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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Collisionless Relaxation of the Ion Ring Distribution in Space Plasma

Energetic processes often produce transversely-heated angular distributions of the magnetized core (lowest energy) plasma. This characteristic is found in solar wind ion pickup, resulting from cometary or interstellar gas ionization, in Earths' ionosphere, and with hot ions formed around the Space Transportation System during gas releases. We investigate the thermalization of O+ ion pickup using the 2.5D hybrid simulation method (with fluid electrons and kinetic ions) of the ion pickup (ring) distributions, formed in the auroral ionosphere, with a range of ring velocities and thermal to magnetic pressure ratios. We find that in the unstable collisonless regime the anisotropy of the non-thermal distribution produces the ion-cyclotron instability, and the nonlinear relaxation is accompanied by wave-particle scattering that results in an emitted power of EMIC waves. We conclude that ionospheric pickup thermalization is slow due to the small ring speed compared to the thermal and Alfven speeds, while in the solar wind and other space plasmas regions with larger ion-ring velocity the collisionless relaxation and thermalization is rapid in terms of O+ ion gyro-period.

Ofman, Leon↗
NASA NTRS2005

Heliophysics: The New Science of the Sun-Solar System Connection. Recommended Roadmap for Science and Technology 2005-2035

This is a Roadmap to understanding the environment of our Earth, from its life-sustaining Sun out past the frontiers of the solar system. A collection of spacecraft now patrols this space, revealing not a placid star and isolated planets, but an immense, dynamic, interconnected system within which our home planet is embedded and through which space explorers must journey. These spacecraft already form a great observatory with which the Heliophysics program can study the Sun, the heliosphere, the Earth, and other planetary environments as elements of a system--one that contains dynamic space weather and evolves in response to solar, planetary, and interstellar variability. NASA continually evolves the Heliophysics Great Observatory by adding new missions and instruments in order to answer the challenging questions confronting us now and in the future as humans explore the solar system. The three heliophysics science objectives: opening the frontier to space environment prediction; understanding the nature of our home in space, and safeguarding the journey of exploration, require sustained research programs that depend on combining new data, theory, analysis, simulation, and modeling. Our program pursues a deeper understanding of the fundamental physical processes that underlie the exotic phenomena of space.

Heliophysics↗
NASA NTRS1993

G-star astropauses - A test for interstellar pressure

Under the assumption of a solar system model, astropause radii are estimated for a sample of 70 G stars near the sun. G-star space velocities and trajectories are calculated. Three stars within 10 pc of the sun have predicted astropause radii larger than 6 arcsec. At least eight stars have traversed low interstellar pressure regions, similar to the path of the sun, over the last 4 Myr. The Galactic influences on these stellar systems thus may be similar to those on the solar system, providing a list of possibly attractive SETI targets. The closest star to the sun 4 Myr ago, in this restricted sample, was HD 147513. The relative dimensions of the astropause radii of G stars with space motions parallel and perpendicular to the surrounding interstellar magnetic field may vary by a factor of 2 and may ultimately yield quantitative estimates of interstellar magnetic field strength near the sun.

Frisch, P. C.↗
NASA NTRS1997

Atomic Physics with the Goddard High Resolution Spectrograph on the Hubble Space Telescope: Oscillator Strengths for Neutral Carbon - III

High quality spectra of interstellar absorption from C I toward beta(sup 1) S(sub co), rho O(sub ph) A, and chi O(sub ph) were obtained with the Goddard High Resolution Spectrograph on HST. Many weak lines were detected within the observed wavelength intervals: 1150-1200 A for beta(sup 1) S(sub co) and 1250-1290 A for rho O(sub ph) A and chi O(sub ph). Curve-of-growth analyses were performed in order to extract accurate column densities and Doppler parameters from lines with precise laboratory-based f-values. These column densities and b-values were used to obtain a self-consistent set of f-values for all the observed C I lines. A particularly important constraint was the need to reproduce data for more than one line of sight. For about 50% of the lines, the derived f-values differ appreciably from the values quoted by Morton.

