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NASA Technical Reports Server (NTRS) (685.044 recursos)

The NTRS is a valuable resource for students, educators, researchers, and the public for access to NASA's current and historical technical literature since it was first released in 1994. NTRS provides access to approximately 500K aerospace related citations, 90K full-text online documents, and 111K images and videos. NTRS numbers continues to grow over time as new scientific and technical information (STI) is created or funded by NASA. The type of information found in NTRS include: conference papers, images, journal articles, photos, meeting papers, movies, patents, research reports, and technical videos.

Mostrando recursos 101 - 120 de 320.502

  1. Solar Wind Implantation into Lunar Regolith: Hydrogen Retention in a Surface with Defects

    Zimmerman, M. I.; Farrell, W. M.; Hurley, D. M.
    Solar wind protons are implanted directly into the top 100 nm of the lunar near-surface region, but can either quickly diffuse out of the surface or be retained, depending upon surface temperature and the activation energy, U, associated with the implantation site. In this work, we explore the distribution of activation energies upon implantation and the associated hydrogen-retention times; this for comparison with recent observation of OH on the lunar surface. We apply a Monte Carlo approach: for simulated solar wind protons at a given local time, we assume a distribution of U values with a central peak, U(sub c)...

  2. Performance of Backshort-Under-Grid Kilopixel TES Arrays for HAWC+

    Irwin, K. D.; Runyan, M. C.; Benford, D. J.; Staguhn, J. G.; Hilton, G. C.; Maher, S. F.; Wollack, E. J.; Moseley, S. H.; Miller, T. M.; Sharp, E. H.; Dowell, C. D.; Fixsen, D. J.; Jhabvala, C. A.
    We present results from laboratory detector characterizations of the first kilopixel BUG arrays for the High- resolution Wideband Camera Plus (HAWC+) which is the imaging far-infrared polarimeter camera for the Stratospheric Observatory for Infrared Astronomy (SOFIA). Our tests demonstrate that the array performance is consistent with the predicted properties. Here, we highlight results obtained for the thermal conductivity, noise performance, detector speed, and first optical results demonstrating the pixel yield of the arrays.

  3. Infrared Continuum and Line Evolution of the Equatorial Ring Around SN 1987A

    Woodward, Charles E.; Dwek, Eli; Bouchet, Patrice; Gehrz, Robert D.; Park, Sangwook; Danziger, I. John; Frank, Kari A.; Arendt, Richard G.
    Spitzer observations of SN 1987A have now spanned more than a decade. Since day approximately 4000, mid-infrared (mid-IR) emission has been dominated by that from shock-heated dust in the equatorial ring (ER). From 6000 to 8000 days after the explosion, Spitzer observations included broadband photometry at 3.6-24 micrometer, and low and moderate resolution spectroscopy at 5-35 micrometer. Here we present later Spitzer observations, through day 10,377, which include only the broadband measurements at 3.6 and 4.5 micrometer. These data show that the 3.6 and 4.5 micrometer brightness has clearly begun to fade after day approximately 8500, and no longer tracks...

  4. Parsec-Scale Accretion and Winds Irradiated by a Quasar

    Dorodnitsyn, A.; Proga, D.; Kallman, T.
    We present numerical simulations of properties of a parsec-scale torus exposed to illumination by the central black hole in an active galactic nucleus (AGN). Our physical model allows to investigate the balance between the formation of winds and accretion simultaneously. Radiation-driven winds are allowed by taking into account radiation pressure due to UV and IR radiation along with X-ray heating and dust sublimation. Accretion is allowed through angular momentum transport and the solution of the equations of radiative, viscous radiation hydrodynamics. Our methods adopt flux-limited diffusion radiation hydrodynamics for the dusty, infrared pressure driven part of the flow, along with...

  5. Recovery of Large Angular Scale CMB Polarization for Instruments Employing Variable-Delay Polarization Modulators

    Moseley, S. H.; Switzer, E. R.; Harrington, K.; Appel, J. W.; Eimer, J.; Fixsen, D. J.; Bennett, C. L.; Marriage, T. A.; Chuss, D. T.; Wollack, E. J.; Rostem, K.; Essinger-Hileman, T.; Watts, D. J.; Miller, N. J.
    Variable-delay Polarization Modulators (VPMs) are currently being implemented in experiments designed to measure the polarization of the cosmic microwave background on large angular scales because of their capability for providing rapid, front-end polarization modulation and control over systematic errors. Despite the advantages provided by the VPM, it is important to identify and mitigate any time-varying effects that leak into the synchronously modulated component of the signal. In this paper, the effect of emission from a 300 K VPM on the system performance is considered and addressed. Though instrument design can greatly reduce the influence of modulated VPM emission, some residual...

