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At least 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

A subauroral and mid-latitude view of substorm activity

Experimental observations from a variety of sources made during a substorm period near 0900 UT on January 2, 1971 have provided evidence confirming mid-latitude and subauroral phenomena associated with magnetic substorm activity. A review of these observations, including ground and balloon observations made near L=4 at the conjugate stations Siple, Antarctica and Roberval, Canada and data obtained from the synchronous-orbit satellite ATS 5 positioned about 2 hours west of the Siple, Roberval meridian, is presented. During the hour before the reported correlated bursts of X rays and VLF noise (Rosenberg et al., 1971), the plasmapause appears to be displaced towards the equator from Siple; resonance conditions along the field lines at Siple were favorable for the observation of results of magnetospheric wave-particle interactions involving electrons with energies exceeding 30 keV. The correlated observations are a potential source of information concerning the relationship of ULF and VHF noise activity to the magnetospheric particle population at middle latitudes; the injection and subsequent drift of low and medium energy electrons during substorms; and enhanced particle precipitation deep within the plasmasphere during substorms.

Carpenter, D. L.↗
NASA NTRS1984

Connection Between the Magnetosphere and Ionosphere

Two decades of space research have produced ample evidence that particles and fields originating in the active Sun can gain entry into the terrestrial magnetosphere and deposit their energy in the ionosphere and atmosphere. The final link in this solar-terrestrial chain is generically referred to as magnetosphere-ionosphere coupling (MIC). Because of the far-reaching implications of recent discoveries in MIC and because a coherent assessment of them has yet to be made, the principal task is to critically assess these new observations and the new perspectives that they may engender. The MIC topics of interest are roughly grouped according to the scale lengths of the phenomena being treated. This particular choice of groupings is mainly for convenience, with perhaps some suggestion as to the direction of energy cascade from the largest scales down to the smaller scale.

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NASA NTRS1993

Gas distribution and starbursts in shell galaxies

Detailed maps of most elliptical galaxies reveal that, whereas the greatest part of their luminous mass originates from a smooth distribution with a surface brightness approximated by a de Vaucouleurs law, a small percentage of their light is contributed by low surface brightness distortions termed 'fine structures'. The sharp-edged features called 'shells' are successfully reproduced by merger and infall models involving accretion from less massive companions. In this context, dwarf spheroidal and compact disk galaxies are likely progenitors of these stellar phenomena. However, it is probable that the sources of shell-forming material also contain significant amounts of gas. This component may play an important role in constraining the formation and evolution of shell galaxies. To investigate the effects of the gaseous component, numerical simulations were performed to study the tidal disruption of dwarf galaxies containing both gas and stars by more massive primaries, and the evolution of the ensuing debris. The calculations were performed with a hybrid N-body/hydrodynamics code. Collisionless matter is evolved using a conventional N-body technique and gas is treated using smoothed particle hydrodynamics in which self-gravitating fluid elements are represented as particles evolving according to Lagrangian hydrodynamic equations. An isothermal equation of state is employed so the gas remains at a temperature 104 K. Owing to the large mass ratio between the primary and companion, the primary is modeled as a rigid potential and the self-gravity of both galaxies is neglected.

Weil, Melinda L.↗
NASA NTRS1996

X-Ray Imaging Study

The space environment in which the Space Station Freedom and other space platforms will orbit is truly a hostile environment. For example, the currently estimated integral fluence for electrons above 1 Mev at 2000 nautical miles is above 2 x 1O(exp 10) electrons/sq cm/day and the proton integral fluence is above 1 x 10(exp 9) protons/sq cm/day. At the 200 - 400 nautical miles, which is more representative of the altitude which will provide the environment for the Space Station, each of these fluences will be proportionally less; however, the data indicates that the radiation environment will obviously have an effect on structural materials exposed to the environment for long durations. The effects of this combined environment is the issue which needs to be understood for the long term exposure of structures in space. At the same time, there will be substantial potential for collisions between the space platforms and space debris. The current NASA catalogue contains over 4500 objects floating in space which are not considered payloads. This debris can have significant effects on collision with orbiting spacecraft. In order to better understand the effect of these hostile phenomena on spacecraft, several types of studies are being performed to simulate at some level the effect of the environment. In particular the study of debris clouds produced by hypervelocity impact on the various surfaces anticipated on the Space Station is very important at this point in time. The need to assess the threat of such debris clouds on space structures is an on-going activity. The Space Debris Impact facility in Building 4612 provides a test facility to monitor the types of damage produced with hypervelocity impact. These facilities are used to simulate space environmental effects from energetic particles. Flash radiography or x-ray imaging has traditionally provided such information and as such has been an important tool for recording damage in situ with the event. The proper operation of the system can provide much useful information with respect to parametric analysis of the hypervelocity experiment. The following report outlines the procedures developed to optimize the operation of the x-ray imaging system and its operational characteristics.