Zsargo, J.↗
NASA NTRS2015

Propulsion Technology Assessment: Science and Enabling Technologies to Explore the Interstellar Medium

The Advanced Concepts Office at NASA’s George C. Marshall Space Flight Center conducted a study to assess what low-thrust advanced propulsion system candidates, existing and near term, could deliver a small, Voyager-like satellite to our solar system’s heliopause, approximately 100 AU from the sun, within 10 years. The advanced propulsion system trade study consisted of three candidates, including a Magnetically Shielded Miniature Hall thruster, a solar sail and an electric sail. A second analysis was conducted to determine which solid rocket motor kick stage(s) would be required to provide additional thrust at various points in the trajectory, assuming a characteristic energy capability provided by a Space Launch System Block 1B vehicle architecture carrying an 8.4 meter payload fairing. Two trajectory profiles were considered, including an escape trajectory using a Jupiter gravity assist and an escape trajectory first performing a Jupiter gravity assist followed by an Oberth maneuver around the sun and an optional Saturn gravity assist. Results indicated that if the Technology Readiness Level of an electric sail could be increased in time, this technology could not only enable a satellite to reach 100 AU in 10 years but it could potentially do so in even less time.

Hopkins, Randall C.↗
NASA NTRS1995

An HST study of galactic inerstellar zinc and chromium

We present a survey of interstellar Zn II and Cr II absorption extracted from the Hubble Space Telescope Goddard High Resolution Spectrograph (HST GHRS) data archive. We find clear evidence for an enhanced depletion of Zn from the gas phase with increasing fractional abundance of molecular hydrogen f(H2). Our lower limit to the Galactic interstellar metallicity is approximately 65% of the solar value as determined by the measured Zn abundances in the lowest f(H2) sightlines, (N(Zn)/N(H(sup 0)(sub tot)) = -0.19 +/- 0.04. The correspondingly high depletion of Cr with respect to solar (N(Cr/N(H(sup 0)(sub tot)) = -1.44 +/- 0.26 indicates that there are significant amounts of dust present in these lines of sight. The Galactic abundances of Zn and Cr in the ISM provide a fundamental reference point which is used to understand the metal enrichment and dust formation history of damped Lyman alpha QSO absorption-line systems, normally believed to arise from intervening precursors to modern disk galaxies. Although the spread in Zn abundances is large for both the local ISM and in damped Lyman alpha systems, we still find a substantial difference (factor of 4-10) in metallicity between the two sets. This survey and future observations of more distant objects which probe the full extent of the Milky Way halo provide a more complete picture of the enrichment and depletion characteristics of present-day galaxies.

Roth, Katherine C.↗
NASA NTRS1982

Paradigm transition in cosmic plasma physics

New discoveries in cosmic plasma physics are described, and their applications to solar, interstellar, galactic, and cosmological problems are discussed. The new discoveries include the existence of double layers in magnetized plasmas and in the low magnetosphere, and energy transfer by electric current in the auroral circuit. It is argued that solar flares and the solar wind-magnetosphere interaction should not be interpreted in terms of magnetic merging theories, and that electric current needs to be explicitly taken account of in understanding these phenomena. The filamentary structure of cosmic plasmas may be caused by electric currents in space, and the pinch effect may have a central role to play in the evolutionary history of interstellar clouds, stars, and solar systems. Space may have a cellular structure, with the cell walls formed by thin electric current layers. Annihilation may be the source of energy for quasars and the Hubble expansion, and the big bang cosmology may well be wrong.

Alfven, H.↗
NASA NTRS1976

Physical processes in comets

The paper discusses physical processes in comets which involve solar and nuclear radial forces that affect the motions of gases and icy grains, gas-phase chemistry very close to the nuclei of large comets near the sun, sublimation of icy grains, dissociation of parent molecules into radicals and of radicals into atoms, and ionization by sunlight and collisions. The composition and dimensions of nuclei are examined along with variations in intrinsic brightness, the nature of volatiles, gas production rates in the coma, characteristics of icy grains in the coma, and the structure of streamers, ion tails, and dust tails. The structure of the coma is described in detail on the basis of spectroscopic observations of several comets. The origin of comets is briefly reviewed together with the relation of comets to earth, the interplanetary complex, and the interstellar medium. Desirable future observations are noted, especially by space missions to comets.

