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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Ultrasonic velocity for estimating density of structural ceramics

The feasibility of using ultrasonic velocity as a measure of bulk density of sintered alpha silicon carbide was investigated. The material studied was either in the as-sintered condition or hot isostatically pressed in the temperature range from 1850 to 2050 C. Densities varied from approximately 2.8 to 3.2 g cu cm. Results show that the bulk, nominal density of structural grade silicon carbide articles can be estimated from ultrasonic velocity measurements to within 1 percent using 20 MHz longitudinal waves and a commercially available ultrasonic time intervalometer. The ultrasonic velocity measurement technique shows promise for screening out material with unacceptably low density levels.

Klima, S. J.↗
NASA NTRS1982

Performance characteristics of a buoyant quad-rotor research aircraft

Performance characteristics of a buoyant, quadrotor research aircraft, which represents a hybrid airship concept for heavy lift application, are described. Ceiling altitude and endurance for hovering at typical power levels, including partial power failure, are predicted. Climb performance at various altitude and gross weight conditions have been examined. Forward flight performance of this vehicle is illustrated in terms of typical performance parameters such as maximum speed, maximum range, and endurance, over the full range of its payload capability. Optimum payload weights have been identified which result in maximum range at sea level density altitude and constant endurance at various altitudes, both during hover and cruise flights.

Nagabhushan, B. L.↗
NASA NTRS1984

Photographic memory: The storage and retrieval of data

The concept of density encoding digital data in a mass-storage computer peripheral is proposed. This concept requires that digital data be encoded as distinguishable density levels (DDLS) of the film to be used as the storage medium. These DDL's are then recorded on the film in relatively large pixels. Retrieval of the data would be accomplished by scanning the photographic record using a relatively small aperture. Multiplexing of the pixels is used to store data of a range greater than the number of DDL's supportable by the film in question. Although a cartographic application is used as an example for the photographic storage of data, any digital data can be stored in a like manner. When the data is inherently spatially-distributed, the aptness of the proposed scheme is even more evident. In such a case, human-readability is an advantage which can be added to those mentioned earlier: speed of acquisition, ease of implementation, and cost effectiveness.

Horton, J.↗
NASA NTRS1983

The X-ray properties of supernova remnants in the Large Magellanic Cloud

Einstein Observatory instruments were used to survey the generic properties of LMC supernova remnants (SNR). The study covered the diffuse optical bar, the 30 Dor nebula, the surrounding H I cloud, and a high fraction of the spiral arms. Twelve SNRs were identified as X-ray sources and two SNR, N157B and 0540 - 69.3, were located from radio emissions. Filamentary H-alpha emissions also revealed five other objects. X-ray intensity data indicated that density levels of the matter surrounding SNR decrease with SNR diameter. The data suggest that Sedov models for SN may not be accurate for LMC SN, which exhibit too great a luminosity scatter in the surrounding interstellar material. The emissions may be accounted for by ejecta from the SN or by multiphase interstellar material.

Long, K. S.↗
NASA NTRS1984

High resolution evidence for the Garrett-Munk spectrum of stratospheric gravity waves

Vertical profiles of scalar horizontal winds have been measured at high resolution (10 m) in the 13 to 37 km region of the stratosphere. This resolution (at that range of altitude) represents the state-of-the-art, and is unique. The technique used smoke trails laid by rockets in the stratosphere, and were taken by AFGL at Wallops Island, VA, White Sands Missile Range, NM, and Ft. Churchill, Canada, in the 1977-78 time period. Two or three cameras were used to give the time-lapse photographs. The goal was to ascertain whether or not the internal waves of the stratosphere behave consistently with the Garrett-Munk model which was originally created for oceanic internal waves. Five profiles of horizontal wind are presented. It is concluded: (1) stratospheric internal waves obey the Garrett-Munk model for vertical wave numbers; (2) there is not statistically significant evidence for a break in the curve at high wave numbers when due allowance is made for aliasing effects; and (3) the power density level of the spectra are almost equal on a log-log scale in spite of the difference in time, season, and geographical location.

