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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Auroral particles

The problems concerning the aurora posed prior to the war are now either solved in principle or were restated in a more fundamental form. The pre-war hypothesis concerning the nature of the auroral particles and their energies was fully confirmed, with the exception that helium and oxygen ions were identified as participating in the auroral particle precipitation in addition to the protons. The nature of the near-Earth energization processes affecting auroral particles was clarified. Charged particle trajectories in various electric field geometries were modeled. The physical problems have now moved from determining the nature and geometry of the electric fields, which accelerate charged particles near the Earth, to accounting for the existence of these electric fields as a natural consequence of the solar wind's interaction with Earth. Ultimately the reward in continuing the work in auroral and magnetospheric particle dynamics will be a deeper understanding of the subtleties of classical electricity and magnetism as applied to situations not blessed with well-defined and invariant geometries.

Evans, David S.↗
NASA NTRS1988

Hypersonic, stratified gas flows past an obstacle - Direct simulation Monte Carlo calculations

Monte Carlo particle dynamics are presently used to study the interaction of a stratified gas that impinges hypersonically on a solid body, whose size is comparable to the gas scale height. Attention is given to the results of these computations for two representative cases, where the obstacle adopted is a short, uniform cylindrical pipe whose upstream end is fully open, facing directly into the flow, while the downstream end is covered by a flat circular endplate containing an 'orifice' at its center. The cases are those of a completely closed and a fully open orifice; together, these bound the full range of obstructed hypersonic, stratified gas flows of interest.

Roberts, William W., Jr.↗
NASA NTRS1988

Space Station gas-grain simulation facility - Microgravity particle research

The proposed Space Station gas-grain simulation facility (GGSF) and the possibilities for research in the facility are discussed. The physics of particles in microgravity is reviewed. The proposed design of the GGSF is illustrated and examined. Examples of experiments which have been suggested for the GGSF are presented, including the formation of organic haze particles in Titan's atmosphere, organic compound synthesis on surfaces of growing particles, fractal particles, planetary ring particle dynamics, aggregation of fine geological particulates in planetary atmospheres, and dipolar grain coagulation and orientation.

Carle, Glenn C.↗
NASA NTRS1987

Planetary impact experimentation

An understanding of impact processes in low- and microgravity environments would be advanced significantly by the construction and use of an impact facility on the Space Station. It is proposed that initial studies begin as soon as possible in ground-based impact laboratories, on the NASA KC-135 Reduced-Gravity Aircraft, and in existing drop towers. The resulting experience and information base could then be applied toward an experiment package designed for use on Shuttle orbiters to support pilot studies in orbital environments. These experiments, as well as the first efforts made on the IOC Space Station, should involve the impact of various free-floating targets; such studies would yield a substantial scientific return while providing valuable experience and engineering information for use in refining the design of the dedicated Space Station Impact Facility. The dedicated facility should be designed to support impact experimentation, including but not limited to cratering, asteroid and ring-particle dynamics, and accretional processes.

Cintala, Mark J.↗
NASA NTRS1987

Aeolian processes aboard a Space Station: Saltation and particle trajectory analysis

The Carousel Wind Tunnel (CWT) proposed to study aeolian processes aboard a Space Station consists of two concentric rotating drums. The space between the two drums comprises the wind tunnel section. Differential rates of rotation of the two drums would provide a wind velocity with respect to either drum surface. Preliminary results of measured velocity profiles made in a CWT prototype indicate that the wall bounded boundary layer profiles are suitable to simuate flat plate turbulent boundary layer flow. The two dimensional flate plate Cartesian coordinate equations of motion of a particle moving through the air are explained. In order to assess the suitability of CWT in the analysis of the trajectories of windblown particles, a series of calculations were conducted comparing cases for gravity with those of zero gravity. Results from the calculations demonstrate that a wind tunnel of the carousel design could be fabricated to operate in a space station environment and that experiments could be conducted which would yield significant results contributing to the understanding of the physics of particle dynamics.

