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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 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

Terrestrial Planet Formation Constrained By Mars and the Structure of the Asteroid Belt

Reproducing the large Earth/Mars mass ratio requires a strong mass depletion in solids within the protoplanetary disc between 1 and 3 au. The Grand Tack model invokes a specific migration history of the giant planets to remove most of the mass initially beyond 1 au and to dynamically excite the asteroid belt. However, one could also invoke a steep density gradient created by inward drift and pile-up of small particles induced by gas drag, as has been proposed to explain the formation of close-in super-Earths. Here we show that the asteroid belt’s orbital excitation provides a crucial constraint against this scenario for the Solar system. We performed a series of simulations of terrestrial planet formation and asteroid belt evolution starting from discs of planetesimals and planetary embryos with various radial density gradients and including Jupiter and Saturn on nearly circular and coplanar orbits. Discs with shallow density gradients reproduce the dynamical excitation of the asteroid belt by gravitational self-stirring but form Mars analogues significantly more massive than the real planet. In contrast, a disc with a surface density gradient proportional to r(exp −5.5) reproduces the Earth/Mars mass ratio but leaves the asteroid belt in a dynamical state that is far colder than the real belt. We conclude that no disc profile can simultaneously explain the structure of the terrestrial planets and asteroid belt. The asteroid belt must have been depleted and dynamically excited by a different mechanism such as, for instance, in the Grand Tack scenario.

Numerical methods↗
NASA NTRSDate not supplied

Application of Regolith Polymer Composite FFF Construction in Simulated Lunar Conditions

NASA’s Artemis program has the lofty goal of creating a sustained lunar presence to provide unprecedented opportunities for scientific discovery and to ensure American industry’s access to the unlimited resources and commercial potential in space. To achieve this goal, NASA must incrementally develop and expand its capabilities beyond the short lunar stays of the Apollo program to a robust continued presence with infrastructure and equipment to reduce mission risk by providing safer and more reliable access to the surface, its resources, and protection from the environment. Kennedy Space Center’s Swamp Works Granular Mechanics and Regolith Operations laboratory has partnered with AI SpaceFactory to develop the architectural and structural design of a robotically constructable unpressurized shelter. The shelter, called Lina is designed to protect astronauts and surface assets from radiation, meteoroid impact, moon quakes and thermal gradients. A Fused Filament Fabrication (FFF) construction process using regolith polymer composites was developed. The construction system and associated print parameters are discussed along with the environmental simulation equipment and a summary of test conditions. Test samples were printed in simulated lunar dirty thermal vacuum conditions (~-180 C, ~10-3 torr) and subjected to a series of tests. The resulting strength properties are summarized here, the full details of the material characteristics are provided in a related paper. Lina’s structural design criteria and the resulting initial structure design are detailed in two related papers, this paper presents an update to Lina’s design based on the achieved material strength properties. Finally, a scaled down version of the updated Lina was built on a regolith simulant surface using a novel anchoring technique in simulated lunar vacuum conditions.

lunar infrastructure↗
DOE OSTI2019

Acceptor Gradient Polymer Donors for Non-Fullerene Organic Solar Cells

In organic solar cells, maximizing the open-circuit voltage ( V OC ) via minimization of the ionization energy or electron affinity offsets of the blended donor and acceptor often comes at the expense of achieving a considerable amount of short-circuit current ( J SC ). To explore a hypothesis for the design of materials that may circumvent this tradeoff, eight structurally similar polymers were synthesized consisting of a fluorinated/non-fluorinated benzothiadiazole (BTDF/BTD) strong acceptor moiety, a thiophene ester (TE) weak acceptor, and various donor units composed of bithiophene (T2), biEDOT, and benzodithiophene (BDT) to form six acceptor gradient and two nongradient polymers. The acceptor gradient motif was designed and theorized to induce more facile exciton dissociation in low driving force solar cells by creating a further separated intramolecular charge-transfer state between the strong BTD acceptor and various donor units through a bridging TE component. Solar cells were fabricated using the eight polymers blended with phenyl-C 71 -butyric-acid methyl ester (PC 71 BM) to reveal two top performing isomeric polymers, T2-BTDF-(TE2) and TE2-BTDF-(T2), which were further tested with several non-fullerene acceptors (NFAs): EH-IDTBR, ITIC, and ITIC- 4 F. In order to fabricate optimally performing solar cells, a 0.2 eV ionization energy offset was found to be essential or the short-circuit current of the NFA cells diminished dramatically. Ultimately, optimized NFA solar cells were fabricated using ITIC-4F paired with each of the top performing polymers to produce an average PCE of 7.3% for TE2-BTDF-(T2) (nongradient) and 3.6% for T2-BTDF-(TE2) (gradient). The acceptor gradient effect was not shown to reduce the amount of charge recombination in NFA solar cells mainly due to the inability to fabricate solar cells, with minimal ionization energy or electron affinity offsets along with morphological complications. This work stresses the importance of acquiring accurate ionization energies and electron affinities when characterizing solar cell energetics, as differences as small as 0.1 eV in the offsets can make a significant impact on overall charge collection.

