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DOE OSTI2024

Power Module Precursors and Prognostics

This project focuses on finding and utilizing electrical properties (precursors) of power electronic devices and modules whose changes have strong correlations with different modes and levels of degradations in order to realize online and lightweight state of health evaluation and fault diagnosis. Results from this project will contribute to higher safety, reliability, and power density of power electronic components. The approaches mainly include reviewing academic literature and industry practices for state of the art precursor identification and extraction, accelerated life cycles (ALC) of various power modules to create different degradations in-house, and developing techniques for gate-driver-integratable precursor detection circuit. In FY24, the results includes two sets of definitively detected aging precursors (on-state resistance and gate threshold voltage) for two sets of power modules respectively, controlled accelerated lifetime cycling of multiple silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) modules, and the development and validation of a gate voltage detection system.

ADVANCED PROPULSION SYSTEMS↗

NASA NTRS2010

Performance Characterization of High Energy Commercial Lithium-ion Cells

The NASA Glenn Research Center Electrochemistry Branch performed characterization of commercial lithium-ion cells to determine the cells' performance against Exploration Technology Development Program (ETDP) Key Performance Parameters (KPP). The goals of the ETDP Energy Storage Project require significant improvements in the specific energy of lithium-ion technology over the state-of-the-art. This work supports the high energy cell development for the Constellation customer Lunar Surface Systems (LSS). In support of these goals, testing was initiated in September 2009 with high energy cylindrical cells obtained from Panasonic and E-One Moli. Both manufacturers indicated the capability of their cells to deliver specific energy of at least 180 Wh/kg or higher. Testing is being performed at the NASA Glenn Research Center to evaluate the performance of these cells under temperature, rate, and cycling conditions relevant to the ETDP goals for high energy cells. The cell-level specific energy goal for high energy technology is 180 Wh/kg at a C/10 rate and 0 C. The threshold value is 165 Wh/kg. The goal is to operate for at least 2000 cycles at 100 percent DOD with greater than 80 percent capacity retention. The Panasonic NCR18650 cells were able to deliver nearly 200 Wh/kg at the aforementioned conditions. The E-One Moli ICR18650J cells also met the specific energy goal by delivering 183 Wh/kg. Though both cells met the goal for specific energy, this testing was only one portion of the testing required to determine the suitability of commercial cells for the ETDP. The cells must also meet goals for cycle life and safety. The results of this characterization are summarized in this report.

Schneidegger, Brianne T.↗

NASA NTRS1987

Coronal mass ejections: The long-term variation of their occurrence rate and the solar wind mass flux

Solar Coronal Mass Ejections (CMEs) from the Sun are an important aspect of coronal physics, and a potentially important contributor to the solar wind mass flux. However, despite significant progress in studies of CMEs since their discovery in the early 70's, questions remain about their effects on the interplanetary medium. A study is done of the long-term variations of the occurrence rates of CMEs, of activity tracers related to CMEs, and of the solar wind particle flux. CMEs are most directly detected by scattered electron radiation in white light. To estimate their long-term occurrence frequency and their contributions to the in-ecliptic solar wind mass flux, observed CME rates must be corrected for instrumental duty cycles, detection efficiency out of the plane of the sky, mass detection thresholds, and geometrical considerations. These corrections are evaluated using data on solar CMEs from the spaceborne Skylab, SMM, and SOLWIND coronagraphs and on interplanetary plasma clouds from the HELIOS white light photometers. Variations in the CME rate and the contribution of CMEs to the solar wind mass flux are traced over nearly a complete solar activity cycle.

