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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

A study of a space-station-associated multiple spacecraft Michelson spatial interferometer

One approach to Michelson spatial interferometry at optical wavelengths involves use of an array of spacecraft in which two widely-separated telescopes collect light from a star and direct it to a third, centrally-located, device which combines the beams in order to detect and measure interference fringes. The original version of a spacecraft array for Michelson spatial interferometry (SAMSI) was modified so that the system uses the fuel resupply capability of a space station. The combination of this fuel resupply capability with a method of obtaining image Fourier transform phase information, necessary for full image reconstruction, permits SAMSI to be used to synthesize images equivalent to those produced by huge apertures in space. Synthesis of apertures in the 100 to 500 meter range is discussed. Reconstruction can be performed to a visual magnitude of at least 8 for a 100 A passband in 9 hours. Data are simultaneously collected for image generation from 0.1 micron to 18 microns. In the one-dimensional mode, measurements can be made every 90 minutes (including acquisition and repointing time) for objects as faint as 19th magnitude in the visible.

Stachnik, R. V.↗
NASA NTRS1984

Bidirectional Spectral Reflectance of Earth Resources: Influence of Scene Complexity and Atmospheric Effects on Remote Sensing

Practical methods for remote sensing when scene complexity and atmospheric effects modify intrinsic reflective properties are developed. The radiation history from ground to space of light reflected from individual leaves is initially multiply scattered within the crop canopy, whose geometry provides a controlling influence, then scattered and attenuated as a result of transmission through the Earth's atmosphere. The experimental and theoretical tools for studying these effects quantitatively are under development. A new radiative transfer code which uses Fourier transforms to solve the 3-D equation of transfer was developed. The initial version permits inhomogeneous non-Lambertian surfaces but assumes horizontal uniformity for the atmosphere. The computational results are in excellent agreement with Monte Carlo calculations. Laboratory apparatus to study the variation of spectral reflectance of individual leaves as a function of illumination incidence angle and reflection angle was used. These data can then be used in models to determine canopy scattering effects. Stress tests by observing leaf reflectance at 0.9 microns as a function of time following clipping from the stem was performed. A reflectance increase due to loss of water has been observed.

Diner, D. J.↗
NASA NTRS1984

A theoretical prediction of the acoustic pressure generated by turbulence-flame front interactions

The equations of momentum annd continuity are combined and linearized yielding the one dimensional nonhomogeneous acoustic wave equation. Three terms in the non-homogeneous equation act as acoustic sources and are taken to be forcing functions acting on the homogeneous wave equation. The three source terms are: fluctuating entropy, turbulence gradients, and turbulence-flame interactions. Each source term is discussed. The turbulence-flame interaction source is used as the basis for computing the source acoustic pressure from the Fourier transformed wave equation. Pressure fluctuations created in turbopump gas generators and turbines may act as a forcing function for turbine and propellant tube vibrations in Earth to orbit space propulsion systems and could reduce their life expectancy. A preliminary assessment of the acoustic pressure fluctuations in such systems is presented.

Huff, R. G.↗
NASA NTRS1983

Properties of echo spectra observed by MST radars

Turbulent scatter and Fresnel reflection are the fundamental echoing mechanisms to interpret the signals observed by Mesosphere-stratosphere-troposphere (MST) radars. Turbulent scattered echoes provide information about the turbulence structure and mean flow of the atmosphere. Observational results with VHF MST radars, however, show the importance of Fresnel reflection due to the infinite gradient of reflectivity at the edges of a scattering layer. This condition is excluded for the weak fluctuation models but it is still possible to include the observed aspect sensitivity by assuming an anisotropic structure of fluctuations. Another explanation of the aspect sensitivity observed by MST radars is advanced. Spectral estimates by the widely used periodogram were related to a four-dimensional spectrum of atmospheric fluctuations with anisotropic structure. Effects of the radar system such as antenna beam width, beam direction and Fast Fourier Transformations (FFT) data length were discussed for the anisotropic turbulent atmosphere. Echo parameters were also estimated.

