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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 217 records · Page 12
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NASA NTRS1995

Synoptic maps of solar wind parameters from in situ spacecraft observations

Solar wind observations from the Interplanetary Monitoring Platform-8 (IMP-8) and Pioneer Venus Orbiter (PVO) spacecraft from 1982 until 1988 are combined to construct synoptic maps of solar wind parameters near 1 AU. Each map consists of 6 months of hourly averaged solar wind data, binned by heliographic latitude and Carrington longitude and projected back to the Sun. These maps show the structure and time evolution of solar wind streams near 1 AU in the heliographic latitudes of +/- 7.25 deg and provide and explicit picture of several phenomena, such as gradients, changes in the inclination of the heliospheric current sheet, and the relative positions of various structures in the inner heliosphere, that is difficult to obtain from single-spacecraft observations. The stream structure varied significantly during the last solar cycle. Between 1982 and early 1985, solar wind parameters did not depend strongly on heliographic latitude. During the last solar minimum, the solar wind developed significant latitudinal structure, and high-speed streams were excluded from the vicinity of the solar equator. The interplanetary magnetic field was strongly correlated with the coronal field, and the current sheet tended to coincide with the coronal neutral line. The solar wind speed showed the expected correlations with temperature, interplanetary magnetic field, and distance from the current sheet. The solar wind speed was anticorrelated with density, but the regions of highest density occurred east of the heliospheric current sheet and the regions of lowest solar wind speed. This is consistent with compression at the leading edge of high-speed streams.

Gazis, P. R.↗
NASA NTRS1986

The interplanetary magnetic field during solar cycle 21 ISEE-3/ICE observations

Temporal variations in the IMF during solar cycle 21 are investigated using magnetic field observations collected by the vector helium magnetometer on the ISEE-3/ICE spacecraft. Analysis of the observations reveal that the IMF magnitude, which had declined to 4.7 nT in 1976, peaked in late 1982 (two years after solar maximum) at 9.0 nT and rapidly decreased during 1983-1984 to an intensity of 6.2 nT in early 1985. The IMF intensities are compared with the auroral AE index; the observed peak in strength during 1981-1983 is related to a 50 percent increase in substorm activity levels. A decrease in Parker spiral angle, revealing the existence of high-speed streams is detected in the declining phase of the solar cycle. Variations in the intensity of the IMF correlate with Mt. Wilson magnetograph measurements of full disk magnetic flux. Source regions for the evolution of solar wind and the IMF are proposed.

Slavin, J. A.↗
NASA NTRS1989

Force-free magnetic fields - Is there a 'loss of equilibrium'?

This paper examines concept in solar physics that is known as loss of equilibrium in which a sequence of force-free magnetic fields, said to represent a possible quasi-static evolution of solar magnetic fields, reaches a critical configuration beyond which no acceptable solution of the prescribed form exists. This concept is used to explain eruptive phenomena ranging from solar flares to coronal mass ejections. Certain sequences of force-free configurations are discussed that exhibit a loss of equilibrium, and it is argued that the concept is devoid of physical significance since each sequence is defined a way that does not represent an acceptable thought experiment. For example, the sequence may be defined in terms of a global constraint on the boundary conditions, or the evolution of the sequence may require the creation of mgnetic flux that is not connected to the photosphere and is not present in the original configuration. The global constraints typically occur in using the so-called generating function method. An acceptance thought experiment is proposed to specify the field configuration in terms of photospheric boundary conditions comprising the normal component of the field and the field-line connectivity. Consider a magnetic-field sequence that, when described in terms of a generating function, exhibits a loss of equilibrium and show that, when one instead defines the sequence in terms of the corresponding boundary conditions, the sequence is well behaved.

Klimchuk, J. A.↗
NASA NTRS1989

Turbulent transport in the solar nebula

It is likely that turbulence played a major role in the evolution of the solar nebula, which is the flattened disk of dust and gas out of which our solar system formed. Relevant turbulent processes include the transport of angular momentum, mass, and heat, which were critically important to the formation of the solar system. This research will break ground in the modeling of compressible turbulence and its effects on the evolution of the solar nebula. The computational techniques which were developed should be of interest to researchers studying other astrophysical disk systems (e.g., active galactic nuclei), as well as turbulence modelers outside the astrophysics community.

