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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 1,549 records · Page 86
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NASA NTRS1986

A survey of the millimeter-wave spectrum of Sagittarius B2

More than 60 percent of the millimeter wave spectrum between 70 and 150 GHz of the giant Sgr B2 molecular cloud was surveyed with the Bell Laboratories 7 m telescope at a spectral resolution of 1 MHz. The observations and instrumentation are described, including beam efficiency and beamwidth as functions of frequency, frequency coverage, and rms noise. The catalog used to identify the 457 lines found is summarized, and the analysis of the data to determine column densities and rotational temperatures is discussed. The range of rotational temperatures obtained and their relation to the kinetic temperature, and their implications for the hydrogen density, are considered. More than 300 lines are transitions of 21 molecules, and the results for these are analyzed, giving excitation diagrams for most of them. A partly successful attempt is made to use ratios of the calculated abundances to predict abundances of as yet undetected species. Finally, the spectra for the entire survey are presented.

Cummins, S. E.↗
NASA NTRS1986

Radar scene generation for tactical decision aids

The Mueller matrix and polarization covariance matrix for polarimetric radar systems was studied. The clutter was modeled by a layer of random permittivity, described by a three-dimensional correlation function, with variance, and horizontal and vertical correlation lengths. This model was applied, using the wave theory with Born approximations carried to the second order, to find the backscattering elements of the polarimetric matrices. Theoretical predictions are matched with experimental data for vegetation fields. The strong fluctuation theory was used to derive the backscattering cross sections. A two-layer anisotropic random medium model was developed for the active and passive microwave remote sensing of ice fields. A three-layer random medium model was adopted to study the volume scattering effects for the active and passive microwave remote sensing of snow-covered ice fields.

Kong, J. A.↗
NASA NTRS1987

User's guide to programming fault injection and data acquisition in the SIFT environment

Described are the features, command language, and functional design of the SIFT (Software Implemented Fault Tolerance) fault injection and data acquisition interface software. The document is also intended to assist and guide the SIFT user in defining, developing, and executing SIFT fault injection experiments and the subsequent collection and reduction of that fault injection data. It is also intended to be used in conjunction with the SIFT User's Guide (NASA Technical Memorandum 86289) for reference to SIFT system commands, procedures and functions, and overall guidance in SIFT system programming.

Elks, Carl R.↗
NASA NTRS1987

Radar scene generation for tactical decision aids

The Mueller matrix and polarization covariance matrix for polarimetric radar systems was studied. The clutter is modeled by a layer of random permittivity, described by a three-dimensional correlation function, with variance, and horizontal and vertical correlation lengths. A general mixing formula was derived for discrete scatters immersed in a host medium. The results are applicable to general multiphase mixtures. The strong fluctuation theory was used to derive the backscattering cross sections, and was further extended to include higher order co-polarized and cross-polarized moments. A two-layer anisotropic random medium model was developed for the active and passive remote sensing of ice fields. A three-layer random medium model was adopted to study the volume scattering effects for the active and passive microwave remote sensing of snow-covered ice fields. The snow layer was simulated by an isotropic random medium and the ice layer by an anisotropic random medium. The vegetation canopy and snow-covered ice field were studied with a three-layer model, an isotropic random medium layer overlying an anisotropic random medium. The dyadic Green's function of the three-layer medium and the scattered electromagnetic intensities with Born approximation were calculated.

Kong, J. A.↗
NASA NTRS1986

Investigation of high efficiency silicon MINP solar cells

This paper includes results of both theoretical and experimental studies of silicon metal insulator n/p cells. Performance calculations are described which give expected efficiencies as a function of base resistivity. Fabrication and characterization of cells are discussed, and detailed analyses of current loss mechanisms are presented. Using 0.2-ohm cm FZ material and Mg tunneling contacts, AM 1 efficiencies in the range of 16.5-17 percent have been achieved.

Olsen, L. C.↗
NASA NTRS1986

Three-wave coupling coefficient in a drifting bi-Maxwellian plasma

A general electrostatic coupling coefficient which satisfies the Manley-Rowe relations is used to derive an explicit expression for the resonant three-wave coupling coefficient between electrostatic normal modes of a uniformly magnetized, infinite, homogeneous plasma with species described by drifting bi-Maxwellian distribution functions. The limit of this expression is taken when the phase velocities of the three waves are much larger than a species thermal speed, and also when the phase velocities are much smaller than the thermal speed. These are fluid limits and are applicable to the three-wave interaction between some low-frequency electrostatic waves, such as ion acoustic and ion cyclotron modes, in a plasma where T(e) is much greater than T(i).