Dewan, E. M.↗
NASA NTRS1985

Morphology of thermospheric composition variations in the quiet polar thermosphere from Dynamics Explorer measurements

Composition data obtained by the Neutral Atmosphere Composition Spectrometer carried aboard the Dynamics Explorer 2 satellite have been examined for variations in the polar regions during magnetically quiet conditions. A persistent enhancement of N2 density and a depletion of He density are present in the vicinity of the magnetic poles with maximum density response in the morning hours (magnetic) on average. A universal time (UT) variation in average density levels is evident near both the geographic and magnetic poles. There are systematic morphology changes with UT and between summer and winter which are qualitatively consistent with the shifting and spreading of thermospheric heating effects by the global circulation systems driven by EUV and magnetospheric sources. The magnitude of the UT variations is larger in the southern hemisphere on average, and the UT variations are larger in local winter than summer.

Hedin, A. E.↗
NASA NTRS1985

On the use of the cross section concept as applied to pulsed CO2 laser dynamics

The 'cross sections' which are commonly used in combination with the molecular vibrational level densities to describe induced transition rates are time dependent in a pulsed discharge. This greatly affects the relative rates of buildup of radiation at the various lines of a molecular gain medium in a nondispersive cavity, and the consequences for line selection by injection in a TEA-CO2 laser are discussed.

Flamant, P. H.↗
NASA NTRS1986

UT/longitudinal variations of composition in DE data

Composition data obtained by the quadrupole mass spectrometer (NACS) carried aboard the DE-B satellite were examined for variations in the polar regions during magnetically quiet conditions. The corresponding predictions of the MSIS-83 model are often used for comparison. The MSIS-83 model is used to emphasize the variations of interest by suppressing all other variations. A persistent enhancement of N2 density and a depletion of He density are present in the vicinity of the magnetic poles with maximum density response in the morning hours (magnetic) on average. A universal time (UT) variation in average density levels is evident near both the geographic and magnetic poles. There are systematic morphology changes with UT and between summer and winter which are qualitatively consistent with the simple concept that thermospheric heating effects are shifted or spread in the downwind direction of the global circulation systems driven by EUV and magnetospheric sources. The magnitude of the UT variations is larger in the southern hemisphere and is larger in local winter than summer.

Hedlin, A. E.↗
NASA NTRS1987

Numerical simulation by TVD schemes of complex shock reflections from airfoils at high angle of attack

The shock-capturing capability of total variation diminishing (TVD) schemes is demonstrated for a more realistic complex shock-diffraction problem for which the experimental data are available. Second-order explicit upwind and symmetric TVD schemes are used to solve the time-dependent Euler equations of gas dynamics for the interaction of a blast wave with an airfoil at high angle-of-attack. The test cases considered are a time-dependent moving curved-shock wave and a contant moving planar-shock wave impinging at an angle-of-attack 30 deg on a NACA 0018 airfoil. Good agreement is obtained between isopycnic contours computed by the TVD schemes and those from experimental interferograms. No drastic difference in flow-field structure is found between the curved- and planar-shock wave cases, except for a difference in density level near the lower surface of the airfoil. Computation for cases with higher shock Mach numbers is also possible. Numerical experiments show that the symmetric TVD scheme is less sensitive to the boundary conditions treatment than the upwind scheme.

Moon, Young J.↗
NASA NTRS1989

Advanced space power PEM fuel cell systems

A model showing mass and heat transfer in proton exchange membrane (PEM) single cells is presented. For space applications, stack operation requiring combined water and thermal management is needed. Advanced hardware designs able to combine these two techniques are available. Test results are shown for membrane materials which can operate with sufficiently fast diffusive water transport to sustain current densities of 300 ma per square centimeter. Higher power density levels are predicted to require active water removal.