Thompson, Kevin W.↗
NASA NTRS2012

Hydrocarbons on Saturns Satellites: Relationship to Interstellar Dust and the Solar Nebula

To understand the origin and evolution of our Solar System, and the basic components that led to life on Earth, we study interstellar and planetary spectroscopic signatures. The possible relationship of organic material detected in carbonaceous meteorites, interplanetary dust particles (IDPs), comets and the interstellar medium have been the source of speculation over the years as the composition and processes that governed the early solar nebula have been explored to understand the extent to which primitive material survived or became processed. The Cassini VIMS has provided new data relevant to this problem. Three of Saturn's satellites, Phoebe, Iapetus, and Hyperion, are found to have aromatic and aliphatic hydrocarbons on their surfaces. The aromatic hydrocarbon signature (C-H stretching mode at 3.28 micrometers) is proportionally significantly stronger (relative to the aliphatic bands) than that seen in other Solar System bodies (e.g., comets) and materials (Stardust samples, IDPs, meteorites) and the distinctive sub-features of the 3.4 micrometer aliphatic band (CH2 and CH3 groups) are reminiscent of those widely detected throughout the diffuse ISM. Phoebe may be a captured object that originated in the region beyond the present orbit of Neptune, where the solar nebula contained a large fraction of original interstellar ice and dust that was less processed than material closer to the Sun. Debris from Phoebe now resident on Iapetus and Hyperion, as well as o Phoebe itself, thus presents a unique blend of hydrocarbons, amenable to comparisons with interstellar hydrocarbons and other Solar System materials. The dust ring surrounding Saturn, in which Phoebe is embedded, probably originated from a collision with Phoebe. Dust ring particles are the likely source of the organic-bearing materials, and perhaps the recently identified small particles of Fe detected on Saturn's satellites. Lab measurements of the absolute band strengths of representative aliphatic and aromatic molecules, together with measurements from the VIMS data, allow us to calculate the number of C atoms to find the relative abundances of C atoms in the two kinds of organic molecules. The strength of the prominent aromatic C-H stretch band relative to the aliphatic band complex in Phoebe and Iapetus indicates that the relative abundance of aromatic to aliphatic carbon is very large (greater than 200). In contract, the aromatic band is nearly imperceptible in spectra of interplanetary dust particles (IDP), returned samples from comet 91P/Wild 2, insoluable carbonaceous material in most meteorites, and the diffuse interstellar dust (DISM) (although aromatics are known in all these materials-here we consider only the spectroscopic signature)

Cruikshank, D. P.↗
NASA NTRS1972

NASA'S second decade in space.

Advances in space science during the last decade are reviewed. The basic scientific goals of NASA's Planetary Program are to increase man's understanding of the origin and evolution of the solar system, the origin and evolution of life, and the earth, through a comparative study of the other planets. Studies of the planets will be continued during the second decade. Aspects of manned space flights are discussed, giving attention to the Skylab workshop, and the Space Shuttle. The applications program is divided into four major areas including meteorology, communications and navigation, geodesy, and earth resources. Areas of aeronautical research are also examined.

Manganiello, E. J.↗
NASA NTRS1994

ISSOL Meeting, 7th, Barcelona, Spain, July 4-9, 1993

The journal issue consists of abstracts presented at the International Society for the Study of the Origins of Life (ISSOL) conference. Topics include research on biological and chemical evolution including prebiotic evolution: cosmic and terrestrial; mechanisms of abiogenesis including synthesis and reactions of biomonomers; and analysis of cometary matter and its possible relationship to organic compounds on Earth. Theories and research on origins of ribonucleic acids (RNA), deoxyribonucleic acid (DNA), and other amino acids and complex proteins including their autocatalysis, replication, and translation are presented. Abiotic synthesis of biopolymers, mechanisms of the Genetic Code, precellular membrane systems and energetics are considered. Earth planetary evolution including early microfossils and geochemical conditions and simulations to study these conditions are discussed. The role of chirality in precellular evolution and the taxonomy and phylogeny of very simple organisms are reported. Past and future explorations in exobiology and space research directed toward study of the origins of life and solar system evolution are described.