OBrien, Susan K.↗
NASA NTRS2004

High-Order Simulation of Non-Linear Oscillations and Shocks in the Solar Atmosphere

The solar atmosphere presents a rich source of highly non-linear magneto-hydrodynamic phenomena: strong gradients and forcing terms result in both large shocks and oscillations. The additional requirements of energy balance and initialization in hydrostatic equilibrium compound the challenge of this problem. A wealth of observational data allows us to check the results of our simulations. The problem of simulating the solar atmosphere provides, in addition to an interesting system in its own right, a challenging testbed for high-order shock-capturing methods. We discuss the challenge of simulating solar atmospheric phenomena, concentrating on various high-order central methods ranging from second to fourth order. Our method is based on the central-upwind scheme of Kurganov, Noelle and Petrova, which we extend to high order via various interpolants. We investigate various initial data for our simulations, corresponding to observed conditions in different regions of the solar surface: the normal quiet sun and sunspots. When non-oscillatory using second- and third-order methods, we are able to reproduce non-trivial observational results. In particular we find a correlation between initial data and both the shock speeds and particle oscillation spectra that match observations in the corresponding regions. When using fourth-order WENO interpolants, we find that while the individual shock profiles at any given time appear non-oscillatory, spurious oscillations appear in the fields after long time integrations. The issue of initialization in hydrostatic equilibrium raises difficult issues. Careful treatment of the gravitational source term can reduce violations of hydrostatic equilibrium, but difficulties remain, primarily due to discontinuities in the piecewise-polynomial reconstructions. In the case of the Euler equations in gravity, the use of high-order methods reduces the violation of hydrostatic equilibrium to a sufficiently low level for the above described results to be obtained. Including various energy flux terms in the equations, however, leads to severe instability when hydrostatic balance is violated. We discuss various strategies to address this problem, including adaptive grid methods.

Bryson, S.↗
NASA NTRS1999

Optical Flow-Field Techniques Used for Measurements in High-Speed Centrifugal Compressors

The overall performance of a centrifugal compressor depends on the performance of the impeller and diffuser as well as on the interactions occurring between these components. Accurate measurements of the flow fields in each component are needed to develop computational models that can be used in compressor design codes. These measurements must be made simultaneously over an area that covers both components so that researchers can understand the interactions occurring between the two components. Optical measurement techniques are being used at the NASA Lewis Research Center to measure the velocity fields present in both the impeller and diffuser of a 4:1 pressure ratio centrifugal compressor operating at several conditions ranging from design flow to surge. Laser Doppler Velocimetry (LDV) was used to measure the intrablade flows present in the impeller, and the results were compared with analyses obtained from two three-dimensional viscous codes. The development of a region of low throughflow velocity fluid within this high-speed impeller was examined and compared with a similar region first observed in a large low-speed centrifugal impeller at Lewis. Particle Image Velocimetry (PIV) is a relatively new technique that has been applied to measuring the diffuser flow fields. PIV can collect data rapidly in the diffuser while avoiding the light-reflection problems that are often encountered when LDV is used. The Particle Image Velocimeter employs a sheet of pulsed laser light that is introduced into the diffuser in a quasi-radial direction through an optical probe inserted near the diffuser discharge. The light sheet is positioned such that its centerline is parallel to the hub and shroud surfaces and such that it is parallel to the diffuser vane, thereby avoiding reflections from the solid surfaces. Seed particles small enough to follow the diffuser flow are introduced into the compressor at an upstream location. A high-speed charge-coupled discharge (CCD) camera is synchronized to the laser pulse rate; this allows it to capture images of seed particle position that are separated by a small increment in time. A crosscorrelation of a particle's position in two consecutive images provides an estimate of flow velocity and direction. Multiple image pairs obtained in rapid succession at a particular flow condition provide enough measurements for statistical significance. PIV provides simultaneous velocity measurements over the entire plane that is illuminated by the light sheet instead of at a single point, as is the case when LDV is used. PIV has a further advantage in that the laser light pulse can be triggered by an external source such as a high-response pressure transducer. This feature will allow PIV to synchronize flow imaging to physical phenomena such as rotating stall or stall precursor waves. We hope that this technique can be used to obtain images of the flow field during and just prior to stall.

