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  • Other Sources  (21)
  • 1990-1994  (21)
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  • 1
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    The ancient oxygen exosphere of Mars: Implications for atmosphere evolution (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: This study involves the calculation, by the 2-stream method of Nagy and Cravens, of 'hot' oxygen exosphere density profiles for 'ancient' atmospheres and ionospheres (e.g., different extreme ultraviolet fluxes) and the associated escaping fluxes. We computed the total production rates above different 'nominal' ionopause altitudes (not taking into account the fact that some will reenter the atmosphere). We do not consider the additional neutral escape due to the sputtering process described by Luhmann and Kozyra. The results presented here thus represent conservative estimations of the neutral escape fluxes, but generous estimates of ion loss rates (except that here we do not consider charge exchange and impact ionization ion production processes). Further work along the lines of Luhmann and Kozyra can lead to estimates of sputtering losses over time and the roles played by impact ionization and charge exchange.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Workshop on the Martian Surface and Atmosphere Through Time; p 175
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  • 2
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    History of oxygen and carbon escape from the Martian atmosphere (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: A fraction of the oxygen in the Martian atmosphere continually escapes to space because dissociative recombination of the O2(+) ions in the ionosphere can impart sufficient energy to the product O atoms. In addition, ionization of the extended atomic oxygen corona resulting from the above process adds to escape since the solar wind can carry away O(+) ions born above a few hundred km altitude. A further by-product of this ion-pickup by the solar wind is an additional population of escaping oxygen atoms that are sputtered from the atmosphere near the exobase by pickup ions that are on reentry rather than escaping trajectories. This sputtering process can also remove carbon in the form of intact or dissociated CO2 since all atoms and molecules in the 'target' gas are subject to the collisional energy transfer that characterizes sputtering. We have estimated the present rates of escape of oxygen and carbon due to these mechanisms, as well as the rates at several epochs in the history of the solar system.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Papers Presented to the Workshop on the Evolution of the Martian Atmosphere; p 19-20
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  • 3
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    Escape of Mars atmospheric carbon through time by photochemical means (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Luhmann et al. recently suggested that sputtering of the Martian atmosphere by re-entering O(+) pickup ions could have provided a significant route of escape for CO2 and its products throughout Mars' history. They estimated that the equivalent of C in an approximately 140-mbar CO2 atmosphere should have been lost this way if the Sun and solar wind evolved according to available models. Another source of escaping C (and O) that is potentially important is the dissociative recombination of ionospheric CO(+) near the exobase. We have evaluated the loss rates due to this process for 'ancient' solar EUV radiation fluxes of 1, 3, and 6 times the present flux in order to calculate the possible cumulative loss over the last 3.5 Gyr.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Mars: Past, Present, and Future. Results from the MSATT Program, Part 1; p 27
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  • 4
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    Discovery concepts for Mars (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Two focused Mars missions that would fit within the guidelines for the proposed Discovery line are discussed. The first mission would deal with the issue of the escape of the atmosphere (Mars') to space. A complete understanding of this topic is crucial to deciphering the evolution of the atmosphere, climate change, and volatile inventories. The second mission concerns the investigation of remanent magnetization of the crust and its relationship to the ionosphere and the atmosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Workshop on the Martian Surface and Atmosphere Through Time; p 93
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  • 5
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    Fatigue testing of plasma-sprayed thermal barrier coatings, volume 2 (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A plasma sprayed thermal barrier coating for diesel engines were fatigue tested. Candidate thermal barrier coating materials were fatigue screened and a data base was generated for the selected candidate material. Specimen configurations are given for the bend fatigue tests, along with test setup, specimen preparation, test matrix and procedure, and data analysis.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA-CR-186726 , NAS 1.26:186726
    Format: application/pdf
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  • 6
