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At least 577 records · Page 32

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NASA NTRS2006

Qualification Testing of Solid Rocket Booster Diagonal Strut Restraint Cable Assembly Part Number 10176-0031-102/103

This Technical Memorandum presents qualification test results for solid rocket booster diagonal strut restraint cable part number 101276-00313-102/103. During flight this assembly is exposed to a range of temperatures. MIL-W-83420 shows the breaking strength of the cable as 798 kg (1,760 lb) at room temperature but does not define cable strength at the maximum temperature to which the cable is exposed during the first 2 min of flight; 669 C (1,236 F). The cable, which can be built from different corrosion resistant steel alloys, may also vary in its chemical, physical, and mechanical properties at temperature. Negative margins of safety were produced by analysis of the cable at temperature using standard knockdown factors. However, MSFC-HDBK-5 allows the use of a less conservative safety factor of 1.4 and knockdown factors verified by testing. Test results allowed a calculated knockdown factor of 0.1892 to be determined for the restraint cables, which provides a minimum breaking strength of 151 kg (333 lb) at 677 C (1,250 F) when combined with the minimum breaking strength of 0.317-cm (0.125- or 1/8-in) diameter, type 1 composition rope.

Malone, T. W.↗

NASA NTRS1987

Quantized synchrotron radiation in strong magnetic fields

Spectra from electrons making synchrotron transitions in high magnetic fields are calculated using the exact quantum transition rates for Landau states up to n = 500, and the results are compared with spectra calculated from the classical formula and the asymptotic quantum formula. The behavior of the transition rates are examined at low and high harmonics as a function of the spin state of the electron. The calculations confirm those of Herold, Ruder, and Wunner (1982) for low Landau states, extending them to higher states and individual spin state transitions. The results also confirm the dominance of ground-state transitions at high field strengths noted by White (1976). Single particle emissivities for electrons with both spin-up and spin-down in the initial state are calculated using these transition rates. Spectra for thermal electron distributions at transrelativistic temperatures and for steady state injection of monoenergetic electrons with isotropic pitch angles are also presented.

Harding, Alice K.↗

NASA NTRS1973

Research of the sonic-boom problem

Wind tunnel tests were conducted to determine the characteristics of sonic booms. A theoretical examination of nonlinear effects in near and far flow fields, as well as sonic boom shock strength, is reported. A study of the Mach lines and bicharacteristics in three dimensional flow was pursued. The direction derivatives if the bicharacteristics were calculated in a general three dimensional flow field. A second order theory for supersonic flow past slender bodies was developed. Formulas relating flow deflections to the Whitham F-function were derived, which permitted determination of the sonic boom strength from wind tunnel measurements fairly close to the body.

Drougge, G.↗

NASA NTRS1978

Comparison of quasi-specular radar scatter from the moon with surface parameters obtained from images

Quasi-specular radar scatter from geologic surfaces displays a variable wavelength dependence in apparent surface roughness. Wavelength dependence will occur whenever a significant fraction of the surface has local radii of curvature comparable to the observing wavelength. This condition can be determined by comparison of the value of the integrated surface curvature spectrum with the radar wavenumber, multiplied by a constant that depends on the geometry. Variations in curvature statistics calculated from photogrammetric reduction of lunar images are consistent with the observed variations in quasi-specular scatter at the same locations. Variations in the strength of the wavelength dependence are correlated with the sizes of lunar craters that lie near the upper size limit for the local steady state distribution. This correlation is also consistent with variations in the curvature spectrum calculated from crater size-frequency distributions.

Tyler, G. L.↗

NASA NTRS1990

Moments of dipole oscillator-strength distribution for the helium sequence

The moments S(mu) for mu at least -6 but no more than 2 and L(mu) for mu = 0, 1, and 2 are calculated for the helium sequence for atomic numbers (Z) up to 30 under a screened hydrogenic model. The model describes the atom by single-particle hydrogenic wave functions and treats the initial and the final state as characterized by two different effective charge parameters Zi and Zf, respectively. The differential oscillator strength of the screened hydrogenic model is asymptotically expanded. Assuming the value of 287.6 for the coefficient of the term epsilon to the -7/2 for helium atoms, the parameter Zf is determined for the helium sequence.

Khan, F.↗

NASA NTRS1973

Theory of disordered Heisenberg ferromagnets

A Green's function technique is used to calculate the magnetic properties of Heisenberg ferromagnets in which the exchange interactions deviate randomly in strength from the mean interaction. Systems of sc, bcc, and fcc topologies and of general spin values are treated. Disorder produces marked effects in the density of spin wave states, in the form of enhancement of the low-energy density and extension of the energy band to higher values. The spontaneous magnetization and the Curie temperature decrease with increasing disorder. The effects of disorder are shown to be more pronounced in the ferromagnetic than in the paramagnetic phase.

