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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 163 records · Page 9
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NASA NTRS2016

Lighting Condition Analysis for Mars' Moon Phobos

This study used high fidelity computer simulation to investigate the lighting conditions, specifically the solar radiation flux over the surface, on Phobos. Ephemeris data from the Jet Propulsion Laboratory (JPL) DE405 model was used to model the state of the Sun, Earth, Moon, and Mars. An occultation model was developed to simulate Phobos' self-shadowing and its solar eclipses by Mars. The propagated Phobos state was compared with data from JPL's Horizon system to ensure the accuracy of the result. Results for Phobos lighting conditions over one Martian year are presented, which include the duration of solar eclipses, average solar radiation intensity, surface exposure time, available energy per unit area for sun tracking arrays, and available energy per unit area for fixed arrays (constrained by incident angle). The results show that: Phobos' solar eclipse time varies throughout the Martian year, with longer eclipse durations during the Martian spring and fall seasons and no eclipses during the Martian summer and winter seasons; solar radiation intensity is close to minimum at the summer solstice and close to maximum at the winter solstice; exposure time per orbit is relatively constant over the surface during the spring and fall but varies with latitude during the summer and winter; and Sun tracking solar arrays generate more energy than a fixed solar array. A usage example of the result is also present in this paper to demonstrate the utility.

Li, Zu Qun↗
NASA NTRS2016

Lighting Condition Analysis for Mars' Moon Phobos

This study used high fidelity computer simulation to investigate the lighting conditions, specifically the solar radiation flux over the surface, on Phobos. Ephemeris data from the Jet Propulsion Laboratory (JPL) DE405 model was used to model the state of the Sun, Earth, Moon, and Mars. An occultation model was developed to simulate Phobos' self-shadowing and its solar eclipses by Mars. The propagated Phobos state was compared with data from JPL's Horizon system to ensure the accuracy of the result. Results for Phobos lighting conditions over one Martian year are presented, which include the duration of solar eclipses, average solar radiation intensity, surface exposure time, and radiant exposure for both sun tracking and fixed solar arrays. The results show that: Phobos' solar eclipse time varies throughout the Martian year, with longer eclipse durations during the Martian northern spring and fall seasons and no eclipses during the Martian northern summer and winter seasons; solar radiation intensity is close to minimum in late spring and close to maximum in late fall; exposure time per orbit is relatively constant over the surface during the spring and fall but varies with latitude during the summer and winter; and Sun tracking solar arrays generate more energy than a fixed solar array. A usage example of the result is also present in this paper to demonstrate the utility.

Li, Zu Qun↗
NASA NTRS1983

Instrumental effects on the temperature and density derived from the light ion mass spectrometer

An expression for the flux into a retarding potential analyzer (RPA) is derived which takes into account the instrumental effect of a dependence on energy of the solid angle of the acceptance cone. A second instrumental effect of a limited bandpass is briefly discussed. Using the (LIMS) instrument on SCATHA, it is shown that temperatures and densities derived without considering the effect of the solid angle dependence on energy will be too low, dramatically so for E(t) E(1), where E(1) is the e folding distance of the solid angle dependence and E(t) is the thermal energy of the plasma. For E(t) E(1), there is effectively no impact on the derived temperatures and densities if the solid angle effect is ignored.

Craven, P. D.↗
NASA NTRS2021

Modeling a Coronal Mass Ejection from an Extended Filament Channel. I. Eruption and Early Evolution

We present observations and modeling of the magnetic field configuration, morphology, and dynamics of a large-scale, high-latitude filament eruption observed by the Solar Dynamics Observatory. We analyze the 2015 July 9–10 filament eruption and the evolution of the resulting coronal mass ejection (CME) through the solar corona. The slow streamer-blowout CME leaves behind an elongated post-eruption arcade above the extended polarity inversion line that is only poorly visible in extreme ultraviolet (EUV) disk observations and does not resemble a typical bright flare-loop system. Magnetohydrodynamic (MHD) simulation results from our data-inspired modeling of this eruption compare favorably with the EUV and white-light coronagraph observations. We estimate the reconnection flux from the simulation’s flare-arcade growth and examine the magnetic-field orientation and evolution of the erupting prominence, highlighting the transition from an erupting sheared-arcade filament channel into a streamer-blowout flux-rope CME. Our results represent the first numerical modeling of a global-scale filament eruption where multiple ambiguous and complex observational signatures in EUV and white light can be fully understood and explained with the MHD simulation. In this context, our findings also suggest that the so-called “stealth CME” classification, as a driver of unexpected or “problem” geomagnetic storms, belongs more to a continuum of observable/non-observable signatures than to separate or distinct eruption processes.

