well as to slew the spacecraft in order to meet the pointing needs of the on-board science instruments. If the estimated imparted torque is larger than it can be controlled by the reaction wheel control system, thrusters are used to control the spacecraft. Having an engineering model that can predict and simulate the external torque imparted on Cassini spacecraft due to the plume density during all projected low-altitude Enceladus flybys is important. Equally important is being able to reconstruct the plume density after each flyby in order to calibrate the model. This paper describes an engineering model of the Enceladus plume density, as a function of the flyby altitude, developed for the Cassini Attitude and Articulation Control Subsystem, and novel methodologies that use guidance, navigation, and control data to estimate the external torque imparted on the spacecraft due to the Enceladus plume and jets. The plume density is determined accordingly. The methodologies described have already been used to reconstruct the plume density for three low-altitude Enceladus flybys of Cassini in 2008 and will continue to be used on all remaining low-altitude Enceladus flybys in Cassini's extended missions.

Sarani, Siamak↗
NASA NTRS1984

Remanent magnetization and 3-dimensional density model of the Kentucky anomaly region

A three-dimensional model of the Kentucky body was developed to fit surface gravity and long wavelength aeromagnetic data. Magnetization and density parameters for the model are much like those of Mayhew et al (1982). The magnetic anomaly due to the model at satellite altitude is shown to be much too small by itself to account for the anomaly measured by Magsat. It is demonstrated that the source region for the satellite anomaly is considerably more extensive than the Kentucky body sensu stricto. The extended source region is modeled first using prismatic model sources and then using dipole array sources. Magnetization directions for the source region found by inversion of various combinations of scalar and vector data are found to be close to the main field direction, implying the lack of a strong remanent component. It is shown by simulation that in a case (such as this) where the geometry of the source is known, if a strong remanent component is present its direction is readily detectable, but by scalar data as readily as vector data.

Mayhew, M. A.↗
NASA NTRS1982

Jacchia-Lineberry upper atmosphere density model

A series of increasingly accurate models which are a careful blend of empirical and theoretical formulae were developed. The exospheric temperature is assumed to be a function of: (1) the average and daily variations in the solar flux, (2) the average and three hourly variations in the geomagnetic index, (3) the angle between the position vector and the axis of the unsymmetric atmospheric bulge, and (4) the angle between the position vector and the geomagnetic pole. The exospheric temperature is related to the density by the solution of the diffusion equilibrium equations for the different constituents of the atmosphere as a function of altitude. Other variations are modeled directly as changes in the density. They are: (1) changes due to the semiannual effect, and (2) changes due to the seasonal latitudinal effect. The causes for these variations are not exactly known but may be modeled sufficiently by empirical formulae. The Jacchia model is assumed to be valid over the altitude range of 90 to 2500 km. The residuals between the observed density from satellite drag observations and the computed densities show the mean relative error to be generally less than 10 percent with occasional peak errors near 50 percent.

Mueller, A. C.↗
DOE OSTI2022

Aboveground biomass density models for NASA’s Global Ecosystem Dynamics Investigation (GEDI) lidar mission

NASA's Global Ecosystem Dynamics Investigation (GEDI) is collecting spaceborne full waveform lidar data with a primary science goal of producing accurate estimates of forest aboveground biomass density (AGBD). This paper presents the development of the models used to create GEDI's footprint-level (~25 m) AGBD (GEDI04_A) product, including a description of the datasets used and the procedure for final model selection. The data used to fit our models are from a compilation of globally distributed spatially and temporally coincident field and airborne lidar datasets, whereby we simulated GEDI-like waveforms from airborne lidar to build a calibration database. We used this database to expand the geographic extent of past waveform lidar studies, and divided the globe into four broad strata by Plant Functional Type (PFT) and six geographic regions. GEDI's waveform-to-biomass models take the form of parametric Ordinary Least Squares (OLS) models with simulated Relative Height (RH) metrics as predictor variables. From an exhaustive set of candidate models, we selected the best input predictor variables, and data transformations for each geographic stratum in the GEDI domain to produce a set of comprehensive predictive footprint-level models. We found that model selection frequently favored combinations of RH metrics at the 98th, 90th, 50th, and 10th height above ground-level percentiles (RH98, RH90, RH50, and RH10, respectively), but that inclusion of lower RH metrics (e.g. RH10) did not markedly improve model performance. Second, forced inclusion of RH98 in all models was important and did not degrade model performance, and the best performing models were parsimonious, typically having only 1-3 predictors. Third, stratification by geographic domain (PFT, geographic region) improved model performance in comparison to global models without stratification. Fourth, for the vast majority of strata, the best performing models were fit using square root transformation of field AGBD and/or height metrics. There was considerable variability in model performance across geographic strata, and areas with sparse training data and/or high AGBD values had the poorest performance. These models are used to produce global predictions of AGBD, but will be improved in the future as more and better training data become available.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2022

