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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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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Detection of High-impedance Arcing Faults in Radial Distribution DC Systems

High voltage, low current arcing faults in DC power systems have been researched at the NASA Glenn Research Center in order to develop a method for detecting these 'hidden faults', in-situ, before damage to cables and components from localized heating can occur. A simple arc generator was built and high-speed and low-speed monitoring of the voltage and current waveforms, respectively, has shown that these high impedance faults produce a significant increase in high frequency content in the DC bus voltage and low frequency content in the DC system current. Based on these observations, an algorithm was developed using a high-speed data acquisition system that was able to accurately detect high impedance arcing events induced in a single-line system based on the frequency content of the DC bus voltage or the system current. Next, a multi-line, radial distribution system was researched to see if the arc location could be determined through the voltage information when multiple 'detectors' are present in the system. It was shown that a small, passive LC filter was sufficient to reliably isolate the fault to a single line in a multi-line distribution system. Of course, no modification is necessary if only the current information is used to locate the arc. However, data shows that it might be necessary to monitor both the system current and bus voltage to improve the chances of detecting and locating high impedance arcing faults

Gonzalez, Marcelo C.↗
NASA NTRS2008

GOES-R Geostationary Lightning Mapper Performance Specifications and Algorithms

The Geostationary Lightning Mapper (GLM) is a single channel, near-IR imager/optical transient event detector, used to detect, locate and measure total lightning activity over the full-disk. The next generation NOAA Geostationary Operational Environmental Satellite (GOES-R) series will carry a GLM that will provide continuous day and night observations of lightning. The mission objectives for the GLM are to: (1) Provide continuous, full-disk lightning measurements for storm warning and nowcasting, (2) Provide early warning of tornadic activity, and (2) Accumulate a long-term database to track decadal changes of lightning. The GLM owes its heritage to the NASA Lightning Imaging Sensor (1997- present) and the Optical Transient Detector (1995-2000), which were developed for the Earth Observing System and have produced a combined 13 year data record of global lightning activity. GOES-R Risk Reduction Team and Algorithm Working Group Lightning Applications Team have begun to develop the Level 2 algorithms and applications. The science data will consist of lightning "events", "groups", and "flashes". The algorithm is being designed to be an efficient user of the computational resources. This may include parallelization of the code and the concept of sub-dividing the GLM FOV into regions to be processed in parallel. Proxy total lightning data from the NASA Lightning Imaging Sensor on the Tropical Rainfall Measuring Mission (TRMM) satellite and regional test beds (e.g., Lightning Mapping Arrays in North Alabama, Oklahoma, Central Florida, and the Washington DC Metropolitan area) are being used to develop the prelaunch algorithms and applications, and also improve our knowledge of thunderstorm initiation and evolution.

Mach, Douglas M.↗
NASA NTRS2021

Trend Detection of Atmospheric Time Series: Incorporating Appropriate Uncertainty Estimates and Handling Extreme Events

This paper is aimed at atmospheric scientists without formal training in statistical theory. Its goal is to, 1) provide a critical review of the rationale for trend analysis of the time series typically encountered in the field of atmospheric chemistry; 2) describe a range of trend-detection methods; and 3) demonstrate effective means of conveying the results to a general audience. Trend detections in atmospheric chemical composition data are often challenged by a variety of sources of uncertainty, which often behave differently to other environmental phenomena such as temperature, precipitation rate, or stream flow, and may require specific methods depending on the science questions to be addressed. Some sources of uncertainty can be explicitly included in the model specification, such as autocorrelation and seasonality, but some inherent uncertainties are difficult to quantify, such as data heterogeneity and measurement uncertainty due to the combined effect of short- and long-term natural variability, instrumental stability, and aggregation of data from sparse sampling frequency. Failure to account for these uncertainties might result in an inappropriate inference of the trends and their estimation errors. On the other hand, the variation in extreme events might be interesting for different scientific questions, for example, the frequency of extremely high surface ozone events and their relevance to human health. In this study we aim to, 1) review trend detection methods for addressing different levels of data complexity in different chemical species; 2) demonstrate that the incorporation of scientifically interpretable covariates can outperform pure numerical curve fitting techniques in terms of uncertainty reduction and improved predictability; 3) illustrate the study of trends based on extreme quantiles that can provide insight beyond standard mean or median based trend estimates; and 4) present an advanced method of quantifying regional trends based on the inter-site correlations of multi-site data. All demonstrations are based on time series of observed trace gases relevant to atmospheric chemistry, but the methods can be applied to other environmental data sets.

