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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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31 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

Characterization of the NEXT Hollow Cathode Inserts After Long-Duration Testing

Hollow dispenser cathode inserts are a critical element of electric propulsion systems, and should therefore be well understood during long term operation to ensure reliable system performance. This work destructively investigated cathode inserts from the NEXT long-duration test which demonstrated 51,184 hours of high-voltage operation, 918 kg of propellant throughput, and 35.5 MN-s of total impulse. The characterization methods used include scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction. Microscopy analysis has been performed on fractured surfaces, emission surfaces, and metallographically polished cross-sections of post-test inserts and unused inserts. Impregnate distribution, etch region thickness, impregnate chemical content, emission surface topography, and emission surface phase identification are the primary factors investigated.

Mackey, Jonathan A.↗
NASA NTRS2021

Post-test Inspection of NASA’s Evolutionary Xenon Thruster Long-Duration Test Hardware: Discharge Chamber

The NEXT Long-Duration Test is part of a comprehensive thruster service life assessment intended to demonstrate overall throughput capability, validate service life models, quantify wear rates as a function of time and operating condition, and identify any unknown life-limiting mechanisms. The test was voluntarily terminated in February 2014after demonstrating 51,184 hours of high-voltage operation, 918 kg of propellant throughput, and 35.5 MN-s of total impulse. The post-test inspection of the thruster hardware began shortly afterwards with a combination of non-destructive and destructive analysis techniques, and is presently nearing completion. This paper presents relevant results of the post-test inspection for the discharge chamber as well as other miscellaneous components such as the high-voltage propellant isolators and electrical cabling. Comparison of magnetic field measurements taken during pretest and post-test inspections indicate that the field strength did not degrade, consistent with performance data obtained during the test. Inspection of discharge chamber mesh samples show a deposition coating primarily composed of grid material that is approximately 15 μm in thickness. This thickness is well within the retention capability of the mesh and is therefore not expected to present any issues. Approximately 3.1 grams of deposition flakes were found at the bottom of the discharge chamber, composed primarily of grid material and carbon. Calculated size histograms of these flakes indicate that 99% have a maximum dimension of 200 μm or smaller, which is significantly less than the ion optics grid gap. Larger flakes that are capable of causing a grid-to-grid short will be analyzed to determine if their formation will occur in flight or is a facility effect. The high-voltage propellant isolators as well as numerous other electrical insulators were inspected and no evidence of arcing or any other issues were found.

Rohit Shastry↗
NASA NTRS2021

Post-test Inspection of NASA’s Evolutionary Xenon Thruster Long-Duration Test Hardware: Discharge and Neutralizer Cathodes

The NEXT Long-Duration Test is part of a comprehensive thruster service life assessment intended to demonstrate overall throughput capability, validate service life models, quantify wear rates as a function of time and operating condition, and identify any unknown life-limiting mechanisms. The test was voluntarily terminated in February 2014 after demonstrating 51,184 h of high-voltage operation, 918 kg of propellant throughput, and 35.5 MN-s of total impulse. The post-test inspection of the thruster hardware began shortly afterwards with a combination of non-destructive and destructive analysis techniques, and is presently nearing completion. This paper presents relevant results of the post-test inspection for both discharge and neutralizer cathodes. Discharge keeper erosion was found to be significantly reduced from what was observed in the NEXT 2 kh wear test and NSTAR Extended Life Test, providing adequate protection of vital cathode components throughout the test with ample lifetime remaining. The area of the discharge cathode orifice plate that was exposed by the keeper orifice exhibited net erosion, leading to cathode plate material building up in the cathode-keeper gap and causing a thermally-induced electrical short observed during the test. Significant erosion of the neutralizer cathode orifice was also found and is believed to be the root cause of an observed loss in flow margin. Deposition within the neutralizer keeper orifice as well as on the downstream surface was thicker than expected, potentially resulting in a facility-induced impact on the measured flow margin from plume mode. Neutralizer keeper wall erosion on the beam side was found to be significantly lower compared to the NEXT 2 kh wear test, likely due to the reduction in beam extraction diameter of the ion optics that resulted in decreased ion impingement. Results from the post-test inspection have led to some minor thruster design improvements.

