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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

A New Method to Resolve X-Ray Halos around Point Sources with Chandra Data and Its Application to Cygnus X-1

With excellent angular resolution, good energy resolution, and a broad energy band, the Chandra Advanced CCD Imaging Spectrometer (ACIS) is the best instrument for studying the X-ray halos around some Galactic X-ray point sources caused by the dust scattering of X-rays in the interstellar medium. However, the direct images of bright sources obtained with the ACIS usually suffer from severe pileup. Making use of the fact that an isotropic image could be reconstructed from its projection in to any direction, we can reconstruct the images of the X-ray halos from the data obtained with the High Energy Transition Grating Spectrometer (HETGS) and/or in continuos clocking (CC) mode. These data have no or less serious pileup and enable us to take full advantage of the excellent angular resolution of Chandra. With the reconstructed high-resolution images, we can probe the X-ray halos as close as 1" to their associated point sources. Applying this method to Cygnus X-1 observed with the Chandra HETGS in CC mode, we derived an energy-dependent radial halo flux distribution and concluded that in a circular region (2' in radius) centered a the point source: (1) relative to the total intensity, the fractional halo intensity is about 15% at keV and drops to aboout 5% at approximately 6 keV (2) about 50% of the halo photons are within the region of a radius less than 40 inches and (3) the spectrum of the pooint source is slightly distorted by the halo contamination.

Yao, Yangsen↗
NASA NTRS1990

Mutual coupling between circular apertures on an infinite conducting ground plane and radiating into a finite width slab

The problem of electromagnetic coupling between two horns is of interest for the Microwave Reflectometer Ionization Sensor (MRIS) that will be used in the Aeroassist Flight Experiment (AFE). Laboratory measurements of mutual coupling between conical horns (using a flat metallic reflector to simulate a critically dense plasma outside) have shown a strong dependence on the finite dimensions of the shuttle tile over the apertures. Since both, the dielectric tile and the plasma outside the tile reflect microwaves, a study should be done to isolate the two mechanisms so that the MRIS reentry flight data can be interpreted correctly. Once the coupling due to the tile itself is determined then the location of the critial electron number density layers can be determined. As a first attempt to tackle this problem the Geometrical Theory of Diffraction was used to modify the existing solution to mutual coupling between apertures with infinite dielectric sheets. By using the equivalent current method, aperture theory to determine the radiated fields inside the dielectric tiles, and ray tracing the contributions to mutual coupling were determined. Results from two cases with different tile thicknesses have indicated that the main contribution to mutual coupling is due to diffraction from the bottom and top (back and front) wedges.

Christodoulou, Christos↗
NASA NTRS1975

Modelling the magnetosphere of Mercury

A model magnetosphere for Mercury is presented using an upstream image-dipole and nightside 2-dimensional tail current sheet method. The tail field is represented by an analytical formulation. Magnetic field data from the Mercury 1 encounter by Mariner 10 in March 1974 are used to determine quantitative parameters of the model magnetosphere, using the method of least squares. The magnetopause crossing points directly observed are used to determine the size of the magnetosphere, and the solar wind conditions are used to determine the magnetospheric field at the stagnation point. The model produces a magnetosphere-like region with planetary field lines that are confined in nearly circular cross-sections transverse to the sun-planet line. Results are used to show geometry, field line configuration, and contours of constant field intensity inside the magnetosphere.

Whang, Y. C.↗
NASA NTRS1979

The influence of grazing flow on the acoustic impedance of a cylindrical wall cavity

The acoustic impedance at low frequencies of a circular cylindrical cavity in the wall of a duct in the presence of a low Mach number mean flow is examined. A linearized theoretical model is proposed which involves the unsteady shedding of vorticity from the upstream edge of the cavity aperture. The shed vorticity causes a 'potential difference' to be established across the aperture which modifies the reciprocating volume flux and results in the dissipation of acoustic energy. Comparison of theoretical predictions with preliminary experimental data obtained by Parrott (1978) provides tentative support for the present analysis. Certain difficulties associated with the linearized treatment of cavity oscillations are also discussed.

