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At least 1,135 records · Page 63

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NASA NTRS1990

An expert system for geologic mapping with imaging spectrometers

Techniques have been developed for the extraction and characterization of absorption features from visible and infrared reflectance spectra and an expert system has been designed, implemented, and successfully tested that allows automated identification of minerals based on their spectral characteristics. A suite of laboratory spectra of common minerals was analyzed and the absorption band characteristics tabulated and used to develop a generalized knowledge base for analysis of the reflectance spectra. A tree hierarchy was designed to emulate the decision process followed by an experienced analyst for analysis of laboratory and field reflectance spectra and aircraft imaging spectrometer spectra. Good results were obtained with the expert system for all three types of spectra, with the critical factor in the analysis being the signal-to-noise ratio of the spectral data.

Kruse, F. A.↗

NASA NTRS1991

Fe II emission lines. I - Chromospheric spectra of red giants

A 'difference filtering' algorithm developed by Ayers (1979) is used to construct high-quality high-dispersion long-wavelength IUE spectra of three giant stars. Measurements of all the emission lines seen between 2230 and 3100 A are tabulated. The emission spectrum of Fe II is discussed in comparison with other lines whose formation mechanisms are well understood. Systematic changes in the Fe II spectrum are related to the different physical conditions in the three stars, and examples are given of line profiles and ratios which can be used to determine conditions in the outer atomspheres of giants. It is concluded that most of the Fe II emission results from collisional excitation and/or absorption of photospheric photons at optical wavelengths, but some lines are formed by fluorescence, being photoexcited by other strong chromospheric lines. Between 10 and 20 percent of the radiative losses of Fe II arise from 10 eV levels radiatively excited by the strong chromospheric H Ly-alpha line.

Judge, P. G.↗

NASA NTRS1991

Optical nebulosity in X-ray-selected, early type galaxies

This paper presents the results of an H-alpha + N II forbidden line narrowband imaging survey of X-ray-selected E and S0 galaxies. A novel technique is described for objectively optimizing the removal of stellar continuum light while providing well-defined estimates of systematic errors. The procedure has the additional benefit of eliminating sky contamination, specifically in image regions occupied by galaxy light. Consideration of the measured spectral energy distributions is included in the flux calibration procedure, and emission-line luminosities (or upper limits), corrected for Galactic foreground extinction, are tabulated for metric apertures. No connection is found between the 'boxiness' or 'diskiness' of stellar isophotes and emission-line or far-infrared luminosity. It is suggested that optical nebulosity in early-type galaxies contains a significant multiparameter dependence on active Galactic nuclei behavior, accretion from the hot interstellar medium, and mass injection from external sources.

Shields, Joseph C.↗

NASA NTRS1991

High-resolution spectra of the 3.29 micron interstellar emission feature - A summary

High spectral resolution observations of the 3.29-micron interstellar emission feature show two types of profiles. Type 1 has a central wavelength of 3.289-micron and is observed in extended objects such as planetary nebulae and H II regions. Type 2 has a central wavelength of 3.296 microns and is observed around a small number of stellar sources. Type 2 has a full width at half-maximum of 0.020 micron; Type 1 has a broader FWHM, perhaps as much as 0.042 micron, but this is uncertain because of contamination by Pf(delta) emission. These profiles are tabulated for comparison to laboratory data. It is found that no proposed identification for the 3.29-micron emission feature definitely matches the observational spectra, although amorphous aromatic materials and heated polycyclic aromatic hydrocarbons tend to fit the best.

Tokunaga, A. T.↗

NASA NTRS1991

Measurements of forces, moments, and pressures on a generic store separating from a box cavity at supersonic speeds

An experimental investigation was conducted to measure the forces, moments, and pressure distributions on the generic store separating from a rectangular box cavity contained in a flat plate surface at supersonic speeds. Pressure distributions inside the cavity and oil flow and vapor-screen photographs of the cavity flow field were also obtained. The measurements were obtained for the store separating from a flat plate surface, from two shallow cavities having length to depth ratios (L/h) of 16.778 and 12.073, and from a deep cavity having L/h = 6.730. Measurements for the shallow cavities were obtained both with and without rectangular doors attached to sides of the cavities. The tests were conducted at free stream Mach numbers of 1.69, 2.00 and 2.65 for a free stream Reynolds number per foot of 2 x 10(exp 6). Presented here are a discussion of the results, a complete tabulation of the pressure data, figures of both the pressure and force and moment data, and representative oil flow and vapor screen photographs.