  6. A Review of the Handheld X-Ray Fluorescence Spectrometer as a Tool for Field Geologic Investigations on Earth and in Planetary Surface Exploration

    Hodges, Kip V.; Graff, Trevor G.; Evans, Cynthia A.; Young, Kelsey E.; Bleacher, Jacob E.
    X-ray fluorescence (XRF) spectroscopy is a well-established and commonly used technique in obtaining diagnostic compositional data on geological samples. Recently, developments in X-ray tube and detector technologies have resulted in miniaturized, field-portable instruments that enable new applications both in and out of standard laboratory settings. These applications, however, have not been extensively applied to geologic field campaigns. This study investigates the feasibility of using developing handheld XRF (hXRF) technology to enhance terrestrial field geology, with potential applications in planetary surface exploration missions. We demonstrate that the hXRF is quite stable, providing reliable and accurate data continuously over a several year...

  7. Observational Constraints on the Identification of Shallow Lunar Magmatism: Insights from Floor-Fractured Craters

    Jozwiak, L. M.; Head, J. W., III; Neumann, G. A.; Wilson, L.
    Floor-fractured craters are a class of lunar crater hypothesized to form in response to the emplacement of a shallow magmatic intrusion beneath the crater floor. The emplacement of a shallow magmatic body should result in a positive Bouguer anomaly relative to unaltered complex craters, a signal which is observed for the average Bouguer anomaly interior to the crater walls. We observe the Bouguer anomaly of floor-fractured craters on an individual basis using the unfiltered Bouguer gravity solution from GRAIL and also a degree 100-600 band-filtered Bouguer gravity solution. The low-magnitude of anomalies arising from shallow magmatic intrusions makes identification using...

  8. Analysis of One-Way Laser Ranging Data to LRO, Time Transfer and Clock Characterization

    McGarry, J. F.; Oberst, J.; Torrence, M. H.; Bauer, S.; Mazarico, E.; Smith, D. E.; Dirkx, D.; Neumann, G. A.; Zuber, M. T.; Mao, D.; Hussmann, H.
    We processed and analyzed one-way laser ranging data from International Laser Ranging Service ground stations to NASA's Lunar Reconnaissance Orbiter (LRO), obtained from June 13, 2009 until September 30, 2014. We pair and analyze the one-way range observables from station laser fire and spacecraft laser arrival times by using nominal LRO orbit models based on the GRAIL gravity field. We apply corrections for instrument range walk, as well as for atmospheric and relativistic effects. In total we derived a tracking data volume of approximately 3000 hours featuring 64 million Full Rate and 1.5 million Normal Point observations. From a statistical...

  9. Recurrence Rate and Magma Effusion Rate for the Latest Volcanism on Arsia Mons, Mars

    Wilson, James A.; Connor, Charles B.; Kiyosugi, Koji; Bleacher, Jacob E.; Richardson, Jacob A.
    Magmatism and volcanism have evolved the Martian lithosphere, surface, and climate throughout the history of Mars. Constraining the rates of magma generation and timing of volcanism on the surface clarifies the ways in which magma and volcanic activity have shaped these Martian systems. The ages of lava flows on other planets are often estimated using impact crater counts, assuming that the number and size-distribution of impact craters per unit area reflect the time the lava flow has been on the surface and exposed to potential impacts. Here we show that impact crater age model uncertainty is reduced by adding stratigraphic...

  10. Origin of the Anomalously Rocky Appearance of Tsiolkovskiy Crater

    Neish, Catherine D.; Cahill, Joshua T. S.; Greenhagen, Benjamin T.; Lawrence, Samual J.; Petro, Noah E.; Hayne, Paul O.; Bandfield, Joshua L.; Ghent, Rebecca R.; Williams, Jean-Pierre
    Rock abundance maps derived from the Diviner Lunar Radiometer instrument on the Lunar Reconnaissance Orbiter (LRO) show Tsiolkovskiy crater to have high surface rock abundance and relatively low regolith thickness. The location of the enhanced rock abundance to the southeast of the crater is consistent with a massive, well-preserved impact melt deposit apparent in LRO Miniature Radio Frequency instrument circular polarization ratio data. A new model crater age using LRO Lunar Reconnaissance Orbiter Camera imagery suggests that while it originated in the Late Imbrian, Tsiolkovskiy may be the youngest lunar crater of its size ( approximately 180 km diameter). Together...