Whipple, F. L.↗
NASA NTRS1979

Scientific Research with the Space Telescope: International Astronomical Union Colloquium No. 54

The application of the space telescope for extragalactic astronomy, planetary research, and stellar, interstellar, and galactic structural problems is discussed. Topics include investigations of small solar system objects, the physical characteristics of ionized gaseous nebulae, the central regions of active galaxies and quasars, problems of cosmology, and the distribution and composition of interstellar matter.

Longair, M. S.↗
NASA NTRS2005

A Search for PAHs in Astrophysical Environments

We present the results of a dedicated search for the spectral signatures in the visible range of neutral polycyclic aromatic hydrocarbons (PAHs) in astronomical observations representing various astrophysical environments, probing a total column of line of sight material corresponding to Av=50. Laboratory measurements of PAHs in simulated astrophysical conditions are now available (see contribution of Salama et al.) which provide for the first time the exact wavelengths for the spectral features of these molecules, as well as detailed information on the intrinsic line profiles and oscillator strengths. These measurements therefore allow a direct comparison to astronomical observations and an estimate of, or upper limit to, the abundance of individual PAHs in space. As the column densities for individual PAHs in interstellar or circumstellar lines of sight are expected to be very low, such a comparison and analysis requires astronomical observations at very high signal to noise. We present such a data set here for lines of sight representing diffuse clouds and circumstellar environments of carbon stars, and their comparison with gas phase spectra of a representative set of free, cold PAHs.

Salama, F.↗
NASA NTRS2003

1400-1900 GHz local oscillators for the Herschel Space Observatory

JPL continues to develop robust planar, all solid-state sources to cover the 1414 to 1908 GHz band. These sources will be used as local oscillators to drive hot electron bolometer (HEB) heterodyne mixers on the Herschel Space Observatory to observe high resolution spectra in the interstellar medium. We report our current progress and present recent results.

Schottky diode frequency multiplier THz local osci↗
NASA NTRS2017

The Diffuse Interstellar Bands: Solving a Century Old Problem

The Diffuse Interstellar Bands (DIBs) are a set of apporoximately 500 absorption bands that are seen in the spectra of reddened stars (i.e., stars obscured by the presence of interstellar clouds in their line of sight). The first DIBs were detected in the visible over a century ago. Diffuse Interstellar Bands are now detected from the near ultraviolet to the near infrared in the spectra of reddened stars spanning a variety of interstellar environments in our local, and in other galaxies. Although DIB carriers are a significant part of the interstellar chemical inventory as they account for a noticeable fraction of the interstellar extinction, the nature of their carriers is still unknown over a century after the detection of the first bands. DIB carriers are stable and ubiquitous in a broad variety of interstellar environments and play a unique role in interstellar physics and chemistry. It has long been realized that the solving of the DIB problem requires a strong synergy between astronomical observations, laboratory astrophysics and astrochemistry, quantum chemistry calculations and astrophysical modeling of line-of-sights. In this review, we'll present and discuss the current state of this perplexing problem. We'll review the progress and the failures that have been encountered in the long quest for the identification of the carriers of these ubiquitous interstellar bands.

Molecules in Space↗
NASA NTRS1994

Recent Advances in Organic Cosmochemistry

The Astrochemistry Laboratory at NASA's Ames Research Center pursues a variety of activities, most of which center around the use of spectroscopy (ultraviolet to far-infrared) for the interpretation of astronomical and meteoritic data. One of our key activities is the study of the chemical and physical properties of cometary, interstellar, and planetary ice analogs and matrix-isolated molecules of astrophysical interest. As a result of these studies it is now known that a significant fraction of the carbon in the interstellar medium (ISM) is in reasonably complex forms, some of which are clearly of interest for exobiology. Examples of compounds known or suspected to be present in space include polycyclic aromatic hydrocarbons (PAHs), microdiamonds, an aliphatic-rich component found in the diffuse interstellar medium, and a variety of molecular species produced by the irradiation of mixed molecular ices in dense clouds. A number of the species produced by irradiation contain nitrogen and appear to offer an additional means of producing some of the amino acids found in meteorites. I will review these complex carbonaceous materials and discuss how they are connected with each other and the organic materials that ultimately ended up as part of our own Solar System. Specific points that will probably be covered include: (1) the composition of the ices in interstellar dense molecular clouds; (2) the more complex organic compounds produced when these ices are irradiated and/or warmed; (3) the detection of microdiamonds in space; (4) the discovery that aliphatic materials may constitute as much as 15% of all the carbon in the diffuse ISM, appears to be present everywhere in the galaxy, and yet seems to be present everywhere in the galaxy, and yet seems to be significantly concentrated towards the center of the galaxy.