White, Bruce R.↗
NASA NTRS1988

Modeling magnetospheric plasma; Proceedings of the First Huntsville Workshop on Magnetosphere/Ionosphere Plasma Models, Guntersville, AL, Oct. 14-16, 1987

The conference presents papers on the global modeling of magnetospheric plasma processes, the modeling of the midlatitude ionosphere and plasmasphere, the modeling of the auroral zone and boundary layer, the modeling of the polar magnetosphere and ionosphere, and the modeling of the plasma sheet and ring current. Particular attention is given to the kinetic approach in magnetospheric plasma transport modeling, self-consistent neutral point current and fields from single particle dynamics, preliminary statistical survey of plasmaspheric ion properties from observations by DE 1/RIMS, and a model of auroral potential structures based on dynamics explorer plasma data. Other topics include internal shear layers in auroral dynamics, quantitative parameterization of energetic ionospheric ion outflow, and open flux merging in an expanding polarcap model.

Moore, T. E.↗
NASA NTRS1990

Feasibility for EGRET detection of antimatter concentrations in the universe

Although the Grand Unified Theories of elementary particle dynamics have to some extent reduced the aesthetic attraction of matter-antimatter symmetry in the Universe, the idea is still not ruled out. Although first introduced by Alfven (1965), most of the theoretical development related to gamma-ray astronomy was carried out by Stecker, who has proposed (Stecker, Morgan, and Bredekamp, 1971) matter-antimatter annihilation extending back to large redshifts as a possible explanation of the apparently extragalactic diffuse gamma radiation. Other candidate explanations were also proposed, such as superposition of extragalactic discrete sources. Clearly, the existence of significant amounts of antimatter in the universe would be of great cosmological importance; its detection, however, is not simple. Since the photon is its own antiparticle, it carries no signature identifying whether it originated in a matter or an antimatter process; even aggregates of photons (spectra) are expected to be identical from matter and antimatter processes. The only likely indicator of the presence of concentrations of antimatter is evidence of its annihilation with normal matter, assuming there is some region of contact or overlap. The EGRET (Energetic Gamma-Ray Experimental Telescope) on the Gamma Ray Observatory, with a substantial increase in sensitivity compared with earlier high energy gamma ray telescopes, may be able to address this issue. The feasibility of using EGRET in such a search for antimatter annihilation in the Universe is considered.

Hartman, R. C.↗
NASA NTRS1990

Modeling solar flare conduction fronts. I - Homogeneous plasmas and ion-acoustic turbulence. II - Inhomogeneous plasmas and ambipolar electric fields

A one-dimensional, electrostatic, particle-in-cell simulation is used here to model the expansion of a heated electron population in a coronal loop during a solar flare and the characteristics of the associated X-ray emissions. The hot electrons expand outward from the localized region, creating an ambipolar electric field which accelerates a return current of cooler, ambient electrons. Ion-acoustic waves are generated by the return currents as proposed by Brown et al. (1979), but they play little or no role in containing energetic electrons and the conduction front proposed by Brown et al. does not form. The X-ray emission efficiency of the electrons is too low in the corona for them to be the source of hard X-ray bursts. The particle dynamics changes dramatically if the heated plasma is at low altitudes and expands upward into the more tenuous plasma at higher altitudes. Two important applications of this finding are the radio-frequency heating of the corona and the collisional heating of the chromosphere by precipitating energetic electrons. In both cases, the overlying plasma has a density that is too low to supply a balancing return current to the expanding hot electrons. As a result, an ambipolar electric field develops that tends to confine the energetic electrons behind a front that propagate outward at about the speed of sound.

Mckean, M. E.↗
NASA NTRS1990

Strong Langmuir turbulence generated by electron beams - Electric-field distributions and electron scattering

Strong turbulence and transit-time scattering theory are applied here to calculate the statistical distribution of intense Langmuir fields and the consequent beam scattering in plasma turbulence driven by an electron beam. The experimentally observed electric-field distributions are compared with predictions of strong-turbulence theory, concentrating on the wave levels, the Gaussian tail of the high-field distribution observed in one experiment, the arrest scale of collapse, and the fractional volume occupied by the highest fields. The Guassian form of the tail is confirmed, and the results imply that the collapse is arrested at a scale where the peak electrostatic energy density is of the same order as the thermal energy density. The theory of transit-time interactions is generalized to include relativistic particle dynamics and is applied to predict the scattering of the beam electrons in energy and angle as they pass through strong Langmuir turbulence. The results support the validity of the recently developed scaling theory of strong turbulence.

