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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Analytical and Photogrammetric Characterization of a Planar Tetrahedral Truss

Future space science missions are likely to require near-optical quality reflectors which are supported by a stiff truss structure. This support truss should conform closely with its intended shape to minimize its contribution to the overall surface error of the reflector. The current investigation was conducted to evaluate the planar surface accuracy of a regular tetrahedral truss structure by comparing the results of predicted and measured node locations. The truss is a 2-ring hexagonal structure composed of 102 equal-length truss members. Each truss member is nominally 2 meters in length between node centers and is comprised of a graphite/epoxy tube with aluminum nodes and joints. The axial stiffness and the length variation of the truss components were determined experimentally and incorporated into a static finite element analysis of the truss. From this analysis, the root mean square (RMS) surface error of the truss was predicted to be 0.11 mm (0004 in). Photogrammetry tests were performed on the assembled truss to measure the normal displacements of the upper surface nodes and to determine if the truss would maintain its intended shape when subjected to repeated assembly. Considering the variation in the truss component lengths, the measures rms error of 0.14 mm (0.006 in) in the assembled truss is relatively small. The test results also indicate that a repeatable truss surface is achievable. Several potential sources of error were identified and discussed.

Wu, K. Chauncey↗
DOE OSTI2023

Hexaazatriphenylene‐Based Two‐Dimensional Conductive Covalent Organic Framework with Anisotropic Charge Transfer

Abstract The development of covalent organic frameworks (COFs) with efficient charge transport is of immense interest for applications in optoelectronic devices. To enhance COF charge transport properties, electroactive building blocks and dopants can be used to induce extended conduction channels. However, understanding their intricate interplay remains challenging. We designed and synthesized a tailor‐made COF structure with electroactive hexaazatriphenylene (HAT) core units and planar dioxin (D) linkages, denoted as HD‐COF. With the support of theoretical calculations, we found that the HAT units in the HD‐COF induce strong, eclipsed π–π stacking. The unique stacking of HAT units and the weak in‐plane conjugation of dioxin linkages leads to efficient anisotropic charge transport. We fabricated HD‐COF films to minimize the grain boundary effect of bulk COFs, which resulted in enhanced conductivity. As a result, the HD‐COF films showed an electrical conductivity as high as 1.25 S cm −1 after doping with tris(4‐bromophenyl)ammoniumyl hexachloroantimonate.

Kim, Seong‐Wook↗
DOE OSTI2023

Hexaazatriphenylene‐Based Two‐Dimensional Conductive Covalent Organic Framework with Anisotropic Charge Transfer

Here, the development of covalent organic frameworks (COFs) with efficient charge transport is of immense interest for applications in optoelectronic devices. To enhance COF charge transport properties, electroactive building blocks and dopants can be used to induce extended conduction channels. However, understanding their intricate interplay remains challenging. We designed and synthesized a tailor-made COF structure with electroactive hexaazatriphenylene (HAT) core units and planar dioxin (D) linkages, denoted as HD-COF. With the support of theoretical calculations, we found that the HAT units in the HD-COF induce strong, eclipsed π–π stacking. The unique stacking of HAT units and the weak in-plane conjugation of dioxin linkages leads to efficient anisotropic charge transport. We fabricated HD-COF films to minimize the grain boundary effect of bulk COFs, which resulted in enhanced conductivity. As a result, the HD-COF films showed an electrical conductivity as high as 1.25 S cm −1 after doping with tris(4-bromophenyl)ammoniumyl hexachloroantimonate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Crystal structure of oxibendazole, C 12 H 15 N 3 O 3

The crystal structure of oxibendazole has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional theory techniques. Oxibendazole crystallizes in space group C2/c (#15) with a = 23.18673(22), b = 5.35136(5), c = 19.88932(13) Å, β = 97.0876(9)°, V = 2449.018(17) Å 3 , and Z = 8. The structure consists of hydrogen-bonded layers of planar molecules parallel to the bc-plane. Strong N–H∙∙∙N hydrogen bonds link the molecules into dimers, with a graph set R2,2(8). N–H∙∙∙O hydrogen bonds further link these dimers into layers parallel to the bc-plane. The powder pattern has been submitted to ICDD for inclusion in the Powder Diffraction File™ (PDF®).

