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NASA NTRS1992

Galactic OB associations in the northern Milky Way Galaxy. I - Longitudes 55 deg to 150 deg

The literature on all OB associations was reviewed, and their IRAS point source content was studied, between galactic longitude 55 and 150 deg. Only one third of the 24 associations listed by Ruprecht et al. (1981) have been the subject of individual studies designed to identify the brightest stars. Distances to all of these were recomputed using the method of cluster fitting of the B main sequence stars, which makes it poossible to reexamine the absolute magnitude calibration of the O stars, as well as for the red supergiant candidate stars. Also examined was the composite HR diagram for these associations. Associations with the best defined main sequences, which also tend to contain very young clusters, referred to here as OB clusters, have extremely few evolved B and A or red supergiants. Associations with poorly defined main sequences and few OB clusters have many more evolved stars. They also show an effect in the upper HR diagram referred to as a ledge by Fitzpatrick and Garmany (1990) in similar data for the Large Magellanic Cloud. It is suggested that the differences in the associations are not just observational selection effects but represent real differences in age and formation history.

Garmany, C. D.↗
NASA NTRSDate not supplied

3D Material Response of the MSL Heatshield Using NuSil-Coated PICA

The Mars Science Laboratory (MSL) was protected during its atmospheric entry by an instrumented heatshield that used NASA's Phenolic Impregnated Carbon Ablator (PICA) material [1]. PICA is a lightweight carbon fiber/polymeric resin material that offers outstanding performance for protecting probes during planetary entry. Data from the Mars Entry Descent and Landing Instrument (MEDLI) suite on MSL offers unique in-flight validation data for models of material response and atmospheric entry. MEDLI recorded, among other things, time-resolved in-depth temperature data of PICA using thermocouple sensors assembled in the MEDLI Integrated Sensor Plugs (MISP) [2]. A space-grade silicone-based coating commercially known as NuSil CV-1144-0 [3] was applied to the entire MSL heatshield, including the MEDLI plugs, to mitigate the spread of dust from PICA. Modeling the thermal response of PICA-NuSil (PICA-N) system is still an open challenge. Ground testing of PICA-N models exhibited surface temperature jumps of the order of 150 K due to oxide scale formation and sub-sequent NuSil burn-off. It is therefore critical to include a validated model for the material response of the coating in engineering codes. A test campaign has been conducted at the NASA’s Langley HyMETS [4] facility to screen the response of PICA-N and gather detailed data on its behavior [5]. A first model of PICA-N thermal response has been developed using the Hy-METS experiments [6]. The objective of this work is to analyze the material response of the latest PICA-N model compared to the engineering model used to simulate the entry of MSL. The environment and material response around the MSL aeroshell during Mars atmospheric entry is simulated using a collection of tools. The Direct Simulation Monte Carlo SPARTA code [7] is used in the rarefied regime, the Data Parallel Line Relaxation (DPLR) code [8] is used in the continuum regime and radiative heating conditions are provided by the Nonequilibrium air radiation (NEQAIR) code [9] to estimate the environmental conditions. The thermal response inside the material is computed using the Porous material Analysis Toolbox based on Open-FOAM (PATO) [10,11,12]. Thermodynamic and chemistry properties are estimated using the Mutation++ library [13]. The approach implemented in PATO as a first cut PICA-N thermal response model is outlined in Figure 1. While the recession is less than the coating thickness, the Surface mass and energy balance Boundary Condition (SBC) uses the NuSil B’ tables. Once the recession removes the coating, the usual PICA B’ tables are used for the SBC. The B’ tables are computed using an equilibrium solver implemented in Mutation++, given the temperature, pressure, blowing rate, composition of the pyrolysis and environment gases, and the condensed species at the surface. Preliminary results of the 3D material response of the MSL heat-shield at the peak heating (80 sec after Entry Interface) are shown in Figure 2. Current NASA’s mission to Mars, Mars 2020, used the spare heatshield of MSL for thermal protection during entry, descent, and landing. In preparation for Mars 2020 post-flight analysis, the PATO high-fidelity material response capability was benchmarked against flight data from MEDLI. This effort represents an important milestone toward the development of validated predictive capabilities for designing thermal protection systems for planetary probes. This bench-marking is awaiting the final release of the MEDLI-2 data.

