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NASA NTRS2019

Emission-Line Metallicities from the Faint Infrared Grism Survey and VLT/MUSE

We derive direct-measurement gas-phase metallicities of 7.4 < 12 + log(O/H) < 8.4 for 14 low-mass emission- line galaxies at 0.3 < z < 0.8 identiﬁed in the Faint Infrared Grism Survey. We use deep slitless G102 grism spectroscopy of the Hubble Ultra Deep Field, dispersing light from all objects in the ﬁeld at wavelengths between 0.85 and 1.15 μm. We run an automatic search routine on these spectra to robustly identify 71 emission-line sources, using archival data from Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) to measure additional lines and conﬁrm redshifts. We identify 14 objects with 0.3 < z < 0.8 with measurable [O III] λ4363 Å emission lines in matching VLT/MUSE spectra. For these galaxies, we derive direct electron-temperature gas-phase metallicities with a range of 7.4 < 12 + log(O/H) < 8.4. With matching stellar masses in the range of 10(exp 7.9) Solar Mass < M(sub *) < 10(exp 10.4) Solar Mass, we construct a mass–metallicity (MZ) relation and ﬁnd that the relation is offset to lower metallicities compared to metallicities derived from alternative methods (e.g., R(sub 23), O3N2, N2O2) and continuum selected samples. Using star formation rates derived from the Hα emission line, we calculate our galaxies’ position on the Fundamental Metallicity Relation, where we also ﬁnd an offset toward lower metallicities. This demonstrates that this emission-line-selected sample probes objects of low stellar masses but even lower metallicities than many comparable surveys. We detect a trend suggesting galaxies with higher Speciﬁc Star Formation (SSFR) are more likely to have lower metallicity. This could be due to cold accretion of metal-poor gas that drives star formation, or could be because outﬂows of metal-rich stellar winds and SNe ejecta are more common in galaxies with higher SSFR.

Pharo, John↗

NASA NTRS2019

Analytical Techniques for Assessing Gateway and Other Spacecraft Antenna Line-of-Sight

NASA’s Artemis program is committed to landing the next man and the first woman on the Moon by 2024. A critical piece of infrastructure for the mission, the Gateway will inaugurate a sustainable crewed presence beyond low-Earth orbit in cis-lunar space and serve as a staging point for a lunar landing system. The Near Rectilinear Halo Orbit of the Gateway offers numerous operational benefits in terms of its Earth access via the Orion Multipurpose Crew Vehicle, the degree of lunar visibility and surface access it provides, and favorable conditions for station-keeping. To minimize burns during station-keeping and conserve propellant, the Gateway will continually align itself to a solar pressure equilibrium attitude with the Sun; this is convenient for solar array orientation and power generation, but causes difficulties in terms of communication line-of-sight with the Earth, Moon, and visiting vehicles, which appear to be continually rotating about the Gateway’s local frame. A fixed antenna on the Gateway is continually subject to a moving target and can find itself obstructed by the Gateway’s own geometry frequently if not placed carefully. To understand the performance of either Earth-pointing or Moon-pointing antenna placements for a given Gateway geometry, a transient solar system simulation of the Gateway is used to step through orbital ephemeris data and determine the periods in which line-of-sight to a chosen target is achieved and lost. Antenna placements can be tested in the simulation and optimized to increase the average line-of-sight exposure to the target, while also minimizing the maximum duration cut-out in line-of-sight communication experienced; long durations without a successful communication link could pose threats to operations, safety, and mission success. It may be necessary to deviate from the Gateway’s solar pressure equilibrium attitude for short periods of time in order to continue a successful line-of-sight link to a chosen target. Communication coverage spheres can offer insight into what these necessary attitude adjustments may be and are generated by using a 3D mesh of the Gateway and an implementation of the Möller-Trumbore intersection algorithm. This paper outlines the analytical techniques used to perform such antenna placements on the Gateway, offering examples of how line-of-sight strength can be enhanced with an understanding of the Gateway geometry and attitude constraints. These techniques have had direct impact on the writing of communication requirements for NASA and international partner-owned Gateway elements.

