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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Low temperature synthesis of monolithic transparent Ta2O5 gels from hydrolysis of metal alkoxide

Tantalum oxide gels in the form of transparent monoliths and powder were prepared from hydrolysis of tantalum pentaethoxide under controlled conditions using different mole ratios of Ta(OC2H5)5:C2H50H:H20:HCl. Alcohol acts as the mutual solvent and HCl as the deflocculating agent. For a fixed alkoxide:water:HCl ratio, time of gel formation increased with the alcohol to alkoxide mole ratio. Thermal evolution of the physical and structural changes in the gel was monitored by differential thermal analysis, thermogravimetric analysis, x-ray diffraction, and infrared spectroscopy. On heating to approximately 400 C, the amorphous gel crystallized into the low temperature orthorhombic phase Beta-Ta2O5, which transformed into the high temperature tetragonal phase Alpha-Ta2O5 when further heated to approximately 1450 C. The volume fraction of the crystalline phase increased with the firing temperature. The Alpha-Ta205 converted back into the low temperature phase, Beta-Ta2O5, on slow cooling through the transformation temperature of 1360 C indicating a slow but reversible transformation.

Bansal, Narottam P.↗
NASA NTRS1994

Velocity distribution of Earth-crossing asteroid grains

We have systematically studied the evolution of 4- and 9-micrometer-diameter dust particles from three prominent asteroid families, Eos, Koronis, and Themis, until they reach the Earth. We have found that they are quite distinguishable in their (I cos omega, I sin omega) phase space. The different distributions in the inclination space have several important observational consequences, which can be used to identify the origins of these dust particles. We convert the orbital elements of these Earth-crossing dust grains to distinguish them by using any one single velocity component. We conclude that in order to identify the origins of the Earth-crossing dust grains we need all three velocity components to get their orbital elements and find their positions in the inclination space.

Liou, Jer-Chyi↗
NASA NTRS1995

Gravitational radiation from rapidly rotating nascent neutron stars

We study the secular evolution and gravitational wave signature of a newly formed, rapidly rotating neutron star. The neutron star may arise from core collapse in a massive star or from the accretion-induced collapse of a white dwarf. After a brief dynamical phase, the nascent neutron star settles into an axisymmetric, secularly unstable state. Gravitational radiation drives the star to a nonaxisymmetric, stationary equilibrium configuration via the bar-mode instability. The emitted quasi-periodic gravitational waves have a unique signature: the wave frequency sweeps downward from a few hundred Hertz to zero, while the wave amplitude increase from zero to a maximum and then decays back to zero. Such a wave signal could detected by broadband gravitational wave interferometers currently being constructed. We also characterize two other types of gravitational wave signals that could arise in principle from a rapidly rotating, secularly unstable neutron star: a high-frequency (f greater than or approximately = 1000 Hz) wave which increases the pattern-speed of the star, and a wave that actually increases the angular momentum of the star.

Lai, Dong↗
NASA NTRS2010

The Evolution of Gas in Protoplanetary Systems: The Herschel GASPS Open Time Key Programme

The Gas in Protoplanetary Systems (GASPS) Open Time Key Programme for the Herschel Space Observatory will be the first extensive, systematic survey of gas in circumstellar disks over the critical transition from gas-rich protoplanetary through to gas-poor debris. The brightest spectral lines from disks lie in the far-infrared and arise from radii spanning roughly 10 to 100 AU, where giant planets are expected to form. Herschel is uniquely able to observe this wavelength regime with the sensitivity to allow a large scale survey. We will execute a 2-phase study using the PACS instrument. Phase I is a spectroscopic survey about 250 young stars for fine structure emission lines of [CII] (at 157 microns) and [OI] (at 63 microns). In Phase II, the brightest sources will be followed up with additional PACS spectroscopy ([OI] at 145 microns and some rotational lines of water). We expect that the gas mass sensitivity will be more than an order of magnitude lower than that achieved by ISO and Spitzer or expected for SOFIA. We will also measure the dust continuum to an equivalent mass sensitivity. We will observe several nearby clusters with ages from 1 to 30 Myr, encompassing a wide range of disk masses and stellar luminosities. The sample covers disk evolution from protoplanetary disks through to young debris disks, i.e. the main epoch of planet formation. With this extensive dataset, the GASPS project will: 1) trace gas and dust in the planet formation region across a large multivariate parameter space, 2) provide the first definitive measurement of the gas dissipation timescale in disks, 3) elucidate the evolutionary link between protoplanetary and debris disks, 4) investigate water abundances in the planetforming regions of disks, and 5) provide a huge database of disk observations and models with long-lasting legacy value for follow-up studies.