Stallings, Robert L., Jr.↗

NASA NTRS1991

Experimental study of an independently deflected wingtip mounted on a semispan wing

The results of a subsonic wind tunnel test of a semispan wing with an independently deflected tip surface are presented and analyzed. The tip surface was deflected about the quarter chord of the rectangular wing and accounted for 17 percent of the wing semispan. The test was conducted to measure the loads on the tip surface and to investigate the nature of aerodynamic interference effects between the wing and the deflected tip. Results are presented for two swept tip surfaces of similar planform but different airfoil distributions. The report contains plots of tip lift, drag, and pitching moment for various Reynolds numbers and tip deflection angles with respect to the inboard wing. Oil flow visualization photographs for a typical Reynolds number are also included. Important aerodynamic parameters such as lift and pitching moment slopes and tip aerodynamic center location are tabulated. A discussion is presented on the relationship between tip experimental data acquired in a steady flow and the prediction of unsteady tip motion at fixed wing angles of attack.

Martin, D. M.↗

NASA NTRS1991

LAGEOS geodetic analysis-SL7.1

Laser ranging measurements to the LAGEOS satellite from 1976 through 1989 are related via geodetic and orbital theories to a variety of geodetic and geodynamic parameters. The SL7.1 analyses are explained of this data set including the estimation process for geodetic parameters such as Earth's gravitational constant (GM), those describing the Earth's elasticity properties (Love numbers), and the temporally varying geodetic parameters such as Earth's orientation (polar motion and Delta UT1) and tracking site horizontal tectonic motions. Descriptions of the reference systems, tectonic models, and adopted geodetic constants are provided; these are the framework within which the SL7.1 solution takes place. Estimates of temporal variations in non-conservative force parameters are included in these SL7.1 analyses as well as parameters describing the orbital states at monthly epochs. This information is useful in further refining models used to describe close-Earth satellite behavior. Estimates of intersite motions and individual tracking site motions computed through the network adjustment scheme are given. Tabulations of tracking site eccentricities, data summaries, estimated monthly orbital and force model parameters, polar motion, Earth rotation, and tracking station coordinate results are also provided.

Smith, D. E.↗

NASA NTRS1989

Collision integrals and high temperature transport properties for N-N, O-O, and N-O

Accurate collision integrals are reported for the interactions of N(4 S 0) + N(4 S 0), O(3 P), and N(4 S 0) + O(3 P). These are computed from a semiclassical formulation of the scattering using the best available representations of all of the potential energy curves needed to describe the collisions. Experimental RKR curves and other accurate measured data are used where available; the results of accurate ab initio electronic structure calculations are used to determine the remaining potential curves. The high-lying states are found to give the largest contributions to the collision cross sections. The nine collision integrals, needed to determine transport properties to second order, are tabulated for translational temperatures in the range 250 K to 100,000 K. These results are intended to reduce the uncertainty in future predictions of the transport properties of nonequilibrium air, particularly at high temperatures. The viscosity, thermal conductivity, diffusion coefficient, and thermal diffusion factor for a gas composed of nitrogen and oxygen atoms in thermal equilibrium are calculated. It was found that the second order contribution to the transport properties is small. Graphs of these transport properties for various mixture ratios are presented for temperatures in the range 5000 to 15000 K.

Levin, E.↗

NASA NTRS1991

Air-breathing hypersonic vehicle guidance and control studies; An integrated trajectory/control analysis methodology: Phase 1

A tool which generates optimal trajectory/control histories in an integrated manner is generically adapted to the treatment of single-stage-to-orbit air-breathing hypersonic vehicles. The methodology is implemented as a two point boundary value problem solution technique. Its use permits an assessment of an entire near-minimum-fuel trajectory and desired control strategy from takeoff to orbit while satisfying physically derived inequality constraints and while achieving efficient propulsive mode phasing. A simpler analysis strategy that partitions the trajectory into several boundary condition matched segments is also included to construct preliminary trajectory and control history representations with less computational burden than is required for the overall flight profile assessment. A demonstration was accomplished using a tabulated example (winged-cone accelerator) vehicle model that is combined with a newly developed multidimensional cubic spline data smoothing routine. A constrained near-fuel-optimal trajectory, imposing a dynamic pressure limit of 1000 psf, was developed from horizontal takeoff to 20,000 ft/sec relative air speed while aiming for a polar orbit. Previously unspecified propulsive discontinuities were located. Flight regimes demanding rapid attitude changes were identified, dictating control effector and closed-loop controller authority was ascertained after evaluating effector use for vehicle trim. Also, inadequacies in vehicle model representations and specific subsystem models with insufficient fidelity were determined based on unusual control characteristics and/or excessive sensitivity to uncertainty.

