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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 631 records · Page 35
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NASA NTRS2023

Imaging the Milky Way with Millihertz Gravitational Waves

Modern astronomers enjoy access to all-sky images across a wide range of the electromagnetic spectrum from long-wavelength radio to high-energy gamma rays. The most prominent feature in many of these images is our own Galaxy, with different features revealed in each wave band. Gravitational waves (GWs) have recently been added to the astronomers’ toolkit as a nonelectromagnetic messenger. To date, all identified GW sources have been extra-Galactic and transient. However, the Milky Way hosts a population of ultracompact binaries (UCBs), which radiate persistent GWs in the milliHertz band that is not observable with today’s terrestrial gravitational-wave detectors. Space-based detectors such as the Laser Interferometer Space Antenna will measure this population and provide a census of their location, masses, and orbital properties. In this work, we will show how this data can be used to form a false-color image of the Galaxy that represents the intensity and frequency of the gravitational waves produced by the UCB population. Such images can be used to study the morphology of the Galaxy, identify interesting multimessenger sources through cross-matching, and for educational and outreach purposes.

Gravitational Waves↗
NASA NTRS2019

AT2018cow: A Luminous Millimeter Transient

We present detailed submillimeter- through centimeter-wave observations of the extraordinary extragalactic transient AT2018cow. The apparent characteristics—the high radio luminosity, the rise and long-lived emission plateau at millimeter bands, and the sub-relativistic velocity—have no precedent. A basic interpretation of the data suggests E(k) ≳ 4 X 10^(48) erg coupled to a fast but sub-relativistic (v ≈ 0.13c) shock in a dense (n(e) ≈ 3 X 10^(5) per cu. cm) medium. We find that the X-ray emission is not naturally explained by an extension of the radio-submm synchrotron spectrum, nor by inverse Compton scattering of the dominant blackbody UV/optical/IR photons by energetic electrons within the forward shock. By ∆t ≈ 20 days, the X-ray emission shows spectral softening and erratic inter-day variability. Taken together, we are led to invoke an additional source of X-ray emission: the central engine of the event. Regardless of the nature of this central engine, this source heralds a new class of energetic transients shocking a dense medium, which at early times are most readily observed at millimeter wavelengths

Anna Y. Q. Ho↗
NASA NTRS1979

Positions and identifications of galactic X-ray sources

A catalog of compact Galactic X-ray sources with precise positions is presented together with a large bibliography. The catalog provides available X-ray, optical, and radio data for the 96 compact Galactic sources that have been identified and contains the most precise of the available optical, X-ray, or radio positions, the maximum and minimum published intensities, references to finding charts, and a comprehensive referenced list of X-ray, optical, and radio characteristics. The catalog also includes X-ray sources in the Magellanic clouds as well as all unidentified hard (greater than 2 keV) compact sources with an error radius of less than 60 arcsec and a Galactic latitude of less than 10 deg (absolute value). The sources list includes 14 X-ray Doppler or eclipsing binaries, seven or eight other X-ray pulsators, 23 transients or X-ray novae, 15 persistent bright bulge sources, seven X-ray sources associated with globular clusters, nine bursters, seven Galactic Center sources, and 18 other identified sources.

Bradt, H. V.↗
NASA NTRS1983

Coronal disturbances and their terrestrial effects /Tutorial Lecture/

An assessment is undertaken of recent approaches to the prediction of the interplanetary consequences of coronal disturbances, with attention to the relationships of shocks and energetic particles to coronal transients, of proton events to gamma-ray and microwave bursts, of geomagnetic storms to filament eruptions, and of solar wind increases to the flare site magnetic field direction. A discussion is given concerning the novel phenomenon of transient coronal holes, which appear astride the long decay enhancements of 2-50 A X-ray emission following H-alpha filament eruptions. These voids in the corona are similar to long-lived coronal holes, which are the sources of high speed solar wind streams. The transient coronal holes may also be associated with transient solar wind speed increases.

Rust, D. M.↗
NASA NTRS2000

Chandra Observations of the M31

We report on Chandra observations of the nearest Spiral Galaxy, M3l, The nuclear source seen with previous X-ray observatories is resolved into five point sources. One of these sources is within 1 arc-sec of the M31 central super-massive black hole. As compared to the other point sources in M3l. this nuclear source has an unusually soft spectrum. Based on the spatial coincidence and the unusual spectrum. we identify this source with the central black hole. A bright transient is detected 26 arc-sec to the west of the nucleus, which may be associated with a stellar mass black hole. We will report on a comparison of the x-ray spectrum of the diffuse emission and point sources seen in the central few arcmin

Garcia, Michael↗
NASA NTRS1985

Composite Loads Spectra for Select Space Propulsion Structural Components: Probabilistic Load Model Development

This effort is in support of the development of the expert system of computer codes to predict the loads on select structural components of a space propulsion engine. The development will be based primarily on the space shuttle main engine (SSME) test data base. Because of random variations of the many different sources of the loadings on the selected structural components and transients, a probabilistic approach to the problems was adopted. The goal of this task is to characterize all of the individual sources of loads at critical structural locations, such as the turbine blades, the transfer ducts, and liquid oxygen posts, using state-of-the-art probabilistic methods with varying levels of sophistication. The second phase of this work is the development of a composite load model based on a probabilistic synthesis of the individual load model previously developed. This model will be based on the stochastic combination of the load variables and not on the physical process for the combination of the individual loads to the composite load seen by the selected structural components.