Webb, David F.↗

DOE OSTI2025

Assessing the Impact of Large Removable Beryllium Reflector Experiments on HFIR Performance and Safety Metrics

This study investigated the effect of various removable beryllium (RB) experiment configurations on High Flux Isotope Reactor (HFIR) metrics to address increasing interest in these facilities for materials and fuels irradiation research. The RB reflector contains eight large and four small irradiation experiment facilities that offer excellent neutron flux conditions to perform fission and fusion reactor materials and fuels irradiation research. This work aims to outline acceptable RB configurations based on safety, performance, and programmatic metrics. This study assessed experiment effects on reactivity, cycle length, fission rate density distributions, and neutron flux distributions using the Shift, HFIRCON, and SCALE ORIGEN codes. Initial evaluations focused on generic experiment materials including aluminum plugs, stainless steel plugs, molybdenum plugs, and aluminum plugs with gadolinium shields. Subsequent analyses of MiniFuel experiments were performed to evaluate a heterogenous experiment, consisting of a more complex geometry and bearing several materials, and to test the correlations developed with the generic materials on a real experiment. Furthermore, the effects of neutron poison concentrations in the standard beryllium plugs were evaluated. When assuming a reference RB configuration with eight large fresh beryllium plugs, perturbed configurations with three aluminum plugs, one stainless steel plug, one molybdenum plug, one gadolinium-shielded aluminum plug, and one MiniFuel experiment resulted in a cycle length reduction of less than 1.3 days, the current threshold before requiring additional approvals. Configurations with five aluminum plugs, one stainless steel plug, one molybdenum plug, one gadolinium-shielded aluminum plug, and two MiniFuel experiments meet the 1.3 day limit if irradiated beryllium plugs are considered. Fuel element fission rate density distributions remained within safety limits, with maximum local increases under 9%. Neutron flux calculations revealed large thermal flux depressions inside and around the perturbed RB facilities, while epithermal and fast neutron fluxes increased because of reduced neutron moderation by the perturbed materials. These findings provide valuable guidance for optimizing RB configurations to balance safety and performance at HFIR.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

NASA NTRS1960

Flight Investigation of an Automatic Pitchup Control

A flight investigation of an automatic pitchup control has been conducted by the National Aeronautics and Space Administration at the Langley Research Center. The pitching-moment characteristics of a transonic fighter airplane which was subject to pitchup were altered by driving the stabilizer in accordance with a signal that was a function of a combination of the measured angle of attack and the pitching velocity. An angle-of-attack threshold control was used to preset the angle of attack at which the automatic pitchup-control system would begin to drive the stabilizer. No threshold control as such existed for the pitching-velocity signal. A summing linkage in series with the pilot's longitudinal control allowed the automatic pitchup-control system to drive the stabilizer 13.5 percent of the total stabilizer travel independently of the pilot's control. Tests were made at an altitude of 35,000 feet over a Mach number range of 0.80 to 0.90. Various gearings between the control and the sensing devices were investigated. The automatic system was capable of extending the region of positive stability for the test airplane to angles of attack above the basic-airplane pitchup threshold angle of attack. In most cases a limit-cycle oscillation about the airplane pitch axis occurred.

Hurt, George J., Jr.↗

NASA NTRS1987

Interlaminar shear fracture toughness and fatigue thresholds for composite materials

Static and cyclic end notched flexure tests were conducted on a graphite epoxy, a glass epoxy, and graphite thermoplastic to determine their interlaminar shear fracture toughness and fatigue thresholds for delamination in terms of limiting values of the mode II strain energy release rate, G-II, for delamination growth. The influence of precracking and data reduction schemes are discussed. Finite element analysis indicated that the beam theory calculation for G-II with the transverse shear contribution included was reasonably accurate over the entire range of crack lengths. Cyclic loading significantly reduced the critical G-II for delamination. A threshold value of the maximum cyclic G-II below which no delamination occurred after one million cycles was identified for each material. Also, residual static toughness tests were conducted on glass epoxy specimens that had undergone one million cycles without delamination. A linear mixed-mode delamination criteria was used to characterize the static toughness of several composite materials; however, a total G threshold criterion appears to characterize the fatigue delamination durability of composite materials with a wide range of static toughness.

