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  • 11
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    Investigation of Keeper Erosion in the NSTAR Ion Thruster (2001)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: The goal of the present investigation was to determine the cause for the difference in the observed discharge keeper erosion between the 8200 hr wear test of a NASA Solar Electric Propulsion Technology Applications Readiness (NSTAR) engineering model thruster and the ongoing extended life test (ELT) of the NSTAR flight spare thruster. During the ELT, the NSTAR flight spare ion thruster experienced unanticipated erosion of the discharge cathode keeper. Photographs of the discharge keeper show that the orifice has enlarged to slightly more than twice the original diameter. Several differences between the ELT and the 8200 hr wear test were initially identified to determine any effects which could lead to the erosion in the ELT. In order to identify the cause of the ELT erosion, emission spectra from an engineering model thruster were collected to assess the dependence of keeper erosion on operating conditions. Keeper ion current was measured to estimate wear. Additionally, post-test inspection of both a copper keeper-cap was conducted, and the results are presented. The analysis indicated that the bulk of the ion current was collected within 2-mm radially of the orifice. The estimated volumetric wear in the ELT was comparable to previous wear tests. Redistribution of the ion current on the discharge keeper was determined to be the most likely cause of the ELT erosion. The change in ion current distribution was hypothesized to caused by the modified magnetic field of the flight assemblies.
    Keywords: Spacecraft Propulsion and Power
    Type: NASA/TM-2001-211280 , E-13080 , IEPC-01-308 , NAS 1.15:211280 , 27th International Electric Propulsion Conference; Oct 14, 2001 - Oct 19, 2001; Pasadena, CA; United States
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  • 12
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    Non-Intrusive Characterization of the Wear of the HERMeS Thruster Using Optical Emission Spectroscopy (2019)
    In:  CASI
    Details
    Publication Date: 2019-10-12
    Description: The Hall Effect Rocket with Magnetic Shielding (HERMeS) is a 12.5 kW Hall thruster electric propulsion string that has been in development by NASA Glenn Research Center(GRC) and NASA JPL since 2012. Due to the magnetically shielded design, service life-limiting erosion of the boron nitride discharge has been virtually eliminated. The inner front pole cover (IFPC) has now been identified as the component defining erosion-based service life. Optical emission spectroscopy (OES) is used as an in-situ diagnostic to measure relative erosion trends during operation of the HERMeS thruster during a series of short duration wear tests. Erosion trends obtained from the OES data will be compared to traditional erosion data measured with a non-contact profilometer.
    Keywords: Spacecraft Propulsion and Power
    Type: GRC-E-DAA-TN72554 , International Electric Propulsion Conference; Sep 15, 2019 - Sep 20, 2019; Vienna; Austria
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  • 13
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    LIF Density Measurement Calibration Using a Reference Cell (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Flight qualification of ion thrusters typically requires testing on the order of 10,000 hours. Extensive knowledge of wear mechanisms and rates is necessary to establish design confidence prior to long duration tests. Consequently, real-time erosion rate measurements offer the potential both to reduce development costs and to enhance knowledge of the dependency of component wear on operating conditions. Several previous studies have used laser induced fluorescence (LIF) to measure real-time, in situ erosion rates of ion thruster accelerator grids. Those studies provided only relative measurements of the erosion rate. In the present investigation, a molybdenum tube was resistively heated such that the evaporation rate yielded densities within the tube on the order of those expected from accelerator grid erosion. A pulsed UV laser was used to pump the ground state molybdenum at 345.64nm, and the non-resonant fluorescence at 550-nm was collected using a bandpass filter and a photomultiplier tube or intensified CCD array. The sensitivity of the fluorescence was evaluated to determine the limitations of the calibration technique. The suitability of the diagnostic calibration technique was assessed for application to ion engine erosion rate measurements.
