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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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NASA NTRS1976

Observations of limb flares with a soft X-ray telescope

The structure and evolution of 26 limb flares have been observed with a soft X-ray telescope flown on Skylab. The results are: (1) One or more well defined loops were the only structures of flare intensity observed during the rise phase and near flare maximum, except for knots which were close to the resolution of the telescope; (2) the flare core features were always sharply defined during rise phase; and (3) for the twenty events which contained loops, the geometry of the structure near maximum was that of a loop in ten cases, a loop with a spike at the top in four cases, a cusp or triangle in four cases, and a cusp combined with a spike in another two cases. Based on observation of the original film, it is suggested that flares which underwent large scale deformations had become unstable to MHD kinks. This implies that these flares occurred in magnetic flux tubes through which significant currents were flowing.

Gibson, E. G.↗

NASA NTRS1977

Planning for Materials Processing in Space

A systems design study to describe the conceptual evolution, the institutional interrelationshiphs, and the basic physical requirements to implement materials processing in space was conducted. Planning for a processing era, rather than hardware design, was emphasized. Product development in space was examined in terms of fluid phenomena, phase separation, and heat and mass transfer. The effect of materials processing on the environment was studied. A concept for modular, unmanned orbiting facilities using the modified external tank of the space shuttle is presented. Organizational and finding structures which would provide for the efficient movement of materials from user to space are discussed.

Source record↗

NASA NTRS1981

New insight into the physics of atmospheres of early type stars

The phenomenon of mass loss and stellar winds from hot stars are discussed. The mass loss rate of early type stars increases by about a factor of 100 to 1000 during their evolution. This seems incompatible with the radiation driven wind models and may require another explanation for the mass loss from early type stars. The winds of early type stars are strongly variable and the stars may go through active phases. Eclipses in binary systems by the stellar winds can be used to probe the winds. A few future IUE studies are suggested.

Lamers, H. J. G. L. M.↗

NASA NTRS1987

Theory of collapse and protostar formation

Interstellar clouds must increase in density by a factor of more than 10 to the 20th in order to form stars. Because observations of the phases intermediate between dense interstellar clouds and pre-main-sequence stars are difficult, theoretical solutions presently provide the primary means for exploring the collapse phase of protostellar formation. The mathematical formulation of the protostellar collapse problem is presented, and various methods employed in solving the equations are outlined. This tutorial emphasizes the numerical approach to the study of the nonlinear time-dependent evolution of collapsing interstellar clouds, including self-gravitation, rotation, and radiative transfer. Results are summarized for the restricted cases of spherical and axisymmetric symmetry, as well as for fully three-dimensional evolutions, and briefly compared to observations of star formation.

Boss, A. P.↗

NASA NTRS1992

Tidal evolution of globular clusters. II - The effects of Galactic tidal field and diffusion

The tidal evolution of globular clusters subject to various degrees of the internal diffusion process is investigated. In cases of negligible diffusion, clusters are found to be tidally truncated to the theoretical tidal radius at perigalacticon. There is no apparent orbital phase dependence of the tidal radius for clusters with eccentric orbits. In clusters with moderately short two-body relaxation time scales, diffusion processes significantly modify the structure of the outer regions in such a way that the limiting radius may be comparable to the tidal radius at apogalacticon. The Galactical tidal torque induces isotropy in the velocity dispersion of the outer regions of the cluster. For relaxed clusters, the velocity dispersion may be isotropic in the core, anisotropic in the envelope and isotropic near the limiting radius. Disk shocking is also very efficient for isotropizing the orbits of stars in the outer cluster regions. Stars with direct orbits are less stable, so that prolonged tidal interaction can lead to apparent retrograde rotation in the outer regions of the cluster.