Obrien, T. Kevin↗

NASA NTRS1989

Interlaminar shear fracture toughness and fatigue thresholds for composite materials

O'Brien, T. Kevin↗

NASA NTRS1997

T wave alternans during exercise and atrial pacing in humans

INTRODUCTION: Evidence is accumulating that microvolt T wave alternans (TWA) is a marker of increased risk for ventricular tachyarrhythmias. Initially, atrial pacing was used to elevate heart rate and elicit TWA. More recently, a noninvasive approach has been developed that elevates heart rate using exercise. METHODS AND RESULTS: In 30 consecutive patients with a history of ventricular tachyarrhythmias, the spectral method was used to detect TWA during both atrial pacing and submaximal exercise testing. The concordance rate for the presence or absence of TWA using the two measurement methods was 84%. There was a patient-specific heart rate threshold for the detection of TWA that averaged 100 +/- 14 beats/min during exercise compared with 97 +/- 9 beats/min during right atrial pacing (P = NS). Beyond this threshold, there was a significant and comparable increase in level of TWA with decreasing pacing cycle length and increasing exercise heart rates. CONCLUSIONS: The present study is the first to demonstrate that microvolt TWA can be assessed reliably and noninvasively during exercise stress. There is a patient-specific heart rate threshold beyond which TWA continues to increase with increasing heart rates. Heart rate thresholds for the onset of TWA measured during atrial pacing and exercise stress were comparable, indicating that heart rate alone appears to be the main factor of determining the onset of TWA during submaximal exercise stress.

NASA Discipline Regulatory Physiology↗

NASA NTRS1991

Characterizing mode I fatigue delamination of composite materials

Two techniques for characterizing fatigue delamination in double cantilever beams, the delamination growth onset method and the delamination growth and arrest method, are evaluated. Two glass/epoxy systems, S2/SP250 and S2/CE9000, were tested at R = 0.1 and R = 0.5. The values of the strain energy release rate threshold Delta G(Ith) for no onset of delamination growth until one million cycles were compared with the values of Delta G(I) at delamination arrest. The values at arrest were consistently higher because fiber bridging occurred in the tests. Normalizing Delta G(I) by the mode I value of interlaminar fracture toughness G(Ir) at the corresponding delta A gave values of Delta G(I)/G(Ir) at delamination arrest which were closer to the threshold values obtained from the Delta G-N technique. However, this normalization did not represent a generic materials characterization technique and did not allow for delamination onset predictions.

Martin, Roderick H.↗

NASA NTRS2013

Detection Thresholds of Falling Snow From Satellite-Borne Active and Passive Sensors

There is an increased interest in detecting and estimating the amount of falling snow reaching the Earths surface in order to fully capture the global atmospheric water cycle. An initial step toward global spaceborne falling snow algorithms for current and future missions includes determining the thresholds of detection for various active and passive sensor channel configurations and falling snow events over land surfaces and lakes. In this paper, cloud resolving model simulations of lake effect and synoptic snow events were used to determine the minimum amount of snow (threshold) that could be detected by the following instruments: the W-band radar of CloudSat, Global Precipitation Measurement (GPM) Dual-Frequency Precipitation Radar (DPR)Ku- and Ka-bands, and the GPM Microwave Imager. Eleven different nonspherical snowflake shapes were used in the analysis. Notable results include the following: 1) The W-band radar has detection thresholds more than an order of magnitude lower than the future GPM radars; 2) the cloud structure macrophysics influences the thresholds of detection for passive channels (e.g., snow events with larger ice water paths and thicker clouds are easier to detect); 3) the snowflake microphysics (mainly shape and density)plays a large role in the detection threshold for active and passive instruments; 4) with reasonable assumptions, the passive 166-GHz channel has detection threshold values comparable to those of the GPM DPR Ku- and Ka-band radars with approximately 0.05 g *m(exp -3) detected at the surface, or an approximately 0.5-1.0-mm * h(exp -1) melted snow rate. This paper provides information on the light snowfall events missed by the sensors and not captured in global estimates.