Aboveground biomass density models for NASA’s Global Ecosystem Dynamics Investigation (GEDI) lidar mission

NASA’s Global Ecosystem Dynamics Investigation (GEDI) is collecting spaceborne full waveform lidar data with a primary science goal of producing accurate estimates of forest aboveground biomass density (AGBD). This paper presents the development of the models used to create GEDI’s footprint-level (~25 m) AGBD (GEDI04_A) product, including a description of the datasets used and the procedure for final model selection. The data used to fit our models are from a compilation of globally distributed spatially and temporally coincident field and airborne lidar datasets, whereby we simulated GEDI-like waveforms from airborne lidar to build a calibration database. We used this database to expand the geographic extent of past waveform lidar studies, and divided the globe into four broad strata by Plant Functional Type (PFT) and six geographic regions. GEDI’s waveform-to-biomass models take the form of parametric Ordinary Least Squares (OLS) models with simulated Relative Height (RH) metrics as predictor variables. From an exhaustive set of candidate models, we selected the best input predictor variables, and data transformations for each geographic stratum in the GEDI domain to produce a set of comprehensive predictive footprint-level models. We found that model selection frequently favored combinations of RH metrics at the 98th, 90th, 50th, and 10th height above ground-level percentiles (RH98, RH90, RH50, and RH10, respectively), but that inclusion of lower RH metrics (e.g. RH10) did not markedly improve model performance. Second, forced inclusion of RH98 in all models was important and did not degrade model performance, and the best performing models were parsimonious, typically having only 1-3 predictors. Third, stratification by geographic domain (PFT, geographic region) improved model performance in comparison to global models without stratification. Fourth, for the vast majority of strata, the best performing models were fit using square root transformation of field AGBD and/or height metrics. There was considerable variability in model performance across geographic strata, and areas with sparse training data and/or high AGBD values had the poorest performance. These models are used to produce global predictions of AGBD, but will be improved in the future as more and better training data become available.

Laura Duncanson↗
DOE OSTI2019

Exchange current density model for the contact-determined current-voltage behavior of solar cells

An analytic expression for the current–voltage [J(V)] behavior of a solar cell as limited by equilibrium exchange current densities of both carriers at both contacts is derived. The partial currents at both contacts to a generic semiconductor absorber are assumed to be linearly proportional to the excess carrier concentration at the interface with the contacts (e.g., as with Schottky-like contacts). The assumption that the quasi-Fermi levels in the absorber are approximately flat leads to an algebraic solution for the applied voltage as a function of current, which is inverted to obtain the analytic J(V) curve. The J(V) curve reveals distinct behavior associated with electrons and holes, separately, and allows for the determination of all critical performance parameters. In particular, it demonstrates how the characteristic features of the J(V) curve depend on the relative rate at which a particular carrier (electron or hole) is collected at one contact vs the other, rather than the relative rate of electron vs hole collection at a single contact. Furthermore, the model provides a unified explanation of how majority carrier extraction limitations cause nonideal J(V) behaviors such as S-shaped curves and dark/light crossover (i.e., failure of superposition). The efficacy and limitations of the model when applied to Schottky-type and doped semiconductor contacts are discussed. The work serves as a theoretical guide to scientists studying solar cells that are thought to be primarily limited by their contacts.

Solar cells↗