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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Rapid ray motions in barium plasma clouds and auroras

On two evenings in 1968, anomalous field-aligned brightenings or emission enhancements of up to 3X were observed to move rapidly through three different Ba(+) clouds over Andoya, Norway. Similar effects were observed in Ba(+) clouds released from rockets launched from Poker Flat, Alaska, on March 21, 1973 and on March 22, 1980. On these occasions, auroras on or near the Ba(+) L shell also exhibited active rapid ray motions, which prompts the assumption that the two phenomena are related and the expectation that an explanation of the rapid ray motions in the Ba(+) clouds would lead to a better understanding of the physics of auroral ray motions and the auroral atmosphere. Seven possible mechanisms to produce the observed moving emission enhancements are discussed. The observations provide strong evidence for the existence of transient electric fields of order 100 mV/m at altitudes as low as 200 km during active aurora with rapid ray motions.

Wescott, E. M.↗
NASA NTRS1987

A preliminary investigation of large-scale organized motions in a supersonic turbulent boundary layer on a curved surface

An experimental investigation concentrating on the change in the large-scale organized motions of a supersonic turbulent boundary layer subjected to a short region of concave surface curvature is presented. Two flows were studied, a relatively weak and a relatively strong perturbation. In both flows the freestream Mach number was 2.89 and the Reynolds number based on momentum thickness was 81,900. Hot-wire anemometry and schlieren photography provided the principle tools for this investigation. Hot-wire data were analyzed using spectral and correlation methods and conditional sampling techniques. Changes in structure angle and results of conditionally sampled velocity signals are discussed. The strong perturbation is found to increase the structure angle, and in both flows the length scales of the organized motions are altered.

Donovan, J. F.↗
NASA NTRS1983

Low-level flow conditions hazardous to aircraft

Low level flow conditions known to be hazardous to aircraft during takeoff/climbout and approach/landing operations are turbulence, wind shear, and vertical motion. These conditions can and frequently do occur separately and in combinations. The identification and selection were completed of representative data cases to determine magnitude, frequency, duration, and simultaneity of occurrence of turbulence (gustiness and gust factor), wind shear (speed and direction), and vertical motion (updraft and downdraft), along with temperature inversions. New representations of temporal and spatial variations in the atmospheric boundary layer were developed. Efforts continued relative to low level flow conditions where published results imply strong vertical shear with virtually no horizontal shear and where order of magnitude analyses of the equations of motion for an aircraft illustrates that low values of horizontal shear (along the flight path) are much more hazardous than larger values of vertical wind shear (altitude).

Alexander, M. B.↗
NASA NTRS1994

Cosmic bullets as particle accelerators and radio sources

We have simulated in two dimensions the dynamical evolution of dense gas clouds(`cosmic bullets') moving supersonically through a uniform low-density medium. The diffusive shock acceleration of relativistic protons (cosmic rays) and their dynamical feedback on the background flow are included by the two-fluid model for this process. The acceleration of relativistic electrons is approximated by a test-particle model, and a passive magnetic field is followed by a simple advection scheme. Strong bow shocks, with Mach numbers similar to that of a bullet's motion, are the most important particle accelerators in the flow, while tail shocks and shocks inside the bullets do not play generally significant roles in this regard. For our simulation parameters, approximately greater than 10% of the initial bullet kinetic energy is converted to a combination of internal energy of gas and cosmic-ray protons by the time the bullets begin to be disrupted. Characteristically, the cosmic rays gain several percent of the available kinetic energy. Bullet destruction on timescales only a little larger than the ram pressure bullet crushing time begins in response to Kelvin-Helmholtz and especially to Rayleigh-Taylor instabilities along the forward bullet surface. For dense bullets this happens before the bullet is stopped by ram pressure. According to our simple model for synchrotron emission from relativistic electrons accelerated and transported within the flows, that emission increases rapidly as the bullet begins to fragment, when it is strongly dominated by field enhancement in sheared flows. Synchrotron emission from the acceleration region within the bow shock is, by contrast, much weaker.