Wakasugi, K.↗
NASA NTRS1984

Improved resolution rain measurements from spaceborne radar altimeters

Rain measurement of the type described here are considered vital from the standpoint of representing a flag for altimeter data that may be corrupted by rain. It also provides sorely needed rain data over the oceans where little or no such data is available. It is demonstrated that improved resolution measurements of precipitation may be obtained from satellite borne radars with antenna beams having relatively large surface footprints. The method employs deconvolution and Fourier transform procedures, and assumes a knowledge of the antenna beam pattern. As an example, the technique is specifically directed towards the application of future spaceborne radar altimeters which may contain additional range gates to enable the measurement of rain at altitude. It is demonstrated that because of the natural variability of rain in the lateral extent, the standard beam averaging over the footprint could easily produce erroneous interpretations of the intensity of rain and its extent. On the other hand, many of these ambiguities may be removed employing the deconvolution techniques described.

Goldhirsh, J.↗
NASA NTRS1984

Opening of an interface flaw in a layered elastic half-plane under compressive loading

A static analysis is given of the problem of an elastic layer perfectly bonded, except for a frictionless interface crack, to a dissimilar elastic half-plane. The free surface of the layer is loaded by a finite pressure distribution directly over the crack. The problem is formulated using the two dimensional linear elasticity equations. Using Fourier transforms, the governing equations are converted to a pair of coupled singular integral equations. The integral equations are reduced to a set of simultaneous algebraic equations by expanding the unknown functions in a series of Jacobi polynomials and then evaluating the singular Cauchy-type integrals. The resulting equations are found to be ill-conditioned and, consequently, are solved in the least-squares sense. Results from the analysis show that, under a normal pressure distribution on the free surface of the layer and depending on the combination of geometric and material parameters, the ends of the crack can open. The resulting stresses at the crack-tips are singular, implying that crack growth is possible. The extent of the opening and the crack-top stress intensity factors depend on the width of the pressure distribution zone, the layer thickness, and the relative material properties of the layer and half-plane.

Kennedy, J. M.↗
NASA NTRS1984

Computer vision for real-time orbital operations. Center directors discretionary fund

Machine vision research is examined as it relates to the NASA Space Station program and its associated Orbital Maneuvering Vehicle (OMV). Initial operation of OMV for orbital assembly, docking, and servicing are manually controlled from the ground by means of an on board TV camera. These orbital operations may be accomplished autonomously by machine vision techniques which use the TV camera as a sensing device. Classical machine vision techniques are described. An alternate method is developed and described which employs a syntactic pattern recognition scheme. It has the potential for substantial reduction of computing and data storage requirements in comparison to the Two-Dimensional Fast Fourier Transform (2D FFT) image analysis. The method embodies powerful heuristic pattern recognition capability by identifying image shapes such as elongation, symmetry, number of appendages, and the relative length of appendages.

Vinz, F. L.↗
NASA NTRS1984

FTIR analysis of aviation fuel deposits

Five modes of operation of the Nicolet 7199 Fourier Transform Infrared Spectrophotometer have been evaluated for application in analysis of the chemical structure of accelerated storage/thermal deposits produced by jet fuels. Using primarily the absorption and emission modes, the effects of fuel type, stress temperature, stress time, type of spiking agent, spiking agent concentration, fuel flow, and post-depositional treatment on the chemical nature of fuel deposits have been determined.

Helmick, L. S.↗
NASA NTRS1982

Interactive digital signal processor

The Interactive Digital Signal Processor (IDSP) is examined. It consists of a set of time series analysis Operators each of which operates on an input file to produce an output file. The operators can be executed in any order that makes sense and recursively, if desired. The operators are the various algorithms used in digital time series analysis work. User written operators can be easily interfaced to the sysatem. The system can be operated both interactively and in batch mode. In IDSP a file can consist of up to n (currently n=8) simultaneous time series. IDSP currently includes over thirty standard operators that range from Fourier transform operations, design and application of digital filters, eigenvalue analysis, to operators that provide graphical output, allow batch operation, editing and display information.