Kurth, R.↗
NASA NTRS1982

Environmentally induced discharges on satellites

A discharge process whose trigger conditions are a negative exposed metallic surface surrounded by a less negative dielectric, and a large voltage gradient at a dielectric/metal interface is proposed. Analysis of SCATHA data for a discharge substantiates the postulation. Surface discharges cause a small transient charge transfer to space which results in voltage transients. A method of computing these transients, based on the charge lost through the capacitance to space and a fraction of charge stored in the dielectric at the discharge source was developed. It gives an estimate of the discharge transients at the discharge site, which is used as input for coupling code analysis of structure/system response. The transient computations were applied to a three-axis stabilized, geosynchronous satellite for both sunlight and eclipse charging. The energy of the transient pulses are about 1 mJ for sunlight discharge and 8 mJ for eclipse. Changing of selected coatings on the satellite would relieve the stress.

Stevens, N. J.↗
NASA NTRS1976

A model for the X-ray nova A0620-00

The model involves a white dwarf accreting mass from a late-type subgiant companion. The transient behavior of the X-ray source is explained by the instability to mass loss of the companion (as in Algol-type binaries). The brightening, spectrum, and decay timescale of the optical counterpart are explained in terms of re-emission of X-radiation intercepted by the subgiant. It was concluded that A0620-00 can provide an excellent test case for numerical models of stellar atmospheres irradiated by an external X-ray flux.

Endal, A. S.↗
NASA NTRS1978

SAS 3 observations of two X-ray transient events with precursors

SAS 3 has observed two unusual fast transient X-ray events from different sources, one lasting about 150 s and one, approximately 1500 s. Both events were preceded by precursor pulses which lasted a few seconds and which rose and fell in less than 0.4 s. The precursors were separated from the 'main' events by several seconds, during which no X-rays were detected. There are similarities between the two main events and X-ray bursts in both their temporal and spectral evolution. The spectra of the main events started out much softer than the spectra of the precursors, became harder as they approached maximum intensity, and softened as they decayed. In the 1500-s event, X-rays with energies greater than 10 keV were delayed by about 80 s compared with 1.5-6-keV X-rays. A blackbody fit to the spectral data of the main event of approximately 1500-s duration gives a maximum temperature of 29 million K and a radius for the emitting region of at least about 9 km (at a distance of 10 kpc); this is similar to the temperature and sizes found for several X-ray burst sources.

Hoffman, J. A.↗
NASA NTRS1985

I/Q reversal phenomena in 4-phase modified Costas Loops

A method for predicting the occurrence of I/Q reversals in unbalanced QPSK 4-phase modified Costas Loops is discussed. Potential causes for the reversal of in-phase and quadrature outputs of the unbalanced QPSK demodulator during acquisition and tracking are studied. The design of the unbalance QPSK demodulator and loop characteristics are described. The effect of an anomalous condition during a transient interval or demod/remod operation on data source output is examined. Filtering and hard-limiting effects, and the demodulator loop S-curve stability during tracking are evaluated.

Weinberg, A.↗
NASA NTRS1986

Observations of cosmic gamma-ray bursts

Recent observational progress in gamma ray burst research is reviewed. Findings concerning burst temporal and spectral characteristics, source direction and size spectrum studies, and transient event classification are discussed. The theories concerning the origin of the bursts are examined in the light of the recent evidence.

Cline, T. L.↗
NASA NTRS1987

Experiments on thermoacoustic convection heat transfer in gravity and zero-gravity environments

The results of an experimental study of thermoacoustic convection (TAC) heat transfer in gravity and zero-gravity environments are presented. The experimental apparatus consisted of a cylinder containing air as the compressible fluid. The enclosed air was heated electrically at the top surface which consisted of a thin high-resistance steel foil connected to a power source. Thermocouples were used to measure the transient temperature of the air on the axis of the cylinder and the heated surface in the both zero-gravity and gravity environments. The zero-gravity tests were performed in the Zero-Gravity Drop Tower Facility of NASA-Lewis Research Center. The experimental results were corrected for the error due to radiation absorption by the thermocouples. A conduction-only numerical heat transfer model was developed to compute the transient air temperature in the cylindrical geometry. The results were compared to the experimental data to determine the significance of the thermoacoustic convection heat transfer mechanism. It is observed that the rate of heat transfer to the air measured during the experiments is consistently higher than that obtained by the conduction-only solution indicating a significant presence of the TAC heat transfer. Further experiments are planned to measure directly (1) the radiative heat transfer contribution to the rise in the air temperature, and (2) the air pressure oscillations within the cylinder that are responsible for the convective heat transfer mode.

