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NASA NTRS1991

Earth observations during Space Shuttle flight STS-41 - Discovery's mission to planet earth

An overview of space flight STS-41 is presented, including personal observations and comments by the mission astronauts. The crew deployed the Ulysses spacecraft to study the polar regions of the sun and the interplanetary space above the poles. Environmental observations, including those of Lake Turkana, Lake Chad, biomass burning in Madagascar and Argentina, and circular features in Yucatan are described. Observations that include landforms and geology, continental sedimentation, desert landscapes, and river morphology are discussed.

Lulla, Kamlesh P.↗

NASA NTRS2011

Concretions in Exhumed Channels Near Hanksville Utah: Implications for Mars

The landscape near Hanksville, Utah, contains a diversity of Mars analogue features. These included segmented and inverted anatasomosing palaeochannels exhumed from the Late Jurassic Brushy Basin Member of the Morrison Formation that hosts abundant small carbonate concretions. The exhumed and inverted channels closely resemble many seen on the surface of Mars in satellite imagery and which may be visited by surface missions in the near future. The channels contain a wealth of palaeo-environmental information, but intrinsically difficult terrain would make their study challenging on Mars. We show that an unexhumed channel feature can be detected geophysically, this may allow their study in more easily accessed terrain. The concretions morphologically and in their surface expression parallel the haematite blue berries that are strewn across the surface of Meridiani Planum on Mars. They are best developed in poorly cemented medium to coarse channel sandstones and appear to have formed early in the diagenetic history.

Clarke, Jonathan↗

NASA NTRS2022

Global GNSS-RO Electron Density in the Lower Ionosphere

Lack of instrument sensitivity to low electron density (Ne) concentration makes it difficult to measure sharp Ne vertical gradients (four orders of magnitude over 30 km) in the D/E-region. A robust algorithm is developed to retrieve global D/E-region Ne from the high-rate GNSS radio occultation (RO) data, to improve spatio-temporal coverage using recent SmallSat/CubeSat constellations.The new algorithm removes F-region contributions in the RO excess phase profile by fitting a linear function to the data below the D-region.The new GNSS-RO observations reveal many interesting features in the diurnal, seasonal, solar-cycle, and magnetic-field-dependent variations in the Ne morphology. While the D/E-region Ne is a function of solar zenith angle (c), it exhibits strong latitudinal variations for the same c with a distribution asymmetric about noon. In addition, large longitudinal variations are observed along the same magnetic field pitch angle. The summer-midlatitude Ne and sporadic-E(Es) show a distribution similar to each other. The distribution of auroral electron precipitation correlates better with the pitch angle from the magnetosphere than from one at100 km. Finally, anew TEC retrieval technique is developed for the high-rate RO data with a top reaching at least 120 km. For better characterization of the E-to-F transition in Ne and more accurate TEC retrievals, it is recommended to have all GNSS-RO acquisition routinely up to 220 km.

GNSS radio occultation↗

NASA NTRSDate not supplied

Building and Breaking Carbon Composites with REACTER

Carbon composites have become indispensable for aerospace and other high-performance applications, and a detailed picture of their morphology and failure mechanisms remains difficult to obtain through experiment. REACTER is a versatile computational modeling tool for atomistic molecular dynamics designed to model chemical reactions at the speed and length scales of classical force fields.1 In this work, several recent features of REACTER were applied to the creation and subsequent mechanical testing of two classes of carbon composites, carbon-fiber reinforced polymers (CFRP) and carbon nanotube (CNT) composites. Carbon fiber core morphologies were created by the method of Desai et al.,2 but using the advanced reaction constraints framework of REACTER, their proposed multistep procedure was reduced to a single uninterrupted molecular dynamics simulation. The carbon fiber filler was embedded into a polymer matrix by simulated in situ polymerization of several thermosetting resins, including bismaleimide and polyarylacetylene, to obtain the final CFRP model. To generate the second class of carbon composite, CNT networks were grown dynamically using the new ‘create atoms’ feature of REACTER, and similarly infiltrated with resin to obtain CNT composites. The resulting models were compared directly to experiment using simulated high resolution transmission electron microscopy and x-ray diffraction. Failure mechanisms were elucidated by simulating mechanically induced bond breaking, as characterized by third-order DFT-based tight-binding (DFTB3) simulations, via a reaction constraint on the total potential energy of the involved atoms.