Stubbs, R. M.↗

NASA NTRS1977

Theoretical brightness temperature profiles of atmospheric pure H2 rotational quadrupole lines - Jupiter and Uranus

With the advent of high-resolution instruments and their use high above most of the telluric water vapor, the hydrogen pure rotational quadrupole lines at 28, 17, and 12 microns from the atmospheres of the outer planets may be observed. Best values for the line strengths, pressure-broadening coefficients, diffusion constants, and pressure shifts for these rotational transitions are calculated. The collisionally narrowed Galatry profile is used to calculate brightness temperature line profiles for these H2 transitions for the outer planets, Jupiter and Uranus. The effects of the H2 rotational-translational continuum and of the NH3 v2 band are also included.

Goorvitch, D.↗

NASA NTRS1982

Prospects of increasing the strength of aluminum by reinforcing it with stainless steel wire (a review)

The theoretical and experimental strength of aluminum reinforced with stainless steel wire is analyzed. Various methods of producing the composite material and it's static and cyclical strengths are considered. The reinforcement of aluminum with stainless steel wire was accomplished from the perspective of increasing the specific strength of aluminum and it's alloys, increasing the strength of the material with respect to high and low temperatures, as well as increasing the cyclical strength. The production of the composite aluminum-stainless steel wire material with approximated or calculated strengthening is possible by any of the considered methods. The selection of the proper production technology depends on precise details and conditions of application of the material.

Botvina, L. R.↗

NASA NTRS1982

Analysis of the far infrared H2-He spectrum

Previous measurements of the far infrared absorption due to H2-He collisions at the temperatures of 77, 195, and 292 K are analyzed. The spectra are fitted by a semiempirical line shape representing the isotropic induced overlap component and combined anisotropic quadrupolar and overlap components. The experimental spectral moments are evaluated and compared with theory for several induced-dipole and potential models. From the isotropic contribution, the range and strength of the induced dipole is evaluated and compared with the results of ab initio calculations. Fitting parameters are obtained with physically plausible temperature dependences which allow simple and accurate representation of the spectra and of their moments at temperatures different from those of the measurements.

Cohen, E. R.↗

NASA NTRS1984

Timing performance of phased-locked loops in optical pulse position modulation communication systems

An optical digital communication system requires that an accurate clock signal be available at the receiver for proper synchronization with the transmitted signal. Phase synchronization is especially critical in M-ary pulse position modulation (PPM) systems where the optimum decision scheme is an energy detector which compares the energy in each of M time slots to decide which of M possible words was sent. Timing errors cause energy spillover into adjacent time slots (a form of intersymbol interference) so that only a portion of the signal energy may be attributed to the correct time slot. This effect decreases the effective signal, increases the effective noise, and increases the probability of error. A timing subsystem for a satellite-to-satellite optical PPM communication link is simulated. The receiver employs direct photodetection, preprocessing of the detected signal, and a phase-locked loop for timing synchronization. The variance of the relative phase error is examined under varying signal strength conditions as an indication of loop performance, and simulation results are compared to theoretical calculations.

Lafaw, D. A.↗

NASA NTRS1987

The magnetic white dwarfs

Observations of isolated magnetic white dwarfs are compared with those of Angel et al. (1981). A list of 21 currently known magnetic white dwarfs is presented, and additions and deletions of stars from the list of Angel et al. are discussed. The spectrum of the hydrogen atom in extremely strong fields, and the field distribution of stars in the 1-700 MG range are calculated. It is observed that the distribution of magnetic stars has remained constant/decade of field strength from about 10 to the 6th to 10 to the 9th G. Consideration is given to the rotation rates and suface compositions of white dwarfs.

Schmidt, Gary D.↗

NASA NTRS1990

Remote sensing of Earth terrain

The layered random medium model is used to investigate the fully polarimetric scattering of electromagnetic waves from vegetation. The vegetation canopy is modeled as an anisotropic random medium containing nonspherical scatterers with preferred alignment. The underlying medium is considered as a homogeneous half space. The scattering effect of the vegetation canopy are characterized by 3-D correlation functions with variances and correlation lengths respectively corresponding to the fluctuation strengths and the physical geometries of the scatterers. The strong fluctuation theory is used to calculate the anisotropic effective permittivity tensor of the random medium and the distorted Born approximation is then applied to obtain the covariance matrix which describes the fully polarimetric scattering properties of the vegetation field. This model accounts for all the interaction processes between the boundaries and the scatterers and includes all the coherent effects due to wave propagation in different directions such as the constructive and destructive interferences. For a vegetation canopy with low attenuation, the boundary between the vegetation and the underlying medium can give rise to significant coherent effects.

Kong, Jin AU↗

NASA NTRS1994

A methodology to predict damage initiation, damage growth and residual strength in titanium matrix composites

In this research, a methodology to predict damage initiation, damage growth, fatigue life, and residual strength in titanium matrix composites (TMC) is outlined. Emphasis was placed on micromechanics-based engineering approaches. Damage initiation was predicted using a local effective strain approach. A finite element analysis verified the prevailing assumptions made in the formulation of this model. Damage growth, namely, fiber-bridged matrix crack growth, was evaluated using a fiber bridging (FB) model which accounts for thermal residual stresses. This model combines continuum fracture mechanics and micromechanics analyses yielding stress-intensity factor solutions for fiber-bridged matrix cracks. It is assumed in the FB model that fibers in the wake of the matrix crack are idealized as a closure pressure, and an unknown constant frictional shear stress is assumed to act along the debond length of the bridging fibers. This frictional shear stress was used as a curve fitting parameter to the available experimental data. Fatigue life and post-fatigue residual strength were predicted based on the axial stress in the first intact 0 degree fiber calculated using the FB model and a three-dimensional finite element analysis.

