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  • 1
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    Gut Microbiota-Derived Tryptophan Metabolites Modulate Inflammatory Response in Hepatocytes and Macrophages (2018)
    Cell Press
    Details
    Publication Date: 2018-04-01
    Electronic ISSN: 2211-1247
    Topics: Biology
    Published by Cell Press
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    PAPER CURRENT
  • 2
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    Gut Microbiota-Derived Tryptophan Metabolites Modulate Inflammatory Response in Hepatocytes and Macrophages (2019)
    Cell Press
    Details
    Publication Date: 2019-09-01
    Electronic ISSN: 2211-1247
    Topics: Biology
    Published by Cell Press
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    PAPER CURRENT
  • 3
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    Wear Trends of the HERMeS Thruster as a Function of Throttle Point (2019)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: A series of short-duration (200 h) wear tests were conducted with two Hall Effect Rocket with Magnetic Shielding (HERMeS) technology demonstration units. Front pole covers, cathode keeper, and discharge channel wear were characterized as a function of discharge voltage, magnetic field strength, and chamber pressure. No discharge channel erosion was observed. Inner pole cover erosion was shown to be a weak function of discharge voltage with most erosion occurring at the lowest value, 300 V. The Technology Demonstration Unit (TDU) 3 keeper electrode eroded with each operating condition, with high magnetic field yielding the greatest erosion rate. The TDU-1 keeper electrode exhibited net deposition suggesting its configuration is more consistent with meeting overall HERMeS service life requirements. Ratios of molybdenum to graphite erosion rates suggests, with high uncertainty, that the sputtering ions are originating downstream of the thruster exit plane, striking the surface with small angles of incidence.
    Keywords: Spacecraft Propulsion and Power
    Type: NASA/TM-2019-219731 , IEPC?2017?207 , E-19456 , GRC-E-DAA-TN48801 , International Electric Propulsion Conference; Oct 08, 2017 - Oct 12, 2017; Atlanta, GA; United States
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    NASA TECHNICAL REPORTS
  • 4
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    Development Status of a Three-Dimensional Electron Fluid Model for Hall Thruster Plume Simulations (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A 3-D electron fluid model has been developed as a stepping stone to fully describe the electron current flow across magnetic fields inside a vacuum chamber and to provide electron flux to solar arrays for spacecraft surface charging model. A detailed description of the numerical treatment of the electric potential solver, including finite-volume formulation, implementation, and the treatment of boundary conditions, are presented in this paper. Verification tests of the model are presented.
    Keywords: Spacecraft Propulsion and Power
    Type: NASA/TM-2018-219962 , E-19572 , AIAA-2018-4808 , GRC-E-DAA-TN59053 , Joint Propulsion Conference, AIAA Propulsion and Energy Forum; Jul 09, 2018 - Jul 11, 2018; Cincinnati, OH; United States
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  • 5
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    Update of the NEXT Ion Thruster Service Life Assessment with Post-Test Correlation to the Long Duration Test (2017)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: The service life assessment for NASA's Evolutionary Xenon Thruster is updated to incorporate the results from the successful and voluntarily early completion of the 51,184 hour long duration test which demonstrated 918 kg of total xenon throughput. The results of the numerous post-test investigations including destructive interrogations have been assessed against all of the critical known and suspected failure mechanisms to update the life and throughput expectations for each major component. Analysis results of two of the most acute failure mechanisms, namely pit-and-groove erosion and aperture enlargement of the accelerator grid, are not updated in this work but will be published at a future time after analysis completion.
    Keywords: Numerical Analysis; Spacecraft Propulsion and Power
    Type: IEPC-2017-061 , GRC-E-DAA-TN44839 , International Electric Propulsion Conference (IEPC) 2017; Oct 08, 2017 - Oct 12, 2017; Atlanta, GA; United States
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  • 6
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    Hybrid-Particle-In-Cell Simulation of Backsputtered Carbon Transport in the Near-Field Plume of a Hall Thruster (2018)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: Magnetic shielding has eliminated boron nitride erosion as the life limiting mechanism in a Hall thruster but has resulted in erosion of the front magnetic field pole pieces. Recent experiments show that the erosion of graphite pole covers, which are added to protect the magnetic field pole pieces, causes carbon to redeposit on other surfaces, such as boron nitride discharge channel and cathode keeper surfaces. As a part of the risk-reduction activities for Advanced Electric Propulsion System thruster development, this study models transport of backsputtered carbon from the graphite front pole covers and vacuum facility walls. Fluxes, energy distributions, and redeposition rates of backsputtered carbon on the anode, discharge channel, and graphite cathode keeper surfaces are predicted.