remote sensing↗

NASA NTRS1991

Martian dust threshold measurements: Simulations under heated surface conditions

Diurnal changes in solar radiation on Mars set up a cycle of cooling and heating of the planetary boundary layer, this effect strongly influences the wind field. The stratification of the air layer is stable in early morning since the ground is cooler than the air above it. When the ground is heated and becomes warmer than the air its heat is transferred to the air above it. The heated parcels of air near the surface will, in effect, increase the near surface wind speed or increase the aeolian surface stress the wind has upon the surface when compared to an unheated or cooled surface. This means that for the same wind speed at a fixed height above the surface, ground-level shear stress will be greater for the heated surface than an unheated surface. Thus, it is possible to obtain saltation threshold conditions at lower mean wind speeds when the surface is heated. Even though the mean wind speed is less when the surface is heated, the surface shear stress required to initiate particle movement remains the same in both cases. To investigate this phenomenon, low-density surface dust aeolian threshold measurements have been made in the MARSWIT wind tunnel located at NASA Ames Research Center, Moffett Field, California. The first series of tests examined threshold values of the 100 micron sand material. At 13 mb surface pressure the unheated surface had a threshold friction speed of 2.93 m/s (and approximately corresponded to a velocity of 41.4 m/s at a height of 1 meter) while the heated surface equivalent bulk Richardson number of -0.02, yielded a threshold friction speed of 2.67 m/s (and approximately corresponded to a velocity of 38.0 m/s at a height of 1 meter). This change represents an 8.8 percent decrease in threshold conditions for the heated case. The values of velocities are well within the threshold range as observed by Arvidson et al., 1983. As the surface was heated the threshold decreased. At a value of bulk Richardson number equal to -0.02 the threshold friction speed and threshold wind speed appears to level-off to a constant value. This trend also was observed in the MARSWIT experiments involving the 11 micron sized-silt material.

White, Bruce R.↗

NASA NTRS1983

Thermomechanical loading of multilayered cylindrical geometries in thermal cycling from 300 to 1300 K

The principal of multiple material layering is well known as an effective method of reducing heat transfer; however, thermal gradients can impose significant loads and lead to delamination and subsequent component failure. An analysis is developed and experimental data are discussed for the thermomechanical effects of multilayered materials on a heat sink substrate of cylindrical geometry subject to thermal cycling. The geometry is heated in cross-flow by a high-velocity flame and cooled in crossflow by ambient-temperature air from a critical flow orifice. Each layer of material possesses a threshold beyond which small changes in temperature or mechanical loading greatly influence the life in thermal cycling of the layered materials. Comparisons are made between the thermomechanical loads predicted by various numerical codes for the linear case and by a simplified analytic model.

Hendricks, R. C.↗

NASA NTRS1972

Objective evaluation of cutaneous thermal sensivity

The possibility of obtaining reliable and objective quantitative responses was investigated under conditions where only temperature changes in localized cutaneous areas evoked measurable changes in remote sudomotor activity. Both male and female subjects were studied to evaluate sex difference in thermal sensitivity. The results discussed include: sweat rate responses to contralateral cooling, comparison of sweat rate responses between men and women to contralateral cooling, influence of the menstrual cycle on the sweat rate responses to contralateral cooling, comparison of threshold of sweating responses between men and women, and correlation of latency to threshold for whole body sweating. It is concluded that the quantitative aspects of the reflex response is affected by both the density and activation of receptors as well as the rate of heat loss; men responded 8-10% more frequently than women to thermode cooling, the magnitude of responses being greater for men; and women responded 7-9% more frequently to thermode cooling on day 1 of menstruation, as compared to day 15.

Vanbeaumont, W.↗

NASA NTRS1986

Linear-quadratic stationkeeping for the STS Orbiter

An automatic controller for Space Shuttle Orbiter stationkeeping or formationkeeping is presented. The controller uses a feed-forward loop for precise control at non-equilibrium set points, and a discrete-time linear quadratic regulator for disturbance rejection. Selection of sample time and quadratic cost matrices is done to provide good limit cycling performance in the presence of sensor noise and a control threshold nonlinearity. Large position changes are effected by feed-forward of a minimum fuel or straightline maneuver path. Results show that 20 ft precision can be achieved using current sensors, and that 2 ft precision would be possible with enhanced sensors.