Oh, K. S.↗

NASA NTRS1991

Mesoscale and large-scale variability of the Antarctic circumpolar current

This investigation of the physical oceanography of the Southern Ocean will carry out two parallel efforts during the years preceding the launch of TOPEX/POSEIDON. First, the Geosat data will be used to develop a preliminary descriptive picture of the mesoscale and large-scale, low-frequency surface circulation of the Southern Ocean. Some of this analysis of Geosat data has already begun. For example, as a measure of the geographical distribution of mesoscale variability, a color-coded map of the standard deviation of sea level from two years of Geosat data is shown. Efforts are presently under way to investigate the seasonal and year-to-year variability of this mesoscale energy. The data are also being used to generate low-pass filtered fields of sea level from which the temporal evolution of large-scale variability in the Southern Ocean may be investigated. The second parallel effort is the development and test of modeling and data assimilation techniques that will later be applied to TOPEX/POSEIDON data during the postlaunch phase. One objective of the modeling and data assimilation is to investigate the relation between mesoscale sea level variations and eddy flux in the Southern Ocean. Uncertainties in present estimates of the various components of meridional oceanic heat transport are large. The evidence presented indicates that the very energetic mesoscale variability in the ACC apparently accounts for much of the estimated 0.45x10(exp 15) watts of poleward heat transport across the ACC required to balance the heat budget. Eddy variability is strongly coherent vertically in the ACC, at least in the vicinity of Drake Passage where nearly all of the historical in situ data have been collected.

Chelton, Dudley B.↗

NASA NTRS2004

EUPDF-II: An Eulerian Joint Scalar Monte Carlo PDF Module : User's Manual

EUPDF-II provides the solution for the species and temperature fields based on an evolution equation for PDF (Probability Density Function) and it is developed mainly for application with sprays, combustion, parallel computing, and unstructured grids. It is designed to be massively parallel and could easily be coupled with any existing gas-phase CFD and spray solvers. The solver accommodates the use of an unstructured mesh with mixed elements of either triangular, quadrilateral, and/or tetrahedral type. The manual provides the user with an understanding of the various models involved in the PDF formulation, its code structure and solution algorithm, and various other issues related to parallelization and its coupling with other solvers. The source code of EUPDF-II will be available with National Combustion Code (NCC) as a complete package.

Raju, M. S.↗

NASA NTRS2012

Effect of Population III Multiplicity on Dark Star Formation

We numerically study the mutual interaction between dark matter (DM) and Population III (Pop III) stellar systems in order to explore the possibility of Pop III dark stars within this physical scenario. We perform a cosmological simulation, initialized at z approx. 100, which follows the evolution of gas and DM. We analyze the formation of the first mini halo at z approx. 20 and the subsequent collapse of the gas to densities of 10(exp 12)/cu cm. We then use this simulation to initialize a set of smaller-scale 'cut-out' simulations in which we further refine the DM to have spatial resolution similar to that of the gas. We test multiple DM density profiles, and we employ the sink particle method to represent the accreting star-forming region. We find that, for a range of DM configurations, the motion of the Pop III star-disk system serves to separate the positions of the protostars with respect to the DM density peak, such that there is insufficient DM to influence the formation and evolution of the protostars for more than approx. 5000 years. In addition, the star-disk system causes gravitational scattering of the central DM to lower densities, further decreasing the influence of DM over time. Any DM-powered phase of Pop III stars will thus be very short-lived for the typical multiple system, and DM will not serve to significantly prolong the life of Pop III stars.

Stacy, Athena↗

NASA NTRS2025

Hardware in the Loop Performance of Terrestrial Powered Descent Dual Quaternion Guidance With A Custom First-Order Solver

The Safe & Precise Landing Integrated Capabilities Evolution (SPLICE) program continues to push the development of advanced descent and landing technologies. This paper will focus on the improvements made to the SPLICE Dual Quaternion Guidance (DQG) algorithm, which is a critical software component for generating approach phase and hazard avoidance trajectories. The trajectory performance of SPLICE DQG will be evaluated in preparation for a terrestrial flight test that incorporates a hazard avoidance maneuver. Additionally, the implementation of a customized first order Proportional-Integral Projected Gradient solver will be reviewed, along with preliminary execution results on the SPLICE Descent and Landing Computer (DLC).