Skoch, Gary J.↗
NASA NTRS2016

Wind Tunnel Test of a Risk-Reduction Wing/Fuselage Model to Examine Juncture-Flow Phenomena

A wing/fuselage wind-tunnel model was tested in the Langley 14- by 22-foot Subsonic Wind Tunnel in preparation for a highly-instrumented Juncture Flow Experiment to be conducted in the same facility. This test, which was sponsored by the NASA Transformational Tool and Technologies Project, is part of a comprehensive set of experimental and computational research activities to develop revolutionary, physics-based aeronautics analysis and design capability. The objectives of this particular test were to examine the surface and off-body flow on a generic wing/body combination to: 1) choose a final wing for a future, highly instrumented model, 2) use the results to facilitate unsteady pressure sensor placement on the model, 3) determine the area to be surveyed with an embedded laser-doppler velocimetry (LDV) system, 4) investigate the primary juncture corner- flow separation region using particle image velocimetry (PIV) to see if the particle seeding is adequately entrained and to examine the structure in the separated region, and 5) to determine the similarity of observed flow features with those predicted by computational fluid dynamics (CFD). This report documents the results of the above experiment that specifically address the first three goals. Multiple wing configurations were tested at a chord Reynolds number of 2.4 million. Flow patterns on the surface of the wings and in the region of the wing/fuselage juncture were examined using oil- flow visualization and infrared thermography. A limited number of unsteady pressure sensors on the fuselage around the wing leading and trailing edges were used to identify any dynamic effects of the horseshoe vortex on the flow field. The area of separated flow in the wing/fuselage juncture near the wing trailing edge was observed for all wing configurations at various angles of attack. All of the test objectives were met. The staff of the 14- by 22-foot Subsonic Wind Tunnel provided outstanding support and delivered exceptional value to the experiment, which exceeded expectations. The results of this test will directly inform the planning for the first of a series of instrumented-model tests at the same Reynolds number. These tests will be performed on a slightly larger-scale model with the selected wing, and will include off-body measurements with LDV and PIV, steady and unsteady pressure measurements, and the flow-visualization techniques that are discussed in this report.

Kegerise, Michael A.↗
NASA NTRS1994

SEPAC co-investigator support

Mission preparation and support, data reduction and analysis, and modelling of beam phenomenon activities are described with respect to the Space Experiments with Particle Accelerators (SEPAC) project. The SEPAC Electron Beam Accelerator was used in observing the life time and drift velocity of ionization streaks in the upper atmosphere by ground based radars. A second active source, the plasma contactor (PC) electrically neutralized the shuttle orbiter during beam injections. Several observations of plasma density enhancements were correlated with orbiter crossings of the magnetic meridian of the Jicamarca, Peru radar located near the magnetic equator. One of several successful experiments was the artificial aurora experiment in which downward directed electron beam pulses were observed by the onboard AEPI camera. Theoretical and modelling efforts focused on phenomena related to electron beam and plasma cloud injection from spacecraft.

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NASA NTRS1995

Analysis of Static Spacecraft Floating Potential at Low Earth Orbit (LEO)

Spacecraft floating potential is the charge on the external surfaces of orbiting spacecraft relative to the space. Charging is caused by unequal negative and positive currents to spacecraft surfaces. The charging process continues until the accelerated particles can be collected rapidly enough to balance the currents at which point the spacecraft has reached its equilibrium or floating potential. In low inclination. Low Earth Orbit (LEO), the collection of positive ion and negative electrons. in a particular direction. are typically not equal. The level of charging required for equilibrium to be established is influenced by the characteristics of the ambient plasma environment. by the spacecraft motion, and by the geometry of the spacecraft. Using the kinetic theory, a statistical approach for studying the interaction is developed. The approach used to study the spacecraft floating potential depends on which phenomena are being applied. and on the properties of the plasma. especially the density and temperature. The results from kinetic theory derivation are applied to determine the charging level and the electric potential distribution at an infinite flat plate perpendicular to a streaming plasma using finite-difference scheme.