36 MATERIALS SCIENCE↗
NASA NTRS1978

Silicon crystals: Process for manufacturing wafer-like silicon crystals with a columnar structure

Wafer-like crystals suitable for making solar cells are formed by pouring molten Si containing suitable dopants into a mold of the desired shape and allowing it to solidify in a temperature gradient, whereby the large surface of the melt in contact with the mold is kept at less than 200 D and the free surface is kept at a temperature of 200-1000 D higher, but below the melting point of Si. The mold can also be made in the form of a slit, whereby the 2 sides of the mold are kept at different temperatures. A mold was milled in the surface of a cylindrical graphite block 200 mm in diameter. The granite block was induction heated and the bottom of the mold was cooled by means of a water-cooled Cu plate, so that the surface of the mold in contact with one of the largest surfaces of the melt was held at approximately 800 D. The free surface of the melt was subjected to thermal radiation from a graphite plate located 2 mm from the surface and heated to 1500 D. The Si crystal formed after slow cooling to room temperature had a columnar structure and was cut with a diamond saw into wafers approximately 500 mm thick. Solar cells prepared from these wafers had efficiencies of 10 to 11%.

Authier, B.↗
DOE OSTI2021

The surface triple-coupling on single crystalline cathode for lithium ion batteries

Single crystalline (SC) cathode materials, which are less susceptible to micro/nano-cracks formation and offer better structure stability compared to the polycrystalline counterpart, have attained great attention. However, the parasitic side reactions at the cathode-electrolyte interface induces the loss of active species, which consequently leads to continual degradation of the electrochemical performances. Herein, a triple coupling of concentration-gradient Na+, F- co-doping and surface NaF coating are exploited for the first time on SC LiNi 0.5C o 0.2 Mn 0.3 O 2 cathode by the hydrolysis of NaPF 6 . This process regulates the external structure of materials by constructing a “sandwich” configuration from surface to bulk: rock salt - mixing zone - layered phase. The detailed interface transformation mechanism is revealed by Neutron powder diffraction (NPD), spherical aberration corrected high-resolution scanning transmission electron microscopy (HR-STEM), electron energy loss spectroscopy (EELS), and Ar+ sputtering assisted X-ray photoelectron spectroscopy (XPS). The synergistic effects endow the SC cathode with outstanding capacity retentions: 91.3% at 25 °C and 85% at 45 °C, after 500 cycles at 5 C between 3.0 and 4.5 V. In addition, a high full-cell reversible capacity of 168.9 mAh g -1 with a capacity retention of 92.4% is achieved after 300 cycles at 1 C. Multiple characterizations further indicate that these superior results are mainly ascribed to the overall structure integrity of SC material, the thin cathode electrolyte interface, high content of lithium fluoride, and the low solubility of transition metal ions. This work opens a new avenue to construct a benign interface towards high-performance lithium ion batteries.

lithium ion batteries↗
NASA NTRS1977

Results of an investigation of the acoustic and vibrational environment of a full scale space shuttle orbiter structural test panel with simulated TPS in the Ames unitary plan wind tunnel, model 81-0, test OS8A and B

Results of tests OS8A and B and pertinent test and model information are presented. The test was conducted in two parts. Test OS8A was performed in the NASA/ARC unitary 11-foot section and OS8B was conducted in the NASA/ARC unitary 9 x 7 tunnel. Test objectives were to investigate thermal protection system (TPS) tile sensitivity to extreme pressure gradients and vibration and to define the TPS aerodynamic environment. The model utilized for OS8 was a full-scale representation of a portion of the space shuttle orbiter lower wing carry-through structure forward of the aft tank strut and propellant lines. Thermal protection tiles were simulated on the model. The model was instrumented with static pressure orifices, accelerometers, and dynamic pressure transducers (Kulites). A total rake was utilized to obtain boundary layer surveys.