Benjamin J Lynch↗
NASA NTRS1996

Results from monitoring the broad-line radio galaxy 3C 390.3

The broad line radio galaxy 3C 390.3 was observed in a multiwavelength monitoring campaign by the Rosat high resolution imager (HRI), the International Ultraviolet Explorer and ground-based optical, infrared and and radio observations. The preliminary results from the campaign are reported, with emphasis on the X-ray observations. A large amplitude variability is observed. The light curve is dominated by a flare near JD 2449800, characterized by a doubling time scale of 9 days and a general increase in flux after the flare. The optical R and I band light curves show a general increase in flux. Spectra from the Advanced Satellite for Cosmology and Astrophysics (ASCA) obtained before and after the flare can be described by an absorbed power law.

Leighly, K, M.↗
NASA NTRS1972

Interplanetary cosmic dust flux

Pioneer 8 and 9 measured cosmic dust flux rate data are in agreement with astronomy theory, zodiacal light measurements, and ground-based observations, but differ markedly from the high flux rates deduced from earlier in situ measurements. As many as seven orders-of-magnitude separate the small particle end of the high and low flux curves. It was concluded that the data from the multicoincidence cosmic dust sensors have not only measured very low flux for micrometeorites, which is in keeping with astronomy theory, but have also shown how a high flux theory may be based on faulty data.

Berg, O. E.↗
NASA NTRS1990

Short-term FUV flux variability and phase-dependent winds in Be stars

FUV (Far Ultraviolet) light curves and the behavior of the C IV wind line versus phase are discussed for four Be stars. The IUE (International Ultraviolet Explorer) data acquired during three multiwavelength campaigns aimed at determining the cause for short term optical light variability in Be stars and whether it is linked with the mass loss mechanism is presented. The observations confirm that it is a modulation in the star's photospheric temperature that causes the flux variability. A phase dependent variation is seen in the equivalent width and profile in the C IV wind line. The wind absorption tends to be strongest at maximum light and in a Be shell star the absolute flux of its C IV emission component appears to be anticorrelated with the absorption strength and the level of the FUV flux. The observations suggest that nonradial pulsations are responsible for the photometric variability and the generic model of a star pulsating in a sectorial mode.

Peters, G. J.↗
NASA NTRS1980

Effect of molecular anisotropy on the intensity and degree of polarization of light scattered from model atmospheres

Computations of the properties of sunlight scattered from models of the earth-atmosphere system are presented to show the effect of molecular anisotropy on the intensity, flux, and degree of polarization of the scattered light. The values of these parameters change significantly when the anisotropy factor is neglected in the molecular optical thickness and scattering phase matrix. However, if the Rayleigh scattering optical thickness is kept constant and the molecular anisotropy factor is included only in the Rayleigh phase matrix, the flux does not change, the intensity changes by a small amount, but the changes in the degree of polarization are still significant.

Bahethi, O. P.↗
NASA NTRS1973

Observation of MeV gamma-ray events during May 1967 from ERS-18

Gamma-ray fluxes between 25 keV and 6 MeV were observed by instruments aboard the Environmental Research Satellite-18 (ERS-18)during the great solar flares of May 21 and May 23, 1967. Measurements were made with a 6.35-cm-diameter by 7.65-cm-long Nal scintillation counter with five differential channels between 0.25 and 6.0 MeV. Data obtained during the event at 1945 UT on May 23, 1967, can be fitted by a two-part, power-law, differential-number spectrum. One part is of spectral index 3.2 between 8 keV and 0.6 MeV, and the other is of spectral index 1.2 above 0.6 MeV. An upper limit of 0.52 photons is set for 2.23 MeV line strength for this event. In all three bursts, tentatively associated with white light flares, the MeV-range fluxes declined more slowly than the 25-keV fluxes.

