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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 343 records · Page 19

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NASA NTRS1991

Solar particle abundances at energies of greater than 1 MeV per nucleon and the role of interplanetary shocks

The abundances of elements in large solar energetic-particle events in the energy range of 2-12 MeV per nucleon are examined. It is confirmed that the abundances relative to mean values vary approximately monotonically as a function of mass, except for He-4; some events show a gradual depletion of heavy ions, whereas a small number displays a gradual increase. A further organization of abundance data is shown, which depends on the longitude of the source region. Enhancements in Fe/C and other heavy elements relative to C occur when source regions are near west 60 deg; the enhancements are attributed to the sampling of a flare-heated material. Depletions of these elements are found to be greatest for source regions near central meridian; they are matched by a steepening of the spectrum and can be understood in terms of diffusive shock acceleration.

Cane, H. V.↗

NASA NTRS1991

Numerical simulation of the emission and motion of neutral and charged dust from P/Halley

The present numerical model for neutral or charged dust-particle distribution prediction in P/Halley encompasses the spatial and temporal variations of the plasma parameters and magnetic field. A significant difference is noted between results for neutral dust trajectories and the trajectories of charged dust particles with radii smaller than 0.1 micron. While most of the model and in situ mass spectra were in good agreement, there is a shortage of the lowest-mass model particles, as well as an offset of the total counting rate for two outbound mass spectra. A combination of two Lorentzian particle mass-density functions with a 100:1 ratio for the number of particles with the lower and higher density functions yielded the best agreement.

Ellis, Tracy A.↗

NASA NTRS1992

Nutritional Requirements for Space Station Freedom Crews

The purpose of this report was to set preliminary nutritional requirements for crewmembers flying from 90 to 180 day missions on Space Station Freedom. Specific recommendations included providing crewmembers with in flight feedback on nutritional intake, weight and strength, and incorporating issues of energy intake, body weight, body composition, strength, and protein intake in the flight medicine program. Exercise must be considered an integral part of any plan to maintain nutritional status, especially those modes that stress the skeleton and maintain body weight. Nutrient intake, amount of exercise, and drugs ingested must be recorded daily; high priority should be given to development of fully automated record systems that minimize astronauts' effort. A system of nutritional supplements should be developed to provide a method for reducing intake deficits that become apparent. Finally, post flight monitoring should include bone density, muscle mass and function, and iron status at three and six months after landing.

Lane, Helen W.↗

NASA NTRS1993

Hypervelocity impact effects on solar cells

One of the space hazards of concern is the problem of natural matter and space debris impacting spacecraft. This phenomena has been studied since the early sixties and a methodology has been established to determine the relative abundance of meteoroids as a function of mass. As the mass decreases, the probability of suffering collisions increases, resulting in a constant bombardment from particles in the sub-micron range. The composition of this 'cosmic dust' is primarily Fe, Ni, Al, Mg, Na, Ca, Cr, H, O, and Mn. In addition to mechanical damage, impact velocities greater than 5 k m/sec can produce shock induced ionization effects with resultant surface charging and complex chemical interactions. The upper limit of the velocity distribution for these particles is on the order of 70 km/sec. The purpose of this work was to subject samples from solar power arrays to debris flux typical of what would be encountered in space, and measure the degradation of the panels after impact.

Rose, M. Frank↗

NASA NTRS1993

Galaxy tracers in N-body simulations

Using the method of smoothed particle hydrodynamics, we have modeled the formation of a compact group of galaxies with sufficient resolution to trace galaxies. Radiative cooling allows the baryons to dissipate their thermal energy and collapse to overdensities characteristic of real galaxies. With their cross section greatly reduced, these galaxy tracers remain distinct during cluster formation while their dark matter halos merge. In addition, the number density, the mass distribution function, and even the morphology of these objects are similar to those of observed galaxies. A viable population of galaxy tracers can be unambiguously defined.