Herr, Joel L.↗
NASA NTRS2010

Lunary Dust Grain Charging by Electron Impact: Complex Role of Secondary Electron Emissions in Space Environments

Dust grains in various astrophysical environments are generally charged electrostatically by photoelectric emissions with radiation from nearby sources, or by electron/ion collisions by sticking or secondary electron emissions (SEES). The high vacuum environment on the lunar surface leads to some unusual physical and dynamical phenomena involving dust grains with high adhesive characteristics, and levitation and transportation over long distances. Knowledge of the dust grain charges and equilibrium potentials is important for understanding a variety of physical and dynamical processes in the interstellar medium, and heliospheric, interplanetary/ planetary, and lunar environments. It has been well recognized that the charging properties of individual micron-/submicron-size dust grains are expected to be substantially different from the corresponding values for bulk materials. In this paper, we present experimental results on the charging of individual 0.2-13 m size dust grains selected from Apollo 11 and 17 dust samples, and spherical silica particles by exposing them to mono-energetic electron beams in the 10-200 eV energy range. The dust charging process by electron impact involving the SEES discussed is found to be a complex charging phenomenon with strong particle size dependence. The measurements indicate substantial differences between the polarity and magnitude of the dust charging rates of individual small-size dust grains, and the measurements and model properties of corresponding bulk materials. A more comprehensive plan of measurements of the charging properties of individual dust grains for developing a database for realistic models of dust charging in astrophysical and lunar environments is in progress.

Abbas, M. M.↗
NASA NTRS1991

Electrophoresis of small particles and fluid globules in weak electrolytes

An examination is conducted of the influence of partial ionization on the electrophoresis of small particles and fluid globules, with a view to the nature of conditions under which dissociation-association (D-A) alters electrokinetics. It is found that, since D-A processes are important in cases where double-layer polarization and relaxation would otherwise prevail, the predicted effect on electrophoretic mobility is greatest for the drops and bubbles whose surfaces are fluid and convection within the interface is significant. While the computation scheme used applies only to situations where forcing-field magnitude is small, the results obtained indicate that D-A processes involving ionogenic solutes may be significant in apolar liquids where electrokinetic phenomena are driven by strong forcing fields.

Baygents, J. C.↗
NASA NTRS1993

Hypervelocity particle penetration in multi-layered thermal blankets

Micrometeoroid and related hypervelocity particle impacts into 0.04-sq m samples cut from Scheldahl G411500 thermal blankets (STB) covering trays D05 and D07 in the NASA-LDEF satellite are characterized in detail. These impacts usually produced unique penetration features that generally consist of a delamination zone extending tens of penetration-hole diameters, separating the Teflon layer from the silver/Inconel film and the paint backing layers. When viewed from the space-facing side, the penetration holes are usually surrounded by rings or concentric halos within the delamination zone and radial cracks extending from the ejecta-rim surrounding the hole to the edge of the delamination zone. The phenomena responsible for the formation of these features are examined.

Liu, Jean↗
NASA NTRS1978

An investigation of mercury hollow cathode phenomena

An experimental investigation is described in which measurements were made of plasma properties and other physical parameters upstream and downstream of the orifice plate of an operating mercury hollow cathode. These measurements included plasma property profiles, internal surface temperatures, internal pressure, and spectroscopic data of the external discharge. The results show the plume-to-spot mode transition to be characterized by significant changes in the plasma properties downstream of the cathode orifice, including the disappearance of an apparent electron free-fall region which is found to be present in the plume mode. The results also indicate the existence of a very dense plasma (10 to the 10th to 10 to the 14th electrons/cu cm) with steep electron density gradients in the region upstream of the orifice. The upstream data is found to correlate well with a modified form of the Saha equation. The related analysis indicates that the heavy particles approach thermal equilibrium with the electrons in the region of the orifice and that the ionization fraction in the orifice is very high - 80 to 100%.

Siegfried, D. E.↗
NASA NTRS1971

On the relationship between aerosol content and errors in telephotometer experiments.

This paper presents an invariant imbedding theory of multiple scattering phenomena contributing to errors in telephotometer experiments. The theory indicates that there is a simple relationship between the magnitudes of the errors introduced by successive orders of scattering and it is shown that for all optical thicknesses each order can be represented by a coefficient which depends on the field of view of the telescope and the properties of the scattering medium. The verification of the theory and the derivation of the coefficients have been accomplished by a Monte Carlo program. Both monodisperse and polydisperse systems of Mie scatterers have been treated. The results demonstrate that for a given optical thickness the coefficients increase strongly with the mean particle size particularly for the smaller fields of view.