Ferris, James P.↗
NASA NTRS2022

Interplanetary Mesoscale Observatory (InterMeso): A Mission to Untangle Dynamic Mesoscale Structures Throughout the Heliosphere

Mesoscale dynamics are a fundamental process in space physics, but fall within an observational gap of current and planned missions. Particularly in the solar wind, measurements at the mesoscales (100s RE to a few degrees heliographic longitude at 1 au) are crucial for understanding the connection between the corona and an observer anywhere within the heliosphere. Mesoscale dynamics may also be key to revealing the currently unresolved physics regulating particle acceleration and transport, magnetic field topology, and the causes of variability in the composition and acceleration of solar wind plasma. Studies using single-point observations do not allow for investigations into mesoscale solar wind dynamics and plasma variability, nor do they allow for the exploration of the sub-structuring of large-scale solar wind structures like coronal mass ejections (CMEs), co-rotating/stream interaction regions (CIR/SIRs), and the heliospheric plasma sheet. To address this fundamental gap in our knowledge of the heliosphere at these scales, the Interplanetary Mesoscale Observatory (InterMeso) concept employs a multi-point approach using four identical spacecraft in Earth-trailing orbits near 1 au. Varying drift speeds of the InterMeso spacecraft enable the mission to span a range of mesoscale separations in the solar wind, achieving significant and innovative science return. Simultaneous, longitudinally-separated measurements of structures co-rotating over the spacecraft also allow for disambiguation of spatiotemporal variability, tracking of the evolution of solar wind structures, and determination of how the transport of energetic particles is impacted by these variabilities.

solar wind↗
NASA NTRS2022

Interplanetary Mesoscale Observatory (InterMeso): A mission to untangle dynamic mesoscale structures throughout the heliosphere

Mesoscale dynamics are a fundamental process in space physics, but fall within an observational gap of current and planned missions. Particularly in the solar wind, measurements at the mesoscales (100s RE to a few degrees heliographic longitude at 1 au) are crucial for understanding the connection between the corona and an observer anywhere within the heliosphere. Mesoscale dynamics may also be key to revealing the currently unresolved physics regulating particle acceleration and transport, magnetic field topology, and the causes of variability in the composition and acceleration of solar wind plasma. Studies using single-point observations do not allow for investigations into mesoscale solar wind dynamics and plasma variability, nor do they allow for the exploration of the sub-structuring of large-scale solar wind structures like coronal mass ejections (CMEs), co-rotating/stream interaction regions (CIR/SIRs), and the heliospheric plasma sheet. To address this fundamental gap in our knowledge of the heliosphere at these scales, the Interplanetary Mesoscale Observatory (InterMeso) concept employs a multi-point approach using four identical spacecraft in Earth-trailing orbits near 1 au. Varying drift speeds of the InterMeso spacecraft enable the mission to span a range of mesoscale separations in the solar wind, achieving significant and innovative science return. Simultaneous, longitudinally-separated measurements of structures co-rotating over the spacecraft also allow for disambiguation of spatiotemporal variability, tracking of the evolution of solar wind structures, and determination of how the transport of energetic particles is impacted by these variabilities.

solar wind↗
NASA NTRS1978

The radial evolution of the bulk properties of the solar wind

Simultaneous solar-wind proton data obtained at several heliocentric distances during radial alignments are compared. The radial variations associated with two high-speed streams in the solar wind are studied as examples of the radial evolution of the solar-wind speed distribution and of high-speed streams in the solar wind as observed in the ecliptic plane in 1973. Pioneer 11 data on high-speed streams in the solar wind observed at about 1.5 and 3.7 AU are compared with the corresponding high-speed-stream data obtained at earth. These analyses indicate that as these high-speed streams propagated to these extended heliocentric distances, there was an erosion of the highest speeds and a general narrowing of the speed distribution. These observations are consistent with the exchange of momentum in the solar wind between high-speed streams and low-speed streams as they propagate outward from the sun.

Intriligator, D. S.↗
NASA NTRS1987

Analysis of planetary evolution with emphasis on differentiation and dynamics

In order to address the early stages of nebula evolution, a three-dimensional collapse code which includes not only hydrodynamics and radiative transfer, but also the effects of ionization and, possibly, magnetic fields is being addressed. As part of the examination of solar system evolution, an N-body code was developed which describes the latter stages of planet formation from the accretion of planetesimals. To test the code for accuracy and run-time efficiency, and to develop a stronger theoretical foundation, problems were studied in orbital dynamics. A regional analysis of the correlation in the gravity and topography fields of Venus was performed in order to determine the small and intermediate scale subsurface structure.