Kennedy, William J.↗

NASA NTRS2019

Analytical Techniques for Assessing Gateway and Other Spacecraft Antenna Line-of-Sight

Kennedy, William J.↗

NASA NTRSDate not supplied

2020 International Astronautical Congress Conference Presentation - ANALYTICAL TECHNIQUES FOR ASSESSING GATEWAY AND OTHER SPACECRAFT ANTENNA LINE-OF-SIGHT FOR THE ARTEMIS PROGRAM

NASA’s Artemis program is committed to landing the next man and the first woman on the Moon by 2024. The Gateway, a critical piece of infrastructure for the long-term Artemis mission profiles, will inaugurate a sustainable crewed presence beyond low-Earth orbit in cis-lunar space and serve as a staging point for a lunar landing system. The Near Rectilinear Halo Orbit of the Gateway offers numerous operational benefits in terms of its Earth access via the Orion Multipurpose Crew Vehicle, its degree of Earth and lunar visibility, the versatile surface access it provides, and favorable conditions for station-keeping. To minimize burns during station-keeping and conserve propellant, the Gateway will continually align itself to a solar pressure equilibrium attitude with the Sun; this is convenient for solar array orientation and power generation, but causes difficulties in terms of communication line-of-sight with the Earth, Moon, and visiting vehicles, which appear to be continually rotating about the Gateway’s local frame. A fixed antenna on the Gateway is continually subject to a moving target and can find itself obstructed by the Gateway’s own geometry frequently if not placed carefully. To understand the performance of either Earth-pointing or Moon-pointing antenna placements for a given Gateway geometry, a transient solar system simulation of the Gateway is used to step through orbital ephemeris data and determine the periods in which line-of-sight to a chosen target is achieved and lost. Antenna placements can be tested in the simulation and optimized to increase the average line-of-sight exposure to the target, while also minimizing the maximum duration drop-out in line-of-sight communication experienced; long durations without a successful communication link could pose threats to operations, safety, and mission success. It may be necessary to deviate from the Gateway’s solar pressure equilibrium attitude for short periods of time in order to continue a successful line-of-sight link to a chosen target. Communication coverage spheres can offer insight into what these necessary attitude adjustments may be and are generated by using a 3D mesh of the Gateway and an implementation of the Möller-Trumbore intersection algorithm. This paper outlines the analytical techniques used to perform such antenna placements on the Gateway, offering examples of how line-of-sight strength can be enhanced with an understanding of the Gateway geometry and attitude constraints. These techniques have had direct impact on the writing of communication requirements for NASA and international partner-owned Gateway elements.

Gateway↗

NASA NTRS2019

An X-Ray Spectroscopic Search For Dark Matter And Unidentified Line Signatures In The Perseus Cluster With Hitomi

The reported detection of a 3.5 keV emission signal in the Perseus cluster core by Bulbulet al. (2014, ApJ, 789, 13) was ruled out at high confidence in analysis conducted by Aharonian et al. (2017, ApJ, 837, L15) of X-ray spectra at 5 eV energy resolution obtained with the Hitomi observatory Soft X-ray Spectrometer (SXS). Using the same data, we search the full 2–12 keV SXS energy band for previously unidentified emission and absorption features. No significant unidentified line emission or absorption is found. Line flux upper limits (1σper resolution element) vary with photon energy and assumed intrinsic width, decreasing from∼100 at 2 keV to<10 photons cm−2s−1sr−1over most of the 5–10 keV energy range for a Gaussian line with Doppler broadening of 640 kms−1. Limits for narrower and broader lines have a similar energy dependence and are systematically smaller and larger, respectively. These line flux limits are used to constrain the decay rate of hypothetical dark matter candidates. For the sterile neutrino decay rate, we place new constraints over the mass range of 4–24 keV with mass resolution better than any previous X-ray analysis. Additionally, the accuracy of relevant thermal spectral models and atomic data are evaluated. The Perseus cluster spectra may be described by a composite of multi-temperature thermal and active galactic nuclei (AGN) power-law continua. Superposed on these, a few line emission signals possibly originating from unmodeled atomic processes (including SiXIV and FeXXV)are marginally detected and tabulated. Comparisons with previous X-ray upper limits and future prospects for dark matter searches using high-energy resolution spectroscopy are discussed.