Vanderborgh, N. E.↗
NASA NTRS1991

Radio range measurements of coronal electron densities at 13 and 3.6 centimeter wavelengths during the 1988 solar conjunction of Voyager 2

Radio range measurements of total solar plasma delay obtained during the solar conjunction of the Voyager 2 spacecraft in December 1988, which occurred near solar maximum activity in the 11 yr cycle are reported. The radio range measurements were generated by the Deep Space Network at two wavelengths on the downlink from the spacecraft: 3.6 and 13 cm. A direct measurement of the integrated electron density along the ray path between the earth stations and the spacecraft was obtained by differencing the range at the two wavelengths. Coronal electron density profiles have been derived during ingress and egress of the ray path, which approached the sun to within 5 solar radii. At 10 solar radii, the derived density profiles yield 34079 + or - 611/cu cm on ingress and 49688 + or - 983/cu cm on egress. These density levels are significantly higher than observed near previous solar maxima.

Krisher, T. P.↗
NASA NTRS1992

Pressure transducer and system for cryogenic environments

A silicon pressure die is bonded to a borosilicate substrate above the pneumatic port. A Wheatstone bridge circuit is formed on the silicon pressure die and has bridge elements of silicon doped with boron to a deposit density level of approximately 1 x 10(exp 19)-10(exp 21) boron/cc. A current source is provided to excite the Wheatstone bridge circuit. In addition, a temperature sensor is provided to provide temperature readings. An array may be formed of the resulting pressure transducers. This unique solution of materials permits operation of a pressure transducer in cryogenic environments.

Chapman, John J.↗
NASA NTRS1992

Perspectives on hypersonic viscous and nonequilibrium flow research

An attempt is made to reflect on current focuses in certain areas of hypersonic flow research by examining recent works and their issues. Aspects of viscous interaction, flow instability, and nonequilibrium aerothermodynamics pertaining to theoretical interest are focused upon. The field is a diverse one, and many exciting works may have either escaped the writer's notice or been abandoned for the sake of space. Students of hypersonic viscous flow must face the transition problems towards the two opposite ends of the Reynolds or Knudsen number range, which represents two regimes where unresolved fluid/gas dynamic problems abound. Central to the hypersonic flow studies is high-temperature physical gas dynamics; here, a number of issues on modelling the intermolecular potentials and inelastic collisions remain the obstacles to quantitative predictions. Research in combustion and scramjet propulsion will certainly be benefitted by advances in turbulent mixing and new computational fluid dynamics (CFD) strategies on multi-scaled complex reactions. Even for the sake of theoretical development, the lack of pertinent experimental data in the right energy and density ranges is believed to be among the major obstacles to progress in aerothermodynamic research for hypersonic flight. To enable laboratory simulation of nonequilibrium effects anticipated for transatmospheric flight, facilities capable of generating high enthalpy flow at density levels higher than in existing laboratories are needed (Hornung 1988). A new free-piston shock tunnel capable of realizing a test-section stagnation temperature of 10(exp 5) at Reynolds number 50 x 10(exp 6)/cm is being completed and preliminary tests has begun (H. Hornung et al. 1992). Another laboratory study worthy of note as well as theoretical support is the nonequilibrium flow experiment of iodine vapor which has low activation energies for vibrational excitation and dissociation, and can be studied in a laboratory with modest resources (Pham-Van-Diep et al. 1992).

Cheng, H. K.↗
NASA NTRS1991

Interference prediction for deep space spacecraft from ground stations - Interference to the Galileo deep space spacecraft from the GOMS geostationary network

A technique for predicting the interference power spectral density from a ground station to a spacecraft in deep space is described. The interference prediction throughout the complete mission is simulated, and distance between the ground station and the deep space spacecraft is calculated. A power spectral density from the GOMS satellite network to the Galileo spacecraft receiver is computed using the thermal noise density level at the Galileo spacecraft as the interference criterion. Data obtained indicate that all three GOMS stations cause at least 30 minutes of interference during Galileo earth flyby number one, and two GOMS ground stations cause at least four minutes of interference during Galileo earth flyby number.