Kaula, William M.↗
NASA NTRS1982

Nonlinear force-free magnetic fields

The nonlinear properties of force-free magnetic fields are reviewed with particular reference to the mechanisms for the sudden release of stored energy in flares during the quasi-steady evolution of solar fields. It is shown that in the solar atmosphere, force-free fields with a nonconstant scalar function in the field equations are more likely to occur than those with a constant scalar function, and the nonlinear properties of these fields may give rise to many interesting physical effects. Consideration is then given to two possible mechanisms of field evolution: a model in which a force-free field in a medium of infinite electrical conductivity evolves in response to slowly changing boundary conditions brought about by photospheric motions in the solar active region, and a model in which a field in a medium of small finite electrical conductivity evolves in response to the slow Ohmic dissipation of the electric current.

Low, B. C.↗
NASA NTRS1991

The time evolution of magnetic fields on solar-like stars

Magnetic fields play a crucial role in governing the rotational evolution of solarlike stars. Techniques for measuring stellar magnetic fields are reviewed, and the most recent determinations of magnetic-field strengths and surface-area coverages on cool stars are analyzed for correlations with age. Tentative evidence for a decrease in magnetic flux with age is found, primarily caused by a reduction in the magnetic area filling factor with time.

Saar, Steven H.↗
NASA NTRS1994

Low encounter speed comet COMA sample return missions

Comets, being considered the most primitive bodies in the solar system, command the highest priority among solar-system objects for studying solar nebula evolution and the evolution of life through biogenic elements and compounds. The study of comets, and more especially, of material from them, provides an understanding of the physical, chemical, and mineralogical processes operative in the formation and earliest development of the solar systems. These return samples will provide valuable information on comets and serve as a rosetta stone for the analytical studies conducted on interplanetary dust particles over the past two decades, and will provide much needed extraterrestrial samples for the planetary materials community since the Apollo program. Lander sample return missions require rather complex spacecraft, intricate operations, and costly propulsion systems. By contrast, it is possible to take a highly simplified approach for sample capture and return in the case of a comet. In the past, we have considered Earth free-return trajectory to the comet, in which passive collectors intercept dust and volatiles from the cometary coma. However, standard short period cometary free-return trajectories results in the comet to the spacecraft encounter speeds in the range of 10 km/s. At these speeds the kinetic energy of the capture process can render significant modification of dust structure, change of solid phase as well as the lost of volatiles components. This paper presents a class of new missions with trajectories with significant reduction of encounter speeds by incorporating gravity assists and deep space maneuvering. Low encounter speed cometary flyby sample return will enable a marked increase in the value of the return science. Acquiring thousands of samples from a known comet and thousands of images of a comet nucleus would be space firsts. Applying new approach in flight mechanics to generate a new class of low encounter speed cometary sample return trajectories opens new possibilities in science. A systematic search of trajectories for the first decade of the twenty-first century will be made. The target encounter speed is for less than 7 km/s to short period comets.

Tsou, P.↗
NASA NTRS2012

Mega-Impacts on Mars: Implications for the Late Heavy Bombardment in the Inner Solar System, and the Early Evolution of the Earth and Mars

There are about 30 very large impact basins on Mars, > 1000 km in diameter, most of which are revealed by their topographic and/or crustal thickness signatures. Crater retention ages and model absolute ages suggest these all formed in a relatively short time (100-200 million years?), perhaps during a "Late Heavy Bombardment" (LHB) caused by the evolution of the orbits of the giant planets. This so-called "Nice Model" of planetary formation may explain the LHB on the Moon at about 3.9 billion years ago and would have produced a similar bombardment throughout the inner solar system. The formation of 30 very large impact basins would have had catastrophic environmental consequences for Mars, which were further complicated by the demise of the global magnetic field at about the same time. If there are no very large basins on Mars older than the 30 we see and the LHB really lasted everywhere only a short time, there may have been a relatively longer time (~400 million years?) during which Mars and the Earth suffered no major impact trauma and during which conditions on both worlds may have been far more habitable than during the LHB. However, if the formation of the Mars crustal dichotomy was due to an even larger giant impact that predated the very large basins, all record of this earlier and possibly more clement time on Mars may have been erased. Ages of the smaller but still very large basins can be used to approximately date the giant impact (if it occurred). Even the very large basins appear to have reset the crater retention ages of the entire crust of Mars and may have by themselves erased any record of an earlier time.