Aerospace↗
NASA NTRS1975

Low energy particle composition

A review is given of current knowledge of low-energy cosmic ray particles produced in the solar system. It is argued that the notion that the sun alone can accelerate particles in the solar system must be abandoned in light of evidence that Jupiter and earth may be sources of observed low-energy particles. Measurements of the composition and energy spectra of low-energy particles during quiet times are examined, emphasizing the abundance of protons and helium and of anomalous N, O, and Ne. The abundance of heavy particles (B, C, N, O, Ne, Ca and Fe) of unknown origin in the earth magnetosphere is examined. Reported observations of Jovian electrons are discussed and solar particle events with anomalous compositions (He-3 rich events and Fe rich events) are treated in detail. Nuclear abundances of solar particles, emphasizing their temporal and spatial variations are considered together with the nature of nuclear reaction products in solar flares.

Gloeckler, G.↗
NASA NTRS2024

Designing Lightweight Neutron Absorbing Composites Using a Comprehensive Absorber Areal Density Metric

Efforts to lightweight neutron absorbing composites are limited by incomplete understandings of the interaction between absorbing particles and their matrices. In this study, analytical models and a more physically representative simulation evaluated the penalty to neutron absorbing performance due to neutron channeling between large absorbing particles. Models and simulation agreed that B 4 C particles smaller than 100μm and especially those smaller than 10μm did not cause excessive neutron channeling. A more comprehensive neutron absorbing composite design metric – boron-10 equivalent areal density, which considers the particle size penalty and the matrix contribution to absorptivity – was introduced and used to estimate lightweighting via matrix substitution. Calculations using this new metric showed that a non-absorbing Mg matrix reduced mass by up to 35% over Al, constrained by the difference in mass density, while an absorbing Mg–Li matrix reduced mass by up to 60%, exceeding the difference in mass densities alone. Measurement of apparent absorber areal density through two experimental techniques – foil activation and direct counting – validated estimated absorber areal density as a neutron absorbing composite design metric. This updated understanding of the particle size penalty, newly introduced design metric, and experimental validation demonstrate a path to lightweight neutron absorbing composites.

Radiation shielding↗
NASA NTRS1975

Alkali oxide-tantalum, niobium and antimony oxide ionic conductors

The phase equilibrium relations of four systems were investigated in detail. These consisted of sodium and potassium antimonates with antimony oxide and tantalum and niobium oxide with rubidium oxide as far as the ratio 4Rb2O:llB2O5 (B=Nb, Ta). The ternary system NaSbO3-Sb2O4-NaF was investigated extensively to determine the actual composition of the body centered cubic sodium antimonate. Various other binary and ternary oxide systems involving alkali oxides were examined in lesser detail. The phases synthesized were screened by ion exchange methods to determine mobility of the mobility of the alkali ion within the niobium, tantalum or antimony oxide (fluoride) structural framework. Five structure types warranted further investigation; these structure types are (1) hexagonal tungsten bronze (HTB), (2) pyrochlore, (3) the hybrid HTB-pyrochlore hexagonal ordered phases, (4) body centered cubic antimonates and (5) 2K2O:3Nb2O5. Although all of these phases exhibit good ion exchange properties only the pyrochlore was prepared with Na(+) ions as an equilibrium phase and as a low porosity ceramic. Sb(+3) in the channel interferes with ionic conductivity in this case, although relatively good ionic conductivity was found for the metastable Na(+) ion exchanged analogs of RbTa2O5F and KTaWO6 pyrochlore phases.

Roth, R. S.↗
NASA NTRS2020

Machiite, Al2Ti3O9, A New Oxide Mineral from the Murchison Carbonaceous Chondrite: A New Ultra-refractory Phase From the Solar Nebula

