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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

Is Q for Quantum? From Quantum Mechanics to Formation of the Solar System

The realization in 1985 that fullerenes exist in nature [1] as a third form of carbon-carbon clustering, continues to inspire new areas of research. In particular, the study of closed-cage endohedral fullerenes [2-6] is of scientific interest because of its potential application in a number of promising fields from medical imaging to astrophysics. One of these is to provide a possible chronometer for studying the age and origin of certain astromaterials in the solar system. Fullerenes are closed carbon cages that are fundamentally related to a long-standing debate over the "Q-Phase" origin of planetary noble gases in carbonaceous chondrites [7]. Although Q-phase has been identified as the carrier of planetary noble gases [8- 10], its physical nature has not been explained. Our limited understanding of it is based primarily on the laboratory chemical processing which it survives as well as the fact that it must have been widely distributed in the solar nebula [11]. Yet as important as it might be while preoccupying some 30 years of research, the question of what actually is Q-phase remains unresolved.

Wilson, T. L.↗
NASA NTRS2009

MHD Modeling of the Solar Wind with Turbulence Transport and Heating

We have developed a magnetohydrodynamic model that describes the global axisymmetric steady-state structure of the solar wind near solar minimum with account for transport of small-scale turbulence associated heating. The Reynolds-averaged mass, momentum, induction, and energy equations for the large-scale solar wind flow are solved simultaneously with the turbulence transport equations in the region from 0.3 to 100 AU. The large-scale equations include subgrid-scale terms due to turbulence and the turbulence (small-scale) equations describe the effects of transport and (phenomenologically) dissipation of the MHD turbulence based on a few statistical parameters (turbulence energy, normalized cross-helicity, and correlation scale). The coupled set of equations is integrated numerically for a source dipole field on the Sun by a time-relaxation method in the corotating frame of reference. We present results on the plasma, magnetic field, and turbulence distributions throughout the heliosphere and on the role of the turbulence in the large-scale structure and temperature distribution in the solar wind.

Goldstein, M. L.↗
NASA NTRS2005

In-Vacuum Photogrammetry of a 10-Meter Solar Sail

In July 2004, a 10-meter solar sail structure developed by L Garde, Inc. was tested in vacuum at the NASA Glenn 30-meter Plum Brook Space Power Facility in Sandusky, Ohio. The three main objections of the test were to demonstrate unattended deployment from a stowed configuration, to measure the deployed shape of the sail at both ambient and cryogenic room temperatures, and to measure the deployed structural dynamic characteristics (vibration modes). This paper summarizes the work conducted to fulfill the second test objective. The deployed shape was measured photogrammetrically in vacuum conditions with four 2-megapixel digital video cameras contained in custom made pressurized canisters. The canisters included high-intensity LED ring lights to illuminate a grid of retroreflective targets distributed on the solar sail. The test results closely matched pre-test photogrammetry numerical simulations and compare well with ABAQUS finite-element model predictions.

Meyer, Chris G.↗
NASA NTRS1977

Effects of soil maturation on grain size-dependence of trapped solar gases

A description is presented of a simple two-part model which relates the retention of solar-wind-implanted noble gases and N in different grain sizes of lunar soils to the maturation level of that soil. It is assumed that concentrations of solar-wind gases are implanted into surfaces of soil grains in inverse proportion to grain diameter and that differences in irradiation probability and surface saturation as a function of grain diameter generally are not a major factor. The model demonstrates that incorporation of a major fraction of this surface-correlated gas into constructional particles such as agglutinates causes much of the gas to become volume-correlated in mature soils. This volume-correlated gas produces a relative enrichment in gas concentrations in coarser grains and a selective enrichment of more retentive gases (e.g., N) over less retentive gases (e.g., He). It is shown that the maturity model plays a major role in determining the complexities of the distribution of solar-wind gases in soils.