Takayuki Tamura↗

NASA NTRSDate not supplied

Performance and Accuracy Assessment of Line Marching Algorithm Computations Utilizing GPUs Within a Predictive GNSS Quality Service

This paper presents a detailed analysis of the accuracy and performance of line marching algorithms executing on a GPU. In the context of an accurate Global Navigation Satellite System(GNSS) quality of service simulation, horizon sky-plots are a useful tool to determine satellite visibility in the presence of obstructions from objects, such as buildings or dense foliage. In order to accurately model satellite visibility at a point of interest on a map, a horizon plot can identify the viewing angles at which objects are blocking the sky. This computation requires traversing a line starting at the point of interest on a 2D altitude map, moving outward for every azimuth angle. To explore the performance of this computation, we propose a new dynamic stopping condition for the traversal of the line, benefiting from objects close to the point of interest. We compare the accuracy of common line marching algorithms, and consider their parallel performance when developed in CUDA. We find that our proposed stopping condition for line marching provides a significant improvement in performance in urban canyon sky-plots, as compared to previous work. Additionally, these results show that simpler algorithms, such as the digital differential analyzer line algorithm, are better suited for GPUs than more sophisticated schemes such as Bresenham’s algorithm, specifically in the context of sky-plothorizon computations. The trade-off between accuracy and performance is analyzed and providing guidance that depends on the targeted goal of the GNSS application.

GNSS↗

NASA NTRS2021

What it Takes to Compute Highly Accurate Rovibrational Line Lists for Use in Astrochemistry

We review the Best Theory + Reliable High-resolution Experiment (BTRHE) strategy for obtaining highly accurate molecular rovibrational line lists with InfraRed (IR) intensities. The need for highly accurate molecular rovibrational line lists is two-fold: a) assignment of the many rovibrational lines for common stable molecules especially those that exhibit a large amplitude motion, such as NH3, or have a high density of states such as SO2; and b) characterization of the atmospheres of exoplanets which will be one of the main areas of research in astronomy in the coming decades. The first motivation arises due to the need to eliminate lines due to common molecules in an astronomical observation in order to identify lines from new molecules, while the second motivation arises due to the need to obtain accurate molecular opacities in order to characterize the atmosphere of an exoplanet. The BTRHE strategy first consists of using high quality ab initio quantum chemical methods to obtain a global potential energy surface (PES) and dipole moment surface (DMS) that contains the proper physics. The global PES is then refined using a subset of the reliable high-resolution experimental data. The refined PES then gives energy level predictions to an accuracy similar to the reproduction accuracy of the experimental data used in the refinement step in the interpolation region (i.e., within the range of the experimental data used in the refinement step). The accuracy of the energy levels will slowly degrade as they are extrapolated to spectral regions beyond the high-resolution experimental data used in the refinement step. However, because the degradation is slow, the predicted energy levels can be used to assign new high-resolution experiments, and the data from these can then be used in a subsequent refinement step. In this way, the global PES eventually can yield highly accurate energy levels for all desired spectral regions including to very high energies and high J values. We show that IR intensities computed with the BTRHE rovibrational wavefunctions and the DMS can be very accurate provided one has minimized the fitting error of the DMS and tested the completeness of the DMS. Some examples of our work on NH3, CO2, and SO2 are given to highlight the usefulness of the BTRHE strategy and to provide ideas on how to further improve its predictive power in the future. In particular, it is shown how successive refinement steps, once new high-resolution data is available, can lead to PESs that yield highly accurate transition energies to larger spectral regions. The importance of including non-adiabatic corrections to reduce the J-dependence of errors for H-containing molecules is shown with work on NH3. Another very important aspect of the BTRHE approach is the consistency across isotopologues, which allows for highly accurate line lists for any isotopologue once one is obtained for the main isotopologue (which has more high-resolution data available for refinement).

Xinchuan Huang↗

NASA NTRS2022

Helium-Like X-Ray Line Complexes Show That the Hottest Plasma on the O Supergiant ζPuppis Is in Its Wind

We present an analysis of Chandra grating spectra of k ey helium-lik e line comple x es to put constraints on the location with respect to the photosphere of the hottest ( T 6 ×10 6 K) plasma in the wind of the O supergiant ζPup and to explore changes in the 18 yr between two sets of observations of this star. We fit two models –one empirical and one wind-shock-based –to the S XV , Si XIII , and Mg XI line comple x es and show that an origin in the wind flow, abo v e r ≈1.5 R ∗, is strongly fa v oured o v er an origin less than 0.3 R ∗abo v e the photosphere ( r 1.3 R ∗), especially in the more recent, very long-exposure data set. There is a modest increase in the line and continuum fluxes, line widths, wind absorption signatures, and of the hot plasma’s distance from the photosphere in the 18 yr since the first Chandra grating observation of ζPup. Both modes of modelling include the effects of dielectronic recombination satellite emission line blending on the helium-like comple x es –the first time this has been accounted for in the analysis of He-like line ratios in O stars.