Parang, Masood↗
NASA NTRS1986

An experimental and analytical investigation of thermoacoustic convection heat transfer in gravity and zero-gravity environments

An experimental and analytical study of Thermoacoustic Convection heat transfer in gravity and zero-gravity environments is presented. The experimental apparatus consisted of a cylinder containing air as a fluid. The side wall of the cylinder was insulated while the bottom wall was allowed to remain at the ambient temperature. The enclosed air was rapidly heated by the top surface which consisted of a thin stainless steel foil connected to a battery pack as the power source. Thermocouples were used to measure the transient temperature of the air on the axis of the cylinder. The ouput of the thermocouples was displayed on digital thermometers and the temperature displays were recorded on film using a high-speed movie camera. Temperature measurements were obtained in the zero-gravity environment by dropping the apparatus in the 2-Seconds Zero-Gravity Drop Tower Facilities of NASA Lewis Research Center. In addition, experiments were also performed in the gravity environment and the results are compared in detail with those obtained under zero-gravity conditions.

Parang, Masood↗
NASA NTRS1992

Space nuclear power systems 1989; Proceedings of the 6th Symposium, Albuquerque, NM, Jan. 8-12, 1989. Vols. 1 & 2

The present conference discusses such space nuclear power (SNP) issues as current design trends for SDI applications, ultrahigh heat-flux systems with curved surface subcooled nucleate boiling, design and manufacturing alternatives for low cost production of SNPs, a lightweight radioisotope heater for the Galileo mission, compatible materials for uranium fluoride-based gas core SNPs, Johnson noise thermometry for SNPs, and uranium nitride/rhenium compatibility studies for the SP-100 SNP. Also discussed are system issues in antimatter energy conversion, the thermal design of a heat source for a Brayton cycle radioisotope power system, structural and thermal analyses of an isotope heat source, a novel plant protection strategy for transient reactors, and beryllium toxicity.

El-Genk, Mohamed S.↗
NASA NTRS2001

ROSAT/Chandra Observations of a Bright Transient in M81

We present a 10-year X-ray light curve and the spectra of a peculiar X-ray transient in the spiral galaxy M81. The source was below the detection limit of ROSAT PSPC before 1993, but it brightened substantially in 1993, with luminosities exceeding the Eddington limit of a 1.5 solar mass compact accretor. It then faded and was not firmly detected in the ROSAT HRI and PSPC observations after 1994. The Chandra image obtained in 2000 May, however, shows an X-ray source at its position within the instrumental uncertainties. The Chandra source is coincident with a star-like object in the Digitized-Sky-Survey. A Hubble image suggests that the optical object may be extended. While these three observations could be of the same object, which may be an X-ray binary containing a black-hole candidate, the possibility that the ROSAT and Chandra sources are two different objects in a dense stellar environment cannot be ruled out. The Hubble data suggests that the optical object may be a globular cluster yet to be identified.

Ghosh, Kajal K.↗
NASA NTRS2002

9.1 Years of All-Sky Hard X-Ray Monitoring with BATSE

The hard X-ray sky was continuously monitored with the BATSE experiment on the Compton Gamma Ray Observatory using the Earth Occultation method. Known sources were monitored twice every orbit and transients could be detected at about the approximately 50 crab level on a daily basis. Long-term, post-processing of the complete BATSE dataset will produce all-sky, hard X-ray maps at a sensitivity level of approximately 5 mCrab in un-crowded regions. For long period pulsars (greater than 1 second), Fourier transforms and epoch-folded searches were used to measure pulse frequency and pulsed flux. Using these methods, 3 black hole candidates and 6 x-ray pulsars were discovered with BATSE during its 9 years in orbit. I will present highlights from BATSE observations of X-ray binaries from 9 years of monitoring the hard X-ray sky.

Wilson, C. A.↗
NASA NTRS2021

The X-ray Bursts of XTE J1739-285: A NICER Sample

In this work, we report on observations with the Neutron Star Interior Composition Explorer of the known neutron star X-ray transient XTE J1739–285. We observed the source in 2020 February and March, finding it in a highly active bursting state. Across a 20 day period, we detected 32 thermonuclear X-ray bursts, with an average burst recurrence time of-+2.0 hr0.30.4. A timing and spectral analysis of the ensemble of X-ray bursts reveals homogeneous burst properties, evidence for short-recurrence time bursts, and the detection of a 386.5 Hz burst oscillation candidate. The latter is especially notable, given that a previous study of this source claimed a 1122 Hz burst oscillation candidate. We did not find any evidence of variability near 1122 Hz and instead find that the 386.5 Hz oscillation is the more prominent signal of the two burst oscillation candidates. Hence, we conclude it is unlikely that XTE J1739–285 has a submillisecond rotation period.

X-ray burst↗