Bogard, D. D.↗
NASA NTRS1993

Variability of the occurrence frequency of solar flares as a function of peak hard X-ray rate

We study the occurrence frequency of solar flares as a function of the hard X-ray peak count rate, using observations of the Solar Maximum Mission. The size distributions are well represented by power-law distributions with negative indices. As a better alternative to the conventional method, we devise a maximum likelihood method of determining the power-law index of the size distribution. We find that the power-law index of the size distribution changes with time and with the phase of the 154-day periodicity. The size distribution is steeper during the maximum years of solar cycle 21 (1980 and 1981) than during the declining phase (1982-1984). The size distribution, however, is flatter during the maximum phase of the 154-day periodicity than during the minimum phase. The implications of these findings are discussed.

Bai, T.↗
NASA NTRS2007

Submicrometer Organic Grains: Widespread Constituents of the Early Solar System

Primitive meteorites and interplanetary dust particles (IDPs) contain remants of interstellar organic matter, marked by anomalous H and N isotopic ratios. These isotopic anomalies are attributed to mass fractionation during chemical reactions at cryogenic temperatures (10-100K) in a cold molecular cloud. Significant variations in the chemistry and isotopic compositions of organic compounds within and between these samples suggest varying histories of alteration and dilution of the presolar components. Recent studies have reported large H and N isotopic anomalies preserved in sub-m organic inclusions in both meteorites and IDPs. In the Tagish Lake meteorite, the largest H and N isotopic anomalies are associated with sub-m, hollow organic globules. The common physical, chemical, and isotopic characteristics of these globules suggest that they formed before being incorporated into their parent meteorite. These organic globules probably originated as organic ice coatings that formed on preexisting ice or mineral grains in a cold molecular cloud. Radiation driven photochemistry may have processed them into refractory organic grains. This model implies that submicrometer organic grains were widely distributed throughout the solar nebula during the epoch of planet formation. Submicrometer organic particles were detected by the Giotto and Vega encounters with comet Halley, termed CHON particles based on their major element chemistry. The first direct samples of cometary dust (comet Wild-2) were returned by the Stardust spacecraft in January 2006. These samples exhibit widely varying, fine grained mineralogy similar to anhydrous IDPs, including submicrometer carbonaceous grains. The submicrometer organic grains from comet Wild-2 exhibit H and N isotopic anomalies of similar magnitude to those commonly observed in primitive meteorites and IDPs. Isotopically anomalous, submicrometer organic grains have now been observed in meteorites, IDPs, the Oort-cloud comet Halley, and the Kuiper-belt comet Wild-2, suggesting that such grains were prevalent throughout the protoplanetary disk.

Messenger, Scott↗
NASA NTRS1994

Heating during solar nebula formation and Mg isotopic fractionation in precursor grains of CAIs and chondrules

In some Ca-Al-rich inclusion (CAI) grains, mass-dependent isotopic fractionations of Mg, Si, and O are observed and large Mg isotopic fractionation is interpreted to have been produced by cosmochemical processes such as evaporation and condensation. Mass-dependent Mg isotopic fractionation was found in olivine chondrules of Allende meteorites. Presented is an approximate formula for the temperature of the solar nebula that depends on heliocentric distance and the initial gas distribution. Shock heating during solar nebula formation can cause evaporative fractionation within interstellar grains involved in a gas at the inner zone (a less than 3 AU) of the disk. Alternatively collision of late-accreting gas blobs might cause similar heating if Sigma(sub s) and Sigma are large enough. Since the grain size is small, the solid/gas mass ratio is low and solar (low P(sub O2)), and the ambient gas pressure is low, this heating event could not produce chondrules themselves. Chondrule formation should proceed around the disk midplane after dust grains would grow and sediment to increase the solid/gas ratio there. The heating source there is uncertain, but transient rapid accretion through the disk could release a large amount of heat, which would be observed as FU Orionis events.