    Keywords: Spacecraft Propulsion and Power
    Type: NASA/TM-2018-219719 , IEPC-2017-537 , E-19447 , GRC-E-DAA-TN48798 , International Electric Propulsion Conference; Oct 08, 2017 - Oct 12, 2017; Atlanta, GA; United States
    Format: application/pdf
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  • 7
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    Wear Trends of the HERMeS Thruster as a Function of Throttle Point (2017)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: A series of short-duration (200 hour) wear tests were conducted with two Hall Effect Rocket with Magnetic Shielding (HERMeS) technology demonstration units (TDU). Front pole covers, cathode keeper, and discharge channel wear were characterized as a function of discharge voltage, magnetic field strength, and chamber pressure. No discharge channel erosion was observed. Inner pole cover erosion was shown to be a weak function of discharge voltage with most erosion occurring at the lowest value, 300 volts. The TDU-3 keeper electrode eroded with each operating condition, with high magnetic field yielding the greatest erosion rate. The TDU-1 keeper electrode exhibited net deposition suggesting its configuration is more consistent with meeting overall HERMeS service life requirements. Ratios of molybdenum to graphite erosion rates suggests, with high uncertainty, that the sputtering ions are originating downstream of the thruster exit plane, striking the surface with small angles of incidence.
    Keywords: Spacecraft Propulsion and Power
    Type: GRC-E-DAA-TN45507 , International Electric Propulsion Conference; Oct 08, 2017 - Oct 12, 2017; Atlanta, GA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    Hybrid-PIC Simulation of Backsputtered Carbon Transport in the Near-Field Plume of a Hall Thruster (2017)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: Magnetic shielding has eliminated boron nitride erosion as the life limiting mechanism in a Hall thruster but has resulted in erosion of the front magnetic field pole pieces. Recent experiments show that the erosion of graphite pole covers, which are added to protect the magnetic field pole pieces, causes carbon to redeposit on other surfaces, such as boron nitride discharge channel and cathode keeper surfaces. As a part of the risk-reduction activities for AEPS thruster development, this study models transport of backsputtered carbon from the graphite front pole covers and vacuum facility walls. Fluxes, energy distributions, and redeposition rates of backsputtered carbon on the anode, discharge channel, and graphite cathode keeper surfaces are predicted.
    Keywords: Spacecraft Propulsion and Power
    Type: IEPC-2017-537 , GRC-E-DAA-TN45504 , International Electric Propulsion Conference (IEPC); Oct 08, 2017 - Oct 12, 2017; Atlanta, GA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Modeling an Iodine Hall Thruster Plume in the Iodine Satellite (ISAT) (2016)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: An iodine-operated 200-W Hall thruster plume has been simulated using a hybrid-PIC model to predict the spacecraft surface-plume interaction for spacecraft integration purposes. For validation of the model, the plasma potential, electron temperature, ion current flux, and ion number density of xenon propellant were compared with available measurement data at the nominal operating condition. To simulate iodine plasma, various collision cross sections were found and used in the model. While time-varying atomic iodine species (i.e., I, I+, I2+) information is provided by HP Hall simulation at the discharge channel exit, the molecular iodine species (i.e., I2, I2+) are introduced as Maxwellian particles at the channel exit. Simulation results show that xenon and iodine plasma plumes appear to be very similar under the assumptions of the model. Assuming a sticking coefficient of unity, iodine deposition rate is estimated.
    Keywords: Spacecraft Propulsion and Power
    Type: GRC-E-DAA-TN37710 , Liquid Propulsion (LPS) Meeting; Dec 05, 2016 - Dec 08, 2016; Phoenix, AZ; United States|Programmatic and Industrial Base Meeting (PIB) Meeting; Dec 05, 2016 - Dec 08, 2016; Phoenix, AZ; United States|JANNAF Joint Subcommittee Meeting; Dec 05, 2016 - Dec 08, 2016; Phoenix, AZ; United States|Spacecraft Propulsion (SPS) Meeting; Dec 05, 2016 - Dec 08, 2016; Phoenix, AZ; United States|Modeling and Simulation (MSS) Meeting; Dec 05, 2016 - Dec 08, 2016; Phoenix, AZ; United States
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  • 10
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    Modeling an Iodine Hall Thruster Plume in the Iodine Satellite (ISAT) (2016)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: An iodine-operated 200-W Hall thruster plume has been simulated using a hybrid-PIC model to predict the spacecraft surface-plume interaction for spacecraft integration purposes. For validation of the model, the plasma potential, electron temperature, ion current flux, and ion number density of xenon propellant were compared with available measurement data at the nominal operating condition. To simulate iodine plasma, various collision cross sections were found and used in the model. While time-varying atomic iodine species (i.e., I, I+, I2+) information is provided by HPHall simulation at the discharge channel exit, the molecular iodine species (i.e., I2, I2+) are introduced as Maxwellian particles at the channel exit. Simulation results show that xenon and iodine plasma plumes appear to be very similar under the assumptions of the model. Assuming a sticking coefficient of unity, iodine deposition rate is estimated.
    Keywords: Spacecraft Propulsion and Power
    Type: GRC-E-DAA-TN37780 , Programmatic and Industrial Base (PIB) Meeting; Dec 05, 2016 - Dec 08, 2016; Phoenix, AZ; United States|Liquid Propulsion Subcommittee (LPS); Dec 05, 2016 - Dec 08, 2016; Phoenix, AZ; United States|Spacecraft Propulsion Subcommittee (SPS); Dec 05, 2016 - Dec 08, 2016; Phoenix, AZ; United States|Modeling and Simulation Subcommittee (MSS); Dec 05, 2016 - Dec 08, 2016; Phoenix, AZ; United States
    Format: application/pdf
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