SCIENTIFIC AND TECHNICAL AEROSPACE REPORTS
A Biweekly Publication of the National Aeronautics and Space Administration
VOLUME 44, ISSUE 14 - JULY 18, 2006
90 ASTROPHYSICS
Includes cosmology; celestial mechanics; space plasmas; and interstellar and interplanetary gases and dust.
20060019406 Air Force Research Lab., Kirkland AFB, NM USA
Space Plasma Experiment for Thin-Film Solar Cells with Protective Coatings
Tlomak, Pawel; Hausgen, Paul E; Piszczor, Jr , Michael F; Senft, Donna; Merrill, John; Aug 2005; 6 pp.; In English; Original contains color illustrations Report No.(s): AD-A446286; AFRL-VS-PS-TP-2006-1007; No Copyright; ONLINE: http://hdl.handle.net/100.2/ADA446286; Avail.: CASI: A02, Hardcopy
This paper gives an overview of the space plasma test program for thin-film photovoltaics (TFPV) technologies developed at the AFRL. The test program is designed to simulate the interactions between TFPV arrays and plasmas characteristic of LEO and MEO environments. The response of coated amorphous silicon and copper-indium-gallium-diselenide solar cells to the simulated space plasma environment is presented. Solar cells used in these experiments were coated with two types of thin-film, multifunctional, protective coatings, which are designed to provide protection from the space environment, including space plasma, and to aid in passive thermal management of the TFPV arrays.
The test coupons, which contain single cells and interconnected strings, closely resemble the actual configuration of high-voltage TFPV arrays that will be flown on the Demonstration and Science Experiments (DSX). Results of preliminary electrostatic charging, arcing, dielectric breakdown, and parasitic current measurements are presented and analyzed. The preliminary experimental data presented in this paper demonstrate that multifunctional protective coatings developed for TFPV arrays provide effective protection against the plasma environment while minimizing impact on their power generation performance. This effort is part of an ongoing development program for TFPV led by the Space Vehicle Directorate at the Air Force Research Laboratory. Plasma interaction tests were carried out at the NASA Glenn Plasma Interaction Facility. DTIC
Aerospace Environments; Protective Coatings; Solar Cells; Sphinx; Thin Films
20060019508 Saab Aircraft Co., Linkoeping, Sweden
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Flight Test and Development of a New Anti-G System in JAS 39 Gripen
Berglund, Christer; Marklund, Bjorn; Oct 2005; 17 pp.; In English Report No.(s): AD-A446431; No Copyright; ONLINE: http://hdl.handle.net/100.2/ADA446431; Avail.: CASI: A03, Hardcopy
A new oxygen and anti-g system has been implemented in the Swedish forth generation mulitrole aircraft JAS 39 GRIPEN C and D. In the Gripen the pilot is exposed to 9G for long periods of time. Therefore the Anti-G protection is more important than ever. Due to the implementation of OBOGS (On Board Oxygen Generating System), the anti-g system also had to be changed. During the first test flight with high G-loads with the new OBOGS and anti-G system in GRIPEN test aircraft 39-800 (twin-seat) the pilots got a grey-out and after evaluation of data from the flight it was shown that the pressure in the G-suit was below specified limits. At this time it was suspected to be an individual problem with the G-regulators and therefore they were changed to other units, but due to flight tests of the ECS (Environmental Control System) another problem arose before the anti-G testing could go on.
The ECS tests showed that the supply pressure from the ECS during some flight cases was below the minimum requirement that the OBOGS and anti-g system was qualified for. The anti-G tests had to be postponed until the supply pressure to the anti-G system could be guaranteed to be above the minimum requirements. Therefore a number of changes to improve the supply pressure and reduce the pressure drops in the anti-g system were implemented. After a new test period with testing of the modifications, which were successful, the problem with the low pressure in the g-suit still existed even though the G-regulators had been changed.