Jones, T. W.↗
NASA NTRS1972

Photographic Observations of Comet Bennett, 1970II

Direct photography of Comet Bennett with a range of focal lengths shows structure in the coma and strong Type 1 and Type 2 tails. The Type 1 tail shows motion in 15 minutes. The inner coma contains spiral-shaped jets of a type observed visually on occasion in the past but not photographed before. The spiral shape is apparently due to the rotation of the nucleus. On the assumption that the outward velocity of the jets is 0.6 km/sec, as estimated by Delsemme, a rotation period of 1.4 to 1.5 days is derived for the nucleus. The rotation is direct (in the sense of the comet's orbital motion).

Larson, S. M.↗
NASA NTRS1972

Photographic observations of Comet Bennett, 1970II.

Direct photography of Comet Bennett with a range of focal lengths shows structure in the coma and strong Type I and Type II tails. The Type I tail shows motion in 15 minutes. The inner coma contains spiral-shaped jets of a type observed visually on occasion in the past but not photographed before. The spiral shape is apparently due to the rotation of the nucleus. On the assumption that the outward velocity of the jets is 0.6 km/sec, as estimated by Delsemme, a rotation period of 1.4-1.5 days is derived for the nucleus. The rotation is direct (i.e., in the sense of the comet's orbital motion).

Larson, S. M.↗
NASA NTRS1973

Ion kinematics in a plasma focus.

The results of numerical integrations of three-dimensional equations of motion of ions subject to given electric and magnetic fields are presented. The fields represent those which may exist in the pinch phase of the plasma focus, although here they depend only on the radial coordinate. The ions initially have Maxwellian velocity distributions, and their trajectories are interpreted in terms of single-particle constants of the motion. Two models of the axial electric field Ez are considered. For strong Ez away from the axis, there is a cyclotron acceleration which leads to ion heating. For positive Ez on the axis, ions within a Larmor radius of the axis undergo very efficient acceleration; the results for this new model are in general agreement with experimental results.

Gary, S. P.↗
NASA NTRS1978

Observed characteristics of auroral forms

Observed characteristics of discrete auroral arcs and pulsating aurora are described, and a mechanism for the discrete auroras is considered. Strong horizontal and vertical electric fields characterize the discrete auroras, since their motions and their distortions indicate the presence of shear processes involving substantial charge excesses and magnetic field-aligned currents. Pulsating auroras do not exhibit shearing behavior and this lack of shearing shows that substantial electric fields are not involved. Transitional types of auroras, including black aurora, are considered.

Davis, T. N.↗
NASA NTRS1982

A model of Martian slope winds - Implications for eolian transport

Observations of dark Martian wind streaks not associated with visible topographic points of origin (coalesced dark streaks) show these features to favor regions with slopes of 1-10 deg. To investigate the circulation over such slopes, a Boussinesq fluid is adopted and a constant eddy diffusivity parameterization is assumed for small-scale mixing. The equations of motion are scaled to determine the range of slopes over which a strong local circulation due to slope winds can exist. For nighttime conditions, the estimated range compares well with the observed range of slopes favored by coalesced dark streaks. For daytime conditions, the slope wind solution is not valid. A simple one-dimensional analytic model is solved to determine friction velocities and velocity and temperature profiles. For reasonable choices of the input parameters, friction velocities and wind velocities suggestive of active downslope eolian transport on slopes of 1-10 deg are found. Friction velocities are largest over surfaces with low thermal inertia and large roughness length.

Magalhaes, J.↗
NASA NTRS1982

Calculation of pressure statistics in turbulent free shear flows by direct numerical simulation

Accurate numerical simulations of turbulent free shear flows were performed in order to study the behavior of certain critical turbulence quantities which have been difficult to measure in the laboratory. The three-dimensional time-dependent nonlinear Navier-Stokes equations are solved by the direct numerical simulation technique without turbulence modeling or ad hoc closure assumptions. The pressure interaction terms were factored into diffusion and return-to-isotropy components according to two models. Simulations of the evolution of a turbulent wake with and without swirl present were performed at sufficiently high Reynolds numbers to insure that the flows were strongly nonlinear and turbulent, but low enough so that all scales of motion containing significant energy are adequately resolved. It is noted that the presence of swirl tends to enhance the amplitude of the rms pressure levels.