Robinson, P. A.↗
NASA NTRS1989

Mechanisms of atomic oxygen induced materials degradation

This paper includes discussions of mechanisms by which atomic oxygen may attack materials being flown in low earth orbit (LEO), suggestions for development of materials intrinsically resistant to the harsh LEO environment, and results of an Arrhenius fit to mass loss of Kapton under exposure to thermal atomic oxygen in a laboratory environment. Oxygen atoms are powerful oxidizing agents which can rapidly degrade many types of polymeric materials. The process details depend upon the specific material, its detailed bonding, the thermodynamic stability of potential products, temperature, and particle dynamics. With regard to spacecraft, many effects associated with atomic oxygen may be explained simply by ordinary thermal oxidation processes and by the fact that the oxygen has a preferred direction of impingement.

Pippin, H. G.↗
NASA NTRS1992

Energetic ions as remote probes of X type neutral lines in the geomagnetic tail

The study presents a summary of particle orbit signatures of a neutral line in the geomagnetic tail current sheet (CS) as a function of spatial position along the CS boundary layer, as well as within the CS. Six types of CS particle orbits are reviewed: transient B sub z, transient X line, quasi-trapped, trapped, noncrossing X line, and limiting (singular) cases. It is found that for single particle dynamics in a current sheet with neutral line, the phase space ridge is predicted to be found throughout the current sheet if it is not destroyed by collective behavior. An initially tailward flowing distribution causes asymmetries in distributions earthward vs tailward of the neutral line. It is suggested that the chaotic pitch angle scattering may be a dominant mechanism to produce nightside proton isotropy in the auroral zones.

Speiser, T. W.↗
NASA NTRS1992

Heavy ion dynamics and auroral arc formation in the Jovian magnetosphere

This paper gives a brief review of some of the current controversial issues surrounding the Jovian aurora. In particular, the manner of its excitation be it that of electron or heavy ion precipitation is examined critically in the context of proposed models for magnetospheric dynamics, particle energization, and auroral energy input. A model for the X-ray aurora based on bremsstrahlung by a primary electron beam and its ionization secondaries is high-lighted and the connection to the outward magnetospheric transport of heavy ion plasma from the satellite Io is made.

Barbosa, D. D.↗
NASA NTRS1993

A survey of particle image velocimetry applications in Langley aerospace facilities

This paper describes several applications of the global velocity measurement technique known as particle image velocimetry to three different facilities at Langley Research Center. These three applications represent global velocity measurements in distinctly different flows, namely a reacting hydrogen - air flame, a low Reynolds number boundary layer, and hypersonic flow over a wedge. In addition, these applications illustrate the power of the instrument to obtain data such as vorticity and Reynolds stress. Finally, the ability to obtain particle dynamics data in supersonic/hypersonic flows similar to that which can be obtained with point measurement techniques is demonstrated.

Humphreys, W. M.↗
NASA NTRS1994

Design of orbital debris shields for oblique hypervelocity impact

A new impact debris propagation code was written to link CTH simulations of space debris shield perforation to the Lagrangian finite element code DYNA3D, for space structure wall impact simulations. This software (DC3D) simulates debris cloud evolution using a nonlinear elastic-plastic deformable particle dynamics model, and renders computationally tractable the supercomputer simulation of oblique impacts on Whipple shield protected structures. Comparison of three dimensional, oblique impact simulations with experimental data shows good agreement over a range of velocities of interest in the design of orbital debris shielding. Source code developed during this research is provided on the enclosed floppy disk. An abstract based on the work described was submitted to the 1994 Hypervelocity Impact Symposium.