SPLICE↗

NASA NTRS1974

Ballistic missions to Comet Encke in 1980 - A new phase of solar system exploration

A prime mission candidate for initiating exploration of both a comet and asteroids with unmanned spacecraft is available during the 1980 apparition of the short-period Comet Encke. Direct investigation of such bodies is expected to provide the best insight into conditions existing during the early periods of solar system evolution. A discussion is presented on low-cost ballistic mission options to Comet Encke. Particular emphasis is given to the results of a recently-completed study of ballistically-launched, spin-stabilized spacecraft for 1980 missions to Comet Encke and the asteroids Geographos and Toro. Characteristics and utilization of a small, separable probe to enhance comet science return are also described. In conclusion, it is shown that the Encke ballistic flyby can provide the necessary technical foundation to support the planning of more advanced Encke follow-on missions as well as the challenging flyby of Comet Halley in 1986.

Bursnall, W. J.↗

NASA NTRS1990

Evolution and interaction of two- and three-dimensional instability waves

The present work is concerned with the nonlinear interactions of high-amplitude two- and three-dimensional instability waves in jets. A jet is excited by multifrequency axisymmetric and helical modes. Formulations are presented here for the nonlinear development of both the amplitudes and phases of the instability waves. The development of these waves are also coupled with the development of the mean flow and the background turbulence. In formulating this model it is assumed that each flow component can be characterized by conservations equations supplemented by closure models.

Mankbadi, R. R.↗

NASA NTRS2011

Imaging with HST the Time Evolution of Eta Carinae's Colliding Winds

We report new HST/STIS observations that map the high-ionization forbidden line emission in the inner arcsecond of Eta Car, the first that fully image the extended wind-wind interaction region of the massive colliding wind binary. These observations were obtained after the 2009.0 periastron at orbital phases 0.084, 0.163, and 0.323 of the 5.54-year spectroscopic cycle. We analyze the variations in brightness and morphology of the emission, and find that blue-shifted emission (-400 to -200 km/s is symmetric and elongated along the northeast-southwest axis, while the red-shifted emission (+ 100 to +200 km/s) is asymmetric and extends to the north-northwest. Comparison to synthetic images generated from a 3-D dynamical model strengthens the 3-D orbital orientation found by Madura et al. (2011), with an inclination i approx. 138deg, argument of periapsis omega approx. 270deg, and an orbital axis that is aligned at the same PA on the sky as the symmetry axis of the Homunculus, 312deg. We discuss the potential that these and future mappings have for constraining the stellar parameters of the companion star and the long-term variability of the system.

Gull, Theodore R.↗

NASA NTRS1995

Radial evolution of the solar wind from IMP 8 to Voyager 2

Voyager 2 and Interplanetary Monitoring Platform (IMP) 8 data from 1977 through 1994 are presented and compared. Radial velocity and temperature structures remain intact over the distance from 1 to 43 AU, but density structures do not. Temperature and velocity changes are correlated and nearly in phase at 1 AU, but in the outer heliosphere temperature changes lead velocity changes by tens of days. Solar cycle variations are detected by both spacecraft, with minima in flux density and dynamic pressure near solar maxima. Differences between Voyager 2 and IMP 8 observations near the solar minimum in 1986-1987 are attributed to latitudinal gradients in solar wind properties. Solar rotation variations are often present even at 40 AU. The Voyager 2 temperature profile is best fit with a R(exp -0.49 +/- 0.01) decrease, much less steep than an adiabatic profile.