After tests of several G-regulators it was shown that a high percentage of the G-regulators gave a low pressure in the G-suit and quite often below minimum specified values. After some close teamwork with the G-regulator supplier HAY, a modification of the anti-gregulator was made in order to be able to guarantee correct pressure in the g-suit. DTIC
Antigravity; Flight Tests; Gravitational Fields; Jas-39 Aircraft; Oxygen; Pressure Suits
20060019741 Air Force Research Lab., Hanscom AFB, MA USA
Modeling the Connection of the Global Ionospheric Electric Fields to the Solar Winds
Rothwell, Paul L; Jasperse, John R; Mar 10, 2006; 17 pp.; In English Contract(s)/Grant(s): Proj-2311 Report No.(s): AD-A446728; No Copyright; Avail.: CASI: A03, Hardcopy
A global ionospheric electrostatic potential model, which we refer to as Nopper-Carovillano (N-C), can be linked with a magnetospheric potential model. The latter model, which we refer to as Hill-Siscoe-Ober (H-S-O), computes a transpolar potential phipc(H-S-O) based on solar wind parameters and region-1 field-aligned currents (FAC) from the magnetosheath to the ionosphere. The polar ionospheric conductance required by H-S-O is defined by the N-C model. In this way, the transpolar potential and the associated FAC are the same in both models. A distribution of region-1 FAC in the N-C model predicts a two-cell convection pallem which is in reasonable agreement with plasma drifts measured by DMSP (Defense Meteorological Satellite Program) satellites. The H-S-O model, as modified by N-C, is compared with the Weimer potential model and with the transpolar potentials observed by DMSP satellites during the 6-7 April 2000 magnetic storm. Good agreement is found in both cases. The region-2 (J2) current is estimated from the Siscoe (S-RC) ring-current circuit model which is driven by phipc(H-S-O). The resistor values in S-RC, as determined by N-C, when combined with the global potential solution, make it possible to estimate the time profile of the equatorial penetration electric field during the storm's main phase.With the values obtained, shielding occurs within 1 hour of onset. Equatorial plasma bubbles (EPBs) are seen some hours after the initial increase of phipc and are qualitatively consistent with the equatorial penetration electric field calculated by the combined model. DTIC
Electric Fields; Ionospheres; Solar Wind
20060019813 Naval Observatory, Washington, DC USA
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Merlin Astrometry of 11 Radio Stars
Fey, Alan L; Boboltz, David A; Gaume, Ralph A; Johnston, Kenneth J; Garrington, Simon T; Thomasson, Peter; Feb 2006; 7 pp.; In English Report No.(s): AD-A446866; No Copyright; Avail.: CASI: A02, Hardcopy
We report accurate positions in the International Celestial Reference Frame (ICRF) for 11 radio stars.
Observations were made using the Multi-Element Radio Linked Interferometer Network at a radio frequency of 5 GHz.
The positions are estimated to be accurate at the 5 mas level. Positions were obtained directly in the ICRF by phase referencing the radio stars to ICRF quasars whose positions are estimated to be accurate at the 0.25 mas level.
We use our results together with results of previous observations to obtain proper-motion estimates for these stars.
The average proper-motion uncertainties are 1.1 mas yr(-1) in mu(sub alpha cos delta) and 1.2 mas yr(-1) in mu(sub delta), comparable to the Hipparcos values. DTIC
Astrometry; Motion; Radio Astronomy; Radio Stars
20060020074 NASA Goddard Space Flight Center, Greenbelt, MD, USA
High-Energy Emission From the Polar Cap and Slot Gap
Harding, Alice K.; [2006]; 1 pp.; In English; 363rd Heraeus Seminar on Neutron Stars and Pulsars, 14-19 May 2006, Bad Honnef, Germany; No Copyright; Avail.: Other Sources; Abstract Only
Thirty-five years after the discovery of rotation-powered pulsars, we still do not understand the fundamentals of their pulsed emission at any wavelength. I will review the latest developments in understanding the high-energy emission of rotation-powered pulsars, with particular emphasis on the polar cap and slot gap models. Special and general relativistic effects play important roles in pulsar emission, from inertial frame-dragging near the stellar surface to aberration, time-of-flight and retardation of the magnetic field near the light cylinder. Understanding how these effects determine what we observe at different wavelengths is critical to unraveling the emission physics. I will discuss how the next generation of gamma-ray detectors, AGILE and GLAST, will test prediction of these models. Author
Pulsars; Stellar Rotation; Magnetic Fields; Polar Caps
20060020139 Fermi National Accelerator Lab., Batavia, IL, USA, California Univ., Los Angeles, CA, USA
Universal Description of the Particle Flux Distribution in Extended Air Showers
Chou, A. S.; Arisaka, K.; Pernas, M. D.; Barnhill, D.; Billoir, P.; January 2005; 8 pp.; In English Report No.(s): DE2006-875549; FERMILAB-CONF-05-294-E; No Copyright; Avail.: National Technical Information Service (NTIS)