Roberge, A.↗
NASA NTRS1978

The evolution of icy satellite interiors and surfaces

The results obtained by Consolmagno (1975) with regard to the interiors of the smaller icy satellites are presented and the evolution of the surfaces of these objects in the light of the considered models is discussed. In the discussion the icy satellites are divided into two groups. Those with radii larger than 1000 km are composed primarily of high-pressure phases of ice. In the case of satellites of this group, internal heating may produce significant melting and solid-state convection may not be important. Those satellites with radii less than 1000 km will be composed primarily of ice I and rock. They will not significantly melt and internal convection is likely to be important.

Consolmagno, G. J.↗
NASA NTRS1981

A magnetospheric signature of some F layer positive storms

Calculations of electron density distributions in the global thermosphere-ionosphere system perturbed by high-latitude thermospheric heating are presented which indicate a link between the heating and magnetospheric plasma disturbances near the equator. The calculations were made using a self-consistent model of the global sunlit thermosphere-ionosphere system describing the evolution of equatorial plasma disturbances. The heat input is found to cause electron density enhancements that propagate along magnetic field lines from the F2 maximum over mid-latitudes to the equator in the magnetosphere and which correspond to the positive phase of an F layer storm. The positive phase is shown to be generated by the induction of equatorward winds that raise the mid-latitude F layer through momentum transfer from neutral atoms to ionospheric ions, which ions pull electrons with them. Model results are used to identify plasma signatures of equatorward winds and an intensified magnetospheric electric field in Explorer 45 and Arial 4 measurements taken during the positive phase of an F layer storm.

Miller, N. J.↗
NASA NTRS1986

Evolution of the net surface shortwave radiation over the Indian Ocean during summer MONEX (1979) - A satellite description

The evolution of the net shortwave (NSW) radiation fields during the monsoon of 1979 was analyzed, using geostationary satellite data, collected before, during, and after the monsoon onset. It is seen, from the time sequence of NSW fields, that during the preonset phase the characteristics of the NSW field are dominated by a strong maximum in the entire Arabian Sea and by a strong minimum in the central and eastern equatorial Indian Ocean, the minimum being associated with the intense convective activity occurring in that region. As the season evolves, the minima of NSW associated with the large scale convective activity propagate westward in the equatorial ocean. During the monsoon onset, there occurs an explosive onset of the convection activity in the Arabian Sea: the maximum has retreated towards the Somalia coast, and most of the sea then experiences a strong minimum of NSW associated with the intense precipitation occurring along the southwestern coast of the Indian subcontinent.

Gautier, C.↗
NASA NTRS1991

Supernova 1987 A - Prototype of low metallicity type III supernovae or peculiar exception?

New stellar evolution calculations for the SN 1987 A progenitor, including a small but appropriate amount of semiconvection and mixing induced by differential rotation, yield good agreement with many observational constraints, as the HRD position of the progenitor star, a previous red supergiant phase, and CNO surface abundances close to the values obtained with the IUE satellite. The HRD track and surface abundances in different evolutionary stages are found to reflect many general properties of massive stars in the LMC. The results indicate that the SN 1987 A progenitor may have been an average massive star in the LMC, and that blue supergiants may be common SN II progenitors in low metallicity galaxies.

Langer, N.↗
NASA NTRS2004

A Critical Review of the Transport and Decay of Wake Vortices in Ground Effect

This slide presentation reviews the transport and decay of wake vortices in ground effect and cites a need for a physics-based parametric model. The encounter of a vortex with a solid body is always a complex event involving turbulence enhancement, unsteadiness, and very large gradients of velocity and pressure. Wake counter in ground effect is the most dangerous of them all. The interaction of diverging, area-varying, and decaying aircraft wake vortices with the ground is very complex because both the vortices and the flow field generated by them are altered to accommodate the presence of the ground (where there is very little room to maneuver) and the background turbulent flow. Previous research regarding vortex models, wake vortex decay mechanisms, time evolution within in ground effect of a wake vortex pair, laminar flow in ground effect, and the interaction of the existing boundary layer with a convected vortex are reviewed. Additionally, numerical simulations, 3-dimensional large-eddy simulations, a probabilistic 2-phase wake vortex decay and transport model and a vortex element method are discussed. The devising of physics-based, parametric models for the prediction of (operational) real-time response, mindful of the highly three-dimensional and unsteady structure of vortices, boundary layers, atmospheric thermodynamics, and weather convective phenomena is required. In creating a model, LES and field data will be the most powerful tools.