Richardson, John D.↗

NASA NTRS2011

The Time Evolution of Eta Carinae's Colliding Winds

We report new HST/STIS observations that map the high-ionization forbidden line emission in the inner arc second of Eta Car, the first that fully image the extended wind-wind interaction region of the massive colliding wind binary. These observations were obtained after the 2009.0 periastron at orbital phases 0.084, 0.163, and 0.323 of the 5.54-year spectroscopic cycle. We analyze the variations in brightness and morphology of the emission, and find that blue-shifted emission (-400 to -200 km/s is symmetric and elongated along the northeast-southwest axis, while the red-shifted emission (+ 100 to +200 km/s) is asymmetric and extends to the north-northwest. Comparison to synthetic images generated from a 3-D dynamical model strengthens the 3-D orbital orientation found by Madura et al. (2011), with an inclination i = 138 deg, argument of periapsis w = 270 deg, and an orbital axis that is aligned at the same P A on the sky as the symmetry axis of the Homunculus, 312 deg. We discuss the potential that these and future mappings have for constraining the stellar parameters of the companion star and the long-term variability of the system. Plain-Language Abstract: With HST, we resolved the interacting winds of the binary, Eta Carinae. With a 3-D model, we find the binary orbit axis is aligned to the Homunculus axis. This suggests a connection between the binary and Homunculus ejection mechanism.

Gull, Theodore R.↗

NASA NTRS1979

The crop assessment subsystem: System implementation and approaches used for the generation of crop production reports

The primary responsibility of the crop assessment subsystem (CAS) during the three phases of LACIE was to produce crop reports that included estimates of wheat area, yield, and production, as well as a specified set of associated statistical descriptors. The operations of CAS are described with emphasis on sampling strategy, input/output data, evolution of aggregation/reporting system capabilities, and CAS aggregation procedures.

Mcallum, W. E.↗

NASA NTRS1986

High energy observations of June 1980 solar flares

The paper presents a detailed study of the high energy X-ray observations of the most unusual solar events observed on 4 and 7 June, 1980 with the Hard X-Ray Burst Spectrometer (HXRBS) on Solar Maximum Mission (SMM) satellite. The hard X-ray data of the events are also compared with the radio microwave fluxes. The X-ray time profiles of these flares are characterized by the occurrence of impulsive phase superposed with a number of narrow spikes before the occurrence of the main energetic events. Studies of the temporal and spectral properties of these events indicated a quasi-oscillatory nature of the sources. Various models for explaining the evolution of the events are considered and the sequential firing loop model seems to be consistent with the observations of the events.

Lokanadham, B.↗

NASA NTRS1990

An intercomparison of intraseasonal variability in general circulation models and observations

Low frequency oscillations appearing in three GCM seasonal cycle integrations are compared with the analyses of the European Center for Medium Range Weather Forecasting (ECMWF). All three models have the same resolution: 4 deg latitude by 5 deg longitude, with 9 levels. The dominant phase speeds and the differential vertical structure of the heating profiles in the GCMs are in general agreement with current theory involving the positive feedback between latent heating and moist static stability. All three GCMs fail to capture the detailed evolution in the different stages of the development and decay of the oscillation. The results suggest that an improvement in the boundary layer moisture processes may be crucial for a better simulation of the oscillation.

Park, Chung-Kyu↗

NASA NTRS1992

Modeling the quasi-biennial oscillation's effect on the winter stratospheric circulation

The influence of the equatorial quasi-biennial oscillation (QBO) on the winter middle atmosphere is modeled with a mechanistic global primitive equation model. The model's polar vortex evolution is sensitive to the lower stratosphere's tropical winds, with the polar vortex becoming more (less) disturbed as the lower stratospheric winds are more easterly (westerly). This agrees with the observed relationship between wintertime polar circulation strength and the phase of the QBO in the lower stratosphere. In these experiments it is the extratropical planetary Rossby waves that provide the tropical-extratropical coupling mechanism. More easterly tropical winds in the lower stratosphere act to confine the extratropical Rossby waves farther north and closer to the vortex at the QBO altitudes, weakening the vortex relative to the case of westerly QBO phase. While the QBO winds occur in the lower stratosphere, the anomaly in the polar vortex strength is strongest at higher levels.

O'Sullivan, Donal↗