Trace gas↗
NASA NTRS2019

Terrestrial Single-Station Analog for Constraining the Martian Core and Deep Interior: Implications for InSight

We used a terrestrial single-station seismometer to quantify the uncertainty of InSight (INterior explorations using Seismic Investigations, Geodesy and Heat Transport) data for determining Martian core size. To mimic Martian seismicity, we formed a catalog using 917 terrestrial earthquakes, from which we randomly selected events. We stacked ScS amplitudes on modeled arrival times and searched for where ScS produced coherent seismic amplitudes. A core detection was defined by a coherent peak with small offset between predicted and user-selected arrival times. Iterating the detection algorithm with varying signal-to-noise (SNR) ranges and quantity of events determined the selection frequency of each model and quantified core depth uncertainty. Increasing the quantity of events reduced core depth uncertainty while increasing the recovery rate, while increasing event SNR had little effect. Including ScS2 multiples increased the recovery rate and reduced core depth uncertainty when we used low quantities of events. The most-frequent core depths varied by back azimuth, suggesting our method is sensitive to the presence of mantle heterogeneities. When we added 1° in source distance errors, core depth uncertainty increased by up to 11 km and recovery rates decreased by <5%. Altering epicentral distances by 25% added ~35 km of uncertainty and reduced recovery rates to <50% in some cases. From these experiments, we estimate that if InSight can detect five events with high location precision (<10% epicentral distance errors), that there is at least an 88% chance of core depth recovery using ScS alone with uncertainty in core depth approaching 18 km and decreasing as more events are located.

Marusiak, Angela G.↗
NASA NTRS2019

Terrestrial Single-Station Analog for Constraining the Martian Core and Deep Interior: Implications for InSight

We used a terrestrial single-station seismometer to quantify the uncertainty of InSight (INterior explorations using Seismic Investigations, Geodesy and Heat Transport) data for determining Martian core size. To mimic Martian seismicity, we formed a catalog using 917 terrestrial earthquakes, from which we randomly selected events. We stacked ScS amplitudes on modeled arrival times and searched for where ScS produced coherent seismic amplitudes. A core detection was defined by a coherent peak with small offset between predicted and user-selected arrival times. Iterating the detection algorithm with varying signal-to-noise (SNR) ranges and quantity of events determined the selection frequency of each model and quantified core depth uncertainty. Increasing the quantity of events reduced core depth uncertainty while increasing the recovery rate, while increasing event SNR had little effect. Including ScS2 multiples increased the recovery rate and reduced core depth uncertainty when we used low quantities of events. The most-frequent core depths varied by back azimuth, suggesting our method is sensitive to the presence of mantle heterogeneities. When we added 1° in source distance errors, core depth uncertainty increased by up to 11 km and recovery rates decreased by <5%. Altering epicentral distances by 25% added ~35 km of uncertainty and reduced recovery rates to <50% in some cases. From these experiments, we estimate that if InSight can detect five events with high location precision (< 10% epicentral distance errors), that there is at least an 88% chance of core depth recovery using ScS alone with uncertainty in core depth approaching 18 km and decreasing as more events are located.