Kingsland, R. B.↗
DOE OSTI2023

The role of cellular structure, non-equilibrium eutectic phases and precipitates on quasi-static strengthening mechanisms of as-built AlSi10Mg parts 3D printed via laser powder bed fusion

The quasi-static loading strengthening mechanism in the as-built state of an AlSi10Mg alloy 3D-printed via Laser Powder Bed Fusion (LPBF) was thoroughly identified and quantified using state-of-the-art electron microscopy and synchrotron X-ray diffraction techniques. The yield strength was comprehensively modelled through an in-depth characterization and quantification of the microstructural features as well as their effective volumes for strengthening. In particular, the non-equilibrium eutectic network was characterized with a two-fold structure: cell boundary particles as well as intracellular lamellar/fibrous networks, each consisting of discrete phases exhibiting a thru-thickness compositional gradient, a semi-coherent interface with the matrix and an abundance of crystal defects such as nano-sized sub-grains, microstrains and stacking faults. Further, these altogether made the eutectic phase the most potent contributor to the yield strength accounting for ~30–40% of the estimated value (i.e., cell boundary and eutectic network strengthening combined). Precipitates strengthening was identified as the second most potent mechanism via a shearing process only. Moreover, the presented methodology was able to capture the effect of LPBF processing variables on the individual strengthening contributions, e.g., the effect of a lower laser scanning speed on increasing the cell size as well as the mean precipitate size, which are shown to exhibit opposing impacts on strengthening.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Geospatial modeling of near subsurface temperatures of the contiguous United States for assessment of materials degradation

Abstract Understanding subsurface temperature variations is crucial for assessing material degradation in underground structures. This study maps subsurface temperatures across the contiguous United States for depths from 50 to 3500 m, comparing linear interpolation, gradient boosting (LightGBM), neural networks, and a novel hybrid approach combining linear interpolation with LightGBM. Results reveal heterogeneous temperature patterns both horizontally and vertically. The hybrid model performed best achieving a root mean square error of 2.61 °C at shallow depths (50–350 m). Model performance generally decreased with depth, highlighting challenges in deep temperature prediction. State-level analyses emphasized the importance of considering local geological factors. This study provides valuable insights for designing efficient underground facilities and infrastructure, underscoring the need for depth-specific and region-specific modeling approaches in subsurface temperature assessment.

Science & Technology - Other Topics↗
DOE OSTI2024

The effect of temperature oscillations on energy storage rectification in harmonic systems

Abstract Rectification, the preferential transport of a current in one direction through a system, has garnered significant attention in molecules because of its importance for controlling thermal and electronic currents at the nanoscale. Here, we report the presence of energy storage rectification effects in a molecular chain. This phenomenon is generated by subjecting a harmonic molecular chain to an oscillating temperature gradient and showing that the energy absorption rate of the system depends on the direction of the gradient. We examine how the energy storage rectification ratios in the chain are affected by the oscillating gradient, asymmetry in the chain, and the system parameters. We find that energy storage rectification can be observed in harmonic lattice structures with time-dependent temperatures and that, correspondingly, anharmonicity is not required to generate this rectification mechanism in such systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1982

Manufacture of large glass honeycomb mirrors

The problem of making very large glass mirrors for astronomical telescopes is examined, and the advantages of honeycomb mirrors made of borosilicate glass are discussed. Thermal gradients in the glass that degrade the figure of thick borosilicate mirrors during use can be largely eliminated in a honeycomb structure by internal ventilation (in air) or careful control of the radiation environment (in space). It is expected that ground-based telescopes with honeycomb mirrors will give better images than those with solid mirrors. Materials, techniques, and the experience that has been gained making trial mirrors and test castings as part of a program to develop 8-10-m-diameter lightweight mirrors are discussed.