Bakuckas, J. G., Jr.↗

NASA NTRS1961

Project Echo: System Calculations

The primary experimental objective of Project Echo was the transmission of radio communications between points on the earth by reflection from the balloon satellite. This paper describes system calculations made in preparation for the experiment and their adaptation to the problem of interpreting the results. The calculations include path loss computations, expected audio signal-to-noise ratios, and received signal strength based on orbital parameters.

Ruthroff, Clyde L.↗

NASA NTRS2002

Effect of Environment on Fatigue Behavior of a Nicalon(TM)/Si-N-C Ceramic Matrix Composite

The effect of environmental exposure on the fatigue life of Nicalon(TM) /Si-N-C composite was investigated in this study. Test specimens with arrays of 1.8 mm diameter holes and two different open areas, 25 and 35%, were machined. Three environmental conditions were studied: 1) continuous fatigue cycling in air, 2) fatigue cycling in air alternating with humidity exposure, and 3) fatigue cycling in air alternating with exposure to a salt-fog environment. All fatigue testing on specimens with holes was performed with a load ratio, R = 0.05, and at a temperature of 910 C. In general, fatigue lives were shortest for specimens subjected to salt-fog exposure and longest for specimens subjected to continuous fatigue cycling in air. The fatigue data generated on the specimens with holes were compared with fatigue data generated in air on specimens with no holes. Fatigue strength reduction factors for different environmental conditions and open areas investigated in the study were calculated for the Nicalon(TM) /Si-N-C composite.

Kalluri, Sreeramesh↗

NASA NTRS2007

Electric Field Effects on Fiber Alignment Using an Auxiliary Electrode during Electrospinning

This viewgraph presentation reviews auxiliary and electric field effects on fiber alignment during the process of electrospinning. The contents include: 1) Electrospinning Overview; 2) Experimental Set-up; 3) Jet Exit; 4) Auxiliary Electrode Effects; 5) Electrospinning High Speed Video; 6) Effect of Auxiliary Electrode Position; 7) Micro & Nano Fibers Produced; 8) Micro and Nano Fibrous Mats; 9) Field Effect on Fiber Distribution; 10) Modeling; 11) Calculated trajectories: 5, 10, 15 & 20cm electrode spacing; 12) Off Axis Auxiliary Electrode; 13) Field Strength Effects; and 14) Potential Applications.

Carnell, Lisa S.↗

NASA NTRS2025

Line List for the A 2 Π−X 2 Σ + and the B 2 Σ + −X 2 Σ + Band Systems of CaF

The spectral analysis of molecule-rich asymptotic giant branch (AGB) stars is challenging. Although other calcium and fluorine bearing molecules are observed in the microwave and in the visible spectrum of AGB stars, CaF has never been detected, despite favorable chemical equilibrium predictions. Yet, measuring the CaF abundance could give more insight into the fluorine budget of AGB stars and allow better simulation of stellar spectra. In this work, we present an analysis of the visible spectrum of CaF obtained with a Fourier transform spectrometer. CaF A 2 Π−X 2 Σ + and the B 2 Σ + −X 2 Σ + band systems were excited with a hollow cathode discharge. Using previous fluorescence spectroscopy measurements, highly accurate ground state constants, and reasonable extrapolation schemes, the strongest features of CaF in the visible spectrum can be accurately modeled for both band systems. Spectroscopic constants are determined for A 2 Π with v ≤ 16 and for B 2 Σ + with v ≤ 20. Ab initio transition dipole moment curves of both transitions were calculated and scaled, and we provide a line list with Einstein A coefficients and oscillator strengths. This line list can be used to simulate spectra of CaF at temperatures and pressures relevant to astrophysical environments.

Léo Lavy↗

NASA NTRS1984

Implementation of uniform perturbation method for potential flow past axisymmetric and two-dimensional bodies

The aerodynamic characteristics of potential flow past an axisymmetric slender body and a thin airfoil are calculated using a uniform perturbation analysis method. The method is based on the superposition of potentials of point singularities distributed inside the body. The strength distribution satisfies a linear integral equation by enforcing the flow tangency condition on the surface of the body. The complete uniform asymptotic expansion of its solution is obtained with respect to the slenderness ratio by modifying and adapting an existing technique. Results calculated by the perturbation analysis method are compared with the existing surface singularity panel method and some available analytical solutions for a number of cases under identical conditions. From these comparisons, it is found that the perturbation analysis method can provide quite accurate results for bodies with small slenderness ratio. The present method is much simpler and requires less memory and computation time than existing surface singularity panel methods of comparable accuracy.

Wong, T. C.↗