Sasaki, S.↗
NASA NTRS1997

Correlations of solar cycle 22 UV irradiance

The solar ultraviolet spectral irradiance monitor (SUSIM) onboard the upper atmosphere research satellite (UARS) is an absolutely calibrated UV spectrometer which has measured the solar spectral irradiance over the wavelengths 115 nm to 410 nm since October 1991. This data set now extends for about six years from near the peak of solar cycle 22, through its minimum, to the initial rise associated with solar cycle 23. Generally, the time series of UV spectral irradiances obtained shows behavior similar to that of other solar activity indices. The conditions on the sun, which can in result in dominant 13.5-day periodicity, are analyzed and illustrated. It is found that any combination of presence or absence of dominant 13.5-day in UV irradiance and solar wind velocity is possible depending entirely on the particular surface distribution and orientation of solar active regions.

Floyd, L.↗
NASA NTRS2008

Comparison of SOHO/UVCS and MLSO MK4 Coronameter Densities

This paper compares the density distributions of the solar corona obtained by UVCS and the Mauna MLSO MK4 coronameter. This is the first attempt to compare the coronal densities estimated by the two instruments. Two UVCS emission lines (O VI 1032 hand 1037.6 A), which have both radiative and collisional components, were used. The coronal number density is determined from the ratio of these two components. The coronal density can be determined by inverting MLSO MK4 polarization maps. It was found that the mean electron number density in a helmet streamer observed by MK4 on 2003 April 28 is fairly consistent with that observed by UVCS. For a coronal hole and an active region observed on 1999 October 19 and 24, the MK4 coronal densities are close to those from the UVCS. The results demonstrate that MK4 polarization data can provide a coronal density distribution in a large field of view with a time cadence of about three minutes.

Lee, K.-S.↗
NASA NTRS2023

Space Weathering of Genesis Mission Solar-wind Collectors with Inferences for Weathering on Airless Bodies

Samples from the Genesis Solar Wind Sample Return (NASA Discovery 5) are a unique opportunity to study the initial stages of space weathering, i.e., the physical and chemical effects of solar-wind irradiation. Arrays of collectors containing multiple materials were each exposed to a different solar-wind regime (fast, slow, bulk, or coronal mass ejection) at the L1 point for long durations (years). Materials exposed to the solar wind included metals, semiconductors, and insulators. Although the time of exposure was obviously short relative to samples having extraterrestrial origins, optical properties, surface chemical properties, and matrix structure have changed in many collectors due to exposure to solar wind. The thickness of amorphous zones, where present, appears to correspond with the depth of the peak of the solar-wind H distribution in each regime. Damage from high-energy particles was negligible because the collectors were 700 μm or less in thickness and shielded from the back by the spacecraft. Micrometeorite impacts and sputtering were also negligible because of the short exposure times. Our current results are preliminary: We hope future workers will extend this study both to support Genesis characterization efforts and to further understand space-weathering processes on a geologic timescale.

space weathering↗
NASA NTRS2002

The Sun's Impact on Climate

We provide an overview of the impact of the Sun on the Earth atmosphere and climate system, focused on heating of Earth's atmosphere and oceans. We emphasize the importance of the spectral measurements of SIM and SOLSTICE- that we must know how solar variations are distributed over ultraviolet, visible, and infrared wavelengths, since these have separate characteristic influences on Earth's ozone layer, clouds, and upper layers of the oceans. Emphasis is also given to understanding both direct and indirect influences of the Sun on the Earth, which involve feedbacks between Earth's stratosphere, troposphere, and oceans, each with unique time scales, dynamics, chemistry, and biology, interacting non-linearly. Especially crucial is the role of all three phases of water on Earth, water vapor being the primary greenhouse gas in the atmosphere, the importance of trace gases such as CO2 arising from their absorption in the "water vapor window" at 800 - 1250/cm (12.5 to 8 microns). Melting of polar ice is one major response to the post-industrial global warming, enhanced due to "ice-albedo" feedback. Finally, water in liquid form has a major influence due to cloud albedo feedback, and also due to the oceans' absorption of solar radiation, particularly at visible wavelengths, through the visible "liquid water window" that allows penetration of visible light deep into the mixed layer, while nearby ultraviolet and infrared wavelengths do not penetrate past the upper centimeter ocean surface skin layer. A large fraction of solar energy absorbed by the oceans goes into the latent heat of evaporation. Thus the solar heating of the atmosphere-ocean system is strongly coupled through the water cycle of evaporation, cloud formation, precipitation, surface runoff and ice formation, to Earth's energy budget and climate, each different climate component responding to variations in different solar spectral bands, at ultraviolet, visible and infrared wavelengths.