It is shown that the electromagnetic and muonic fluxes in extended air showers (EAS) can be described using a simple model incorporating attenuation and geometrical dispersion. The model uses a reduced set of parameters including the primary energy E, the position of shower maximum X(sub max) relative to the ground, and a muon flux normalization N(sub (mu)). To a good approximation, this set of three physical parameters is sufficient to predict the variability of the particle fluxes due to systematic differences between different models of composition and hadronic interactions, and due to statistical event-by-event differences in shower development. Measurements of these three physical observables are therefore unbiased and very nearly model-independent, in contrast with standard measurement techniques. The theoretical problem of determining primary composition is thus deconvolved from the measurement procedure, and may be approached in a subsequent analysis of the measured distributions of (E, X(sub max), N(sub (mu))). NTIS
Cosmic Ray Showers; Cosmic Rays; Flux (Rate)
20060020709 NASA Ames Research Center, Moffett Field, CA, USA
Following the Water: the Evolution of Ice-forming Regions in the Early Solar Nebula
Davis, Sanford S.; [2006]; 1 pp.; In English; 4th Astrobiology Science Conference, 26-30 Mar. 2006, Washington, DC, USA; No Copyright; Avail.: Other Sources; Abstract Only
The abundances of water-vapor and water-ice during the first ten million years of the protoplanetary solar nebula are simulated using a new condensation/sublimation model. This study builds on a 'snow line' model reported in ApJ 627 L153 (2005); it uses a simple phenomenological model where water vapor molecules evolve from solar atomic abundance and eventually condenses to ice at colder points in the nebula once the water-vapor partial pressure exceeds a value determined by the phase diagram for water. The synthesis of water vapor from elementary species is modeled with a chemical network consisting of about 400 species and 4000 reactions. The evolution of the icy zone (and its relative abundance of solid ice) is traced from a limited region in the early hotter disk to its final state at the time when the gas is expelled and a planetary system begins to form. Possible effects of this dynamic motion on disk chemistry and organic molecule formation are also described. Author
Water Vapor; Solar Nebula; Ice; Organic Chemistry; Phenomenology; Sublimation
20060020741 NASA Johnson Space Center, Houston, TX, USA
Characterization of Asteroidal Basalts through Reflectance Spectroscopy and Implications for the Dawn Mission
Abell, P. A.; Mittlefehdlt, D.W.; Gaffey, M. J.; [2006]; 2 pp.; In English; 69th Meeting of the Meteoritical Society, 6-11 Aug. 2006, Zurich, Switzerland; Copyright; Avail.: CASI: A01, Hardcopy
There are currently five known groups of basaltic achondrites that represent material from distinct differentiated parent bodies. These are the howardite-eucrite-diogenite (HED) clan, mesosiderite silicates, angrites, Ibitira, and Northwest Africa (NWA) 011 [1]. Spectroscopically all these basaltic achondrite groups have absorption bands located near 1 and 2 microns due to the presence of pyroxene. Some of these meteorite types have spectra that are quite similar, but nevertheless have characteristics (e.g. spectral slope, band depths, etc.) that may be used to differentiate them from each other. Author
Basalt; Achondrites; Iron Meteorites; Meteoritic Composition; Reflectance; Pyroxenes; Absorption Spectra
20060021464 NASA Ames Research Center, Moffett Field, CA, USA
Variations in the Peak Position of the 6.2 micron Interstellar Emission Feature: A Tracer of N in the Interstellar Polycyclic Aromatic Hydrocarbon Population
Hudgins, Douglas M.; Bauschlicher, Charles W.; Allamandola, L. J.; The Astrophysical Journal; October 10, 2005; Volume 632, pp. 316-332; In English; Original contains black and white illustrations Contract(s)/Grant(s): UPN 344-58-21-02; UPN 399-20-40; Copyright; Avail.: Other Sources
This paper presents the results of an investigation of the molecular characteristics that underlie the observed peak position and profile of the nominal 6.2 micron interstellar emission band generally attributed to the CC stretching vibrations of polycyclic aromatic hydrocarbons (PAHs). It begins with a summary of recent experimental and theoretical studies of the spectroscopic properties of large (\g30 carbon atoms) PAH cations as they relate to this aspect of the astrophysical problem. It then continues with an examination of the spectroscopic properties of a number of PAH variants within the context of the interstellar 6.2 micron emission, beginning with a class of compounds known as polycyclic aromatic nitrogen heterocycles (PANHs; PAHs with one or more nitrogen atoms substituted into their carbon skeleton).
In this regard, we summarize the results of recent relevant experimental studies involving a limited set of small PANHs and their cations and then report the results of a comprehensive computational study that extends that work to larger PANH cations including many nitrogen-substituted variants of coronene(+) (C24H12(+)), ovalene(+) (C32H14(+)), circumcoronene(+) (C54H18(+)), and circum-circumcoronene(+) (C96H24(+)). Finally, we report the results of more focused computational studies of selected representatives from a number of other classes of PAH variants that share one or more of the key attributes of the PANH species studied.