Bergmann, Rachelle↗
NASA NTRS1987

Operating characteristics of a 10 kW xenon ion propulsion module

Performance testing of a two-engine functional model xenon ion propulsion module is described. Use of highly modified J-series 30 cm ion engines reconfigured for xenon propellant, a computer controlled operating system, and precise flow control system are shown to result in very reliable ion module operation at high input power levels. Ion engine operation at a nominal 4.0 ampere beam current and 30.0 volt discharge gives a specific impulse of 3310 sec, a total engine efficiency of 64.3 percent, and a thrust-to-power ratio of 39.5 mN/kW at an input power level of 5.10 kW. These modified J series ion engines are shown to be capable of throttling over an 8:1 range from a power level of 5.48 kW at 3285 sec to a power level of 0.70 kW at 1856 sec. In addition, complete ion engine performance mapping of important system level parameters such as thrust, specific impulse, efficiency and thrust-to-power ratio are presented.

Aston, Graeme↗
NASA NTRS1987

Periodicities of the flare occurrence rate in solar cycle 19

The occurrence rate of major flares during solar cycle 19 has been analyzed. A periodicity of 51 d is found, which is one-third of the period found from the flare rates of solar cycles 20 and 21 by various authors. The statistical significance of the periodicity is estimated to be at 99.85-percent confidence level. This periodicity is though to be related to the 153-d periodicity. The template of the phase diagram is well described by a constant plus a sine function. Additionally, an 18-month periodicity is found in the flare rate of the northern hemisphere.

Bai, T.↗
NASA NTRS1987

Theoretical models for polarimetric radar clutter

The Mueller matrix and polarization covariance matrix are described for polarimetric radar systems. The clutter is modeled by a layer of random permittivity, described by a three-dimensional correlation function, with variance, and horizontal and vertical correlation lengths. This model is applied, using the wave theory with Born approximations carried to the second order, to find the backscattering elements of the polarimetric matrices. It is found that 8 out of 16 elements of the Mueller matrix are identically zero, corresponding to a covariance matrix with four zero elements. Theoretical predictions are matched with experimental data for vegetation fields.

Borgeaud, M.↗
NASA NTRS1987

Determination of the scaled optical thickness of clouds from reflected solar radiation measurements

A method for determination of scaled optical thickness from reflected solar radiation measurements is described in which measurements of the reflected function are compared with asymptotic expressions for the reflection function of optically thick layers. Analytic formulas are derived which show the dependence of the reflection and transmission functions of nonabsorbing atmospheres on cloud optical thickness, ground albedo, and the asymmetry factor. An expression is derived which shows that the ground albedo produces a constant bias in the derived optical thickness, regardless of the value of the measured reflection function. Results from an analysis of high-resolution images, obtained in Oklahoma, of the reflection function of clouds shows the impact of details of the single scattering phase function on the derived optical thickness.

King, Michael D.↗
NASA NTRS1988

Design mobile satellite system architecture as an integral part of the cellular access digital network

The Cellular Access Digital Network (CADN) is the access vehicle through which cellular technology is brought into the mainstream of the evolving integrated telecommunications network. Beyond the integrated end-to-end digital access and per call network services provisioning of the Integrated Services Digital Network (ISDN), the CADN engenders the added capability of mobility freedom via wireless access. One key element of the CADN network architecture is the standard user to network interface that is independent of RF transmission technology. Since the Mobile Satellite System (MSS) is envisioned to not only complement but also enhance the capabilities of the terrestrial cellular telecommunications network, compatibility and interoperability between terrestrial cellular and mobile satellite systems are vitally important to provide an integrated moving telecommunications network of the future. From a network standpoint, there exist very strong commonalities between the terrestrial cellular system and the mobile satellite system. Therefore, the MSS architecture should be designed as an integral part of the CADN. This paper describes the concept of the CADN, the functional architecture of the MSS, and the user-network interface signaling protocols.

Chien, E. S. K.↗
NASA NTRS1988

Forty-eight-inch lidar aerosol measurements taken at the Langley Research Center, May 1974 to December 1987

A ground based lidar system located at NASA Langley Research Center in Hampton, Va., was used to obtain high resolution vertical profiles of the stratospheric and upper tropospheric aerosol since 1974. More than 200 measurements obtained at a wavelength of 0.6943 microns during 1974 to 1987 are summarized. Plots of peak backscatter mixing ratio and integrated backscatter vs time are presented for the entire measurement sequence. The plots highlight the influence of several major volcanic eruptions on the long term stratospheric aerosol layer. In particular, the eruptions of El Chichon in late Mar. to early Apr. 1982, produced a massive aerosol layer. Aerosol enhancement from El Chichon reached Hampton, Va. by May 1982, with a scattering ratio of approx. 50 detected on Jul. 1, 1982. In addition, scattering ratio profiles for June 1982 to December 1987, along with tables containing numerical values of the backscatter ratio and backscattering function versus altitude, are included to further describe the upper tropospheric and stratospheric aerosol layer. A 14 year summary is presented, in a ready to use format, of lidar observations at a fixed midlatitude location to be used for further study.