Gruber, D. E.↗
NASA NTRS1992

Effect of gas mass flux on cryogenic liquid jet breakup

A scattered-light scanning instrument developed at NASA Lewis Research Center was used to measure the characteristic drop size of clouds of liquid nitrogen droplets. The instrument was calibrated with suspensions of monosized polystyrene spheres. In this investigation of the mechanism of liquid nitrogen jet disintegration in a high-velocity gas flow, the Sauter mean diameter, D32, was found to vary inversely with the nitrogen gas mass flux raised to the power 1.33. Values of D32 varied from 5 to 25 microns and the mass flux exponent of 1.33 agrees well with theory for liquid jet breakup in high-velocity gas flows. The loss of very small droplets due to the high vaporization rate of liquid nitrogen was avoided by sampling the spray very close to the atomizer, i.e., 1.3 cm downstream of the nozzle orifice. The presence of high velocity and thermal gradients in the gas phase also made sampling of the particles difficult. As a result, it was necessary to correct the measurements for background noise produced by both highly turbulent gas flows and thermally induced density gradients in the gas phase.

Ingebo, R. D.↗
NASA NTRS2008

Phase Change Material Heat Exchanger Life Test

Low Lunar Orbit (LLO) poses unique thermal challenges for the orbiting space craft, particularly regarding the performance of the radiators. The emitted infrared (IR) heat flux from the lunar surface varies drastically from the light side to the dark side of the moon. Due to the extremely high incident IR flux, especially at low beta angles, a radiator is oftentimes unable to reject the vehicle heat load throughout the entire lunar orbit. One solution to this problem is to implement Phase Change Material (PCM) Heat Exchangers. PCM Heat Exchangers act as a "thermal capacitor," storing thermal energy when the radiator is unable to reject the required heat load. The stored energy is then removed from the PCM heat exchanger when the environment is more benign. Because they do not use an expendable resource, such as the feed water used by sublimators and evaporators, PCM Heat Exchangers are ideal for long duration Low Lunar Orbit missions. The Advanced Thermal Control project at JSC is completing a PCM heat exchanger life test to determine whether further technology development is warranted. The life test is being conducted on four nPentadecane, carbon filament heat exchangers. Fluid loop performance, repeatability, and measurement of performance degradation over 2500 melt-freeze cycles will be performed and reported in the current document.

Lillibridge, Sean↗
NASA NTRS2008

High-Pressure Oxygen Generation for Outpost EVA

Low Lunar Orbit (LLO) poses unique thermal challenges for the orbiting space craft, particularly regarding the performance of the radiators. The emitted infrared (IR) heat flux from the lunar surface varies drastically from the light side to the dark side of the moon. Due to the extremely high incident IR flux, especially at low beta angles, a radiator is oftentimes unable to reject the vehicle heat load throughout the entire lunar orbit. One solution to this problem is to implement Phase Change Material (PCM) Heat Exchangers. PCM Heat Exchangers act as a "thermal capacitor, storing thermal energy when the radiator is unable to reject the required heat load. The stored energy is then removed from the PCM heat exchanger when the environment is more benign. Because they do not use an expendable resource, such as the feed water used by sublimators and evaporators, PCM Heat Exchangers are ideal for long duration Low Lunar Orbit missions. The Advanced Thermal Control project at JSC is completing a PCM heat exchanger life test to determine whether further technology development is warranted. The life test is being conducted on four nPentadecane, carbon filament heat exchangers. Fluid loop performance, repeatability, and measurement of performance degradation over 2500 meltfreeze cycles will be performed and reported in the current document.

Jeng, Frank↗
NASA NTRS1994

ASCA observations of the coronal X-ray emission of Algol

We report a 1.7 day ASCA X-ray observation of the 2.87 day binary Algol (Beta Per), centered on the secondary eclipse. Spectra accumulated for different intensity states show a prominent He-like iron K line at 6.7 keV. A two-temperature variable abundance plasma model applied to the spectra yielded temperatures of approximately 8 and approximately 30 MK. The modeled coronal abundances of Fe, O, Mg, Si, S, Ar, and Ca were a factor of 2-3 below the solar photospheric value, and N less than 0.1. These model abundance anomalies are similar to those found from the ASCA spectra of other late-type stars and may indicate either true deviations from solar abundances or problems with the assumptions and atomic physics of the plasma models. The X-ray light curve shows a factor of 2 increase in flux over 13 hr beginning in the middle of the secondary eclipse, with a shallow eclipse centered on phase 0.45. The orbital light curve is similar to that observed by ROSAT 1 year earlier. The rise in flux is caused by an increase in the emission measure of the higher temperature component. The intensity variation is not associated with any major change in the abundances or temperature of the two components.