Angel, J. R. P.↗
NASA NTRS1987

Adaptive momentum management for large space structures

Momentum management is discussed for a Large Space Structure (LSS) with the structure selected configuration being the Initial Orbital Configuration (IOC) of the dual keel space station. The external forces considered were gravity gradient and aerodynamic torques. The goal of the momentum management scheme developed is to remove the bias components of the external torques and center the cyclic components of the stored angular momentum. The scheme investigated is adaptive to uncertainties of the inertia tensor and requires only approximate knowledge of principle moments of inertia. Computational requirements are minimal and should present no implementation problem in a flight type computer and the method proposed is shown to be effective in the presence of attitude control bandwidths as low as .01 radian/sec.

Hahn, E.↗
NASA NTRS1987

Adaptive momentum management for the dual keel Space Station

The report discusses momentum management for a large space structure with the structure selected configuration being the Initial Orbital Configuration of the dual-keel Space Station. The external torques considered were gravity gradient and aerodynamic torques. The goal of the momentum management scheme developed is to remove the bias components of the external torques and center the cyclic components of the stored angular momentum. The scheme investigated is adaptive to uncertainties of the inertia tensor and requires only approximate knowledge of principal moments of inertia. Computational requirements are minimal and should present no implementation problem in a flight-type computer. The method proposed is shown to be effective in the presence of attitude control bandwidths as low as 0.01 radian/sec.

Hopkins, M.↗
NASA NTRS1988

Directional solidification of Cu-Pb and Bi-Ga monotectic alloys under normal gravity and during parabolic flight

Cu-Pb and Bi-Ga monotectic alloys of nominal hypermonotectic compositions were directionally solidified under various furnace translation rates, temperature gradients, and gravity levels. Gravity was varied by solidifying the alloys under ground conditions and in the furnace aboard NASA KC-135 aircraft, flying on parabolic trajectories. High translation rates, high gradients, high gravity levels, and higher density and lower thermal conductivity of the L2 phase favored the formation of fiber composite structure, while the opposite conditions resulted in structures consisting of L2 droplets in alpha matrix. A modified particle engulfment theory as originally enunciated by Ulhmann et al. (1964) is proposed to explain these observations.

Dhindaw, B. K.↗
NASA NTRS1988

Gravity gradient measurements

It is shown that, for floated satellite gradiometers subject to very low levels of unmodeled forces and torques, dynamic estimation can dramatically reduce rotation correction errors. The filter structure is developed, and the value of factorization techniques is examined. Numerical examples are given for a few practical cases using plausible instrument ensembles. To achieve these early results, great simplifications have been made, and important error sources have been suppressed.

Sonnabend, D.↗
NASA NTRS1990

Modeling the pressure-strain correlation of turbulence: An invariant dynamical systems approach

The modeling of the pressure-strain correlation of turbulence is examined from a basic theoretical standpoint with a view toward developing improved second-order closure models. Invariance considerations along with elementary dynamical systems theory are used in the analysis of the standard hierarchy of closure models. In these commonly used models, the pressure-strain correlation is assumed to be a linear function of the mean velocity gradients with coefficients that depend algebraically on the anisotropy tensor. It is proven that for plane homogeneous turbulent flows the equilibrium structure of this hierarchy of models is encapsulated by a relatively simple model which is only quadratically nonlinear in the anisotropy tensor. This new quadratic model - the SSG model - is shown to outperform the Launder, Reece, and Rodi model (as well as more recent models that have a considerably more complex nonlinear structure) in a variety of homogeneous turbulent flows. Some deficiencies still remain for the description of rotating turbulent shear flows that are intrinsic to this general hierarchy of models and, hence, cannot be overcome by the mere introduction of more complex nonlinearities. It is thus argued that the recent trend of adding substantially more complex nonlinear terms containing the anisotropy tensor may be of questionable value in the modeling of the pressure-strain correlation. Possible alternative approaches are discussed briefly.