36 MATERIALS SCIENCE↗
DOE OSTI2022

Humble planar defects in SiGe nanopillars

We report a {001} planar defect found in SiGe nanopillars. The defect structure, determined by atomic-resolution electron microscopy, matches the Humble defect model proposed for diamond. We also investigate several possible variants of the Humble structure using first-principles calculations and find that the one lowest in energy is in agreement with the scanning transmission electron microscope images. The pillar composition has been analyzed with electron energy loss spectroscopy, which hints at how the defect is formed. Our results show that the structure and formation process of defects in nanostructured group IV semiconductors can be different from their bulk counterparts.

36 MATERIALS SCIENCE↗
NASA NTRS1982

The origin of the Kirkwood gaps - A mapping for asteroidal motion near the 3/1 commensurability

A mapping of the phase space onto itself with the same low-order resonance structure as the 3/1 commensurability in the planar-elliptic restricted three-body problem is obtained. This mapping is about 1,000 times faster than the usual method of numerically integrating the averaged equations of motion. It exhibits some surprising behavior that might provide a key to the origin of the Kirkwood gaps. It is noted that a test asteroid placed in the gap may evolve for a million years with low eccentricity (less than 0.05) and then suddenly jump to large eccentricity (greater than 0.3), becoming a Mars crosser. The removal of the asteroid by a close encounter with Mars would then be possible. As a first test of this hypothesis, a distribution of 300 test asteroids in the area of the 3/1 commensurability was evolved for two million years. When the Mars crossers are removed, the distribution of initial conditions reveals a gap at the location of the 3/1 Kirkwood gap.

Wisdom, J.↗
NASA NTRS1983

Slotted waveguide array antennas for spaceborne SAR applications

Starting with mission definitions and constraints for the NASA proposed Shuttle Active Microwave Experiments (SAMEX) and Free Flying Imaging Radar Experiment (FIREX), Hughes Aircraft Company has compiled and studied the technology available for slotted waveguide planar array antennas suitable for spaceborne SAR application. Antenna performance is derived, and fabrication techniques are discussed. Mission requirements will always lead to an aperture subdivided into waveguide modules, thereby validating a module definition for other mission building blocks. Finally, a specific design is proposed for a SAMEX mission using the modules as RF aperture building blocks, resulting in a (nominal) 15.1 meter by 5.5 meter extensile dual polarized L-, C-, and X-band planar array with an associated extensile graphite/epoxy support structure. Antenna development begin with a fabrication method development study involving a representative portion of an antenna module.

Bostrom, D. E.↗
NASA NTRS1990

Microstrip reflectarray antenna for the SCANSCAT radar application

This publication presents an antenna system that has been proposed as one of the candidates for the SCANSCAT (Scanned Scatterometer) radar application. It is the mechanically steered planar microstrip reflectarray. Due to its thin, lightweight structure, the antenna's mechanical rotation will impose minimum angular momentum for the spacecraft. Since no power-dividing circuitry is needed for its many radiating microstrip patches, this electrically large array antenna demonstrates excellent power efficiency. In addition, this fairly new antenna concept can provide many significant advantages over a conventional parabolic reflector. The basic formulation for the radiation fields of the microstrip reflectarray is presented. This formulation is based on the array theory augmented by the Uniform Geometrical Theory of Diffraction (UTD). A computer code for analyzing the microstrip reflectarray's performances, such as far-field patterns, efficiency, etc., is also listed in this report. It is proposed here that a breadboard unit of this microstrip reflectarray should be constructed and tested in the future to validate the calculated performance. The antenna concept presented here can also be applied in many other types of radars where a large array antenna is needed.