Molecular Dynamics↗

NASA NTRS1986

Microstructure-property relationships in directionally solidified single crystal nickel-base superalloys

Some of the microstructural features which influence the creep properties of directionally solidified and single crystal nickel-base superalloys are discussed. Gamma precipitate size and morphology, gamma-gamma lattice mismatch, phase instability, alloy composition, and processing variations are among the factors considered. Recent experimental results are reviewed and related to the operative deformation mechanisms and to the corresponding mechanical properties. Special emphasis is placed on the creep behavior of single crystal superalloys at high temperatures, where directional gamma coarsening is prominent, and at lower temperatures, where gamma coarsening rates are significantly reduced. It can be seen that very subtle changes in microstructural features can have profound effects on the subsequent properties of these materials.

Mackay, R. A.↗

NASA NTRS2017

Lava Eruption and Emplacement: Using Clues from Hawaii and Iceland to Probe the Lunar Past

Investigating recent eruptions on Earth is crucial to improving understanding of relationships between eruption dynamics and final lava flow morphologies. In this study, we investigated eruptions in Holuhraun, Iceland, and Kilauea, Hawaii to gain insight into the lava dynamics near the source vent, the initiation of lava channels, and the origin of down-channel features. Insights are applied to Rima Bode on the lunar nearside to deduce the sequence of events that formed this lunar sinuous rille system.These insights are crucial to correctly interpreting whether the volcanic features associated with Rima Bode directly relate to eruption conditions at the vent and, thus, can help us understand those eruption dynamics, or, alternatively, whether the features formed as a result of more localized influences on lava flow dynamics. For example, if the lava channel developed early in the eruption and was linked to pulses in vent activity, its morphology can be analyzed to interpret the flux and duration of the eruption. Conversely, if the lava channel initiated late in the eruption as the result of a catastrophic breaching of lava that had previously pooled within the vent [e.g., 1], then the final channel morphology will not indicate eruption dynamics but rather local dynamics associated with that breach event. Distinguishing between these two scenarios is crucial for correctly interpreting the intensity and duration of volcanic history on the Moon.

sinuous rille↗

NASA NTRS2017

Lava Eruption and Emplacement: Using Clues from Hawaii and Iceland to Probe the Lunar Past

Investigating recent eruptions on Earth is crucial to improving understanding of relationships between eruption dynamics and final lava flow morphologies. In this study, we investigated eruptions in Holuhraun, Iceland, and Kilauea, Hawaii to gain insight into the lava dynamics near the source vent, the initiation of lava channels, and the origin of down-channel features. Insights are applied to Rima Bode on the lunar nearside to deduce the sequence of events that formed this lunar sinuous rille system. These insights are crucial to correctly interpreting whether the volcanic features associated with Rima Bode directly relate to eruption conditions at the vent and, thus, can help us understand those eruption dynamics, or, alternatively, whether the features formed as a result of more localized influences on lava flow dynamics. For example, if the lava channel developed early in the eruption and was linked to pulses in vent activity, its morphology can be analyzed to interpret the flux and duration of the eruption. Conversely, if the lava channel initiated late in the eruption as the result of a catastrophic breaching of lava that had previously pooled within the vent [e.g., 1], then the final channel morphology will not indicate eruption dynamics but rather local dynamics associated with that breach event. Distinguishing between these two scenarios is crucial for correctly interpreting the intensity and duration of volcanic history on the Moon.

Needham, Debra Hurwitz↗

NASA NTRS2002

Plasmaspheric Density Troughs: Global IMAGE EUV Observations and Analysis via Global Core Plasma Modeling

To date, the IMAGE EUV camera has observed several plasmaspheric density trough features inside the plasmapause under a wide range of geomagnetic activity. From the perspective of EUV, a density trough feature appears as a channel of diminished pixel counts which spans a width of L-shell (DELTA L) and magnetic local time (MLT) inside the plasmapause. Plasmaspheric density troughs are found to be morphologically complex possessing considerable spatial and temporal variability. We present an analysis of the evolution of trough DELTA L and MLT extent as functions of associated D (sub ST) and K (sub p) history. Trough features range in size from 0.16 less than or equal to DELTA L less than or equal to 1.2 with azimuthal extent from 1500 less than or equal to MLT less than or equal to 1200. All cases of plasmaspheric density troughs studied to date appear to have evolved as a result of the inner edge of the afternoon/evening plasma drainage plume being wrapped around through the nightside plasmasphere. The structure of plasmaspheric density trough features is further probed by analyzing simulated EUV images produced by forward modeling artificially introduced regions of depleted density into both static and dynamic global core plasmaspheric models. Forward modeling suggests that (1) L-shell refilling of density troughs during storm recovery can be modeled as filling from the ionosphere toward the equator (i.e., bottom-up refilling), and (2) that an erosion process is operating within flux tubes beyond the outer L-shell wall of the observed density troughs.