Howe, M. S.↗
NASA NTRS1983

An experimental study of entrainment and transport in the turbulent near wake of a circular cylinder

Attention is given to an experimental investigation of transport processes in the near wake of a circular cylinder, for a Reynolds number of 140,000, in which an X-array of hot wire probes mounted on a pair of whirling arms was used for flow measurement. Rotation of the arms in a uniform flow applies a wide range of relative flow angles to these X-arrays, making them inherently self-calibrating in pitch. A phase signal synchronized with the vortex-shedding process allowed a sorting of the velocity data into 16 populations, each having essentially constant phase. An ensemble average for each population yielded a sequence of pictures of the instantaneous mean flow field in which the vortices are frozen, as they would be on a photograph. The measurements also yield nonsteady mean data for velocity, intermittency, vorticity, stress, and turbulent energy production, as a function of phase. Emphasis is given in a discussion of study results to the nonsteady mean flow, which emerges as a pattern of centers and saddles in a frame of reference that moves with the eddies. The kinematics of the vortex formation process are described in terms of the formation and evolution of saddle points between vortices in the first few diameters of the near wake.

Cantwell, B.↗
NASA NTRS1992

Navier-Stokes simulation of flow through a highly contoured subsonic diffuser

The flow through a highly offset subsonic diffuser with cross-sectional profiles that varied from rectangular at the duct entrance to circular at the engine face was numerically simulated. A multizonal approach combined with a two-grid topology was used to represent both the internal and external flowfields, and an implicit, approximately-factored, partially flux-split finite-difference algorithm was used to solve the three-dimensional thin-layer Navier-Stokes equations. The computed static pressures along the inlet wall and total pressures on the engine face were compared with experimental data. In addition, the overall flowfield within the duct was examined in detail. Good agreement is shown between experiment and computations, with the limiting factor being the lack of a reliable turbulence model for internal flow problems.

Chyu, W. J.↗
NASA NTRS1992

Correcting x ray spectra obtained from the AXAF VETA-I mirror calibration for pileup, continuum, background and deadtime

The VETA-I mirror was calibrated with the use of a collimated soft X-ray source produced by electron bombardment of various anode materials. The FWHM, effective area and encircled energy were measured with the use of proportional counters that were scanned with a set of circular apertures. The pulsers from the proportional counters were sent through a multichannel analyzer that produced a pulse height spectrum. In order to characterize the properties of the mirror at different discrete photon energies one desires to extract from the pulse height distribution only those photons that originated from the characteristic line emission of the X-ray target source. We have developed a code that fits a modeled spectrum to the observed X-ray data, extracts the counts that originated from the line emission, and estimates the error in these counts. The function that is fitted to the X-ray spectra includes a Prescott function for the resolution of the detector a second Prescott function for a pileup peak and a X-ray continuum function. The continuum component is determined by calculating the absorption of the target Bremsstrahlung through various filters correcting for the reflectivity of the mirror and convolving with the detector response.

Chartas, G.↗
NASA NTRS1993

Correcting X-ray spectra obtained from the AXAF VETA-I mirror calibration for pileup, continuum, background and deadtime

The VETA-I mirror was calibrated with the use of a collimated soft X-ray source produced by electron bombardment of various anode materials. The FWHM, effective area and encircled energy were measured with the use of proportional counters that were scanned with a set of circular apertures. The pulsers from the proportional counters were sent through a multichannel analyzer that produced a pulse height spectrum. In order to characterize the properties of the mirror at different discrete photon energies one desires to extract from the pulse height distribution only those photons that originated from the characteristic line emission of the X-ray target source. We have developed a code that fits a modeled spectrum to the observed X-ray data, extracts the counts that originated from the line emission, and estimates the error in these counts. The function that is fitted to the X-ray spectra includes a Prescott function for the resolution of the detector a second Prescott function for a pileup peak and a X-ray continuum function. The continuum component is determined by calculating the absorption of the target Bremsstrahlung through various filters, correcting for the reflectivity of the mirror and convolving with the detector response.

Chartas, G.↗
NASA NTRS1975

Calculation of the flow on a blunted cone at high angle of attack

A new technique for calculating the entire flow-field on spherically blunted circular cones at high angles of attack and high Reynolds numbers is described. The calculations are based on a single-layer system of three-dimensional parabolic equations which are approximations to the full steady Navier-Stokes equations. Initial conditions at the sphere-cone tangency plane are provided by using an inviscid time-dependent solution added to a viscous nonsimilar boundary layer solution. Calculated results are compared with experimental heat transfer and pressure data for a 15 deg half-angle cone with a 1-in. spherical nose at 15 deg angle of attack. The free-stream Mach number is 10.6, and the free-stream Reynolds number is 1,200,000 per foot. Excellent agreement between the calculated and experimental data for both pressure and heat transfer is obtained.