Bishop, Dennis F.↗
NASA NTRS1990

Cosmic rays and the dynamic balance in the Large Magellanic Cloud

Present and future measurement of the Large Magellanic Cloud (LMC) particularly in the radio and high energy gamma ray range offer the possibility of understanding the density and distribution of the cosmic rays in a galaxy other than our own and the role that they play in galactic dynamic balance. After a study of the consistency of the measurements and interpretation of the synchrotron radiation from our own galaxy, the cosmic ray distribution for the LMC is calculated under the assumption that the cosmic ray nucleon to electron ratio is the same and the relation to the magnetic fields are the same, although the implications of alternatives are discussed. It is seen that the cosmic ray density level appears to be similar to that in our own galaxy, but varying in position in a manner generally consistent with the concept of correlation with the matter on a broad scale.

Fichtel, Carl E.↗
NASA NTRS1992

Piezoresistive stress sensors on (110) silicon wafers

Structural reliability of electronic packages has become an increasing concern for a variety of reasons including the advent of higher integrated circuit densities, power density levels, and operating temperatures. A powerful method for experimental evaluation of die stress distributions is the use of test chips incorporating integral piezoresistive sensors. In this paper, the basic equations needed for the design of stress sensors fabricated on the surface of (110) oriented silicon wafers have been presented. Several sensor rosette configurations have been explored, including the familiar three-element 0-45-90 rosette. Rosette designs have been found which minimize the necessary calibration procedures and permit more stress components to be measured. It has been established that stress sensors on the surface of (110) test chips are sensitive to four out of the six stress components at a point.

Kang, Y. L.↗
NASA NTRS1994

Contribution of low-energy ionospheric protons to the plasma sheet

The magnetospheric transport of low-energy ionospheric ions is examined by means of three-dimensional particle codes. Emphasis is placed on the behavior of polar wind and cleft originating protons. It is demonstrated that, via nonadiabatic motion inside the neutral sheet, these ions can significantly contribute to the populations of the plasma sheet. The importance of this contribution is found to depend critically upon the dynamics of particles originating from the highest latitudes, as these possibly have access to the distant tail. Hence it is shown that polar wind H(+) expelled into the magnetosphere at very low energies (in the electron volt range) preferentially feed the plasma sheet during quiet times, experiencing accelerations up to several kiloelectron volts upon return into the inner magnetosphere. In contrast, during disturbed times, the intensifying magnetospheric convection confines this population to low L shells where it travels in a nearly adiabatic manner. As for the protons originating from the cleft fountain, the simulations reveal that they can be transported up to the vicinity of the distant neutral line in the nightside sector. Via interaction with the neutral sheet, these ionospheric ions are rapidly raised to the characteristic plasma sheet energy range. The density levels contributed by these populations are quite substantial when compared to those measured in situ. These simulations establish an active role of low-energy ionospheric ions in the overall magnetospheric dynamics.

Delcourt, D. C.↗
NASA NTRS1996

Study of Analytic Statistical Model for Decay of Light and Medium Mass Nuclei in Nuclear Fragmentation

The angular momentum independent statistical decay model is often applied using a Monte-Carlo simulation to describe the decay of prefragment nuclei in heavy ion reactions. This paper presents an analytical approach to the decay problem of nuclei with mass number less than 60, which is important for galactic cosmic ray (GCR) studies. This decay problem of nuclei with mass number less than 60 incorporates well-known levels of the lightest nuclei (A less than 11) to improve convergence and accuracy. A sensitivity study of the model level density function is used to determine the impact on mass and charge distributions in nuclear fragmentation. This angular momentum independent statistical decay model also describes the momentum and energy distribution of emitted particles (n, p, d, t, h, and a) from a prefragment nucleus.

Cucinotta, Francis A.↗