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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 433 records · Page 24
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NASA NTRS1949

Flight Test of the Aerojet 7KS-6000 T-27 Jato Rocket Motor

A flight test of the Aero jet Engineering Corporation's 7KS-6000 T-27 Jato rocket motor was conducted at the Langley Pilotless Aircraft Research Station at Wallops Island, Va, to determine the flight performance characteristics of the motor. The flight test imposed an absolute longitudinal acceleration of 9.8 g upon the rocket motor at 2.8 seconds after launching. The total impulse developed by the motor was 43,400 pound-seconds, and the thrusting time was 7.58 seconds. The maximum thrust was 7200 pounds and occurred at 4.8 seconds after launching. No thrust irregularities attributable to effects of the flight longitudinal acceleration were observed. Certain small thrust irregularities occurred in the flight test which appear to correspond to irregularities observed in static tests conducted elsewhere. A hypothesis regarding the origin of these small irregularities is presented.

Bond, Aleck C.↗
NASA NTRS2011

Characterization of the as Manufactured Variability in a CVI SiC/SiC Woven Composite

The microstructure of a 2D woven ceramic matrix composite displays significant variability and irregularity. For example, a chemical vapor infiltrated (CVI) SiC/SiC composite exhibits significant amount of porosity arranged in irregular patterns. Furthermore, the fiber tows within a ply frequently have irregular shape and spacing, and the stacked plies are often misaligned and irregularly nested within each other. The goal of an ongoing project at NASA Glenn is to investigate the effects of the complex microstructure and its variability on the properties and the durability of the material. One key requirement for this effort is the development of methods to characterize the distribution in as-fabricated ceramic matrix composite (CMC) microstructures with the objective of correlating microstructural distribution parameters with mechanical performance. An initial task in this effort was to perform quantitative image analysis of polished cross sections of CVI SiC/SiC composite specimens. This analysis provided sample distributions of various microstructural composite features, including: inter-tow pore sizes and shapes, transverse sectioned tow sizes and shapes, and within ply tow spacing. This information can then be used to quantify the effect of extreme values of these features on the local stress state with the goal of determining the likelihood of matrix cracking at a given external load.

Bonacuse, Peter J.↗
NASA NTRS1971

Relationship between Fe /+/ ions and equatorial spread F.

Evaluation of observations from the retarding potential analyzer on Ogo 6 near the magnetic equator, demonstrating an intimate relationship between the presence of Fe(+) ions and irregularities in the total ion concentration. The ionospheric irregularities (or structure) are probably another manifestation of equatorial spread F, although this has not yet been verified. Nearly half the nighttime equatorial crossings below 700 km exhibit both Fe(+) and structure, but only 10% of the passes without Fe(+) have structure. Approximately one-third of the passes with Fe(+) are not structured, which indicates that Fe(+) may be a necessary but not sufficient condition for structure formation. The Atlantic region shows an extremely high and detailed correlation between Fe(+) ions and the irregularities.

Hanson, W. B.↗
NASA NTRS1973

A noncoherent model for microwave emissions and backscattering from the sea surface

The two-scale (small irregularities superimposed upon large undulations) scattering theory proposed by Semyonov was extended and used to compute microwave apparent temperature and the backscattering cross section from ocean surfaces. The effect of the small irregularities upon the scattering characteristics of the large undulations is included by modifying the Fresnel reflection coefficients; whereas the effect of the large undulations upon those of the small irregularities is taken into account by averaging over the surface normals of the large undulations. The same set of surface parameters is employed for a given wind speed to predict both the scattering and the emission characteristics at both polarizations.

Wu, S. T.↗
NASA NTRS1973

On the cause of equatorial spread F.

It is suggested that convective electric fields in the equatorial ionosphere are generated by neutral winds (zonal or meridional) which act on regions having structure in their field aligned Pedersen conductivity integrals. The conductivity structure is presumably caused by long-lived metallic ions concentrated irregularly below the F layer at altitudes where their collision and gyrofrequencies are comparable. The resulting plasma convection leads to large-scale irregularities and sets up gradients in the electric field that drive other instability mechanisms to produce small-scale irregularities. The mechanism proposed requires a different velocity above and below 200 km for winds in the magnetic east-west direction, but for winds in the magnetic meridian direction, an altitude gradient is not required.