Mish, W. H.↗
NASA NTRS1983

Processing techniques for software based SAR processors

Software SAR processing techniques defined to treat Shuttle Imaging Radar-B (SIR-B) data are reviewed. The algorithms are devised for the data processing procedure selection, SAR correlation function implementation, multiple array processors utilization, cornerturning, variable reference length azimuth processing, and range migration handling. The Interim Digital Processor (IDP) originally implemented for handling Seasat SAR data has been adapted for the SIR-B, and offers a resolution of 100 km using a processing procedure based on the Fast Fourier Transformation fast correlation approach. Peculiarities of the Seasat SAR data processing requirements are reviewed, along with modifications introduced for the SIR-B. An Advanced Digital SAR Processor (ADSP) is under development for use with the SIR-B in the 1986 time frame as an upgrade for the IDP, which will be in service in 1984-5.

Leung, K.↗
NASA NTRS1983

Navier-Stokes solution on the CYBER-203 by a pseudospectral technique

A three-level, time-split, mixed spectral/finite difference method for the numerical solution of the three-dimensional, compressible Navier-Stokes equations has been developed and implemented on the Control Data Corporation (CDC) CYBER-203. This method uses a spectral representation for the flow variables in the streamwise and spanwise coordinates, and central differences in the normal direction. The five dependent variables are interleaved one horizontal plane at a time and the array of their values at the grid points of each horizontal plane is a typical vector in the computation. The code is organized so as to require, per time step, a single forward-backward pass through the entire data base. The one-and two-dimensional Fast Fourier Transforms are performed using software especially developed for the CYBER-203.

Lambiotte, J. J.↗
NASA NTRS1983

High-resolution infrared spectroscopy of planetary atmospheres

Various techniques for high-resolution infrared spectroscopy of planetary atmospheres are reviewed. Resolving powers of a million are now possible at 1-5 microns with Fourier transform spectrometers and at 10 microns with heterodyne spectrometers. The extension of high-resolution spectroscopy to the far-infrared is currently under development. The role of ground-based high-resolution spectroscopy compared to observations by spacecraft is discussed.

Tokunaga, A. T.↗
NASA NTRS1983

Absolute intensity measurements of the (11/1/0)II-00/0/0 band of (C-12)(O-16)2 at 5.2 microns

A nonlinear least-squares fitting procedure has been used to derive absolute intensities for lines in the P, R, and Q branches of the (11/1/0)II-00/0/0 band of (C-12)(O-16)2 (band center = 1932/cm) from long-path 0.01/cm resolution laboratory spectra. The spectral data were recorded at room temperature and low pressure (less than 10 torr) with the Fourier transform spectrometer in the McMath solar telescope complex at Kitt Peak National Observatory. The observed line intensities were analyzed to derive the vibrational band intensity and F-factor coefficients. To obtain a good fit to the data, it was necessary to include terms in the expression for the F factor, which account for Coriolis-type and Fermi-type interactions and centrifugal distortion effects.

Rinsland, C. P.↗
NASA NTRS1983

Resin characterization in cured graphite fiber reinforced composites using diffuse reflectance-FTIR

The feasibility of using diffuse reflectance in combination with Fourier transform infrared spectroscopy to obtain information on cured graphite fiber reinforced polymeric matrix resin composites was investigated. Several graphite/epoxy, polysulfone, and polyimide composites exposed to thermal or radiation environments were examined. An experimental polyimide-sulfone adhesive tape was also studied during processing. In each case, significant changes in resin molecular structure was observed due to environmental exposure. These changes in molecular structure were correlated with previously observed changes in material properties providing new insights into material behavior.