Antunes, A.↗
NASA NTRS1995

Seasonal variability of light availability and utilization in the Sargasso Sea

A 2 year time series of optical, biogeochemical, and physical parameters, taken near the island of Bermuda, is used to evaluate the sources of temporal variability in light avaliability and utilization in the Sargasso Sea. Integrated assessments of light availability are made by examining the depth of constant percent incident photosynthetically available radiation (% PAR) isolumes. To first order, changes in the depth %PAR isolumes were caused by physical processes: deep convection mixing in the winter which led to the spring bloom and concurrent shallowing of %PAR depths and the occurrence of anomalous thermohaline water masses during the summer and fall seasons. Spectral light availability variations are assessed using determinations of diffuse attenuation coefficient spectra which illustrates a significant seasonal cycle in colored detrital particulate and/or dissolved materials that is unrelated to changes in chlorophyll pigment concentrations. Temporal variations in the photosynthetic light utilization index Psi are used to assess vertically intergrated light utilization variations. Values of Psi are highly variable and show no apparent seasonal pattern which indicates that Psi is not simply a 'biogeochemical constant.' Determinations of in situ primary production rates and daily mean PAR fluxes are used to diagnose the relative role of light limitation in determining vertically integrated rates of primary production integral PP. The mean depth of the light-saturated zone (the vertical region where the daily mean PAR flux was greater than or equal to the saturation irradiance) is only approximately 40 m, although more than one half of interal PP occurred within this zone. Production model results illustrate that accurate predictions of integral PP are dependent upon rates of light-saturated production rather than upon indices of light limitation. It seems unlikely that significant improvements in simple primary production models will come from the partitioning of the Earth's seas into biogeochemical provinces.

Siegel, David A.↗
NASA NTRS1973

Lunar ion flux and energy

The dynamics of the lunar ionosphere and resulting flux of lunar ions to the lunar surface are reviewed. In the Lunar rest frame, ions formed from the neutral lunar atmosphere are accelerated by the interplanetary electric and magnetic fields. The trajectories of heavier ions are primarily along the electric field; the ion flux is in a direction perpendicular to the solar wind flow, correlated to the orientation of the interplanetary magnetic field, and impacts the surface with energies of tens of electron volts to a few keV. Thus we predict a relatively energetic (compared to thermal energies), highly directional, lunar ion flux but with the possibility that light ions such as hydrogen can execute orbits that return them to portions of the lunar surface not directly exposed to the solar wind. The effects of surface electric and magnetic fields are discussed, as is the ion energy spectrum. We calculate the trapping of atmospheric ions which impact the surface and from this the density of neutral Ar 40 in the lunar atmosphere. We show that using the acceleration model, the lunar atmosphere total neutral number density can be calculated from ion detector data.

Manka, R. H.↗
NASA NTRS1977

Morphology and physical parameters of a solar flare

The chromospheric and coronal morphology of the flare of June 15, 1973, (1B/M3) in NOAA active region 131 (McMath 12379) is discussed, and results of quantitative analysis of Skylab soft X-ray observations of the event are presented. H-alpha and white-light observations reveal evidence of emerging flux near the site of the H-alpha flare onset. Preflare and early flare filament activity and its spatial and temporal correlation with the flare are discussed. Spatially resolved soft X-rays are compared with H-alpha and magnetic-field measurements. Full-disk high-temporal-resolution soft X-ray flux measurements and time profiles of the resultant temperature and density calculations are also presented which yield a peak temperature of about 14.2 million K and a peak electron density of approximately 3.5 deg 10 to the -10th power per cu cm and show a preflash-phase temperature rise to about 9 million K. The peak values should be compared with the respective values of approximately 25 million K and 4.5 by 10 to the -10th power per cu cm deduced from the spatially resolved data.

Smith, J. B., Jr.↗
NASA NTRS1980

A survey of chromospheric Ca II H and K emission in field stars of the solar neighborhood

Fluxes in 1 A bands at the centers of the H and K lines are being measured in main-sequence F-G-K-M stars in the northern half of the Woolley et al. (1970) 'Catalog of stars within twenty-five parsecs of the sun', in a survey not yet completed. Results for 486 stars are presented in the form of flux-color diagrams and discussed in light of evidence that chromospheric activity declines with age in main-sequence stars. Support is noted for the reality of the Sirius moving group. The relative numbers of more-active (Hyades-like) and less-active (solar-like) F-G stars are tolerably in agreement with a nearly constant rate of formation, but there exists an apparent deficiency in the number of F-G stars exhibiting intermediate activity. The possibility that the gap is an accidental characteristic of the sample will be investigated by extending the survey to southern declinations and greater distances.

Vaughan, A. H.↗