Adrian, M. L.↗

NASA NTRS1988

Microstructure-property relationships in directionally solidified single-crystal nickel-base superalloys

This paper discusses some of the microstructural features which influence the creep properties of directionally solidified and single-crystal nickel-base superalloys. Gamma prime precipitate size and morphology, gamma-gamma (prime) lattice mismatch, phase instability, alloy composition, and processing variations are among the factors considered. Recent experimental results are reviewed and related to the operative deformation mechanisms and to the corresponding mechanical properties. Special emphasis is placed on the creep behavior of single-crystal superalloys at high temperatures, where directional gamma (prime) coarsening is prominent, and at lower temperatures, where gamma (prime) coarsening rates are significantly reduced. It can be seen that very subtle changes in microstructural features can have profound effects on the subsequent properties of these materials.

Mackay, Rebecca A.↗

NASA NTRS1979

High-latitude E and F region ionospheric predictions

The physical processes and morphology of the high latitude E and F layers are discussed. The existence and adequacy of models, and features to be included are examined, as well as reliability of ionospheric predictions.

Hunsucker, R. D.↗

NASA NTRS1985

The quasars 1038 + 528 A and B

The results of VLBI observations of the quasars 1038 + 528 A and B at 2.8, 3.6, 13, and 18 cm at various times between November 1979 and March 1981 are reported. The observations and data calibration are described, as are the mapping and astrometric techniques applied in the study. Both quasars are found to have 'core-jet' morphologies. The core of the A quasar dominates its morphology at centrimetric wavelengths with the brightness temperature of its 400 pc long jet being about 1/100 that of the core. By contrast, the 'jet' in the B quasar is very short (about 70 pc); the tail of this jet has the steepest spectral index found to date in extragalactic compact sources, indicating that high electron losses are responsible for the shortness of the jet. No evidence for appreciable morphological change in the B quasar was found over the time span of the study, whereas a new feature may be emerging from the A quasar core at superluminal speed.

Marcaide, J. M.↗

NASA NTRS1987

Relative ages of lava flows at Alba Patera, Mars

Many large lava flows on the flanks of Alba Patera are astonishing in their volume and length. As a suite, these flows suggest tremendously voluminous and sustained eruptions, and provide dimensional boundary conditions typically a factor of 100 larger than terrestrial flows. One of the most striking features associated with Alba Patera is the large, radially oriented lava flows that exhibit a variety of flow morphologies. These include sheet flows, tube fed and tube channel flows, and undifferentiated flows. Three groups of flows were studied; flows on the northwest flank, southeast flank, and the intracaldera region. The lava flows discussed probably were erupted as a group during the same major volcanic episode as suggested by the data presented. Absolute ages are poorly constrained for both the individual flows and shield, due in part to disagreement as to which absolute age curve is representative for Mars. A relative age sequence is implied but lacks precision due to the closeness of the size frequency curves.

Schneeberger, Dale M.↗

NASA NTRS1988

Statistics of galaxy orientations - Morphology and large-scale structure

Using the Uppsala General Catalog of bright galaxies and the northern and southern maps of the Lick counts of galaxies, statistical evidence of a morphology-orientation effect is found. Major axes of elliptical galaxies are preferentially oriented along the large-scale features of the Lick maps. However, the orientations of the major axes of spiral and lenticular galaxies show no clear signs of significant nonrandom behavior at a level of less than about one-fifth of the effect seen for ellipticals. The angular scale of the detected alignment effect for Uppsala ellipticals extends to at least theta of about 2 deg, which at a redshift of z of about 0.02 corresponds to a linear scale of about 2/h Mpc.

Lambas, Diego G.↗

NASA NTRS1991

Impact craters on Venus - Initial analysis from Magellan

The general features of impact craters are described emphasizing two aspects: the effect of the atmosphere on crater and ejecta morphology and the implications of the distribution and appearance of the craters for the volcanic and tectonic resurfacing history of Venus. Magellan radar images reveal 135 craters about 15 km in diameter containing central peaks, multiple central peaks, and peak rings. Craters smaller than 15 km exhibit multiple floors or appear in clusters. Surface flows of material initially entrained in the atmosphere are characterized. Zones of low radar albedo originated from deformation of the surface by the shock or pressure wave associated with the incoming meteoroid surround many craters. A spectrum of surface ages on Venus ranging from 0 to 800 million years indicates that Venus must be a geologically active planet.