Machiite (IMA 2016-067), Al2Ti3O9, is a new mineral that occurs as a single euhedral crystal, 4.4 mm in size, in contact with an euhedral corundum grain, 12 mm in size, in a matrix of the Murchison CM2 carbonaceous chondrite. The mean chemical composition of holotype machiite by electron probe microanalysis is (wt%) TiO2 59.75, Al2O3 15.97, Sc2O3 10.29, ZrO2 9.18, Y2O3 2.86, FeO 1.09, CaO 0.44, SiO2 0.20, MgO 0.10, total 99.87, giving rise to an empirical formula (based on 9 oxygen atoms pfu) of (Al1.17Sc0.56Y0.10Ti4+0.08Fe0.06Ca0.03Mg0.01)(Ti4+2.71Zr0.28Si0.01)O9. The general formula is (Al,Sc)2(Ti4+,Zr)3O9. The end-member formula is Al2Ti3O9. Machiite has the C2/c schreyerite-type structure with a = 17.10 Å, b = 5.03 Å, c = 7.06 Å, b = 107°, V = 581 Å3, and Z = 4, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 4.27 g/cm3. The machiite crystal is highly 16O-depleted relative to the coexisting corundum grain (D17O = –0.2 ± 2.4‰ and –24.1 ± 2.6‰, respectively; where D17O = d17O – 0.52 × d18O). Machiite is a new member of the schreyerite (V2Ti3O9) group and a new Sc,Zr-rich ultrarefractory phase formed in the solar nebula, either by gas-solid condensation or as a result of crystallization from a Ca,Al-rich melt having solar-like oxygen isotopic composition (D17O ~ –25‰) under high-temperature (~1400–1500 °C) and low-pressure (~10-4–10-5 bar) conditions in the CAI-forming region near the protosun. The currently observed disequilibrium oxygen isotopic composition between machiite and corundum may indicate that machiite subsequently experienced oxygen isotopic exchange with a planetary-like 16O-poor gaseous reservoir either in the solar nebula or on the CM chondrite parent body. The name machiite is in honor of Chi Ma, mineralogist at California Institute of Technology, for his contributions to meteorite mineralogy and discovery of many new minerals representing extreme conditions of formation.

Alexander N Krot↗
NASA NTRS2020

Machiite, Al2Ti3O9, a New Oxide Mineral from the Murchison Carbonaceous Chondrite: A New Ultra-refractory Phase from the Solar Nebula

Machiite (IMA 2016-067), Al2Ti3O9, is a new mineral that occurs as a single euhedral crystal, 4.4 mm in size, in contact with an euhedral corundum grain, 12 mm in size, in a matrix of the Murchison CM2 carbonaceous chondrite. The mean chemical composition of holotype machiite by electron probe microanalysis is (wt%) TiO2 59.75, Al2O3 15.97, Sc2O3 10.29, ZrO2 9.18, Y2O3 2.86, FeO 1.09, CaO 0.44, SiO2 0.20, MgO 0.10, total 99.87, giving rise to an empirical formula (based on 9 oxygen atoms pfu) of (Al1.17Sc0.56Y0.10Ti4+0.08Fe0.06Ca0.03Mg0.01)(Ti4+2.71Zr0.28Si0.01)O9. The general formula is (Al,Sc)2(Ti4+,Zr)3O9. The end-member formula is Al2Ti3O9. Machiite has the C2/c schreyerite-type structure with a = 17.10 Å, b = 5.03 Å, c = 7.06 Å, b = 107°, V = 581 Å3, and Z = 4, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 4.27 g/cm3. The machiite crystal is highly 16O-depleted relative to the coexisting corundum grain (D17O = –0.2 ±2.4‰ and –24.1 ± 2.6‰, respectively; where D17O = d17O – 0.52 ×d18O). Machiite is a new member of the schreyerite (V2Ti3O9) group and a new Sc,Zr-rich ultrarefractory phase formed in the solar nebula, either by gas-solid condensation or as a result of crystallization from a Ca, Al-rich melt having solar-like oxygen isotopic composition (D17O ~ –25‰) under high-temperature (~1400–1500 °C) and low-pressure (~10-4–10-5 bar) conditions in the CAI-forming region near the protosun. The currently observed disequilibrium oxygen isotopic composition between machiite and corundum may indicate that machiite subsequently experienced oxygen isotopic exchange with a planetary-like 16O-poor gaseous reservoir either in the solar nebula or on the CM chondrite parent body. The name machiite is in honor of Chi Ma, mineralogist at California Institute of Technology, for his contributions to meteorite mineralogy and discovery of many new minerals representing extreme conditions of formation.

Machiite↗
NASA NTRS1985

Ringed planets - Still mysterious. II

The morphology of the rings of Saturn and the mechanisms proposed to explain their fluctuations and origin are discussed and illustrated with photographs and diagrams in a general review. The kinks and braids of the F ring are attributed to the gravitational effects of the known shepherding satellites and/or a number of as yet unseen moonlets; the irregular gaps in the B and inner A rings, to particle interactions (diffusion-instability processes); and the flickering spokes of the central B ring, to the rotation of the Saturn magnetic field. It is pointed out that the composition of the single Jovian ring and of the Jovian satellites can be explained if both are remnants of the planet's primordial disk, but that the rock-ice compositions of the rings and inner satellites of Saturn require a more sophisticated model, perhaps involving meteoroid erosion. The rings of Uranus and Neptune are briefly considered.