These alternative classes of PAH variants include (1) oxygen- and silicon-substituted PAH cations; (2) PAH-metal ion complexes (metallocenes) involving the cosmically abundant elements magnesium and iron; and (3) large, asymmetric PAH cations. Overall, the studies reported here demonstrate that increasing PAH size alone is insuEcient toaccount for the position of the shortest wavelength interstellar 6.2 micron emission bands, as had been suggested by earlier studies. On the other hand, this work reveals that substitution of one or more nitrogen atoms within the interior of the carbon skeleton of a PAH cation induces a significant blueshift in the position of the dominant CC stretching feature of these compounds that is suf6cient to account for the position of the interstellar bands.
Subsequent studies of the effects of substitution by other heteroatoms (O and Si), metal ion complexation (Fe(+), Mg(+), and Mg(2+)), and molecular symmetry variation-all of which fail to reproduce the blueshift observed in the PANH cations-indicate that N appears to be unique in its ability to accommodate the position of the interstellar 6.2 micron bands while simultaneously satisfying the other constraints of the astrophysical problem. This result implies that the peak position of the interstellar feature near 6.2 micron traces the degree of nitrogen substitution in the population, that most of the PAHs responsible for the interstellar IR emission features incorporate nitrogen within their aromatic networks, and that a lower limit of 1%-2% of the cosmic nitrogen is sequestered within the interstellar PAH population.
Finally, in view of the ubiquity and abundance of interstellar PAHs and the permanent dipoles and distinctive electronic structures of these nitrogen-substituted variants, this work impacts a wide range of observational phenomena outside of the infrared region of the spectrum including the forest of unidentified molecular rotational features and the anomalous Galactic foreground emission in the microwave, and the diffuse interstellar bands (DIBs) and other structure in the interstellar extinction curve in the ulhviolet/visible. These astrophysical ramifications are discussed, and the dipole moments and rotational constants are tabulated to facilitate further investigations of the astrophysical role of nitrogen-substituted aromatic compounds. Author
Polycyclic Aromatic Hydrocarbons; Diffuse Interstellar Bands; Cations; Vibration; Interstellar Extinction; Infrared Spectra
20060021475 NASA Ames Research Center, Moffett Field, CA, USA Dust Spectroscopy and the Nature of Grains
Tielens, A. G. G. M.; [2006]; 1 pp.; In English; Les Houches 2006 Meeting, 30 Apr. - 6 may 2006, France; No Copyright; Avail.: Other Sources; Abstract Only
Ground-based, air-borne and space-based, infrared spectra of a wide variety of objects have revealed prominent absorption and emission features due to large molecules and small dust grains. Analysis of this data reveals a highly diverse interstellar and circumstellar grain inventory, including both amorphous materials and highly crystalline compounds (silicates and carbon). This diversity points towards a wide range of physical and chemical birthsites as well as a complex processing of these grains in the interstellar medium. In this talk, I will review the dust inventory contrasting and comparing both the interstellar and circumstellar reservoirs. The focus will be on the processes that play a role in the lifecycle of dust in the interstellar medium. Author
Amorphous Materials; Infrared Spectra; Interstellar Matter; Dust; Stellar Envelopes; Carbon; Crystallinity
20060021486 NASA Ames Research Center, Moffett Field, CA, USA
The Stardust Discovery Mission - Returning Unique Samples of Early Solar System Organics
Sandford, Scott; January 2006; 1 pp.; In English; 2006 Astrobiology Science Conference, 26-30 Mar. 2006, Washington, DC, USA Contract(s)/Grant(s): WBS 21-624-08-01; No Copyright; Avail.: Other Sources; Abstract Only
On January 2,2004, the STARDUST spacecraft made the closest ever flyby (236 km) of the nucleus of a comet - Comet Wild 2. During the flyby the spacecraft collected samples of dust from the coma of the comet. These samples were successfully returned to Earth on January 15,2006. After a six-month preliminary examination to establish the nature of the returned samples, they will be made available to the general scientific community for study. During my talk I will discuss the scientific goals of the STARDUST mission and provide a brief overview of the mission's design and flight. I will also discuss the recovery of the Stardust Sample Return Capsule (SRC), with an emphasis on those aspects of the recovery important for minimizing the degree of contamination (particularly organic contamination) of the samples. Finally, the first samples are only just now being distributed for preliminary examination, but I hope to be able to talk about some of the preliminary findings from the returned comet samples. Author
Flyby Missions; Stardust Mission; Wild 2 Comet; Dust; Comet Nuclei
Source: NASA
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