  11. James Webb Space Telescope Observations of Stellar Occultations by Solar System Bodies and Rings

    Zhang, Z-W.; Tancredi, G.; Duffard, R.; Braga-Ribas, F.; Young, Leslie; Ortiz, J. L.; Santos-Sanz, P.; Milam, Stefanie N.; Bosh, A.; Mueller, Th.; French, R. G.; Lellouch, E.; Pinilla-Alonso, N.; Stansberry, J.; Vilenius, E.; Lin, Z-Y.
    In this paper, we investigate the opportunities provided by the James Webb Space Telescope (JWST) for significant scientific advances in the study of Solar System bodies and rings using stellar occultations. The strengths and weaknesses of the stellar occultation technique are evaluated in light of JWST's unique capabilities. We identify several possible JWST occultation events by minor bodies and rings and evaluate their potential scientific value. These predictions depend critically on accurate a priori knowledge of the orbit of JWST near the SunEarth Lagrange point 2 (L2). We also explore the possibility of serendipitous stellar occultations by very small minor...

  12. Editorial Introduction: Lunar Reconnaissance Orbiter, Part II

    Keller, John W.; Petro, Noah E.; Gaddis, Lisa R.
    The Lunar Reconnaissance Orbiter (LRO) mission has shifted our understanding of the history of the Moon. The seven instruments on LRO each have contributed to creating new paradigms for the evolution of the Moon by providing unprecedented measurements of the surface, subsurface, and lunar environment. In this second volume of the LRO Special Issue, we present 21 papers from a broad range of the areas of investigation from LRO, from the volatile inventory, to the shape of the Moon's surface, to its rich volcanic history, and the interactions between the lunar surface and the space environment. These themes provide rich...

  13. Subsurface Morphology and Scaling of Lunar Impact Basins

    Zuber, M. T.; Soderblom, J. M.; Johnson, B. C.; Wieczorek, M. A.; Miljkovic, K.; Neumann, G. A.; Collins, G. S.
    Impact bombardment during the first billion years after the formation of the Moon produced at least several tens of basins. The Gravity Recovery and Interior Laboratory (GRAIL) mission mapped the gravity field of these impact structures at significantly higher spatial resolution than previous missions, allowing for detailed subsurface and morphological analyses to be made across the entire globe. GRAIL-derived crustal thickness maps were used to define the regions of crustal thinning observed in centers of lunar impact basins, which represents a less unambiguous measure of a basin size than those based on topographic features. The formation of lunar impact basins...

  14. Demonstration of Orbit Determination for the Lunar Reconnaissance Orbiter Using One-Way Laser Ranging Data

    Mazarico, E.; Mao, D.; Dirkx, D.; Oberst, J.; Neumann, G. A.; Zuber, M. T.; McGarry, J. F.; Hussmann, H.; Smith, D. E.; Bauer, S.; Torrence, M. H.
    We used one-way laser ranging data from International Laser Ranging Service (ILRS) ground stations to NASA's Lunar Reconnaissance Orbiter (LRO) for a demonstration of orbit determination. In the one-way setup, the state of LRO and the parameters of the spacecraft and all involved ground station clocks must be estimated simultaneously. This setup introduces many correlated parameters that are resolved by using a priori constraints. More over the observation data coverage and errors accumulating from the dynamical and the clock modeling limit the maximum arc length. The objective of this paper is to investigate the effect of the arc length, the...

  15. Gravity Field of the Orientale Basin from the Gravity Recovery and Interior Laboratory Mission

    Phillips, Roger J.; Wieczorek, Mark A.; Zuber, Maria T.; Goossens, Sander; Kiefer, Walter S.; Head, James W.; Lemoine, Frank G.; Konopliv, Alexander S.; McGovern, Patrick J.; Solomon, Sean C.; Nimmo, Francis; Smith, David E.; Park, Ryan S.; Andrews-Hanna, Jeffrey C.; Jansen, Johanna C.; Johnson, Brandon C.; Keane, James T.; Asmar, Sami W.; Yuan, Dah-Ning; Melosh, H. Jay; Williams, James G.; Matsuyama, Isamu; Miljkovic, Katarina; Mazarico, Erwan; Soderblom, Jason M.; Taylor, G. Jeffrey; Watkins, Michael M.; Neumann, Gregory A.
    The Orientale basin is the youngest and best-preserved major impact structure on the Moon. We used the Gravity Recovery and Interior Laboratory (GRAIL) spacecraft to investigate the gravitational field of Orientale at 3- to 5-kilometer (km) horizontal resolution. A volume of at least (3.4 +/- 0.2) 10(exp 6) cu km of crustal material was removed and redistributed during basin formation. There is no preserved evidence of the transient crater that would reveal the basin's maximum volume, but its diameter may now be inferred to be between 320 and 460 km. The gravity field resolves distinctive structures of Orientale's three rings...