Ion engine↗
NASA NTRS2021

Post-test Inspection of NASA’s Evolutionary Xenon Thruster Long Duration Test Hardware: Ion Optics

A Long Duration Test (LDT) was initiated in June 2005 as a part of NASA’s Evolutionary Xenon Thruster (NEXT) service life validation approach. Testing was voluntarily terminated in February 2014, with the thruster accumulating 51,184 hours of operation, processing 918 kg of xenon propellant, and delivering 35.5 MN-s of total impulse. The post-test inspection objectives for the ion optics were derived from the original NEXT LDT test objectives, such as service life model validation, and expanded to encompass other goals that included verification of in situ measurements, test issue root causes, and past design changes. The ion optics cold grid gap had decreased only by an average of 7% of pretest center grid gap, so efforts to stabilize NEXT grid gap were largely successful. The upstream screen grid surface exhibited a chamfered erosion pattern. Screen grid thicknesses were ≥ 86% of the estimated pretest thickness, indicating that the screen grid has substantial service life remaining. Deposition was found on the screen aperture walls and downstream surfaces that was primarily composed of grid material and back-sputtered carbon, and this deposition likely caused the minor decreases in screen grid ion transparency during the test. Groove depths had eroded through up to 35% of the accelerator grid thickness. Minimum accelerator aperture diameters increased only by about 5-7% of the pretest values and downstream surface diameters increased by about 24-33% of the pretest diameters. These results suggest that increasing the accelerator aperture diameters, improving manufacturing tolerances, and masking down the perforated diameter to 36 cm were successful in reducing the degree of accelerator aperture erosion at larger radii.

George C. Soulas↗
DOE OSTI2020

Materials Data on MnS2 by Materials Project

MnS2 is Pyrite structured and crystallizes in the cubic Pa-3 space group. The structure is three-dimensional. Mn4+ is bonded to six equivalent S2- atoms to form corner-sharing MnS6 octahedra. The corner-sharing octahedral tilt angles are 64°. All Mn–S bond lengths are 2.30 Å. S2- is bonded in a 3-coordinate geometry to three equivalent Mn4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnS by Materials Project

MnS is Zincblende, Sphalerite structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. Mn2+ is bonded to four equivalent S2- atoms to form corner-sharing MnS4 tetrahedra. There are one shorter (2.32 Å) and three longer (2.42 Å) Mn–S bond lengths. S2- is bonded to four equivalent Mn2+ atoms to form corner-sharing SMn4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnS by Materials Project

MnS is Halite, Rock Salt structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Mn2+ is bonded to six equivalent S2- atoms to form a mixture of corner and edge-sharing MnS6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Mn–S bond lengths are 2.56 Å. S2- is bonded to six equivalent Mn2+ atoms to form a mixture of corner and edge-sharing SMn6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnS by Materials Project

MnS is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Mn2+ is bonded to four equivalent S2- atoms to form corner-sharing MnS4 tetrahedra. There are one shorter (2.34 Å) and three longer (2.42 Å) Mn–S bond lengths. S2- is bonded to four equivalent Mn2+ atoms to form corner-sharing SMn4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mn2S3 by Materials Project

Mn2S3 is Corundum structured and crystallizes in the trigonal R-3c space group. The structure is three-dimensional. Mn3+ is bonded to six equivalent S2- atoms to form a mixture of face, edge, and corner-sharing MnS6 octahedra. The corner-sharing octahedra tilt angles range from 47–54°. There are three shorter (2.29 Å) and three longer (2.35 Å) Mn–S bond lengths. S2- is bonded to four equivalent Mn3+ atoms to form a mixture of distorted edge and corner-sharing SMn4 trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mn3S by Materials Project

Mn3S is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Mn is bonded in a distorted square co-planar geometry to four equivalent S atoms. All Mn–S bond lengths are 2.53 Å. S is bonded to twelve equivalent Mn atoms to form a mixture of face and corner-sharing SMn12 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnS2 by Materials Project

MnS2 crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Mn4+ is bonded to four equivalent S2- atoms to form corner-sharing MnS4 tetrahedra. All Mn–S bond lengths are 2.10 Å. S2- is bonded in a bent 120 degrees geometry to two equivalent Mn4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnS2 by Materials Project

MnS2 is Marcasite structured and crystallizes in the orthorhombic Pnnm space group. The structure is three-dimensional. Mn4+ is bonded to six equivalent S2- atoms to form a mixture of edge and corner-sharing MnS6 octahedra. The corner-sharing octahedral tilt angles are 57°. There are two shorter (2.25 Å) and four longer (2.28 Å) Mn–S bond lengths. S2- is bonded in a 3-coordinate geometry to three equivalent Mn4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnS2 by Materials Project

MnS2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Mn4+ is bonded to five S2- atoms to form a mixture of distorted edge and corner-sharing MnS5 trigonal bipyramids. There are a spread of Mn–S bond distances ranging from 2.16–2.43 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a water-like geometry to two equivalent Mn4+ atoms. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three equivalent Mn4+ atoms.

36 MATERIALS SCIENCE↗