Young, P. R.↗
NASA NTRS1983

Latitudinal distributions and temporal changes of stratospheric HCl and HF

Hydrogen chloride and hydrogen fluoride are important sinks in the stratosphere for free halogens. The major sources of chlorine and fluorine in the stratosphere are anthropogenic; therefore, a measurement of HCl and HF gives information about the magnitude of anthropogenic effects on stratospheric chemistry and may give some information about the stratospheric hydroxyl concentration as well. The total column amount of HCl and HF above 12 km has been determined by measuring infrared absorption spectra with a high-resolution Fourier transform spectrometer flown on a jet aircraft. The HCl column varies from 0.7 x 10 to the 15th molecules/ sq cm near the equator to 2.7 x 10 to the 15th molecules/sq cm at 70 N; the HF column is about a factor of 5 lower. The HCl:HF ratio is almost independent of latitude, and neither constituent shows substantial seasonal or diurnal variation. At mid-latitudes, the data from 1978 to 1982 show an annual increase of 5 percent per year for HCl and 12 percent per year for HF.

Mankin, W. G.↗
NASA NTRS1984

Effects of boundary layer refraction and fuselage scattering on fuselage surface noise from advanced turboprop propellers

An acoustic disturbance's propagation through a boundary layer is discussed with a view to the analysis of the acoustic field generated by a propfan rotor incident to the fuselage of an aircraft. Applying the parallel flow assumption, the resulting partial differential equations are reduced to an ordinary acoustic pressure differential equation by means of the Fourier transform. The methods used for the solution of this equation include those of Frobenius and of analytic continuation; both yield exact solutions in series form. Two models of the aircraft fuselage-boundary layer system are considered, in the first of which the fuselage is replaced by a flat plate and the acoustic field is assumed to be two-dimensional, while in the second the fuselage is a cylinder in a fully three-dimensional acoustic field. It is shown that the boundary layer correction improves theory-data comparisons over simple application of a pressure-doubling rule at the fuselage.

Mcaninch, G. L.↗
NASA NTRS1983

Measurements of mantle wave velocities and inversion for lateral heterogeneity and anisotropy. I - Analysis of great circle phase velocities

The global lateral heterogeneity of the upper mantle is investigated using the classical Fourier-transform method of Sato(1958) and IDA/GDSN data from 25 1980 earthquakes. The great-circle phase velocities of 200 Love and 250 Rayleigh 100-330-sec-period fundamental-mode wave paths are determined and interpreted in terms of regional phase-velocity variation, using additional data on surface tectonics to extrapolate odd-harmonic information from the even-harmonic data. The results are presented in extensive tables, maps, and graphs. Regionalized inversion using the seven-region model of Okal (1977) is found to give maximum variance reductions of 65 percent for Love waves and 85 percent for Rayleigh waves, compared to 60 and 90 percent for l(max) = 2 inversion. Significant interregion differences are found in the regionalized Love-wave phase velocities.

Nakanishi, I.↗
NASA NTRS1983

Thermal infrared lines of methane broadened by nitrogen at low temperatures

Measurements of spectral transmittance in the nu4-fundamental band of (C-12)H4 have been performed at low temperatures using a Fourier transform spectrometer with apodized spectral resolution of 0.06 per cm. With applications to lines formed in the atmospheres of Titan and earth in mind, N2 has been used as the broadening gas. Comparisons of observed and computed spectral transmittances on a line-by-line basis have yielded line strengths, N2-broadened half-widths and their variation with temperature. Best agreement between measured and computed spectra was obtained when the absolute intensity of the band was taken as 128 per (sq cm-atm) at 296 K. Line widths were found to vary as T to the n power with n = -1.0 for lines of the F-species and 0.63 for the A-species. The measured line widths are considerably larger than those used in the AFGL compilation.

Varanasi, P.↗