Sarpkaya, T.↗
NASA NTRS2008

Gravitational Radiation Characteristics of Nonspinning Black-Hole Binaries

"We present a detailed descriptive analysis of the gravitational radiation from binary mergers of non-spinning black holes, based on numerical relativity simulations of systems varying from equal-mass to a 6:1 mass ratio. Our analysis covers amplitude and phase characteristics of the radiation, suggesting a unified picture of the waveforms' dominant features in terms of an implicit rotating source. applying uniformly to the full wavetrain, from inspiral through ringdown. We construct a model of the late-stage frequency evolution that fits the $\ell = m$ modes, and identify late-time relationships between waveform frequency and amplitude. These relationships allow us to construct a predictive model for the late-time waveforms, an alternative to the common practice of modelling by a sum of quasinormal mode overtones. We demonstrate an application of this in a new effective-one-body-based analytic waveform model."

Kelly, Barnard↗
NASA NTRS2008

Gravitational Radiation Characteristics of Nonspinning Black-Hole Binaries

We present a detailed descriptive analysis of the gravitational radiation from binary mergers of non-spinning black holes, based on numerical relativity simulations of systems varying from equal-mass to a 6:1 mass ratio. Our analysis covers amplitude and phase characteristics of the radiation, suggesting a unified picture of the waveforms' dominant features in terms of an implicit rotating source, applying uniformly to the full wavetrain, from inspiral through ringdown. We construct a model of the late-stage frequency evolution that fits the l = m modes, and identify late-time relationships between waveform frequency and amplitude. These relationships allow us to construct a predictive model for the late-time waveforms, an alternative to the common practice of modelling by a sum of quasinormal mode overtones. We demonstrate an application of this in a new effective-one-body-based analytic waveform model.

Kelly, B. J.↗
NASA NTRS2013

Water in Nominally Anhydrous Minerals from Nakhlites and Shergottites

Estimating the amount of water in the interior of terrestrial planets has tremendous implications on our understanding of solar nebula evolution, planet formation and geological history, and extraterrestrial volcanism. Mars has been a recent focus of such enquiry with complementary datasets from spacecrafts, rovers and martian meteorite studies. In planetary interiors, water can be dissolved in fluids or melts and hydrous phases, but can also be locked as protons attached to structural oxygen in lattice defects in nominally anhydrous minerals (NAM) such as olivine, pyroxene, or feldspar [1-3]. Measuring water in Martian meteorite NAM is challenging because the minerals are fragile and riddled with fractures from impact processes that makes them break apart during sample processing. Moreover, curing the sample in epoxy causes problems for the two main water analysis techniques, Fourier transform infrared spectrometry (FTIR) and secondary ionization mass spectrometry (SIMS). Measurements to date have resulted in a heated debate on how much water the mantle of Mars contains. SIMS studies of NAM [4], amphiboles [5], and apatites [6-8] from Martian meteorites report finding enough water in these phases to infer that the martian mantle is as hydrous as that of the Earth. On the other hand, a SIMS study of glass in olivine melt inclusions from shergottites concludes that the Martian mantle is much drier [9]. The latter interpretation is also supported by the fact that most martian hydrous minerals generally have the relevant sites filled with Cl and F instead of H [10,11]. As for experimental results, martian basalt compositions can be reproduced using water as well as Cl in the parent melts [12,13]. Here FTIR is used to measure water in martian meteorite minerals in order to constrain the origin of the distribution of water in martian meteorite phases.

Peslier, Anne H.↗
NASA NTRS2021

Improved Constraints for the XUV Luminosity Evolution of Trappist-1

We re-examine the XUV luminosity evolution of TRAPPIST-1 utilizing new observational constraints of the current stellar parameters (XUV and bolometric luminosity) from multi-epoch X-ray/UV photometry. Following the formalism presented on Fleming et al. (2020), we infer that TRAPPIST-1maintained a saturated XUV luminosity, relative to the bolometric luminosity, of log10(LXUV/Lbol)=−3.03+0.25−0.23at early times for a period of tsat= 3.14+2.22−1.46Gyr. After the saturation phase, we find LXUV decayed over time by an exponential rate ofβXUV=−1.17+0.27−0.28. Compared to our inferred age of the system, age = 7.96+1.78−1.87Gyr, our result for tsat suggests that there is only a∼4% chance thatTRAPPIST-1 still remains in the saturated phase today, which is significantly lower than the previous estimate of 40%. Despite this reduction in tsat, our results remain consistent in the conclusion that the TRAPPIST-1 planets likely received an extreme amount XUV energy—an estimated integrated XUV energy of∼1030−1032erg over the star’s lifetime—that is∼15% lower than the original result.