Metcalfe, R. W.↗
NASA NTRS1988

Survey of impact damper performance

An overall picture of the impact damper is obtained by using time-history solutions of the system motion for the oscillator in free decay. The impactor behavior depends very strongly on oscillator amplitude, and free decay can sample the full range of behavior from an infinite number of impacts per cycle at high amplitude to no impacts at low amplitude. The overall picture cannot be obtained by analysis of steady-state forced response. Yet, the predictions are relevant to forced response behavior when the damping is relatively light. Three major regimes of impact behavior are shown to exist: low, middle and high amplitude ranges.

Brown, Gerald V.↗
NASA NTRS1989

The spin bag mechanism of high temperature superconductivity

In oxide superconductors the local suppression of antiferromagnetic correlations in the vicinity of a hole lowers the energy of the system. This quasi two-dimensional bag of weakened spin order follows the hole in its motion. In addition, holes prefer to share a bag, leading to a strong pairing attraction and a high Tc superconductivity. There are many experimental consequences of this mechanism for both the superconducting and normal phases.

Schrieffer, J. R.↗
NASA NTRS1989

Low-altitude signatures of the cusp and flux transfer events

Cusp-like ion injection was studied using DE-2 satellite data obtained during strongly southward IMF. Although magnetosheath ion injection signatures are detected, the satellite motion and convection are opposed, and it is suggested that the observed falling energy dispersion of the precipitating ions may have arisen from a static moving or growing source. The spatial scale of the flux is found to be typical of that of a flux transfer event (FTE). A simple model of the ionospheric signature of an FTE is able to reproduce the observed electric and magnetic field perturbations. Precipitating electrons with peak energies of about 100 eV lie on the predicted boundary of the newly opened tube and are similar to those noted on the edges of FTEs at the magnetopause.

Lockwood, Mike↗
NASA NTRS1989

Observation of organized structure in turbulent flow within and above a forest canopy

Data obtained with seven triaxial sonic anemometer/thermometers and three Lyman-alpha hygrometers at an experimental site in Ontario, Canada reveal the coherent occurrence of ramp patterns of temperature and humidity at several levels within and above the deciduous forest considered. The ramps appear most clearly in the middle and upper portion of the forest, and near the top of the forest they are composed of a weak ejecting motion transporting warm and/or moist air out of the forest, followed by strong sweeps of cool and/or dry air penetrating into the canopy. In the middle and upper parts of the canopy, the sweeps are found to conduct a large proportion of the overall transfer between the forest and the lower atmosphere, with a lesser contribution from ejections.

Gao, W.↗
NASA NTRS1992

The modeling of piezoceramic patch interactions with shells, plates and beams

General models describing the interactions between a pair of piezoceramic patches and elastic substructures consisting of a cylindrical shell, plate and beam are presented. In each case, the manner in which the patch loads enter both the strong and weak forms of the time-dependent structural equations of motion is described. Through force and moment balancing, these loads are then determined in terms of material properties of the patch and substructure (thickness, elastic properties, Poisson ratios), the geometry of the patch placement, and the voltages into the patches. In the case of the shell, the coupling between banding and inplane deformations, which is due to the curvature, is retained. These models are sufficiently general to allow for potentially different patch voltages which implies that they can be suitably employed when using piezoceramic patches for controlling system dynamics when both extensional and bending vibrations are present.