Angela G Marusiak↗
NASA NTRS2022

Influence of Large-Scale Interplanetary Structures on the Propagation of Solar Energetic Particles: the Multi-Spacecraft Event on 2021 October 9

An intense solar energetic particle (SEP) event was observed on 2021 October 9 by multiple spacecraft distributed near the ecliptic plane at heliocentric radial distances R ≲ 1 au and within a narrow range of heliolongitudes. A stream interaction region (SIR), sequentially observed by Parker Solar Probe (PSP) at R = 0.76 au and 48° east from Earth (ϕ = E48°), STEREO-A (at R = 0.96 au, ϕ = E39°), Solar Orbiter (SolO; at R = 0.68 au, ϕ = E15°), BepiColombo (at R = 0.33 au, ϕ = W02°), and near-Earth spacecraft, regulated the observed intensity-time profiles and the anisotropic character of the SEP event. PSP, STEREO-A, and SolO detected strong anisotropies at the onset of the SEP event, which resulted from the fact that PSP and STEREO-A were in the declining-speed region of the solar wind stream responsible for the SIR and from the passage of a steady magnetic field structure by SolO during the onset of the event. By contrast, the intensity-time profiles observed near Earth displayed a delayed onset at proton energies ≳13 MeV and an accumulation of ≲5 MeV protons between the SIR and the shock driven by the parent coronal mass ejection (CME). Even though BepiColombo, STEREO-A, and SolO were nominally connected to the same region of the Sun, the intensity-time profiles at BepiColombo resemble those observed near Earth, with the bulk of low-energy ions also confined between the SIR and the CME-driven shock. This event exemplifies the impact that intervening large-scale interplanetary structures, such as corotating SIRs, have in shaping the properties of SEP events.

D. Lario↗
NASA NTRS2005

Intelligent systems in space : the EO-1 Autonomous Sciencecraft

The Autonomous Sciencecraft Software (ASE) is currently flying onboard the Earth Observing One (EO-1) Spacecraft. This software enables the spacecraft to autonomously detect and respond to science events occurring on the Earth. The package includes software systems that perform science data analysis, deliberative planning, and runtime robust execution. Because of the deployment to the EO-1 spacecraft, the ASE software has stringent constraints of autonomy and limited computing resources. We describe these constraints and how they are reflected in our operations approach. A summary of the final results of the experiment is also included. This software has demonstrated the potential for space missions to use onboard decision-making to detect, analyze, and respond to science events, and to downlink only the highest value science data. As a result, ground-based mission planning and analysis functions have been greatly simplified, thus reducing operations cost.

Earth Observing One (EO-1) Spacecraft↗
NASA NTRS2019

GROWTH on S190510g: DECam Observation Planning and Follow-up of a Distant Binary Neutron Star Merger Candidate

The first two months of the third Advanced LIGO and Virgo observing run (2019 April–May) showed that distant gravitational-wave (GW) events can now be readily detected. Three candidate mergers containing neutron stars (NS) were reported in a span of 15 days, all likely located more than 100 Mpc away. However, distant events such as the three new NS mergers are likely to be coarsely localized, which highlights the importance of facilities and scheduling systems that enable deep observations over hundreds to thousands of square degrees to detect the electromagnetic counterparts. On 2019 May 10 02:59:39.292 UT the GW candidate S190510g was discovered and initially classified as a binary neutron star (BNS) merger with 98% probability. The GW event was localized within an area of 3462 deg2, later refined to 1166 deg2 (90%) at a distance of 227 ± 92 Mpc. We triggered Target-of-Opportunity observations with the Dark Energy Camera (DECam), a wide-field optical imager mounted at the prime focus of the 4 m Blanco Telescope at Cerro Tololo Inter-American Observatory in Chile. This Letter describes our DECam observations and our real-time analysis results, focusing in particular on the design and implementation of the observing strategy. Within 24 hr of the merger time, we observed 65% of the total enclosed probability of the final skymap with an observing efficiency of 94%. We identified and publicly announced 13 candidate counterparts. S190510g was reclassified 1.7 days after the merger, after our observations were completed, with a "BNS merger" probability reduced from 98% to 42% in favor of a "terrestrial classification.