Hattis, Philip D.↗

NASA NTRS1991

Organic synthesis in the outer Solar System: Recent laboratory simulations for Titan, the Jovian planets, Triton and comets

We tabulate the most abundant gases and their radiation yields, for two experimental pressures: 0.24 mb, more relevant to upper atmosphere excitation, and 17 mb, more relevant to tropospheric, cosmic ray excitation. The yields computed in the 0.24 mb experiment combined with measured electronic fluxes and a simple, eddy diffusion model of Titan's atmosphere predict abundances of detected molecules in agreement with those found by Voyager and for heavier products, in somewhat better agreement with observation than photochemical absolute reaction rate kinetics models. All Voyager organics are accounted for and no detectable products are found that Voyager did not detect. A striking increase of products with multiple bonds is found with decreasing pressure. Hydrocarbon abundances decline slowly with increasing carbon number. Additionally, we list preliminary estimates for the yield of the heteropolymer, which seems to be produced in a quantity comparable (in moles of C+N consumed) to the total amount of gaseous product. The production rate required to sustain Titan's haze against sedimentation also indicates yields of this order. As can be seen from the table, over 10(exp 9) years substantial amounts of these products can accumulate on the surface -- ranging from cm thickness for the (C+N equals 4) species to a meter or more for HCN and C2H2; we also expect a meter or more of tholins. Similar analyses have been or are being done for the Jovian planets and Triton. Charged particle irradiation of hydrocarbon clathrates or mixed hydrocarbon/water ices produces a range of organic products, reddening and darkening of the ices and characteristic infrared spectra. From such spectra, the predicted emission by fine particles in cometary comae well-matches the observed 3.4 micron emission spectra of Comet Halley and other recent comets. Heliocentric evolution of organic emission features in comets is predicted. Organic products of such ice irradiation may account for colors and albedos on some of the satellites in the outer solar system, especially Triton and Pluto, where solid methane is known to exist.

Sagan, C.↗

NASA NTRS1991

Analysis of pressure-broadened ozone spectra in the 3 micron region

This work involves the analysis of a series of McMath Fourier Transform Infrared (FTIR) spectra of ozone broadened by mixing with air (four different pressures), nitrogen (three pressures), or oxygen (three pressures). Each spectrum covers the region from 2396 to 4057 cm(-1). This study focused on the 3 sub nu sub 3 band in t 3000 to 3060 cm(-1). The band is analyzed by first dividing its region into small intervals containing a few well isolated absorption lines of reasonable intensity. Each of these small intervals is fit by multiple iterations of the nonlinear least squares program until residuals (the difference between calculated and observed spectrum, as a percent of the strongest intensity in the interval) are minimized to a reasonable value which corresponds to the noise level of the measured spectrum. Position, intensity, and half-width are recorded for later analysis. From the measured half-widths, a pressure broadening coefficient was determined for each absorption line. Pressure shifts were determined by comparing observed line positions in the spectra of the diluted ozone samples to tabulated line positions determined from spectra of pure gas samples. Comparisons to other work on ozone indicate that the broadening and shift coefficients determined in this study are consistent with those determined in other spectral regions.

Prochaska, Eleanor S.↗

NASA NTRS1989

Trends in stratospheric minor constituents

Photochemical models predict that increasing source gas concentrations are also expected to lead to changes in the concentrations of both catalytically active radical species (such as NO2, ClO, and OH) and inactive reservoir species (such as HNO3, HCl, and H2O). For simplicity, we will refer to all these as trace species. Those species that are expected to have increasing concentration levels are investigated. Additionally, the trace species concentration levels are monitored for unexpected changes on the basis of the measure increase in source gases. Carrying out these investigations is difficult due to the limited data base of measurements of stratospheric trace species. In situ measurements are made only infrequently, and there are few satelliteborne measurements, most over a time space insufficient for trend determination. Instead, ground-based measurements of column content must be used for many species, and interpretation is complicated by contributions from the troposphere or mesosphere or both. In this chapter, we examine existing measurements as published or tabulated.

Stolarski, R. S.↗

NASA NTRS1992

Crustal dynamics project data analysis, 1991: VLBI geodetic results, 1979 - 1990

The Goddard VLBI group reports the results of analyzing 1412 Mark II data sets acquired from fixed and mobile observing sites through the end of 1990 and available to the Crustal Dynamics Project. Three large solutions were used to obtain Earth rotation parameters, nutation offsets, global source positions, site velocities, and baseline evolution. Site positions are tabulated on a yearly basis from 1979 through 1992. Site velocities are presented in both geocentric Cartesian coordinates and topocentric coordinates. Baseline evolution is plotted for 175 baselines. Rates are computed for earth rotation and nutation parameters. Included are 104 sources, 88 fixed stations and mobile sites, and 688 baselines.