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    Mechanical testing of advanced coating system, volume 1 (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The Electron Beam Physical Vapor Deposition (EBPVD) coating material has a highly columnar microstructure, and as a result it was expected to have very low tensile strength. To be able to fabricate the required compression and tensile specimens, a substrate was required to provide structural integrity for the specimens. Substrate and coating dimensions were adjusted to provide sufficient sensitivity to resolve the projected loads carried by the EBPVD coating. The use of two distinctively different strain transducer systems, for tension and compression loadings, mandated two vastly different specimen geometries. Compression specimen and tensile specimen geometries are given. Both compression and tensile test setups are described. Data reduction mathematical models are given and discussed in detail as is the interpretation of the results. Creep test data is also given and discussed.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA-CR-186725 , NAS 1.26:186725
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  • 7
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    Dynamics explorer interdisciplinary scientist investigations (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This document is a final report on research activities and accomplishments that occurred during the funding period of 10-1-90 through 1-30-94. The focus of our interdisciplinary investigation during the Dynamics Explorer Mission was on the complex coupling processes that tap the magnetic-storm energy, stored in the ring current particle reservoir, and transport this energy into the subauroral, midlatitude and even equatorial ionospheric regions. The transport of energy through the inner magnetosphere and into the underlying ionospheric regions is a critical element in our understanding of the impact of solar and magnetic disturbances on upper atmospheric and ionospheric regions equatorward of the auroral zone.
    Keywords: GEOPHYSICS
    Type: NASA-CR-195226 , NAS 1.26:195226 , UMICH-021979
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  • 8
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    Physical processes in the plasma mantle of Venus (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The results are presented of a study, which analyzed data from 10 Pioneer Venus orbits in order to see whether similar wave particle interaction processes also exist in the corresponding region around Venus. The first conclusion is that the apparent physical processes in the mantle are indeed similar around Venus and Mars. The planetary thermal O(+) ions outside the ionopause interact with the shocked solar wind and excite electrostatic waves close to the lower hybrid frequency. These waves propagate inwards, heating first the electron and deeper down in the ionosphere the thermal ion population. The observed superthermal ions are believed to be the product of this wave particle interaction process. It is also concluded that the wave energy transferred to the thermal electrons is of the right magnitude (about 4 x 10 exp 9 eV/sq cm s) to provide the supplemental heat source necessary to reconcile observed and calculated electron temperatures in the ionosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 18; 2305-230
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  • 9
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    Helium in the polar wind (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The coupled time-dependent continuity, momentum, and energy equations for four charged species (H(+), He(+), O(+) and electrons) moving through a stationary upper neutral atmosphere (composed of O2, N2, O, He, and H) were solved along open geomagnetic field lines using a modified version of the Gombosi et al. (1985) model. The thermospheric densities and temperatures, obtained from the MSIS-86 model (Hedin, 1987), were used to calculate neutral-ion sources, sinks, and collision frequencies. The various cross sections and conductivities employed by the Gombosi et al. model were also updated. The paper presents the first time-dependent solutions for the He(+) component of the polar wind. Special attention is paid to the solar cycle variation of the ion upflows.
    Keywords: GEOPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 12; 6 19
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  • 10
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    On the possible source of the ionization in the nighttime Martian ionosphere. I - Phobos 2 HARP electron spectrometer measurements (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The measurements of electron spectra in the Martian magnetosphere by the HARP instrument on board the Phobos 2 orbiter are presented. The energy of the electrons (a few tens of electron volts) is sufficient for the impact ionization of the planetary neutral gas, and the characteristic flux of electrons (about 10 exp 8/sq cm per sec) could produce the nightside ionospheric layer with a peak density of a few thousands of electrons per cubic centimeter, which corresponds to densities observed earlier during radio occultations of the Mars 4 and 5 and Viking 1 and 2 spacecraft. The possibility of magnetospheric electron precipitation into the nightside atmosphere of Mars is in agreement with the mainly induced nature of the magnetic field in the planetary magnetotail (as at Venus), while the variability of the Martian nightside ionosphere may be explained by the partial screening of the atmosphere by a weak intrinsic magnetic field of the planet.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 19
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