Maurice A Leutenegger↗

NASA NTRS2022

Testing Lyα Emission-line Reconstruction Routines at Multiple Velocities in One System

The 1215.67 Å H ו Lyα emission line dominates the ultraviolet flux of low-mass stars, including the majority of known exoplanet hosts. Unfortunately, strong attenuation by the interstellar medium (ISM) obscures the line core in most stars, requiring the intrinsic Lyα flux to be reconstructed based on fits to the line wings. We present a test of the widely used Lyα emission-line reconstruction code ւʏᴀᴘʏ using phase-resolved, medium-resolution STIS G140M observations of the close white dwarf–M dwarf binary EG UMa. The Doppler shifts induced by the binary orbital motion move the Lyα emission line in and out of the region of strong ISM attenuation. Reconstructions of each spectrum should produce the same Lyα profile regardless of phase, under the well-justified assumption that there is no intrinsic line variability between observations. Instead, we find that the reconstructions underestimate the Lyα flux by almost a factor of 2 for the lowest velocity, most attenuated spectrum, due to a degeneracy between the intrinsic Lyα and ISM profiles. Our results imply that many stellar Lyα fluxes derived from G140M spectra reported in the literature may be underestimated, with potential consequences for, for example, estimates of extreme-ultraviolet stellar spectra and ultraviolet inputs into simulations of exoplanet atmospheres.

M dwarf stars↗

NASA NTRSDate not supplied

Computer Controlled High Vacuum Gas Purification and Analysis Line

Light stable isotope work requires the handling of gasses such a way that does not alter isotopic composition. To do this, there are a large number of analytical and experimental procedures which involve the use of a vacuum line, numerous “egg timers” and a human hand on a valve. Unfortunately, the human hand is inconsistent and inadvertent small, and commonly large, differences in timing can have a measurable effect on outcomes. We have constructed a computer controlled high-vacuum line to be used as an expandable platform for future experimental and analytical procedures. The vacuum line consists of an electropolished 316 stainless steel system of cryogenic u-traps partitioned by pneumatic valves. The code to operate the line has been developed using the LabView platform and will allow for automated timing, consistent valve opening speed and unattended operation of long analytical procedures. The aim of this project is to address a need in the light stable isotope laboratory for a general-purpose vacuum line for handling and manipulation of gasses. When combined with existing instrumentation it allows for a significant expansion of current analytical capabilities. The system allows for better handling of standards, gas conversion techniques and gas sample collection for interlaboratory comparisons. The basic structure of the line, automation hardware and software were chosen and designed to provide a base for future expansion of the system to incorporate new automated analytical techniques as laboratory instrumentation and analytical needs expand.

High vacuum↗

NASA NTRSDate not supplied

Statistically Consistent Dispersions of Line Loads to Uncertain Integrated Forces and Moments

This work presents a method to generate line loads that are consistent with integrated force and moment constraints, while also following the statistical distribution underlying known line load data. The motivation for this method is to address a particular problem that can arise during the pre-flight analysis of an ascent vehicle. That problem is constructing separate databases, for line loads and integrated aerodynamic coefficients, that contain different data and thus different amounts of quantified uncertainty. A dispersed line load method is described and applied to a data set generated by 29 computational fluid dynamics simulations at various angles of attack and sideslip. The statistical similarity of the generated line loads to the known data is confirmed by using the Maximum Mean Discrepancy 2-sample test. The promising results from this novel method are compared against results from applying an existing line load adjustment procedure to the same data set. Finally, potential future avenues of research are briefly discussed.

Aaron C. Burkhead↗

DOE OSTI2024

Residual Dose Rates Analyses from Vent Lines Shield Block on the Target Cart at Spallation Neutron Source

The target carriage supports the mercury target vessel in the Spallation Neutron Source (SNS) in a cantilevered fashion and supplies the liquid mercury flowing to and from the target vessel. The target carriage is designed to move the target vessel into its target monolith position to receive the proton beam and then remove it horizontally back into an adjacent service cell, where the target vessel can be exchanged about 2-3 times per calendar year. At the time of the performed studies, the SNS mercury target can accept a proton beam at 1 GeV energy and 1.4 MW power; however, it will be upgraded to receive 1.3 GeV energy at 2 MW by the end of 2024 year [1]. The cart is practically a shield block on wheels to minimize fluxes and dose rates in the service cell downstream of the carriage. There are vent lines located inside a passage on top of the target carriage, and they are covered by a stepping-up steel shield block (vent lines shield block). Vent lines are permanently attached to the shield block. New vent lines with a different design are going to be installed. These lines are shielded by the new steel block to which the vent lines are attached. The estimate of the residual dose rates from the block after it is extracted from the target carriage is performed to estimate the radiation fields and to decide on the type of storage container to be used.