Lubard, S. C.↗
NASA NTRS1975

Shuttle/spacelab MMAP/electromagnetic environment experiment phase B definition study

Progress made during the first five months of the Phase B definition study for the MMAP/Electromagnetic Environment Experiment (EEE) was described. An antenna/receiver assembly has been defined and sized for stowing in a three pallet bay area in the shuttle. Six scanning modes for the assembly are analyzed and footprints for various antenna sizes are plotted. Mission profiles have been outlined for a 400 km height, 57 deg inclination angle, circular orbit. Viewing time over 7 geographical areas are listed. Shuttle interfaces have been studied to determine what configuration the antenna assembly must have to be shared with other experiments of the Microwave Multi-Applications Payload (MMAP) and to be stowed in the shuttle bay. Other results reported include a frequency plan, a proposed antenna subsystem design, a proposed receiver design, preliminary outlines of the experiment controls and an analysis of on-board and ground data processing schemes.

Horton, J. B.↗
NASA NTRS1992

Application of space-time neural networks to detect tether skiprope phenomenon in space operations

The feasibility of operating tethered payloads in earth orbit will be studied during a space shuttle flight scheduled for 1992. Tethered systems may exhibit a circular transverse oscillation or skiprope phenomenon due to interaction between the earth's magnetic field and current pulsing through the tether. Effective damping of this skiprope motion depends on rapid and accurate detection of its magnitude and phase. Satellite attitude motion has characteristic oscillations as well as many other perturbations and therefore the relationship between skiprope parameters and attitude time history is very complex and nonlinear. A space-time neural network (STNN) for filtering satellite rate gyro data is proposed for rapid detection and prediction of skiprope magnitude and phase. A validated orbital operations simulator and STNN software will be used for training and testing of this skiprope detection system. The advantages of STNNs are discussed and STNN configurations and preliminary results are presented.

Lea, Robert N.↗
NASA NTRS1961

Aerodynamic Force Characteristics of a Series of Lifting Cone and Cone-Cylinder Configurations at a Mach Number of 6.83 and Angles of Attack up to 130 Deg

Force tests of a series of right circular cones having semivertex angles ranging from 5 deg to 45 deg and a series of right circular cone-cylinder configurations having semivertex angles ranging from 5 deg to 20 deg and an afterbody fineness ratio of 6 have been made in the Langley 11-inch hypersonic tunnel at a Mach number of 6.83, a Reynolds number of 0.24 x 10.6 per inch, and angles of attack up to 130 deg. An analysis of the results made use of the Newtonian and modified Newtonian theories and the exact theory. A comparison of the experimental data of both cone and cone-cylinder configurations with theoretical calculations shows that the Newtonian concept gives excellent predictions of trends of the force characteristics and the locations with respect to angle of attack of the points of maximum lift, maximum drag, and maximum lift-drag ratio. Both the Newtonian a.nd exact theories give excellent predictions of the sign and value of the initial lift-curve slope. The maximum lift coefficient for conical bodies is nearly constant at a value of 0.5 based on planform area for semivertex angles up to 30 deg. The maximum lift-drag ratio for conical bodies can be expected to be not greater than about 3.5, and this value might be expected only for slender cones having semivertex angles of less than 5 deg. The increments of angle of attack and lift coefficient between the maximum lift-drag ratio and the maximum lift coefficient for conical bodies decrease rapidly with increasing semivertex angles as predicted by the modified Newtonian theory.

Penland, Jim A.↗
NASA NTRS1994

Orbital maneuvering and reaction control systems

Orbital maneuvering systems (OMS) and reaction control systems (RCS) provide capabilities to spacecraft that include orbit circularization, rendezvous maneuvers, attitude control, and re-entry delta velocity. The mission and vehicle requirements can place severe demands on the orbital maneuvering and reaction control systems. In order to perform proper trade studies and to design these systems, the mission and vehicle configuration must be well defined. In the absence of a clearly defined mission and vehicle configuration, the research and development of basic technologies must support future design efforts by providing a range of options and data from which to select. This paper describes the key OMS and RCS requirements and technology.