Summers, F. J.↗

NASA NTRS1992

Jovian large-scale stratospheric circulation

An attempt is made to diagnose the annual-average mean meridional residual Jovian large-scale stratospheric circulation from observations of the temperature and reflected sunlight that reveal the morphology of the aerosol heating. The annual mean solar heating, total radiative flux divergence, mass stream function, and Eliassen-Palm flux divergence are shown. The stratospheric radiative flux divergence is dominated the high latitudes by aerosol absorption. Between the 270 and 100 mbar pressure levels, where there is no aerosol heating in the model, the structure of the circulation at low- to midlatitudes is governed by the meridional variation of infrared cooling in association with the variation of zonal mean temperatures observed by IRIS. The principal features of the vertical velocity profile found by Gierasch et al. (1986) are recovered in the present calculation.

West, R. A.↗

NASA NTRS1955

Estimation of Inlet Lip Forces at Subsonic and Supersonic Speeds

The effects of lip thickness on inlet performance are estimated as functions of mass flow for subsonic and supersonic flight speeds. At subsonic speeds, pressure-recovery losses and additive drag are shown to decrease linearly with increasing lip frontal area if the maximum suction force is attained. At supersonic speeds, inlet drag increases linearly with inlet lip frontal area at full mass flow. For reduced mass flow, some reduction in additive drag is possible with lips of moderate thickness, but the magnitude of this reduction becomes negligible as flight speed increases.

Moeckel, W E↗

NASA NTRS1993

Musculoskeletal adaptation to mechanical forces on Earth and in space

A major concern of the US and Russian space programs is the health and safety of astronauts and cosmonauts. One of the areas receiving the most attention has been the effects of long duration space flight on the musculoskeletel system. After three decades of space flight and research, questions continue. Can exercise in space maintain musculoskeletal tissue mass and function in an adult? The objective of this paper is to address this question in a way that hopefully provides a rational basis for quantifying and evaluating the influnence of daily activities on muscle and bone on Earth and in space.

Whalen, Robert↗

NASA NTRS1994

Quasi-periodic atmosphere-regolith-cap CO2 redistribution in the martian past

Our earlier Mars regolith-atmosphere-cap CO2 distribution model (Fanale et al., 1982, Icarus 50, 381-407) has been improved, revised, and extended back over Mars' mid to late history. The present model takes into account four new factors: (1) a more realistic long-term obliquity cycle, (2) thermal conduction as it affects the surface energy balance, (3) the changing solar constant, and (4) atmospheric erosion 3.5 byr ago to the present. Solar insolation and temperatures are computed for the full range of obliquities, latitudes, and epochs, and a CO2 adsorption relation is used, together with a conservation of mass constraint, to calculate atmospheric pressures and exchangeable CO2 mass as functions of obliquity and epoch for the regolith, atmosphere, and polar caps for two assumed thicknesses of a basalt regolith. It is found that the heat conduction term in the surface boundary condition has an important effect in reducing the range of atmospheric pressures over the obliquity cycle at all epochs.

Fanale, Fraser P.↗

NASA NTRS1996

Investigation of Two-Phase Flows in Piping Bends and Elbows

An experimental investigation of the hydrodynamic characteristics of two-phase R-113 flow has been carried out. Straight tube pressure drop data, as a function of mass flow rate (mass flux) and flow quality has been obtained using the Two-Phase Flow Test Facility located in the Advanced Thermal Laboratories of the Crew and Thermal Systems Division at the Lyndon B. Johnson Space Center. Additionally, after successfully obtaining the straight tube pressure drop data, the test facility was modified in order to obtain pressure drop data for the flow of two-phase R-113 through 180 deg piping bends. Inherent instabilities of the test facility prevented the successful acquisition of pressure drop data through the piping bends. The experimental straight tube data will be presented and compared with existing predictive correlations in an attempt to gain insight into the utility of such correlations as the basis for developing design criteria. A discussion of the instabilities which rendered successful acquisition of the piping bend data will be presented and suggestions will be made for eliminating these system tendencies. Finally, recommendations for future investigations, based on successful reconfiguration of the test facility, will be made.