Phillips, Roger J.↗

NASA NTRS1994

Feature isolation and quantification of evolving datasets

Identifying and isolating features is an important part of visualization and a crucial step for the analysis and understanding of large time-dependent data sets (either from observation or simulation). In this proposal, we address these concerns, namely the investigation and implementation of basic 2D and 3D feature based methods to enhance current visualization techniques and provide the building blocks for automatic feature recognition, tracking, and correlation. These methods incorporate ideas from scientific visualization, computer vision, image processing, and mathematical morphology. Our focus is in the area of fluid dynamics, and we show the applicability of these methods to the quantification and tracking of three-dimensional vortex and turbulence bursts.

Source record↗

NASA NTRS2015

Mars: Periglacial Morphology and Implications for Future Landing Sites

At the Mars Phoenix landing site and in much of the Martian northern plains, there is ice-cemented ground beneath a layer of dry permafrost. Unlike most permafrost on Earth, though, this ice is not liquid at any time of year. However, in past epochs at higher obliquity the surface conditions during summer may have resulted in warmer conditions and possible melting. This situation indicates that the ice-cemented ground in the north polar plains is likely to be a candidate for the most recently habitable place on Mars as near-surface ice likely provided adequate water activity approximately 5 Myr ago. The high elevation Dry Valleys of Antarctica provide the best analog on Earth of Martian ground ice. These locations are the only places on Earth where ice-cemented ground is found beneath dry permafrost. The Dry Valleys are a hyper-arid polar desert environment and in locations above 1500 m elevation, such as University Valley, air temperatures do not exceed 0 C. Thus, similarly to Mars, liquid water is largely absent here and instead the hydrologic cycle is dominated by frozen ice and vapor phase processes such as sublimation. These conditions make the high elevation Dry Valleys a key Mars analog location where periglacial processes and geomorphic features can be studied in situ. This talk will focus on studies of University Valley as a Mars analog for periglacial morphology and ice stability. We will review a landing site selection study encompassing this information gleaned from the Antarctic terrestrial analog studies plus Mars spacecraft data analysis to identify candidate landing sites for a future mission to search for life on Mars.

Martian ground ice↗

NASA NTRS1993

Scalloped margin domes: What are the processes responsible and how do they operate?

Studies of scalloped margin domes (SMD) indicate the scallops are the result of slope failure. SMD's have similar but smaller average diameters (26.5 km) to unmodified domes (29.8 km), and the majority plot at altitudes ranging from 0.5-4.7 km, relative to the mean planetary diameter. A range of morphological types exist from those least modified to those that show heavy modification. Of the 200 SMD's examined, 33 have clearly discernible debris aprons. Examination and comparison of debris aprons with mass movement features on the Moon, Mars, and in sub-aerial and submarine environments on Earth using H/L against area (km(sup 2)), suggests there are three main types of failure; debris avalanche, slumps, and debris flow. The five examples representing the morphological range within the SMD's, show the different modified forms and the different types of slope failures that have occurred.

Bulmer, M. H.↗

NASA NTRS2007

Highly Collimated Jets and Wide-angle Outflows in HH 46/47: New Evidence from Spitzer Infrared Images

We present new details of the structure and morphology of the jets and outflows in HH 46/47 as seen in Spitzer infrared images from IRAC and MIPS, reprocessed using the 'HiRes' deconvolution technique. HiRes improves the visualization of spatial morphology by enhancing resolution (to subarcsecond levels in IRAC bands) and removing the contaminating side lobes from bright sources. In addition to sharper views of previously reported bow shocks, we have detected (1) the sharply delineated cavity walls of the wide-angle biconical outflow, seen in scattered light on both sides of the protostar, (2) several very narrow jet features at distances approximately 400 AU to approximately 0.1 pc from the star, and (3) compact emissions at MIPS 24 m with the jet heads, tracing the hottest atomic/ionic gas in the bow shocks. Together the IRAC and MIPS images provide a more complete picture of the bow shocks, tracing both the molecular and atomic/ionic gases, respectively. The narrow width and alignment of all jet-related features indicate a high degree of jet collimation and low divergence (width of approximately 400 AU increasing by only a factor of 2.3 over 0.2 pc). The morphology of this jet, bow shocks, wide-angle outflows, and the fact that the jet is nonprecessing and episodic, constrain the mechanisms for producing the jet's entrained molecular gas, and origins of the fast jet, and slower wide-angle outflow.

Herbig-Haro objects↗