  16. Martian Polar Vortices: Comparison of Reanalyses

    Wilson, R. J.; Waugh, D. W.; Toigo, A. D.; Greybush, S. J.; Guzewich, S. D.; Montabone, L.
    The structure and evolution of the Martian polar vortices is examined using two recently available reanalysis systems: version 1.0 of the Mars Analysis Correction Data Assimilation (MACDA) and a preliminary version of the Ensemble Mars Atmosphere Reanalysis System (EMARS). There is quantitative agreement between the reanalyses in the lower atmosphere, where Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) data are assimilated, but there are differences at higher altitudes reflecting differences in the free-running general circulation model simulations used in the two reanalyses. The reanalyses show similar potential vorticity (PV) structure of the vortices: There is near-uniform small PV equatorward...

  17. Tidal Disruption of Phobos as the Cause of Surface Fractures

    Asphaug, E.; Spitale, J. N.; Henning, W. G.; Walker, M.; Hemingway, D.; Kattenhorn, S. A.; Bills, B. G.; Rhoden, A. R.; Hurford, T. A.
    Phobos, the innermost satellite of Mars, displays an extensive system of grooves that are mostly symmetric about its sub-Mars point. Phobos is steadily spiraling inward due to the tides it raises on Mars lagging behind Phobos' orbital position and will suffer tidal disruption before colliding with Mars in a few tens of millions of years. We calculate the surface stress field of the deorbiting satellite and show that the first signs of tidal disruption are already present on its surface. Most of Phobos' prominent grooves have an excellent correlation with computed stress orientations. The model requires a weak interior that...

  18. Discovery of Rapidly Moving Partial X-Ray Absorbers Within Cassiopeiae

    Petre, R.; Morihana, K.; Oskinova, L.; Russell, C. M. P.; Ishida, M.; Hamaguchi, K.; Enoto, T.
    Gamma Cassiopeiae is an enigmatic Be star with unusually strong hard X-ray emission. The Suzaku observatory detected six rapid X-ray spectral hardening events called "softness dips" in a approx.100 ks observation in 2011. All the softness dip events show symmetric softness-ratio variations, and some of them have flat bottoms apparently due to saturation. The softness dip spectra are best described by either approx.40% or approx.70% partial covering absorption to kT approx.12 keV plasma emission by matter with a neutral hydrogen column density of approx.(28) 10(exp 21)/sq cm, while the spectrum outside these dips is almost free of absorption. This result...

  19. Achievable Human Exploration of Mars: Highlights from The Fourth Community Workshop (AM IV)

    Thronson, Harley; Cassady, Joseph
    About a half decade ago, several professionals working mainly in industry on scenarios for initial human exploration of Mars together recognized that, under generally similar assumptions, there was a fair degree of similarity among these scenarios. Moreover, opportunities should be sought for greater community input into NASA's own scenario-building for the future of human space flight. A series of focused community workshops were considered to be effective to assess these scenarios and involve more directly the science community, including planetary protection, with industry. Four workshops to date each involve about sixty professional scientists, engineers, technologists, and strategists from NASA, academia,...

  20. Observing Planetary Rings and Small Satellites with the James Webb Space Telescope: Science Justification and Observation Requirements

    Milam, Stefanie N.; Hedman, Matthew M.; Tiscareno, Matthew S.; Cuzzi, Jeffrey N.; Tamayo, Daniel; Hamilton, Douglas P.; Verbiscer, Anne J.; Stansberry, John A.; Nicholson, Philip D.; French, Richard G.; Showalter, Mark R.; de Pater, Imke; Burns, Joseph A.
    The James Webb Space Telescope (JWST) will provide unprecedented opportunities to observe the rings and small satellites in our Solar System, accomplishing three primary objectives: (1) discovering new rings and moons, (2) unprecedented spectroscopy, and (3) time-domain observations. We give details on these science objectives and describe requirements that JWST must fulfill in order to accomplish the science objectives.

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