Fahrenthold, Eric P.↗
NASA NTRS1994

Acceleration of interstellar pickup ions in the disturbed solar wind observed on Ulysses

Acceleration of interstellar pickup H(+) and He(+) as well as of solar wind protons and alpha particles has been observed on Ulysses during the passage of a corotating interaction region (CIR) at approximately 4.5 AU. Injection efficiencies for both the high thermal speed interstellar pickup ions (H(+) and He(+)) and the low thermal speed solar wind ions (H(+) and He(++) are derived using velocity distribution functions of protons, pickup He(+) and alpha particles from less than 1 to 60 keV/e and of ions (principally protons) above approximately 60 keV. The observed spatial variations of the few keV and the few hundred keV accelerated pickup protons across the forward shock of CIR indicate a two stage acceleration mechanism. Thermal ions are first accelerated to speeds of 3 to 4 times the solar wind speed inside the CIR, presumably by some statistical mechanism, before reaching higher energies by a shock acceleration process. Our results also indicate that (1) the injection efficiencies for pickup ions are almost 100 times higher than they are for solar wind ions, (2) pickup H(+) and He(+) are the two most abundant suprathermal ion species and they carry a large fraction of the particle thermal pressure, (3) the injection efficiency is highest for protons, lowest for He(+), and intermediate for alpha particles, (4) both H(+) and He(+) have identical spectral shapes above the cutoff speed for pickup ions, and (5) the solar wind frame velocity distribution function of protons has the form F(w) = F(sub o)w(sup -4) for 1 is less than w is less than approximately 5, where w is the ion speed divided by the solar wind speed. Above w approximately 5-10 the proton spectrum becomes steeper. These results have important implications concerning acceleration of ions by shocks and CIRs, acceleration of anomalous cosmic rays, and particle dynamics in the outer heliosphere.

Gloeckler, G.↗
NASA NTRS1998

An Assessment of Molten Metal Detachment Hazards During Electron Beam Welding in Space