Frey, Herbert↗
NASA NTRS1994

Surface ices in the outer solar system

Planetary volatile inventories are products of several factors: (1) condensation-accretion of pre-planetary material which determines the bulk volatile inventory; (2) energy history of a planet, including timing, causes, and mechanisms of degassing; (3) the volatile sinks, including temporary, long term, and permanent; and (4) external processes operating on the volatile inventory. Information regarding the current surface compositions provide insight into both internal and surface-atmosphere evolutionary history. Our discussion focuses upon the surface composition of outer solar system planets and satellites as determined by spacecraft and telescopic spectral observations. We provide a review and an update of the recent work by Cruikshank and Brown that includes more recent observations and interpretations. In the context of formation and evolution of solar system bodies, the interesting ices typically considered are simple molecules formed from elements having high cosmic abundances. These mainly include ices of H2O, NH3, SO2, H2S, CH4, CO, CO2, and N2. In the solid state, these ices have vibrational spectral features, analogous to their gaseous counterparts but rotational transitions are quenched, that lie in the near- and mid-infrared. The overtone and combination modes, occurring in the visible and near-IR region, are of particular importance as standard observational techniques used to identify these ices rely upon reflected solar energy. Table I summarizes the ices found on various bodies in the outer solar system. H2O is most abundant surface material in the inner and middle regions while more volatile species appear to dominate surfaces in the outermost edge of the outer solar system.

Roush, Ted L.↗
NASA NTRS2004

The Search for Young Planetary Systems And the Evolution of Young Stars

The Space Interferometer Mission (SIM) will provide a census of planetary systems by con- ducting a broad survey of 2,000 stars that will be sensitive to the presence of planets with masses as small as approx. 15 Earth masses (1 Uranus mass) and a deep survey of approx. 250 of the nearest, stars with a mass limit of approx.3 Earth masses. The broad survey will include stars spanning a wide range of ages, spectral types, metallicity, and other important parameters. Within this larger context, the Young Stars and Planets Key Project will study approx. 200 stars with ages from 1 Myr to 100 Myr to understand the formation and dynamical evolution of gas giant planets. The SIM Young Stars and Planets Project will investigate both the frequency of giant planet formation and the early dynamical history of planetary systems. We will gain insight into how common the basic architecture of our solar system is compared with recently discovered systems with close-in giant planets by examining 200 of the nearest (less than 150 pc) and youngest (1-100 Myr) solar-type stars for planets. The sensitivity of the survey for stars located 140 pc away is shown in the planet mass-separation plane. We expect to find anywhere from 10 (assuming that only the presently known fraction of stars. 5-7%, has planets) to 200 (all young stars have planets) planetary systems. W-e have set our sensitivity threshold to ensure the detection of Jupiter-mass planets in the critical orbital range of 1 to 5 AU. These observations, when combined with the results of planetary searches of mature stars, will allow us to test theories of planetary formation and early solar system evolution. By searching for planets around pre-main sequence stars carefully selected to span an age range from 1 to 100 Myr, we will learn a t what epoch and with what frequency giant planets are found at the water-ice snowline where they are expected to form. This will provide insight into the physical mechanisms by which planets form and migrate from their place of birth, and about their survival rate. With these data in hand, we will provide data, for the first time, on such important questions as: What processes affect the formation and dynamical evolution of planets? When and where do planets form? What is initial mass distribution of planetary systems around young stars? How might planets be destroyed? What is the origin of the eccentricity of planetary orbits? What is the origin of the apparent dearth of companion objects between planets and brown dwarfs seen in mature stars? The observational strategy is a compromise between the desire to extend the planetary mass function as low as possible and the essential need to build up sufficient statistics on planetary occurrence. About half of the sample will be used to address the "where" and "when" of planet formation. We will study classical T Tauri stars (cTTs) which have massive accretion disks and post- accretion, weak-lined T Tauri stars (wTTs). Preliminary estimates suggest the sample will consist of approx. 30% cTTs and approx. 70% wTTs, driven in part by the difficulty of making accurate astrometric measurements toward objects with strong variability or prominent disks.

Beichman, Charles A.↗