Hurlbert, Eric↗
NASA NTRS1984

Hydrodynamic impeller stiffness, damping, and inertia in the rotordynamics of centrifugal flow pumps

The lateral hydrodynamic forces experienced by a centrifugal pump impeller performing circular whirl motions within several volute geometries were measured. The lateral forces were decomposed into: (1) time averaged lateral forces and (2) hydrodynamic force matrices representing the variation of the lateral forces with position of the impeller center. It is found that these force matrices essentially consist of equal diagonal terms and skew symmetric off diagonal terms. One consequence of this is that during its whirl motion the impeller experiences forces acting normal and tangential to the locus of whirl. Data on these normal and tangential forces are presented; it is shown that there exists a region of positive reduced whirl frequencies, within which the hydrodynamic forces can be destablizing with respect to whirl.

Jery, S.↗
NASA NTRS2012

Morphology Of A Hot Prominence Cavity Observed with Hinode/XRT and SDO/AIA

Prominence cavities appear as circularly shaped voids in coronal emission over polarity inversion lines where a prominence channel is straddling the solar limb. The presence of chromospheric material suspended at coronal altitudes is a common but not necessary feature within these cavities. These voids are observed to change shape as a prominence feature rotates around the limb. We use a morphological model projected in cross-sections to fit the cavity emission in Hinode/XRT passbands, and then apply temperature diagnostics to XRT and SDO/AIA data to investigate the thermal structure. We find significant evidence that the prominence cavity is hotter than the corona immediately outside the cavity boundary. This investigation follows upon "Thermal Properties of A Solar Coronal Cavity Observed with the X-ray Telescope on Hinode" by Reeves et al., 2012, ApJ, in press.

Weber, Mark A.↗
NASA NTRS1977

Ocean current surface measurement using dynamic elevations obtained by the GEOS-3 radar altimeter

Remote Sensing of the ocean surface from the GEOS-3 satellite using radar altimeter data has confirmed that the altimeter can detect the dynamic ocean topographic elevations relative to an equipotential surface, thus resulting in a reliable direct measurement of the ocean surface. Maps of the ocean dynamic topography calculated over a one month period and with 20 cm contour interval are prepared for the last half of 1975. The Gulf Stream is observed by the rapid slope change shown by the crowding of contours. Cold eddies associated with the current are seen as roughly circular depressions.

Leitao, C. D.↗
NASA NTRS1987

Combined optimization of image-gathering and image-processing systems for scene feature detection

The relationship between the image gathering and image processing systems for minimum mean squared error estimation of scene characteristics is investigated. A stochastic optimization problem is formulated where the objective is to determine a spatial characteristic of the scene rather than a feature of the already blurred, sampled and noisy image data. An analytical solution for the optimal characteristic image processor is developed. The Wiener filter for the sampled image case is obtained as a special case, where the desired characteristic is scene restoration. Optimal edge detection is investigated using the Laplacian operator x G as the desired characteristic, where G is a two dimensional Gaussian distribution function. It is shown that the optimal edge detector compensates for the blurring introduced by the image gathering optics, and notably, that it is not circularly symmetric. The lack of circular symmetry is largely due to the geometric effects of the sampling lattice used in image acquisition. The optimal image gathering optical transfer function is also investigated and the results of a sensitivity analysis are shown.

Halyo, Nesim↗
NASA NTRS1992

Space Network Interoperability Panel (SNIP) study

The Space Network Interoperability Panel (SNIP) is described in terms of the panel's composition, purpose, history, and ongoing activities. SNIP is a consortium comprising NASA, ESA, and NASDA that is dedicated to the study of interoperability of the data-relay satellite (DRS) systems of the three groups. S-band and Ka-band interoperability are addressed by the SNIP study program by means of defining operations concepts, technical subjects, and other matters relevant to international DRS system compatibility. The potential users of the interoperability scheme are listed, cross-support techniques are described, and the load situations of the three agencies are characterized. A common 'interoperability frequency framework' is proposed, and both left-and right-hand circular polarization are incorporated to enhance flexibility and minimize interference. An operations concept is outlined based on these and other recommendations as developed by the international SNIP study.

Ryan, Thomas↗