Fuller, W. H., Jr.↗
NASA NTRS1987

Spatial data software integration - Merging CAD/CAM/mapping with GIS and image processing

The integration of CAD/CAM/mapping with image processing using geographic information systems (GISs) as the interface is examined. Particular emphasis is given to the development of software interfaces between JPL's Video Image Communication and Retrieval (VICAR)/Imaged Based Information System (IBIS) raster-based GIS and the CAD/CAM/mapping system. The design and functions of the VICAR and IBIS are described. Vector data capture and editing are studied. Various software programs for interfacing between the VICAR/IBIS and CAD/CAM/mapping are presented and analyzed.

Logan, Thomas L.↗
NASA NTRS1989

Flow fields of low pressure vent exhausts

The flow field produced by low pressure gas vents are described based on experimental data obtained from tests in a large vacuum chamber. The gas density, pressure, and flux at any location in the flow field are calculated based on the vent plume description and the knowledge of the flow rate and velocity of the venting gas. The same parameters and the column densities along a specified line of sight traversing the plume are also obtained and shown by a computer-generated graphical representation. The fields obtained with a radially scanning Pitot probe within the exhausting gas are described by a power of the cosine function, the mass rate and the distance from the exit port. The field measurements were made for gas at pressures ranging from 2 to 50 torr venting from pipe fittings with diameters of 3/16 inch to 1-1/2 inches I.D. (4.76 mm to 38.1 mm). The N(2) mass flow rates ranged from 2E-4 to 3.7E-1 g/s.

Scialdone, John J.↗
NASA NTRS1989

A numerically exact full wave packet approach to molecule-surface scattering

A numerically exact spectral method for solving the time-dependent Schroedinger equation in spherical coordinates is described. The angular dependence of the wave function is represented on a two-dimensional grid of evenly spaced points. The fast Fourier transform algorithm is used to transform between the angle space representation of the wave function and its conjugate representation in momentum space. The time propagation of the wave function is evaluated using an expansion of the time evolution operator as a series of Chebyshev polynomials. Calculations performed for a model system representing H2 scattering from a rectangular corrugated surface yield transition probabilities that are in excellent agreement with those obtained using the close-coupling wave packet (CCWP) method. However, the new method is found to require substantially more computation time than the CCWP method because of the large number of grid points needed to represent the angular dependence of the wave function and the variation in the number of terms required in the Chebyshev representation of the time evolution operator.

Mowrey, R. C.↗
NASA NTRS1990

Anomalies due to single event upsets

The description of single event upsets (SEUs) in the spacecraft Anomalies Handbook is reviewed. The basic mechanism involved in SEUs is summarized and discussed in terms of circuit analysis. Calculation of SEU rate is analytically described and discussed. Departures from single step function dependence in the SEU rate is addressed.

Robinson, P. A., Jr.↗
NASA NTRS1990

Simulation of microwave brightness temperatures of an evolving hailstorm at SSM/I frequencies

A simulation of the appearance of an intense hailstorm in the passive microwave spectrum is used to characterize the vertical sources of radiation contributing to the microwave brightness temperatures at the top of the atmosphere. The four frequencies studied correspond to those used on the USAF Special Sensor Microwave Imager. The origin and movement of the radiation are described by two vertically resolved radiative structure functions. Consideration is given to problems relating to precipitation retrieval through passive remote sensing.

Mugnai, Alberto↗
NASA NTRS1990

Flow fields of low pressure vent exhausts

The flow field produced by low pressure gas vents are described based on experimental data obtained from tests in a large vacuum chamber. The gas density, pressure, and flux at any location in the flow field are calculated based on the vent plume description and the knowledge of the flow rate and velocity of the venting gas. The same parameters and the column densities along a specified line of sight traversing the plume are also obtained and shown by a computer generated graphical representation. The fields obtained with a radically scanning Pitot probe within the exhausting gas are described by a power of the cosine function, the mass rate, and the distance from the exit port. The field measurements were made for gas at pressures ranging from 2 to 50 torr venting from pipe fittings with diameters to 3/16 to 1-1/2 inches I.D. (4.76 to 38.1 mm). The N2 mass flow rates ranged from 2E-4 to 3.7E-1 g/s.

Scialdone, John J.↗