Cuzzi, J. N.↗
NASA NTRS1994

The volcanic signal in Goddard Institute for Space Studies three-dimensional model simulations

Transient calculations of the Goddard Institute for Space Studies general circulation model for the climatic signal of volcanic eruptions are analyzed. By compositing the output for two different volcanoes for scenario A and five different volcanoes for scenario B, the natural variability is suppressed and the volcanic signals are extracted. Significant global mean surface air temperature cooling and precipitation reduction are found for several years following the eruptions, with larger changes in the Northern Hemisphere (NH) than in the Southern Hemisphere. The global-average temperature response lasts for more than four years, but the precipitation response disappears after three years. The largest cooling in the model occurs in the NH summer of the year after spring eruptions. Significant zonal-average temperature reductions begin in the tropics immediately after the eruptions and extend to 45 deg S - 45 deg N in the year after the eruptions. In the second year, cooling is still seen from 30 deg S to 30 deg N. Because of the low variability in this model as compared to the real world, these signals may appear more significant here than they would by attempting to isolate them using real data. The results suggest that volcanoes can enhance the drought in the Sahel. No evidence was found that stratospheric aerosols from the low-atitude volcanic eruptions can trigger El Nino-Southern Oscillation (ENSO) events in this model.

Robock, Alan↗
NASA NTRS2004

Processing Robustness for A Phenylethynyl Terminated Polyimide Composite

The processability of a phenylethynyl terminated imide resin matrix (designated as PETI-5) composite is investigated. Unidirectional prepregs are made by coating an N-methylpyrrolidone solution of the amide acid oligomer (designated as PETAA-5/NMP) onto unsized IM7 fibers. Two batches of prepregs are used: one is made by NASA in-house, and the other is from an industrial source. The composite processing robustness is investigated with respect to the prepreg shelf life, the effect of B-staging conditions, and the optimal processing window. Prepreg rheology and open hole compression (OHC) strengths are found not to be affected by prolonged (i.e., up to 60 days) ambient storage. Rheological measurements indicate that the PETAA-5/NMP processability is only slightly affected over a wide range of B-stage temperatures from 250 deg C to 300 deg C. The OHC strength values are statistically indistinguishable among laminates consolidated using various B-staging conditions. An optimal processing window is established by means of the response surface methodology. IM7/PETAA-5/NMP prepreg is more sensitive to consolidation temperature than to pressure. A good consolidation is achievable at 371 deg C (700 deg F)/100 Psi, which yields an RT OHC strength of 62 Ksi. However, processability declines dramatically at temperatures below 350 deg C (662 deg F), as evidenced by the OHC strength values. The processability of the IM7/LARC(TM) PETI-5 prepreg was found to be robust.

Hou, Tan-Hung↗
NASA NTRS2014

The Radiation, Interplanetary Shocks, and Coronal Sources (RISCS) Toolset

We outline a plan to develop a physics based predictive toolset RISCS to describe the interplanetary energetic particle and radiation environment throughout the inner heliosphere, including at the Earth. To forecast and "nowcast" the radiation environment requires the fusing of three components: 1) the ability to provide probabilities for incipient solar activity; 2) the use of these probabilities and daily coronal and solar wind observations to model the 3D spatial and temporal heliosphere, including magnetic field structure and transients, within 10 AU; and 3) the ability to model the acceleration and transport of energetic particles based on current and anticipated coronal and heliospheric conditions. We describe how to address 1) - 3) based on our existing, well developed, and validated codes and models. The goal of RISCS toolset is to provide an operational forecast and "nowcast" capability that will a) predict solar energetic particle (SEP) intensities; b) spectra for protons and heavy ions; c) predict maximum energies and their duration; d) SEP composition; e) cosmic ray intensities, and f) plasma parameters, including shock arrival times, strength and obliquity at any given heliospheric location and time. The toolset would have a 72 hour predicative capability, with associated probabilistic bounds, that would be updated hourly thereafter to improve the predicted event(s) and reduce the associated probability bounds. The RISCS toolset would be highly adaptable and portable, capable of running on a variety of platforms to accommodate various operational needs and requirements.