Popova, Irina I↗

DOE OSTI2025

Impact assessment of geomagnetic induced current neutral blocking devices with power electronics sources on distance relay for 230 kV transmission lines

Electrical grids increased the integration of power electronics sources onto transmission lines. In addition, recent reports show a significant rise in geomagnetic storms occurring in 2024. These geomagnetic storms can affect transmission lines by inducing electrical currents within them, potentially causing power outages due to overloaded power transformers. Geomagnetic induced current neutral blocking devices (GIC-NBDs) are capacitors on the ground of wye power transformers, to avoid damage caused by geomagnetic storms. The integration of distance relays and transmission lines with power electronics sources and GIC-NBDs needs to be studied to observe if GIC-NBDs and power electronics sources could adversely affect operation of the electrical grid. In this analysis, the effect of 2 MW power electronics sources and GIC-NBDs on distance relays is assessed for different 230 kV transmission line lengths in radial and nonradial power systems. The simulations measured the apparent impedances, with different electrical faults. Results for a typical 2,650 μF GIC-NBD application were presented on impedance plots, and the distance relay model operations were assessed. In conclusion, the tests for radial and nonradial power systems showed the behavior of the distance elements and source impedance ratios, assessing the effect of power electronics sources and GIC-NBDs on 230 kV transmission lines.

Distance relays↗

DOE OSTI2025

Scalable edge clustering of dynamic graphs via weighted line graphs

Timestamped relational datasets consisting of records (or connections) between pairs of entities are ubiquitous in network science. For applications like peer-to-peer communication, email, various social network interactions, and computer network security, it is useful to organize these records into groups based on how and when they are occurring. Weighted line graphs offer a natural way to model how records are related in such datasets but for large real-world graph topologies, building and utilizing the line graph is prohibitively expensive. Here, we present the framework to cluster the edges of a dynamic graph via the associated line graph that contains two major contributions. The first is a method to work with the line graph implicitly and the second is a distributed scale implementation of an agglomerative hierarchical graph clustering algorithm. We outline a novel hierarchical dynamic graph edge clustering approach that efficiently breaks massive relational datasets into small sets of edges containing events at various timescales. This is in stark contrast to traditional graph clustering algorithms that prioritize highly connected (clique-like) community structures. Our approach relies on constructing a sufficient subgraph of a weighted line graph and applying a hierarchical agglomerative clustering. This approach is related to scalable techniques from spatial clustering, nonlinear-dimension reduction, topological data analysis, and draws particular inspiration from HDBSCAN. As an edge clustering, this method yields an overlapping node clustering. Our algorithm is parallelizable and we demonstrate efficient clustering of a billion-scale, real-world dynamic graph into small edge sets that correlate in topology and time. The entire clustering process for a graph with tens of billions of edges takes just a few minutes of run time on 256 nodes of a distributed compute environment. We argue how the output of the edge clustering is useful for a multitude of data visualization and powerful machine learning tasks, both involving the original massive dynamic graph data and metadata associated with the nodes and edges. Finally, we describe how this approach can be extended to dynamic hypergraphs and dynamic graphs/hypergraphs with unstructured data living on vertices and edges.

Data Analysis↗

DOE OSTI2024

Electronic structure in a rare-earth based nodal-line semimetal candidate PrSbTe

Nodal-line semimetals feature topologically protected band crossings between the bulk valence and conduction bands that extend along a finite dimension in the form of a line or a loop. While ZrSiS and similar materials have attracted extensive research as hosts for the nodal-line semimetallic phase, an alternative avenue has emerged in the form of isostructural rare-earth (RE)-based RESbTe materials. Such systems possess intriguing potentialities for harboring elements of magnetic ordering and electronic correlations owing to the presence of 4f electrons intrinsic to the RE elements. In this study, we have carried out angle-resolved photoemission spectroscopy (ARPES) and thermodynamic measurements in conjunction with first-principles computations on PrSbTe to elucidate its electronic structure and topological characteristics. Magnetic and thermal characterizations indicate the presence of well-localized 4f states with the absence of any discernible phase transition down to 2 K. The ARPES results reveal the presence of gapless Dirac crossings that correspond to a nodal-line along the X-R direction in the three-dimensional Brillouin zone. Furthermore, Dirac crossing that makes up the nodal line, which forms a diamond-shaped nodal plane centered at the center of the Brillouin zone, is also identified within the experimental resolution. In conclusion, this study on the electronic structure of PrSbTe contributes to the understanding of the pivotal role played by spin-orbit coupling in the context of the RESbTe family of materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS2014