Igor Andreoni↗
NASA NTRS1982

Evidence for solar magnetic loops beyond 1 AU

A description is presented of observations of energetic particles emitted by solar flares into interplanetary magnetic loop-like structures during two different events. In one of these events, the IMP-7 spacecraft detected particles which were injected into an apparently preexisting 'magnetic loop' during the onset of a solar flare particle event. The energetic particles appear to bounce between two magnetic mirrors. During the second event, the spacecraft entered a magnetic field regime where the energetic particle intensities had already reached a characteristic angular distribution indicative of a stably trapped population. Observations of the evolution of the angular distributions of the energetic particle intensities during the solar events reveal the occurrence of unusual particle anisotropies.

Sarris, E. T.↗
NASA NTRS1983

The hard X-ray burst spectrometer event listing 1980, 1981 and 1982

A comprehensive reference for the hard X-ray bursts detected with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission for the time of launch on February 14, 1980 to March 1983 is provided. Over 6300 X-ray events were detected in the energy range from 30 to approx 500 keV with the vast majority being solar flares. The listing includes the start time, peak time, duration and peak rate of each event.

Dennis, B. R.↗
NASA NTRS2019

The SDO/EVE Solar Irradiance Coronal Dimming Index Catalog. I. Methods and Algorithms

When a coronal mass ejection departs, it leaves behind a temporary void. That void is known as coronal dimming, and it contains information about the mass ejection that caused it. Other physical processes can cause parts of the corona to have transient dimmings, but mass ejections are particularly interesting because of their influence in space weather. Prior work has established that dimmings are detectable even in disk-integrated irradiance observations, i.e., Sun-as-a-star measurements. The present work evaluates four years of continuous Solar Dynamics Observatory Extreme Ultraviolet Experiment (EVE) observations to greatly expand the number of dimmings we may detect and characterize, and collects that information into James’s EVE Dimming Index catalog. This paper details the algorithms used to produce the catalog, provides statistics on it, and compares it with prior work. The catalog contains 5051 potential events (rows), which correspond to all robustly detected solar eruptive events in this time period as defined by >C1 flares. Each row has a corresponding 27,349 elements of metadata and parameterizations (columns). In total, this catalog is the result of analyzing 7.6 million solar ultraviolet light curves.

James’s EVE Dimming Index (JEDI)↗
NASA NTRS1976

A study of meteor spectroscopy and physics from earth-orbit: A preliminary survey into ultraviolet meteor spectra

Preliminary data required to extrapolate available meteor physics information (obtained in the photographic, visual and near ultraviolet spectral regions) into the middle and far ultraviolet are presented. Wavelength tables, telluric attenuation factors, meteor rates, and telluric airglow data are summarized in the context of near-earth observation vehicle parameters using moderate to low spectral resolution instrumentation. Considerable attenuation is given to the problem of meteor excitation temperatures since these are required to predict the strength of UV features. Relative line intensities are computed for an assumed chondritic composition. Features of greatest predicted intensities, the major problems in meteor physics, detectability of UV meteor events, complications of spacecraft motion, and UV instrumentation options are summarized.

Meisel, D. D.↗
NASA NTRS1977

Satellite observations of the onset and growth of severe local storms

The mesoscale nature of the forcing and evolution of these storms was investigated, with emphasis on techniques to aid in the early detection of such severe events. In the pre-storm environment (t-4 to t-2 hours), the satellite wind fields were combined with moisture parameters to derive horizontal moisture flux information. Low level moisture convergence was indicative of regions of subsequent severe storm genesis. Dynamic parameters such as boundary layer vorticity production and relative vorticity were also useful prognosticators of subsequent severe activity.