Redding, D. C.↗

NASA NTRS2001

A Radiation-Tolerant, Low-Power Non-Volatile Memory Based on Silicon Nanocrystal Quantum Dots

Nanocrystal nonvolatile floating-gate memories are a good candidate for space applications - initial results suggest they are fast, more reliable and consume less power than conventional floating gate memories. In the nanocrystal based NVM device, charge is not stored on a continuous polysilicon layer (so-called floating gate), but instead on a layer of discrete nanocrystals. Charge injection and storage in dense arrays of silicon nanocrystals in SiO2 is a critical aspect of the performance of potential nanocrystal flash memory structures. The ultimate goal for this class of devices is few- or single-electron storage in a small number of nanocrystal elements. In addition, the nanocrystal layer fabrication technique should be simple, 8-inch wafer compatible and well controlled in program/erase threshold voltage swing was seen during 100,000 program and erase cycles. Additional near-term goals for this project include extensive testing for radiation hardness and the development of artificial layered tunnel barrier heterostructures which have the potential for large speed enhancements for read/write of nanocrystal memory elements, compared with conventional flash devices. Additional information is contained in the original extended abstract.

Bell, L. D.↗

NASA NTRS2017

Large-Scale Traveling Weather Systems in Mars Southern Extratropics

Between late fall and early spring, Mars' middle- and high-latitude atmosphere supports strong mean equator-to-pole temperature contrasts and an accompanying mean westerly polar vortex. Observations from both the MGS Thermal Emission Spectrometer (TES) and the MRO Mars Climate Sounder (MCS) indicate that a mean baroclinicity-barotropicity supports intense, large-scale eastward traveling weather systems (i.e., transient synoptic-period waves). Such extratropical weather disturbances are critical components of the global circulation as they serve as agents in the transport of heat and momentum, and generalized scalar/tracer quantities (e.g., atmospheric dust, water-vapor and ice clouds). The character of such traveling extratropical synoptic disturbances in Mars' southern hemisphere during late winter through early spring is investigated using a moderately high-resolution Mars global climate model (Mars GCM). This Mars GCM imposes interactively-lifted and radiatively-active dust based on a threshold value of the surface stress. The model exhibits a reasonable "dust cycle" (i.e., globally averaged, a dustier atmosphere during southern spring and summer occurs). Compared to the northern-hemisphere counterparts, the southern synoptic-period weather disturbances and accompanying frontal waves have smaller meridional and zonal scales, and are far less intense. Influences of the zonally asymmetric (i.e., east-west varying) topography on southern large-scale weather are investigated, in addition to large-scale up-slope/down-slope flows and the diurnal cycle. A southern storm zone in late winter and early spring presents in the western hemisphere via orographic influences from the Tharsis highlands, and the Argyre and Hellas impact basins. Geographically localized transient-wave activity diagnostics are constructed that illuminate dynamical differences amongst the simulations and these are presented.

Hollingsworth, Jeffery L.↗

NASA NTRS1974

Solar proton fluences for 1977-1983 space missions

The probability with which any given solar proton fluence level will be exceeded during a space mission is computed for mission to be flown during the active phase of the next solar cycle (1977-1983). This probability is a function of fluence level, proton energy threshold, and mission duration. Calculations are based on 1966-1972 data only. In estimating mission fluences, a distinction is made between ordinary and anomalously large events. Probable numbers of each type of event are estimated from Burrell's extension of Poisson statistics. Fluences of all anomalously large events are assumed to have a spectrum given by the August 1972 event, while fluences of the ordinary events are assumed to obey a log normal distribution.

King, J. H.↗

NASA NTRS1985

The cosmic ray interplanetary radial gradient from 1972 - 1985

It is now established that the solar modulation of cosmic rays is produced by turbulent magnetic fields propagated outward by the solar wind. Changes in cosmic ray intensity are not simultaneous throughout the modulation region, thus requiring time dependent theories for the cosmic ray modulation. Fundamental to an overall understanding of this observed time dependent cosmic ray modulation is the behavior of the radial intensity gradient with time and heliocentric distance over the course of a solar modulation cycle. The period from 1977 to 1985 when data are available from the cosmic ray telescopes on Pioneer (P) 10, Voyager (V) 1 and 2, and IMP 8 spacecraft is studied. Additional data from P10 and other IMP satellites for 1972 to 1977 can be used to determine the gradient at the minimum in the solar modulation cycle and as a function of heliocentric distance. All of these telescopes have thresholds for protons and helium nuclei of E 60 MeV/nucleon.

Webber, W. R.↗