Simultaneous NuSTAR and XMM-Newton 0.5-80 KeV Spectroscopy of the Narrow-Line Seyfert 1 Galaxy SWIFT J2127.4+5654

We present a broad-band spectral analysis of the joint XMM-Newton and Nuclear Spectroscopic Telescope Array observational campaign of the narrow-line Seyfert 1 SWIFT J2127.4+5654, consisting of 300 kiloseconds performed during three XMM-Newton orbits. We detect a relativistic broadened iron K-alpha line originating from the innermost regions of the accretion disc surrounding the central black hole, from which we infer an intermediate spin of a = 0.58 (sup +0.11) (sub −0.17). The intrinsic spectrum is steep (gamma = 2.08 plus or minus 0.01) as commonly found in narrow-line Seyfert 1 galaxies, while the cutoff energy (E (sub c) = 108 (sup +11) (sub −10) kiloelectronvolts) falls within the range observed in broad-line Seyfert 1 galaxies. We measure a low-frequency lag that increases steadily with energy, while at high frequencies, there is a clear lag following the shape of the broad Fe K emission line. Interestingly, the observed Fe K lag in SWIFT J2127.4+5654 is not as broad as in other sources that have maximally spinning black holes. The lag amplitude suggests a continuum-to-reprocessor distance of about 10-20 radius of gyration. These timing results independently support an intermediate black hole spin and a compact corona.

Nuclear Spectroscopic Telescope Array↗

NASA NTRS2017

Unreported Emission Lines of Rb, Ce, La, Sr, Y, Zr, Pb and Se Detected Using Laser-Induced Breakdown Spectroscopy

Information on emission lines for major and minor elements is readily available from the National Institute of Standards and Technology (NIST) as part of the Atomic Spectra Database. However, tabulated emission lines are scarce for some minor elements and the wavelength ranges presented on the NIST database are limited to those included in existing studies. Previous work concerning minor element calibration curves measured using laser-induced break-down spectroscopy found evidence of Zn emission lines that were not documented on the NIST database. In this study, rock powders were doped with Rb, Ce, La, Sr, Y, Zr, Pb and Se in concentrations ranging from 10 percent to 10 parts per million. The difference between normalized spectra collected on samples containing 10 percent dopant and those containing only 10 parts per million were used to identify all emission lines that can be detected using LIBS (Laser-Induced Breakdown Spectroscopy) in a ChemCam-like configuration at the Mount Holyoke College LIBS facility. These emission spectra provide evidence of many previously undocumented emission lines for the elements measured here.

LIBS↗

NASA NTRSDate not supplied

High Pressure Vent Line Mishap: Investigation Summary

During testing on the E-1 Test Stand, the High Pressure (HP) Liquid Hydrogen (LH) vent line was displaced off its supports, damaging the expansion joints (EJ), piping, and pipe supports of the line. The damage to the vent line is believed to have occurred during Cell 3 testing on Thursday, September 21, during the first test of the day. The fuel systems being used for Cell 3 testing are connected to the LP and HP LH Vent systems and are being used in Liquid Natural Gas (LNG) service. The Cell 3 interface bleed valve that discharges to the HP LH Vent system was inadvertently left at 100% open during the chill-in process for longer than the typical amount of time. Since this valve is usually at a lower set point or intermittently closed during the chill-in process, more than the typical amount of LNG flowed into the vent line as pre-test procedures continued as normal. The open bleed valve was noticed before test preparations were completed and prior to refilling of the HP LH Tank before test. The test sequence was started, run, and shutdown normally. Video of the flare stack showed an atypical discharge of liquid at the flare stack exit. Pressure downstream of the Cell 3 interface bleed valve (a valve connected to the southernmost part of the vent system) spiked to a higher-than-normal level. No evidence of damage was captured at the time of the event. The system was used in a typical fashion after the event and for 4 subsequent tests on Thursday and Friday, before the damage was observed. A drive-by inspection of the flare stack was performed on Friday (September 22nd) morning before sunrise and before test activities began, but no damage of the vent line was observed at that time. No abnormal system behavior was observed during testing on Friday. The damage was discovered and reported to NASA Test Operations on Monday, initiating the Incident Response Team. The Mishap appointment letter was issued September 27th to formally initiate the Mishap Investigation.

LNG↗