Duncan, Allen B.↗

NASA NTRS2001

Large Eddy Simulation of Gravitational Effects on Transitional and Turbulent Gas-Jet Diffusion Flames

The basic objective of this work is to assess the influence of gravity on "the compositional and the spatial structures" of transitional and turbulent diffusion flames via large eddy simulation (LES), and direct numerical simulation (DNS). The DNS is conducted for appraisal of the various closures employed in LES, and to study the effect of buoyancy on the small scale flow features. The LES is based on our "filtered mass density function"' (FMDF) model. The novelty of the methodology is that it allows for reliable simulations with inclusion of "realistic physics." It also allows for detailed analysis of the unsteady large scale flow evolution and compositional flame structure which is not usually possible via Reynolds averaged simulations.

Givi, Peyman↗

NASA NTRS2003

Coronal Activity in the R CrA T Association

For this project we intend to extract net counts and variability information for the X-ray sources found in 9 archival ROSAT PSPC and 6 archival ROSAT HRI images in the region of the R CrA T association. These data will be merged with an extensive database of optical photometry and spectroscopy plus published near-infrared photometry to (1) identify new association members and (2) derive, for the first time, an accurate coronal luminosity function for the T Tauri members of this T association. These data will be used to make direct comparisons between the coronal luminosity functions for other T associations and those of large clusters to assess (a) the importance of the star-formation environment in initial coronal activity levels, (b) the effects of PMS evolution on dynamo activity as a function of mass and age, and (c) the level of contamination by field post-T Tauri stars on association membership surveys.

Patten, Brian M.↗

NASA NTRS2004

Studies of Circumstellar Disk Evolution

Spitzer Space Telescope infrared data for our program on disk evolution has been taken (the main IRAC - 3-8 micron exposures; the 24 and 70 micron MIPS data are to come later). We now have deep maps in the four IRAC bands of the 3-Myr-old cluster Trumpler 37, and the 10-Myr-old cluster NGC 7160. Analysis of these data has now begun. We will be combining these data with our ground-based photometric and spectroscopic data to obtain a complete picture of disk frequency as a function of mass through this important age range, which spans the likely epoch of (giant) planet formation in most systems. Analysis of the SIRTF data, and follow-on ground-based spectroscopy on the converted MMT telescope using the wide-field, fiber-fed, multiobject spectrographs, Hectospec and Hectochelle, will be the major activity during the next year.Work was also performed on the following: protoplanetary disk mass accretion rates in very low-mass stars; the inner edge of T Tauri disks; accretion in intermediate-mass T Tauri stars (IMPS); and the near-infrared spectra of the rapidly-accreting protostellar disks FU Ori and V1057 Cyg.

Hartmann, Lee W.↗

NASA NTRS2003

Quadrature Moments Method for the Simulation of Turbulent Reactive Flows

A sub-filter model for reactive flows, namely the DQMOM model, was formulated for Large Eddy Simulation (LES) using the filtered mass density function. Transport equations required to determine the location and size of the delta-peaks were then formulated for a 2-peak decomposition of the FDF. The DQMOM scheme was implemented in an existing structured-grid LES solver. Simulations of scalar shear layer using an experimental configuration showed that the first and second moments of both reactive and inert scalars are in good agreement with a conventional Lagrangian scheme that evolves the same FDF. Comparisons with LES simulations performed using laminar chemistry assumption for the reactive scalar show that the new method provides vast improvements at minimal computational cost. Currently, the DQMOM model is being implemented for use with the progress variable/mixture fraction model of Pierce. Comparisons with experimental results and LES simulations using a single-environment for the progress-variable are planned. Future studies will aim at understanding the effect of increase in environments on predictions.

Raman, Venkatramanan↗

NASA NTRS2003

Large Eddy Simulation Of Gravitational Effects In Transitional And Turbulent Gas-Jet Diffusion Flames

The influence of gravity on the spatial and the compositional structures of transitional and turbulent hydrocarbon diffusion flames are studies via large eddy simulation (LES) and direct numerical simulation (DNS) of round and planar jets. The subgrid-scale (SGS) closures in LES are based on the filtered mass density function (FMDF) methodology. The FMDF represents the joint probability density function (PDF) of the SGS scalars, and is obtained by solving its transport equation. The fundamental advantage of LES/FMDF is that it accounts for the effects of chemical reaction and buoyancy exactly. The methodology is employed for capturing some of the fundamental influences of gravity in equilibrium flames via realistic chemical kinetic schemes. Some preliminary investigation of the gravity effects in non-equilibrium flames is also conducted, but with idealized chemical kinetics models.