Zank, G. P.↗
NASA NTRS2014

Development and Transition of the Radiation, Interplanetary Shocks, and Coronal Sources (RISCS) Toolset

We outline a plan to develop and transition a physics based predictive toolset called The Radiation, Interplanetary Shocks, and Coronal Sources (RISCS) to describe the interplanetary energetic particle and radiation environment throughout the inner heliosphere, including at the Earth. To forecast and "nowcast" the radiation environment requires the fusing of three components: 1) the ability to provide probabilities for incipient solar activity; 2) the use of these probabilities and daily coronal and solar wind observations to model the 3D spatial and temporal heliosphere, including magnetic field structure and transients, within 10 Astronomical Units; and 3) the ability to model the acceleration and transport of energetic particles based on current and anticipated coronal and heliospheric conditions. We describe how to address 1) - 3) based on our existing, well developed, and validated codes and models. The goal of RISCS toolset is to provide an operational forecast and "nowcast" capability that will a) predict solar energetic particle (SEP) intensities; b) spectra for protons and heavy ions; c) predict maximum energies and their duration; d) SEP composition; e) cosmic ray intensities, and f) plasma parameters, including shock arrival times, strength and obliquity at any given heliospheric location and time. The toolset would have a 72 hour predicative capability, with associated probabilistic bounds, that would be updated hourly thereafter to improve the predicted event(s) and reduce the associated probability bounds. The RISCS toolset would be highly adaptable and portable, capable of running on a variety of platforms to accommodate various operational needs and requirements. The described transition plan is based on a well established approach developed in the Earth Science discipline that ensures that the customer has a tool that meets their needs

Spann, James F.↗
NASA NTRSDate not supplied

Trace Element Abundances Measured in Concentric and Texturally Distinct Fine-Grained Rims Surrounding Allende Chondrules

Layered rims of dust-sized material surround some chondrules and other early formed nebular particles, such as calcium aluminum inclusions in chondritic meteorites. In the Allende meteorite most chondrules(~85%) are un-rimmed and in direct contact with the host matrix material [1]. When present, rim thickness appears correlated to underlying particle size in both the Allende and Murchison chondrites [1,2]. This diverse behavior strongly argues for pre-parent body formation of rimmed particles as they traversed distinct (cooler and/or dustier) nebular environments [1]. Nebular rim formation involves accretion of unequilibrated dust to chondrule surfaces, recording evidence for the formation of at least two separate particle populations (chondrules and dust) that interacted in the nebula, and therefore potentially record distinct nebular reservoirs (e.g. [3-5]). Additionally, some particles exhibit textural evidence for multiple rim layers, (e.g., [1], further investigated herein). Herein, we evaluate the chemistry of concentrically and texturally distinct chondrule rim layers to investigate the possibility of discrete rim formation events recorded by individual chondrules (Fig. 1A,B). Using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) we measure major, minor, and trace elements of the rims and particles in Allende. Samples were characterized in detail previously by electron microanalysis for their mineralogy, textures, particle size, and rim thickness(es) [1].

Chondrites↗
NASA NTRS2017

Development of Advanced Environmental Barrier Coatings for SiC/SiC Ceramic Matrix Composites: Path Toward 2700 F Temperature Capability and Beyond

Advanced environmental barrier coating systems for SiC-SiC Ceramic Matrix Composite (CMC) turbine and combustor hot section components are currently being developed to meet future turbine engine emission and performance goals. One of the significant coating development challenges is to achieve prime-reliant environmental barrier coating systems to meet the future 2700F EBC-CMC temperature stability and environmental durability requirements. This presentation will emphasize recent NASA environmental barrier coating system testing and down-selects, particularly the development path and properties towards 2700-3000F durability goals by using NASA hafnium-hafnia-rare earth-silicon-silicate composition EBC systems for the SiC-SiC CMC turbine component applications. Advanced hafnium-based compositions for enabling next generation EBC and CMCs capabilities towards ultra-high temperature ceramic coating systems will also be briefly mentioned.

Ceramic Matrix Composite↗
NASA NTRS1981

Development and demonstration of manufacturing processes for fabricating graphite/Larc-160 polyimide structural elements, part 4, paragraph B

Progress in the development of processes for production of Celion/LARC-160 graphite-polyimide materials, quality control, and the fabrication of Space Shuttle composite structure components is reported. Liquid chromatographic analyses of three repeatibility batches were performed and are compared to previous Hexcel standard production and to variables study LARC-160 intermediate resins. Development of processes for chopped fiber molding are described and flexural strength, elastic modulus, and other physical and mechanical properties of the molding are presented.

Source record↗