Negri, A. J.↗
NASA NTRS1979

Acceleration of energetic protons by interplanetary shocks

The University of Iowa instrument aboard Pioneer 11 detected 69 energetic proton events (EPE) (in the 0.6-3.4 MeV energy range) during 1973-1974 in the heliocentric radial range 1-5 AU. Sixty percent of the EPE peak within plus or minus 5 hours of a corotating interaction region (CIR) boundary, while 19% peak inside and 21% peak outside the interaction regions. Of the CIR boundaries at which an EPE peaks with plus or minus 5 hours, 80% have associated shocks. The observed intensities and pitch angle distributions of protons near shock fronts are consistent with a theoretical simulation of the acceleration of protons by a drift in the electric field at the shock front.

Pesses, M. E.↗
NASA NTRS1982

Planetary radio astronomy observations from Voyager 2 near Saturn

Planetary radio astronomy measurements obtained by Voyager 2 near Saturn have added further evidence that Saturnian kilometric radiation is emitted by a strong dayside source at auroral latitudes in the northern hemisphere and by a weaker source at complementary latitudes in the southern hemisphere. These emissions are variable because of Saturn's rotation and, on longer time scales, probably because of influences of the solar wind and Dione. The electrostatic discharge bursts first discovered by Voyager 1 and attributed to emissions from the B ring were again observed with the same broadband spectral properties and an episodic recurrence period of about 10 hours, but their occurrence frequency was only about 30 percent of that detected by Voyager 1. While crossing the ring plane at a distance of 2.88 Saturn radii, the spacecraft detected an intense noise event extending to above 1 megahertz and lasting about 150 seconds. The event is interpreted to be a consequence of the impact, vaporization, and ionization of charged, micrometer-size G ring particles distributed over a vertical thickness of about 1500 kilometers.

Warwick, J. W.↗
NASA NTRS1982

A model of human decisionmaking in multiple process monitoring situations

It is proposed that human decisionmaking performance in multiple process monitoring situations can be modeled in terms of the detection of process related events and the allocation of attention among processes once events are felt to have occurred. An elementary pattern recognition technique, discriminant analysis, is used to generate estimates of event occurrence probability. A queueing theory framework is then utilized to incorporate these probabilities as well as other task characteristics into the solution of the attention allocation problem. The performance of the model is compared with that of subjects in two experiments.

Greenstein, J. S.↗
NASA NTRS1982

Microchannel intensified electrography

Although electrography is an attractive electronic imaging technique, it suffers at low light levels from limitations imposed by microphotometer and emulsion grain noise. The use of microchannel intensification allows individual photoelectron events to be unambiguously detected and measured, with little loss of achievable resolution. A series of quantitative studies have been conducted to determine the gains in detectivity and SNR yielded by the use of this technique, through microphotometry and computer analysis of images identical or similar to laboratory light sources, by means of both unintensified and microchannel-intensified electromagnetic Schmidt cameras. Applications of the technique to far-UV wide field imaging and nebular spectrograph experiments are described.

Heckathorn, H. M.↗
NASA NTRS1985

Detection of gamma-ray lines from the direction of the Crab Nebula

The Crab Nebula and its associated pulsar NP0531+21 were observed during a balloon flight of the Durham MK1 high resolution spectrometer on June 6, 1981. The data indicate two significant line features of energies of 404.7 and 1049.8 keV with intensities of (7.2 + or - 2.1) x 0.001 and (12.0 + or - 0.5) x 0.01/5. After subtracting instrumental resolution, the widths of these lines were determined to be (3.5 + or - 1.4) keV and (6.3 + or - 1.6) keV at 404.7 and 1049.8 keV respectively. A third line at 78.8 keV was detected as a transient event with a peak intensity of (1.1 + or - 0.3) x 0.01 photons sq cm/s and a width 1.5 keV. It is shown that all three line features are consistent with a point source located at the Crab.

Owens, A.↗