Thomas, R. W. L.↗
NASA NTRS1996

Pressure wall hole size and maximum tip-to-tip crack length following orbital debris penetration

The threat of damage from high speed meteoroid and orbital debris particle impacts has become a significant design consideration in the development and construction of long duration earth-orbiting spacecraft. Historically, significant amounts of resources have been devoted to developing shielding for such structures as a means of reducing the penetration potential of high speed on-orbit impacts. These efforts have typically focused on simply whether or not the inner (or 'pressure') walls of candidate multi-wall structural systems would be perforated. Only recently the nature and extent of pressure wall penetration damage have begun to be explored. This report presents the results of a study whose objective was to characterize the hole formation and cracking phenomena associated with the penetration of the multi-wall systems being considered for the International Space Station Alpha (ISSA).

Schonberg, William P.↗
NASA NTRS2018

PIV and Rotational Raman-Based Temperature Measurements for CFD Validation in a Single Injector Cooling Flow

NASA's Turbulent Heat Flux (THX) task under the Transformational Tools & Technologies project is focused on acquiring benchmark temperature and velocity data in turbulent shear layers for validation of computational fluid dynamics (CFD) codes. Standard CFD turbulence models lack the ability to accurately calculate a number of fundamental flow phenomena, including the turbulent transport of heat. In nearly all production class Reynolds-averaged Navier-Stokes (RANS) CFD codes, a gradient-diffusion approximation is used whereby a constant turbulent Prantdl number, Prt, is used to relate an eddy viscosity calculated for the momentum terms, to the turbulent heat flux terms. The default in most CFD codes is Prt = 0.9, however this is not representative of all flows. As discussed in Yoder et al. (2015) and Reynolds (1974), Prt = 0.7 is felt to be more appropriate for jets. Recent work, as discussed in Yoder (2016a), has explored more complex formulations including variable turbulent Prantdl number models. PARTICLE IMAGE VELOCIMETRY; TEMPERATURE MEASURING INSTRUMENTS; FILM COOLING; HIGH TEMPERATURE GASES; COMPUTATIONAL FLUID DYNAMICS; PREDICTION ANALYSIS TECHNIQUES; TURBULENCE MODELS; RAMAN SPECTRA; VELOCITY; MACH NUMBER; GAS TURBINE ENGINES; NOZZLE FLOW; THERMOCOUPLES; LASER INDUCED FLUORESCENCE; COOLING FLOWS (ASTROPHYSICS); RAMAN SPECTROSCOPY; HEAT FLUX

Wernet, Mark P.↗
NASA NTRS1985

A cosmic ray super high energy multicore family event. 2: Structure and fragmentation characteristics of the jets

Quarks and gluons are not directly observable, but may be displayed through fragmentation in the form of hadronic jets, the evidence of which was first revealed in cosmic ray interactions before the advent of the modern theory of strong interactions. Experimental results from ISR and SPPS collider rendered the jet phenomena more confident and definite. All the properties of jets observed up to now at ISR and SPPS collider are in agreement with the predictions of QCD. In order to make further test of QCD in still higher energy regions, detailed study of super high energy jet events in cosmic rays is very desirable. The event KO E19 observed in the Mt. Kambala emulsion chamber is an interesting event for such study. The general features of KO E19 is described. Its total visible energy is sigma E sub gamma = 1537 TeV(E sub min = 1.5 TeV) and production height H=(70 + or - 30)m, with a hadron as its primary particle. Besides about forty small clusters, there are five super high energy cores or jets, one lying near the center of the event while the other four surrounding it, having incident directions making small angles with that of the primary particle. Detailed analysis is done on the emulsion plates inserted in the chamber, making full use of their fine granularity, superior in detecting and analyzing jet events, specially their substructures.

Source record↗
NASA NTRS1989

Effects of space radiation on electronic microcircuits

The single event effects or phenomena (SEP), which so far have been observed as events falling on one or another of the SE classes: Single Event Upset (SEU), Single Event Latchup (SEL) and Single Event Burnout (SEB), are examined. Single event upset is defined as a lasting, reversible change in the state of a multistable (usually bistable) electronic circuit such as a flip-flop or latch. In a computer memory, SEUs manifest themselves as unexplained bit flips. Since latchup is in general caused by a single event of short duration, the single event part of the SEL term is superfluous. Nevertheless, it is used customarily to differentiate latchup due to a single heavy charged particle striking a sensitive cell from more ordinary kinds of latchup. Single event burnout (SEB) refers usually to total instantaneous failure of a power FET when struck by a single particle, with the device shorting out the power supply. An unforeseen failure of these kinds can be catastrophic to a space mission, and the possibilities are discussed.

Kolasinski, W. A.↗