    Keywords: Spacecraft Propulsion and Power
    Type: 29th International Conference of Plasma Science; May 27, 2002 - May 30, 2002; Banff; Canada
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  • 14
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    The High Power Electric Propulsion (HiPEP) Ion Thruster (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Practical implementation of the proposed Jupiter Icy Moon Orbiter (JIMO) mission, which would require a total delta V of approximately 38 km/s, will require the development of a high power, high specific impulse propulsion system. Initial analyses show that high power gridded ion thrusters could satisfy JIMO mission requirements. A NASA GRC-led team is developing a large area, high specific impulse, nominally 25 kW ion thruster to satisfy both the performance and the lifetime requirements for this proposed mission. The design philosophy and development status as well as a thruster performance assessment are presented.
    Keywords: Spacecraft Propulsion and Power
    Type: NASA/TM-2004-213194 , E-14693 , AIAA Paper 2004-3812 , 40th Joint Propulsion Conference and Exhibit; Jul 11, 2004 - Jul 14, 2004; Fort Lauderdale, FL
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  • 15
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    High Current Hollow Cathode Plasma Plume Measurements (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Plasma plume measurements are reported for a hollow cathode assembly (HCA) oper-ated at discharge currents of 50, 70, and 100 A at xenon ow rates between 19 - 46 sccm.The HCA was centrally mounted in the annulus of the NASA-300MS Hall Thruster andwas operated in the spot and plume modes with additional data taken with an appliedmagnetic eld. Langmuir probes, retarding potential analyzers, and optical emission spec-troscopy were employed to measure plasma properties near the orice of the HCA and toassess the charge state of the near-eld plasma. Electron temperatures (2-6 eV) and plasmapotentials are consistent with probe-measured values in previous investigations. Operationwith an applied-eld yields higher discharge voltages, increased Xe III production, andincreased signals from the 833.5 nm C I line. While operating in plume mode and with anapplied eld, ion energy distribution measurements yield ions with energies signicantlyexceeding the applied discharge voltage. These ndings are correlated with high-frequencyoscillations associated with each mode.
    Keywords: Electronics and Electrical Engineering
    Type: IEPC-2013-076 , GRC-E-DAA-TN11563 , International Electric Propulsion Conference; Oct 06, 2013 - Oct 10, 2013; Washington DC; United States
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  • 16
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    Derated ion thruster development status (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A 30 cm diameter xenon ion thruster is under development at NASA to provide an ion propulsion option for auxiliary and primary propulsion on missions of national interest. Specific efforts include thruster design optimizations, component life testing and validation, vibration testing, and performance characterizations. Under this program, the ion thruster will be brought to engineering model development status. This paper discusses the activities and preliminary test results to develop a 30 cm engineering model thruster.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: AIAA PAPER 93-2225 , ; 15 p.|AIAA, SAE, ASME, and ASEE, Joint Propulsion Conference and Exhibit; Jun 28, 1993 - Jun 30, 1993; Monterey, CA; United States
    Format: text
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  • 17
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    Wear Testing of the HERMeS Thruster (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The Hall-Effect Rocket with Magnetic Shielding (HERMeS) thruster is being developed and tested at NASA GRC and NASA JPL through support of the Space Technology Mission Directorate (STMD) as primary propulsion for the Asteroid Redirect Robotic Mission (ARRM). This thruster is advancing the state-of-the-art of Hall-effect thrusters and is intended to serve as a precursor to higher power systems for human interplanetary exploration. A 2000-hour wear test has been initiated at NASA GRC with the HERMeS Technology Demonstration Unit One and three of four test segments have been completed totaling 728 h of operation. This is the first test of a NASA-designed magnetically shielded thruster to extend beyond 300 hr of continuous operation. Trends in performance, component wear, thermal design, plume properties, and back-sputtered deposition are discussed for two wear-test segments of 246 h and 360 h. The first incorporated graphite pole covers in an electrical configuration where cathode was electrically connected to thruster body. The second utilized traditional alumina pole covers with the thruster body floating. It was shown that the magnetic shielding in both configurations completely eliminated erosion of the boron nitride discharge channel but resulted in erosion of the inner pole cover. The volumetric erosion rate of the graphite pole covers was roughly 2/3 that of the alumina pole covers and the thruster exhibited slightly better performance. Buildup of back-sputtered carbon on the BN channel at a rate of roughly 1.5 m/kh is shown to have negligible impact on the performance.