Sandford, Scott A.↗
NASA NTRS1997

Gauche Ethyl Alcohol: Laboratory Assignments and Interstellar Identification

Ethyl alcohol (ethanol) is known to possess a pair of closely spaced excited torsional substates (gauche+, gauche-) at an energy of approximately 57 K above the ground (trans) torsional substate. We report an extended analysis of some gauche - gauche+ Q-branch ((Delta)J = 0) transitions with a three-substate fixed frame axis method (FFAM) Hamiltonian. Our approach accounts for complex trans-gauche interactions for the first time. In addition, we are able to obtain intensities for perturbed rotational transitions, and to determine the trans to gauche+ separation to be 1185399.1 MHz. A complete ground state rotational-torsional partition function accounting for the previously neglected gauche substates is presented. Based on our analysis, a total of 14 U lines obtained towards Orion KL can now be assigned to gauche substates of ethanol. Analysis of these lines yields a rotational temperature of 223 K and a total (trans + gauche) column density of 7.0 x 10(exp 15)/sq cm. The column density is in reasonable agreement with the recent value of 2-3 x 10(exp 15)/sq cm based on observations of trans-ethanol by Ohishi et al., although there is some disparity in the rotational temperatures. Eight additional U lines in the literature are assigned to transitions of gauche ethanol.

Pearson, J. C.↗
NASA NTRS2010

Ultraviolet Irradiation of Pyrimidine in Interstellar Ice Analogs: Formation and Photo-Stability of Nucleobases

Astrochemistry laboratory experiments recently showed that molecules of prebiotic interest can potentially form in space, as supported by the detection of amino acids in organic residues formed by the UV photolysis of ices simulating interstellar and cometary environments (H2O, CO, CO2, CH3OH, NH3, etc.). Although the presence of amino acids in the interstellar medium (ISM) is still under debate, experiments and the detection of amino acids in meteorites both support a scenario in which prebiotic molecules could be of extraterrestrial origin, before they are delivered to planets by comets, asteroids, and interplanetary dust particles. Nucleobases, the informational subunits of DNA and RNA, have also been detected in meteorites, although they have not yet been observed in the ISM. Thus, these molecules constitute another family of prebiotic compounds that can possibly form via abiotical processes in astrophysical environments. Nucleobases are nitrogen-bearing cyclic aromatic species with various functional groups attached, which are divided into two classes: pyrimidines (uracil, cytosine, and thymine) and purines (adenine and guanine). In this work, we study how UV irradiation affects pyrimidine mixed in interstellar ice analogs (H2O, NH3, CH3OH). In particular, we show that the UV irradiation of H2O:pyrimidine mixtures leads to the production of oxidized compounds including uracil, and show that both uracil and cytosine are formed upon irradiation of H2O:NH3:pyrimidine mixtures. We also study the photostability of pyrimidine and its photoproducts formed during these experiments.

Nuevo, Michel↗
NASA NTRS2001

Deuterium Fractionation in Analogs of Interstellar Ices: Laboratory Measurements

A question of key interest in the field of Astrobiology is the extent to which organic compounds made in space may play a role in the origin of life in planetary systems. In general, the best proof that at least some interstellar materials survive incorporation into forming stellar/planetary systems is their identification in extraterrestrial samples through detection of the isotopic anomalies they may carry. In the case of organic compounds, the chief isotopic anomalies that might be expected are the enrichment of D and 15N. and such enrichments are seen in primitive extraterrestrial materials, for example, in the organics in carbonaceous chondrites and interplanetary dust particles. In my talk I will review the various astrochemical processes by which deuterium can become enriched in organic compounds and will discuss some recent laboratory experiments that examine one of these processes in particular. name]y the UV photolysis of interstellar ices. Finally, I will review the current state of our knowledge of D enrichments in primitive solar system materials and discuss the constraints these data place on the relative importance of the various possible interstellar D enrichment processes.

Sandford, Scott A.↗