Ma, C.↗

NASA NTRS1992

Fluid mechanics experiments in oscillatory flow. Volume 1: Report

Results of a fluid mechanics measurement program in oscillating flow within a circular duct are presented. The program began with a survey of transition behavior over a range of oscillation frequency and magnitude and continued with a detailed study at a single operating point. Such measurements were made in support of Stirling engine development. Values of three dimensionless parameters, Re(sub max), Re(sub w), and A(sub R), embody the velocity amplitude, frequency of oscillation and mean fluid displacement of the cycle, respectively. Measurements were first made over a range of these parameters which included operating points of all Stirling engines. Next, a case was studied with values of these parameters that are representative of the heat exchanger tubes in the heater section of NASA's Stirling cycle Space Power Research Engine (SPRE). Measurements were taken of the axial and radial components of ensemble-averaged velocity and rms-velocity fluctuation and the dominant Reynolds shear stress, at various radial positions for each of four axial stations. In each run, transition from laminar to turbulent flow, and its reverse, were identified and sufficient data was gathered to propose the transition mechanism. Models of laminar and turbulent boundary layers were used to process the data into wall coordinates and to evaluate skin friction coefficients. Such data aids in validating computational models and is useful in comparing oscillatory flow characteristics to those of fully-developed steady flow. Data were taken with a contoured entry to each end of the test section and with flush square inlets so that the effects of test section inlet geometry on transition and turbulence are documented. Volume 1 contains the text of the report including figures and supporting appendices. Volume 2 contains data reduction program listings and tabulated data (including its graphical presentation).

Seume, J.↗

NASA NTRS1992

Atomic oxygen exposure of LDEF experiment trays

Atomic oxygen exposures were determined analytically for rows, longerons, and end bays of the Long Duration Exposure Facility (LDEF). The calculations are based on an analytical model that accounts for the effects of thermal molecular velocity, atmospheric temperature, number density, spacecraft velocity, incidence angle, and atmospheric rotation on atomic oxygen flux. Results incorporate variations in solar activity, geomagnetic index, and orbital parameters occurring over the 6-year flight of the spacecraft. To facilitate use of the data, both detailed tabulations and summary charts for atomic oxygen fluences are presented.

Bourassa, R. J.↗

NASA NTRS1992

Overview of NASA supported Stirling thermodynamic loss research

NASA is funding research to characterize Stirling machine thermodynamic losses. NASA's primary goal is to improve Stirling design codes to support engine development for space and terrestrial power. However, much of the fundamental data is applicable to Stirling cooling and heat pump applications. The research results are reviewed. Much was learned about oscillating flow hydrodynamics, including laminar/turbulent transition, and tabulated data was documented for further analysis. Now, with a better understanding of the oscillating flow field, it is time to begin measuring the effects of oscillating flow and oscillating pressure level on heat transfer in heat exchanger flow passages and in cylinders.

Tew, Roy C.↗

NASA NTRS1992

Windshear radar calibration: Transmitter power and receiver gain stability

An experimental windshear Doppler radar was flown on 27 occasions during a series of flight experiments in 1991. Radar calibrations were performed by the flight team to monitor the transmitter power and receiver gain from pre-flight to post-flight and from one day to another. From the recorded calibration data, the receiver gain and effective receiver system noise were calculated and tabulated, together with the transmitter power. These quantities of interest are compared for two receiver/transmitter (R/T) units and two intermediate frequency (IF) bandwidths that were tested in various modes. It was found that, in most operating modes, gain stayed within a 2.5-dB range and transmitter power stayed within a 20-watt range. R/T number 1 had 0.8 dB more gain and 1.2 dBm less noise power than R/T number 2. The 7-MHz IF bandwidth resulted in 1 dB more gain and 1 dBm less noise than the 2-MHz IF bandwidth. Depending on the R/T unit and IF bandwidth, the effective system noise power averaged between -107.3 dBm and -109.5 dBm.

Mackenzie, Anne I.↗

NASA NTRS1992

Laser anemometer measurements and computations in an annular cascade of high turning core turbine vanes

An advanced laser anemometer (LA) was used to measure the axial and tangential velocity components in an annular cascade of turbine stator vanes designed for a high bypass ratio engine. These vanes were based on a redesign of the first-stage stator, of a two-stage turbine, that produced 75 degrees of flow turning. Tests were conducted on a 0.771 scale model of the engine size stator. The advanced LA fringe system was designed to employ thinner than usual laser beams resulting in a 50-micron-diameter probe volume. Window correction optics were used to ensure that the laser beams did not uncross in passing through the curved optical access port. Experimental LA measurements of velocity and turbulence were obtained both upstream, within, and downstream of the stator vane row at the design exit critical velocity ratio of 0.896 at the hub. Static pressures were also measured on the vane surface. The measurements are compared, where possible with calculations from a 3-D inviscid flow analysis. The data are presented in both graphic and tabulated form so that they may be readily used to compare against other turbomachinery computations.

Goldman, Louis J.↗