    Keywords: Spacecraft Propulsion and Power
    Type: GRC-E-DAA-TN33637 , AIAA/SAE/ASEE Joint Propulsion Conference; Jul 25, 2016 - Jul 27, 2016; Salt Lake City, UT; United States
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  • 18
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    Vaporization and Zonal Mixing in Performance Modeling of Advanced LOX-Methane Rockets (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Initial modeling of LOX-Methane reaction control (RCE) 100 lbf thrusters and larger, 5500 lbf thrusters with the TDK/VIPER code has shown good agreement with sea-level and altitude test data. However, the vaporization and zonal mixing upstream of the compressible flow stage of the models leveraged empirical trends to match the sea-level data. This was necessary in part because the codes are designed primarily to handle the compressible part of the flow (i.e. contraction through expansion) and in part because there was limited data on the thrusters themselves on which to base a rigorous model. A more rigorous model has been developed which includes detailed vaporization trends based on element type and geometry, radial variations in mixture ratio within each of the "zones" associated with elements and not just between zones of different element types, and, to the extent possible, updated kinetic rates. The Spray Combustion Analysis Program (SCAP) was leveraged to support assumptions in the vaporization trends. Data of both thrusters is revisited and the model maintains a good predictive capability while addressing some of the major limitations of the previous version.
    Keywords: Spacecraft Propulsion and Power
    Type: AIAA Paper 2012-4036 , E-664017 , AIAA/ASME/SAE/ASEE Joint Propulsion Conference; Jul 29, 2012 - Aug 01, 2012; Atlanta, GA; United States
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  • 19
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    Advanced Diagnostic Characterization of High-Power Hall Thruster Wear and Operation (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Spacecraft Propulsion and Power
    Type: E-664018 , AIAA Paper 2012-4036 , AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit; Jul 29, 2012 - Aug 01, 2012; Atlanta, GA; United States
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  • 20
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    Optical Diagnostic Characterization of High-Power Hall Thruster Wear and Operation (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Optical emission spectroscopy is employed to correlate BN insulator erosion with high-power Hall thruster operation. Specifically, actinometry leveraging excited xenon states is used to normalize the emission spectra of ground state boron as a function of thruster operating condition. Trends in the strength of the boron signal are correlated with thruster power, discharge voltage, and discharge current. In addition, the technique is demonstrated on metallic coupons embedded in the walls of the HiVHAc EM thruster. The OES technique captured the overall trend in the erosion of the coupons which boosts credibility in the method since there are no data to which to calibrate the erosion rates of high-power Hall thrusters. The boron signals are shown to trend linearly with discharge voltage for a fixed discharge current as expected. However, the boron signals of the higher-power NASA 300M and NASA 457Mv2 trend with discharge current and show an unexpectedly weak to inverse dependence on discharge voltage. Electron temperatures measured optically in the near-field plume of the thruster agree well with Langmuir probe data. However, the optical technique used to determine Te showed unacceptable sensitivity to the emission intensities. Near-field, single-frequency imaging of the xenon neutrals is also presented as a function of operating condition for the NASA 457 Mv2.
    Keywords: Spacecraft Propulsion and Power
    Type: AIAA Paper 2012-4036 , E-664016 , AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit; Jul 29, 2012 - Aug 01, 2012; Atlanta, GA; United States|International Energy Conversion Engineering Conference; Jul 29, 2012 - Aug 01, 2012; Atlanta, GA; United States
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