Banks, H. T.↗
NASA NTRS1991

A strongly goal-directed close-range vision system for spacecraft docking

In this presentation, we will propose a strongly goal-oriented stereo vision system to establish proper docking approach motions for automated rendezvous and capture (AR&C). From an input sequence of stereo video image pairs, the system produces a current best estimate of: contact position; contact vector; contact velocity; and contact orientation. The processing demands imposed by this particular problem and its environment dictate a special case solution; such a system should necessarily be, in some sense, minimalist. By this we mean the system should construct a scene description just sufficiently rich to solve the problem at hand and should do no more processing than is absolutely necessary. In addition, the imaging resolution should be just sufficient. Extracting additional information and constructing higher level scene representations wastes energy and computational resources and injects an unnecessary degree of complexity, increasing the likelihood of malfunction. We therefore take a departure from most prior stereopsis work, including our own, and propose a system based on associative memory. The purpose of the memory is to immediately associate a set of motor commands with a set of input visual patterns in the two cameras. That is, rather than explicitly computing point correspondences and object positions in world coordinates and trying to reason forward from this information to a plan of action, we are trying to capture the essence of reflex behavior through the action of associative memory. The explicit construction of point correspondences and 3D scene descriptions, followed by online velocity and point of impact calculations, is prohibitively expensive from a computational point of view for the problem at hand. Learned patterns on the four image planes, left and right at two discrete but closely spaced instants in time, will be bused directly to infer the spacecraft reaction. This will be a continuing online process as the docking collar approaches.

Boyer, Kim L.↗
NASA NTRS2004

Modeling Studies of the MODIS Solar Diffuser Attenuation Screen and Comparison with On-Orbit Measurements

The MODIS instrument relies on solar calibration to achieve the required radiometric accuracy. This solar calibration occurs as the TERRA spacecraft comes up over the North Pole. The earth underneath the spacecraft is still dark for approximately one minute and the sun is just rising over the earth's north polar regions. During this time the sun moves through about 4 degrees, the scan mirror rotates about 19 times and about 50 frames (exposures) are made of the white solar diffuser. For some of MODIS'S bands the brightness of the screen is reduced, to prevent detector saturation, by means of a pinhole screen, which produces approximately 600 pinhole images of the sun within the field of view of any one detector. Previous attempts at creating a detailed radiometric model of this calibration scenario produced intensity variations on the focal planes with insufficient detail to be useful. The current computational approach produces results, which take into account the motion of the sun and the scan mirror and produces variations, which strongly resemble the observed focal plane intensity variations. The computational approach and results and a comparison with actual observational data are presented.

Waluschka, Eugene↗
NASA NTRS2015

Key Recent Scientific Results from the Opportunity Rover's Exploration of Endeavour Crater, Mars

The Opportunity Rover is currently in its 11th year of operations, exploring the rim of the approximately 22 km wide Noachian-age Endeavour Crater. Opportunity spent its 5th winter season in Cook Haven, a gentle swale along Murray Ridge. Two small rocks serendipitously overturned by rover wheel motions show evidence for aqueous precipitation of sulfates, and interaction with a strong oxidant (e.g., O2) to form a thin, high valence state Mn oxide coating. After the winter, Opportunity headed south to Cape Tribulation and explored Shoemaker formation impact breccias, finding numerous Ca-sulfate veins cutting across outcrops. A key target for Opportunity's measurements has been the Spirit of Saint Louis crater (SoSL), which is approximately 25 m wide, oval in plan view, shallow, flat-floored, and has a slightly raised rim. SoSL crater is surrounded by an apron of bright, polygonally-shaped outcrops and is superimposed on a gentle swale in Cape Tribulation. Rocks in a thin reddish zone on the rim are enriched in hematite, Si, and Ge, and depleted in Fe, relative to surrounding rocks. Apron rocks include an outcrop also enriched in Si and Ge, and slightly depleted in Fe. In general rocks in the crater and apron have elevated S relative to Shoemaker formation breccias, tracking values observed in the Cook Haven and the Hueytown (fracture running perpendicular to Cape Tribulation) outcrops. SoSL crater lies just to the west of Marathon Valley, a key target for exploration by Opportunity because five separate CRISM observations indicate the presence of Fe/Mg smectites on the upper valley floor. Opportunity data show that low relief, relatively bright polygonal outcrops dominate the valley floor where not covered by scree and soil shed from surrounding walls. Initial reconnaissance shows that the outcrops are breccias with compositions similar to the typical SoSL crater apron and floor rocks, although only the very upper portion of the valley has been explored as of August 2015. Pervasive but modest aqueous alteration of Endeavour's rim is implied by the combination of CRISM and Opportunity data, providing insight into early aqueous processes dominated in this location by relatively low water to rock ratios, and at least in part associated with enhanced fluid flow along fractures.

Arvidson, R. E.↗