Jaberi, Farhad A.↗

NASA NTRS1994

Organelle sedimentation in gravitropic roots of Limnobium is restricted to the elongation zone

Roots of the aquatic angiosperm Limnobium spongia (Bosc) Steud. were evaluated by light and electron microscopy to determine the distribution of organelle sedimentation towards gravity. Roots of Limnobium are strongly gravitropic. The rootcap consists of only two layers of cells. Although small amyloplasts are present in the central cap cells, no sedimentation of any organelle, including amyloplasts, was found. In contrast, both amyloplasts and nuclei sediment consistently and completely in cells of the elongation zone. Sedimentation occurs in one cell layer of the cortex just outside the endodermis. Sedimentation of both amyloplasts and nuclei begins in cells that are in their initial stages of elongation and persists at least to the level of the root where root hairs emerge. This is the first modern report of the presence of sedimentation away from, but not in, the rootcap. It shows that sedimentation in the rootcap is not necessary for gravitropic sensing in at least one angiosperm. If amyloplast sedimentation is responsible for gravitropic sensing, then the site of sensing in Limnobium roots is the elongation zone and not the rootcap. These data do not necessarily conflict with the hypothesis that sensing occurs in the cap in other roots, since Limnobium roots are exceptional in rootcap origin and structure, as well as in the distribution of organelle sedimentation. Similarly, if nuclear sedimentation is involved in gravitropic sensing, then nuclear mass would function in addition to, not instead of, that of amyloplasts.

NASA Discipline Plant Biology↗

NASA NTRS2000

The Effect of Companions on the SIM Reference Frame

The Space Interferometry Mission (SIM) is a 10-m Michelson space-based optical interferometer designed for precision astrometry (4 microarcseconds, 3 microarcseconds/year) with better accuracy than before over a narrow field of view. One of the primary objectives of the SIM instrument is to determine accurately the directions to a grid of stars, together with their proper motions and parallax, improving a priori knowledge by nearly three orders of magnitude over Hipparcos and one order of magnitude over FAME's planned accuracy (Johnston, 2000). The instrument does not measure directly the angular separation between stars, but rather it measures the projection of each star's direction vector onto the interferometer baseline vector by measuring the pathlength delay of starlight as it passes through the two arms of the interferometer. The accuracy and stability of SIM's celestial reference frame is subject to degradation over the 5-year mission from the reflex motion induced by massive companions of the objects used to construct the celestial reference frame. The authors present the results of simulations that show the sensitivity of reference frame accuracy to companions as a function of mass and period. They assume that pre-launch ground surveys will eliminate all objects with RMS radial velocity greater than 10 m/s. They further assume that the standard astrometric parameters of position, parallax, and proper motion plus acceleration terms in right ascension and declination will be allowed to absorb reflex motion.

ASTROMETRY↗

NASA NTRS2005

Coronal Activity in the R CrA T Association

Brian Patten is the Principal Investigator of the NASA ROSS-ADP project Coronal Activity in the R CrA T Association. For this project we have extracted net counts and variability information for all of the X-ray sources found in 23 archival ROSAT PSPC and HRI images in the region of the R CrA T association. These data have been merged with an extensive database of optical and near-infrared photometry, optical spectroscopy, and parallax data. These data have been used to (1) identify new association members and clarify the membership status of a number of previously suspected members of the association, and (2) derive, for the first time, an accurate coronal luminosity function for the T Tauri members of this T association and make direct comparisons between the coronal luminosity functions for other T associations and those of large clusters. We have used our survey data to assess (a) the importance of the star-formation environment in initial coronal activity levels, (b) the effects of PMS evolution on dynamo activity as a function of mass and age, and (c) the level of contamination by field post-T Tauri stars on association membership surveys.

Patten, Brian M.↗