Speziale, Charles G.↗
NASA NTRS1990

The onset of the new solar modulation cycle in 1987-1988 as a function of heliocentric radius and latitude

The onset of a new solar modulation cycle were studied in 1987 and 1988, on the basis of data on counting rates of particles with E greater than 60 MeV, observed at the IMP, Voyager (V), and Pioneer (P) satellites. It was found that the decrease at earth was rapid after the intensity maximum in early 1987 and was closely correlated with the increase in the average tilt of the heliospheric current sheet. The initial rapid intensity decrease was found to be related to three small Forbush decreases which are superimposed on a more gradual decrease. By the end of 1988, the intensity decreased by about 40 percent at earth, 30 percent at V2, and 18 percent at P10. This overall decrease was accompanied by an increase in the average integral radial gradient as well as a decrease in the radial dependence of the gradient. The onset of the new solar modulation cycle seems to be related to the complete altering of the solar magnetic structure as observed on the surface of the sun.

Webber, W. R.↗
NASA NTRS1991

Modelling the pressure-strain correlation of turbulence - An invariant dynamical systems approach

The modeling of the pressure-strain correlation of turbulence is examined from a basic theoretical standpoint with a view toward developing improved second-order closure models. Invariance considerations along with elementary dynamical systems theory are used in the analysis of the standard hierarchy of closure models. In these commonly used models, the pressure-strain correlation is assumed to be a linear function of the mean velocity gradients with coefficients that depend algebraically on the anisotropy tensor. It is proven that for plane homogeneous turbulent flows the equilibrium structure of this hierarchy of models is encapsulated by a relatively simple model which is only quadratically nonlinear in the anisotropy tensor. This new quadratic model - the SSG model - is shown to outperform the Launder, Reece, and Rodi model (as well as more recent models that have a considerably more complex nonlinear structure) in a variety of homogeneous turbulent flows. Some deficiencies still remain for the description of rotating turbulent shear flows that are intrinsic to this general hierarchy of models and, hence, cannot be overcome by the mere introduction of more complex nonlinearities. It is thus argued that the recent trend of adding substantially more complex nonlinear terms containing the anisotropy tensor may be of questionable value in the modeling of the pressure-strain correlation. Possible alternative approaches are discussed briefly.

Speziale, Charles G.↗
NASA NTRS1996

Adaptive grid methods for RLV environment assessment and nozzle analysis

Rapid access to highly accurate data about complex configurations is needed for multi-disciplinary optimization and design. In order to efficiently meet these requirements a closer coupling between the analysis algorithms and the discretization process is needed. In some cases, such as free surface, temporally varying geometries, and fluid structure interaction, the need is unavoidable. In other cases the need is to rapidly generate and modify high quality grids. Techniques such as unstructured and/or solution-adaptive methods can be used to speed the grid generation process and to automatically cluster mesh points in regions of interest. Global features of the flow can be significantly affected by isolated regions of inadequately resolved flow. These regions may not exhibit high gradients and can be difficult to detect. Thus excessive resolution in certain regions does not necessarily increase the accuracy of the overall solution. Several approaches have been employed for both structured and unstructured grid adaption. The most widely used involve grid point redistribution, local grid point enrichment/derefinement or local modification of the actual flow solver. However, the success of any one of these methods ultimately depends on the feature detection algorithm used to determine solution domain regions which require a fine mesh for their accurate representation. Typically, weight functions are constructed to mimic the local truncation error and may require substantial user input. Most problems of engineering interest involve multi-block grids and widely disparate length scales. Hence, it is desirable that the adaptive grid feature detection algorithm be developed to recognize flow structures of different type as well as differing intensity, and adequately address scaling and normalization across blocks. These weight functions can then be used to construct blending functions for algebraic redistribution, interpolation functions for unstructured grid generation, forcing functions to attract/repel points in an elliptic system, or to trigger local refinement, based upon application of an equidistribution principle. The popularity of solution-adaptive techniques is growing in tandem with unstructured methods. The difficultly of precisely controlling mesh densities and orientations with current unstructured grid generation systems has driven the use of solution-adaptive meshing. Use of derivatives of density or pressure are widely used for construction of such weight functions, and have been proven very successful for inviscid flows with shocks. However, less success has been realized for flowfields with viscous layers, vortices or shocks of disparate strength. It is difficult to maintain the appropriate mesh point spacing in the various regions which require a fine spacing for adequate resolution. Mesh points often migrate from important regions due to refinement of dominant features. An example of this is the well know tendency of adaptive methods to increase the resolution of shocks in the flowfield around airfoils, but in the incorrect location due to inadequate resolution of the stagnation region. This problem has been the motivation for this research.

Thornburg, Hugh J.↗