Huang, John↗
NASA NTRS1994

Analytical investigation of the dynamics of tethered constellations in Earth orbit, phase 2

This final report covers nine years of research on future tether applications and on the actual flights of the Small Expendable Deployment System (SEDS). Topics covered include: (1) a description of numerical codes used to simulate the orbital and attitude dynamics of tethered systems during station keeping and deployment maneuvers; (2) a comparison of various tethered system simulators; (3) dynamics analysis, conceptual design, potential applications and propagation of disturbances and isolation from noise of a variable gravity/microgravity laboratory tethered to the Space Station; (4) stability of a tethered space centrifuge; (5) various proposed two-dimensional tethered structures for low Earth orbit for use as planar array antennas; (6) tethered high gain antennas; (7) numerical calculation of the electromagnetic wave field on the Earth's surface on an electrodynamically tethered satellite; (8) reentry of tethered capsules; (9) deployment dynamics of SEDS-1; (10) analysis of SEDS-1 flight data; and (11) dynamics and control of SEDS-2.

Lorenzini, Enrico C.↗
NASA NTRS2002

Photonic Bandgaps in Mie Scattering by Concentrically Stratified Spheres

The Mie formulation for homogeneous spheres is generalized to handle core/shell systems and multiple concentric layers in a manner that exploits an analogy with stratified planar systems, thereby allowing concentric multi-layered structures to be treated as photonic bandgap materials. Representative results from a Mie code employing this analogy demonstrate that photonic bands are present for periodic concentric spheres, though not readily apparent in extinction spectra. Rather, the periodicity simply alters the scattering profile, enhancing the ratio of backscattering to forward scattering inside the bandgap, whereas modification of the interference structure is evident in extinction spectra in accordance with the optical theorem

Smith, David D.↗
NASA NTRS2006

Free-jet Testing of a REST Scramjet at Off-Design Conditions

Scramjet flowpaths employing elliptical combustors have the potential to improve structural efficiency and performance relative to those using planar geometries. NASA Langley has developed a scramjet flowpath integrated into a lifting body vehicle, while transitioning from a rectangular capture area to both an elliptical throat and combustor. This Rectangular-to-Elliptical Shape Transition (REST) scramjet, has a design point of Mach 7.1, and is intended to operate with fixed-geometry between Mach 4.5 and 8.0. This paper describes initial free-jet testing of the heat-sink REST scramjet engine model at conditions simulating Mach 5.3 flight. Combustion of gaseous hydrogen fuel at equivalence ratios between 0.5 and 1.5 generated robust performance after ignition with a silane-hydrogen pilot. Facility model interactions were experienced for fuel equivalence ratios above 1.1, yet despite this, the flowpath was not unstarted by fuel addition at the Mach 5.3 test condition. Combustion tests at reduced stagnation enthalpy indicated that the engine self-started following termination of the fuel injection. Engine data is presented for the largest fuel equivalence ratio tested without facility interaction. These results indicate that this class of three-dimensional scramjet engine operates successfully at off-design conditions.

Smart, Michael K.↗
NASA NTRS2019

Distorted Perovskites for High Voltage Dielectric Capacitors

There are several mechanisms which have been proposed for the existence of colossal dielectric constant in the class of perovskite calcium copper titanate (CaCu3Ti4O12 or CCTO) materials. Researches indicate that existence of twinning parallel to (100) (001) and (010) planes causes planar defects and causes changes in local electronic structure. This change can cause insulating barriers locally which contribute to the large dielectric values irrespective of processing. The combination of insulating barriers, defects and displacements caused by twinning have been attributed to the generation of large dielectric constant in CCTO. To examine some of these arguments some researchers replaced Ca with other elements and evaluated this concept. In this study we present the synthesis and characterization of Ga2/3Cu3Ti4O12-xNx (GCTON) material. This provides both distortion due to atomic size difference and defects due to insertion of nitrogen. The morphology of the compound was determined to show that processing has tremendous effect on the dielectric values. The resistivity of GCTON was several order higher than CCTO and dielectric constant was higher than 10,000.