The safety issue has been raised with regards to potential molten metal detachments from the weld pool and cold filler wire during electron beam welding in space. This investigation was undertaken to evaluate if molten metal could detach and come in contact with astronauts and burn through the fabric of the astronauts' Extravehicular Mobility Unit (EMU) during electron beam welding in space. Molten metal detachments from either the weld/cut substrate or weld wire could present harm to a astronaut if the detachment was to burn through the fabric of the EMU. Theoretical models were developed to predict the possibility and size of the molten metal detachment hazards during the electron beam welding exercises at Low Earth Orbit (LEO). The primary molten metal detachment concerns were those cases of molten metal separation from the metal surface due to metal cutting, weld pool splashing, entrainment and release of molten metal due to filler wire snap-out from the weld puddle, and molten metal accumulation and release from the end of the weld wire. Some possible ways of obtaining molten metal drop detachments would include an impulse force, or bump, to the weld sample, cut surface, or filler wire. Theoretical models were developed for these detachment concerns from principles of impact and kinetic energies, surface tension, drop geometry, surface energies, and particle dynamics. The surface tension represents the force opposing the liquid metal drop from detaching whereas the weight of the liquid metal droplet represents a force that is tending to detach the molten metal drop. Theoretical calculations have indicated that only a small amount of energy is required to detach a liquid metal drop; however, much of the energy of an impact is absorbed in the sample or weld plate before it reaches the metal drop on the cut edge or surface. The tendency for detachment is directly proportional to the weld pool radius and metal density and inversely proportional to the surface tension of the liquid metal. For a detachment the initial kinetic energy of the weld pool with respect to the plate has to exceed the energy to form the extra surface required for the detachment of the pool. The difficulty is in transferring the energy from the point of impact through the plate and sample to the cut edge. It is likely that not all of the kinetic energy is available for detaching the pool; some may be sequestered in weld pool oscillations. The coefficient of restitution for the collision will be lower than one if irreversible deformation, for example plastic flow deformation, takes place during the collision. Thus determining the amount of energy from an impact that actually reaches the molten metal droplet is critical. Various molten metal detachment scenarios were tested experimentally in an enclosed vacuum chamber using the Ukrainian Universal Hand Tool, an electron beam welder designed for space welding. The experimental testing was performed in a 4 ft. X 4 ft. vacuum chamber at Marshall Space Flight Center, evacuated to vacuum levels of at least 50 microTorr, and also some welding garment material was utilized to observe the effect of the molten metal detachments on the material. A "carillon" apparatus consisting of four pendulum hammer strikers, each weighing approximately 3.65 lbs, raised to predetermined specific heights was used to apply an impact force to the weld sample/plate during electron beam welding and cutting exercises. The strikers were released by switching on an electric motor to rotate a pin holding wires retaining the strikers at desired heights. The specimens were suspended so as to be free to respond to the blows with a sudden velocity increment. The specimens were mounted on a hinged plate for minimizing effective mass with the option to fasten it down so as to raise its effective mass closer to that anticipated for an actual space welding scenario. Measurements were made of the impact energy and the horizontal fling distances of the detached metal drops. It was not particularly easy to generate the detachments for this experiment. This document presents the details of the theoretical modeling effort and a summary of the experimental effort to measure molten metal drop detachments from terrestrial electron beam welding in the enclosed vacuum chamber. The results of the experimental effort have shown that molten metal detachments can occur from the sample/weld plate only if a sufficiently large impact force is applied to the weld plate. A "weld pool detachment parameter" was determined to indicate whether detachment would occur. Detachment can be either full or partial (dripping), Partial detachment means that the weld pool detached from one side of the liquid-solid boundary so as to leave a hole at the puddle site but remained attached over part of the liquid-solid boundary and dripped down the plate with no fully detached material detected. Full detachment, however, does not necessarily mean that the whole pool fully detached; in some cases only a smaller portion of the pool detached, the remainder dripping down the plate. The weld pool detachment parameter according to theory and according to the empirical data allows a determination of whether full detachments might occur. Theoretical calculations indicated titanium alloy would be the most difficult from which to detach molten metal droplets followed by stainless steel and then by aluminum. The experimental results were for the most part consistent with the theoretical analysis and predictions. The above theory is applicable to other situations as desired for assessing the potential for molten metal detachments.

Fragomeni, James M.↗
NASA NTRS2000

SHIVA: Spaceflight Holography Investigation in a Virtual Apparatus

SHIVA, a NASA spaceflight program, will exploit a unique, holography-based, diagnostics tool to test and apply a new, more general analytical solution to a fundamental equation of motion. The equation describes particle dynamics in fluids in a microgravity environment, and our solution represents the first analytical solution of it. When gravity is removed the equation becomes much more complex and had been solved previously only by numerical means. After our analytical solution has been validated it will be used as a tool for making additional measurements of the gravity environment. Our experiment will be optimized for testing the model, measuring g, g-jitter, and other microgravity phenomena. We will also collect data for which no current theory exists, This paper describes ground experiments and analysis that have been conducted by the investigator team to support the flight experiment.

Trolinger, James D.↗
NASA NTRS2003

Effect of Gravity Level on the Particle Shape and Size During Zeolite Crystal Growth

A microscopic diffusion model is developed to represent solute transport in the boundary layer of a growing zeolite crystal. This model is used to describe the effect of gravity on particle shape and solute distribution. Particle dynamics and crystal growth kinetics serve as the boundary conditions of flow and convection-diffusion equations. A statistical rate theory is used to obtain the rate of solute transport across the growing interface, which is expressed in terms of concentration and velocity of solute species. Microgravity can significantly decrease the solute velocity across the growing interface compared to its earth-based counterpart. The extent of this reduction highly depends on solute diffusion constant in solution. Under gravity, the flow towards the crystal enhances solute transport rate across the growing interface while the flow away from crystals reduces this rate, suggesting a non-uniform growth rate and thus an elliptic final shape. However, microgravity can significantly reduce the influence of flow and obtain a final product with perfect spherical shape. The model predictions compare favorably with the data of space experiment of zeolites grown in space.

Song, Hong-Wei↗