Stellar evolution↗
NASA NTRS1987

Evolution of the inner asteroid belt: Paradigms and paradoxes from spectral studies

Recent years have witnessed a significant increase in the sophistication of asteroidal surface material characterizations derived from spectral data. An extensive data base of moderate to high spectral resolution, visible and near-infrared asteroid spectra is now available. Interpretive methodologies and calibrations were developed to determine phase abundance and composition in olivine-pyroxene assemblages and to estimate NiFe metal abundance from such spectra. A modified version of the asteroid classifications system more closely parallels the mineralogic variations of the major inner belt asteroid types. These improvements permit several general conclusions to be drawn concerning the nature of inner belt objects; their history, and that of the inner solar system; and the relationship between the asteroids and meteorites. Essentially all large belt asteroids have or are fragments of parent bodies which have undergone strong post-accretionary heating, varying degrees of melting and magmatic differentiation, and subsequent collisional disruption. These asteroids show a systematic, but not yet well characterized, mineralogic variation with semi-major axis. This suggests that the S-type asteroid families represent relatively recent collisions onto the cores of previously disrupted parent bodies.

Gaffey, Michael J.↗
NASA NTRS1994

Mass loss during the RR Lyrae phase of the horizontal branch: Mass dispersion on the horizontal branch and RR Lyrae period changes

Mass loss on the horizontal branch has been invoked in the literature to explain such phenomena as the color (mass) dispersion of the horizontal branch and the observed distribution of period changes in RR Lyrae stars. To test these claims, the Yale stellar evolution code was used to evolve horizontal branch models of masses 0.64, 0.66, 0.68, 0.70, and 0.72 solar mass with Z of 0.001, core mass of 0.4893, main-sequence helium abundance of 0.23, and constant mass loss rates of 0, 10(exp -10), 5 x 10(exp -10), and 10(exp -9) solar mass/yr. Mass loss was assumed to occur only in the instability strip, where a mechanism is most likely to exist. Synthetic horizontal branches, constructed from the models, show that mass loss on the horizontal branch cannot produce the observed color dispersion even for the highest mass-loss rate of 10(exp -9) solar mass/yr. Mass loss is unlikely to occur at a higher rate without significant effects on the horizontal branch morphology, which would destroy the good agreement between standard synthetic models without mass loss and observed horizontal branches. Periods and period changes were calculated for all models. The period changes are not significantly larger for models with mass loss. The effect of mass loss in clusters of other metallicities is discussed.

Koopmann, Rebecca A.↗
NASA NTRS1997

X-Ray Spectral Evolution of the Crab Pulse

The Crab Pulsar was observed with the X-ray detectors on the Rossi X-ray Timing Explorer (RXTE) on May 2, 1996. The large area, high time resolution, extended energy range, and moderate energy resolution of the RXTE instruments provided an unprecedented measurement of the Crab pulsar spectrum as it evolved in phase across the 33 msec pulse.

Crab Pulsar nebular↗
NASA NTRS2018

Venera-D Mission Concept to Study Atmosphere, Surface and Plasma Environment: Phase II Report of the Venera-D Joint Science Definition Team

Venus and Earth were formed approximately the same distance from the Sun, and have almost the same masses and volumes: they should be the most similar pair of planets in the Solar System. A vital, outstanding question is how and when these planets diverged in their atmospheric evolutions. Significantly, recent investigations present evidence for microbial life in Venus' cloud deck. Venus presents us with fundamental questions about the origin and evolution of planetary bodies and life in our Solar System.Venera-D (D stands for the Russian word for "long-lived:" dolgozhivushaya) is a potential mission that would combine simultaneous observations of Venus' atmosphere, plasma environment, and surface to try to answer these essential questions.

Zasova, L.↗
NASA NTRS2012

Designing Mission Operations for the Gravity Recovery and Interior Laboratory Mission

NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission, to understand the internal structure and thermal evolution of the Moon, offered unique challenges to mission operations. From launch through end of mission, the twin GRAIL orbiters had to be operated in parallel. The journey to the Moon and into the low science orbit involved numerous maneuvers, planned on tight timelines, to ultimately place the orbiters into the required formation-flying configuration necessary. The baseline GRAIL mission is short, only 9 months in duration, but progressed quickly through seven very unique mission phases. Compressed into this short mission timeline, operations activities and maneuvers for both orbiters had to be planned and coordinated carefully. To prepare for these challenges, development of the GRAIL Mission Operations System began in 2008. Based on high heritage multi-mission operations developed by NASA's Jet Propulsion Laboratory and Lockheed Martin, the GRAIL mission operations system was adapted to meet the unique challenges posed by the GRAIL mission design. This paper describes GRAIL's system engineering development process for defining GRAIL's operations scenarios and generating requirements, tracing the evolution from operations concept through final design, implementation, and validation.

MOS↗