Gill, Puneet↗
DOE OSTI2025

Two-Frequency RF Fields Induced Multipactor in Coaxial Transmission Lines

Multipactor is a nonlinear discharge phenomenon that occurs in vacuum RF systems, potentially leading to signal distortion, power loss, and even permanent damage to high-power components. This study presents a detailed investigation of two-surface multipactor in coaxial transmission lines under two-frequency excitation, using one-dimensional (1D) Monte Carlo simulations validated by three-dimensional (3D) Particle-in-Cell (PIC) results and experimental data. Introducing a second carrier mode is shown to suppress multipactor by reshaping and shrinking the susceptibility region, with the extent and location of suppression strongly dependent on the device aspect ratio and the relative phase of the second mode. Distinct suppression patterns emerge across different frequency–gap distance (fd) regimes, and in certain cases, susceptibility expansion is also observed. The study identifies and distinguishes pure and mixed multipactor modes in coaxial geometry, where analytical mode boundaries are not readily defined. Unlike planar systems, pure-mode regions in coaxial structures overlap with mixed-mode domains, complicating classification. Image charge forces are found to have minimal effect on susceptibility thresholds but do influence electron growth rates. These findings provide new insights into waveform-driven control of multipactor in high-power RF systems.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Materials Data on PdPbF4 by Materials Project

PdPbF4 crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. Pd2+ is bonded in a square co-planar geometry to four equivalent F1- atoms. All Pd–F bond lengths are 2.02 Å. Pb2+ is bonded in a 8-coordinate geometry to eight equivalent F1- atoms. All Pb–F bond lengths are 2.58 Å. F1- is bonded in a distorted trigonal planar geometry to one Pd2+ and two equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Rh3Cl4 by Materials Project

Rh3Cl4 crystallizes in the cubic Pm-3n space group. The structure is three-dimensional. Rh is bonded in a square co-planar geometry to four equivalent Cl atoms. All Rh–Cl bond lengths are 2.33 Å. Cl is bonded in a trigonal planar geometry to three equivalent Rh atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg(Hg11N3)2 by Materials Project

Mg(Hg11N3)2 crystallizes in the tetragonal I4/m space group. The structure is three-dimensional. Mg is bonded in a square co-planar geometry to four equivalent N atoms. All Mg–N bond lengths are 2.13 Å. There are five inequivalent Hg sites. In the first Hg site, Hg is bonded in a single-bond geometry to one Hg and one N atom. The Hg–Hg bond length is 2.71 Å. The Hg–N bond length is 2.20 Å. In the second Hg site, Hg is bonded in a single-bond geometry to one Hg and one N atom. The Hg–Hg bond length is 2.98 Å. The Hg–N bond length is 2.14 Å. In the third Hg site, Hg is bonded in a single-bond geometry to two Hg and one N atom. There are one shorter (3.10 Å) and one longer (3.27 Å) Hg–Hg bond lengths. The Hg–N bond length is 2.46 Å. In the fourth Hg site, Hg is bonded in a 9-coordinate geometry to nine Hg atoms. In the fifth Hg site, Hg is bonded in a 4-coordinate geometry to four equivalent Hg atoms. There are two inequivalent N sites. In the first N site, N is bonded in a distorted trigonal bipyramidal geometry to five Hg atoms. In the second N site, N is bonded in a trigonal planar geometry to one Mg and two equivalent Hg atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1990

Pressure-based real-time measurements in compressible free shear layers

A preliminary experimental study has been conducted to gain insight into the temporal and spatial contents of largescale structures in a convective Mach number = 0.51 high Reynolds number planar two-dimensional compressible free shear layer. Power spectra, coherence, and space-time correlations were obtained using single- and two-point pressure measurements. Both developing and fully developed regions of the flow were investigated. The passage frequency of structures were found to be 10-15 kHz in the developing region and 4-8 kHz in the fully developed region. The convective velocity obtained from the space-time correlation in the middle of the shear layer was close to the theoretical value but varied toward the edge of the shear layer. The structures were shown to be surprisingly three-dimensional even in this low compressibility level shear layer. The structures size and spacing were also determined and discussed.

Samimy, M.↗
DOE OSTI2020

Materials Data on BaLiSb by Materials Project

BaLiSb crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Li1+ is bonded in a trigonal planar geometry to three equivalent Sb3- atoms. All Li–Sb bond lengths are 2.85 Å. Ba2+ is bonded to six equivalent Sb3- atoms to form a mixture of face, edge, and corner-sharing BaSb6 octahedra. The corner-sharing octahedral tilt angles are 46°. All Ba–Sb bond lengths are 3.67 Å. Sb3- is bonded in a distorted trigonal planar geometry to three equivalent Li1+ and six equivalent Ba2+ atoms.

36 MATERIALS SCIENCE↗