Cahalan, Robert↗
NASA NTRS1998

The Generation of Lighting in the Solar Nebula

The process that melted and formed the chondrules, mm-sized glassy beads within meteorites, has not been conclusively identified. Origin by lightning in the solar nebula is consistent with many features of chondrules, but no viable model of lightning has yet been advanced. We present a model demonstrating how lightning could be generated in the solar nebula which differs from previous models in three important aspects. First, we identify a new', powerful charging mechanism that is based on the differences in contact potentials between particles of different composition, a form of triboelectric charging. In the presence of fine silicate grains and fine iron metal grains, large silicate particles (the chondrules) can acquire charges of +10(exp 5) e. Second, we assume that the chondrule precursor particles are selectively concentrated in clumps 1 - 100 km in size by the turbulent concentration mechanism described by Cuzzi et al. (1996). The concentration of these highly charged particles into clumps, in a background of negatively charged metal grains, is what generates the strong electric fields. Third, we make refinements in the estimates of the breakdown electric field and the ionization rate. We calculate that electric fields large enough to trigger breakdown easily could have existed over regions large enough (approx. 100km) to generate very large discharges of electrical energy (approx. 10(exp 16)erg). The discharges would have been sufficiently energetic and frequent to have formed the chondrules. We place constraints on the generation of lightning and conclude that it could not be generated if the abundance of Al-26 in chondrules was as high as the level in the CAls. This conclusion is consistent with isotopic analyses of chondrules. This possibly implies that Al-26 was non-uniformly distributed in the solar nebula or that the chondrules formed several Myr after the CAIs.

Cuzzi, Jeffrey↗
NASA NTRS1975

Anisotropy measurements of nearly 50 KeV solar protons

The Energetic Particles Experiment on IMP-7 measures the angular distribution of 50-200 keV solar protons in 16 sectors. The velocity of 50 keV protons may be less than 5 times that of the solar wind. A generalized nonlinear Compton-Getting point transformation into the co-moving frame that contains no assumptions as to the angular distribution of either the spectrum or intensity is presented. Nearly 50 keV proton data in the spacecraft frame exhibit an anisotropy ratio that is large (not less than 5) and radial throughout the October 29, 1972 event lasting more than 9 days at this energy. This anisotropy argues against impulsive injection and diffusive decay in the inner solar system. Application of the transformation to the data reveals a long lasting residual anisotropy in the co-moving frame with protons streaming from the sun. Differences between the co-moving frame and solar wind frame velocities suggest residual electric fields upstream from the bow shock.

Gold, R. E.↗
NASA NTRS1972

Spatial distribution of energetic plasma sheet electrons.

The spatial distribution of energetic plasma sheet electrons (E greater than 50 keV) out to a radial distance of 24 earth radii using data from electron spectrometer and fluxgate magnetometer experiments on Ogo 5 is presented. A comparison of distributions in geocentric solar magnetospheric coordinates (GSM) prepared with and without the use of a neutral sheet model indicates that the use of such a model facilitates organization of plasma sheet data. The percentage of flux occurrence above a given flux threshold falls off rapidly with distance from the neutral sheet. Contours of constant percentage of occurrence diverge slightly from the neutral sheet at local times away from midnight. This effect decreases with increasing flux threshold.

Walker, R. J.↗