Hanson, W. B.↗
NASA NTRS1973

Dynamics of midlatitude light ion trough and plasmatails

Light ion trough measurements near midnight made by the RF ion mass spectrometer on OGO-4 operating in the high resolution mode in Feb. 1968 reveal the existence of irregular structure on the low latitude side of the midlatitude trough. Using two different relations between the equatorial convection electric field, assumed spatially invariant and directed from dawn to dusk, and Kp (one based on plasmapause measurements, the other on polar cap E field measurements) a model development was made of the outer plasmasphere. The model calculations produced multiple plasmatail extensions of the plasmasphere which compare favorably with the observed irregularities. Due to magnetic local time differences between the Northern and Southern Hemisphere along OGO's orbit, the time dependent irregularity structure observed is not symmetrical about the equator. The model development produces an outer plasmasphere boundary location which varies similarly to the observed minimum density point of the light ion trough. However the measurements are not extensive enough to yield conclusive proof that one of the electric field models is better than the other.

Chen, A. J.↗
NASA NTRS1975

The role of the magnetosphere in satellite and radio-star scintillation

A theory is developed to account for the scintillation phenomenon observed in equatorial regions when using communications satellites in the SHF band. The same theory is also used qualitatively to explain strong scintillations in the VHF band. Instead of confining irregularities to a narrow interval of height in the F-region and assuming that they are strong, the alternative hypothesis is used that the irregularities are weak but extend from the F-region upwards into the magnetosphere. It is suggested that the irregularities are field-aligned and extend at least up to an L-shell of 1.3 and possibly up to 2 or more.

Booker, H. G.↗
NASA NTRS1975

Scintillation estimates for a Jupiter entry probe: Phase 1

A model of the electron density irregularities in the Jovian ionosphere is constructed based on a preliminary interpretation of the Pioneer 10 Jovian ionospheric scintillations. The ionospheric irregularities exist over an altitude range of 3000 km. The structure constant c sub n of refractive index fluctuations is constant throughout this altitude range. The spatial wavenumber spectrum of the electron density irregularities follows the Kolmogorov spectrum and the outer scale size is greater than 6 km. Estimates of scintillation for a Jovian entry probe based on this model indicate that it is small at S-band but could be substantial at 4000 MHz. The temporal frequency spectrum of the log-amplitude fluctuation is less than 1 Hz and is consequently rather narrow.

Woo, R.↗
NASA NTRS1976

The partially aligned gradient instability in the ionosphere

Ionization irregularities which are almost but not exactly aligned along the magnetic field may grow much more rapidly than purely aligned irregularities in the presence of a background gradient of ionization and current flow. The stability of these irregularities is considered, taking into account the finite thickness of the gradient and shear in the ion motion. It is shown in particular that the normal E region of the ionosphere is usually stable, whereas sporadic E is often unstable, and this may limit the compression of metallic ions to form such layers. The F region may sometimes be unstable. Temperate zone conditions are considered throughout.

Whitehead, J. D.↗
NASA NTRS1977

Probing the solar wind with radio measurements of the second moment field

The dependence of spectral broadening on anisotropic electron-density irregularities and velocity fluctuations in the solar wind is investigated on the basis of results for a second moment mutual coherence function obtained by a parabolic-equation method. It is found that although anisotropic irregularities and wind-velocity fluctuations decrease the bandwidth of the spectrum relative to that for isotropic irregularities and no velocity fluctuations, the shape of the spectrum remains unchanged. Examination of the frequency dependence and shape of a computed angular spectrum indicates that the electron-density spectrum is consistent with a power law having a spectral index close to the value appropriate for the Kolmogorov spectrum. It is proposed that multiple-station observations of some total field be employed to measure the solar wind.

Woo, R.↗
NASA NTRS1980

Long wavelength PbSnTe lasers with CW operation above 77 K

Lead tin telluride diode lasers with emission wavelengths of 6 to 9 micrometers easily operate continuously at temperatures above 77K. These lasers have the Pb(1-y) Sn(y) TE/Pb(1-y) Te/Pb(1-y) Sn(y) Te/PbTe (substrate), (x y) double heterostructure. To prepare this structure by LPE, the growth temperature must be below 600 C to suppress diffusion of the tin during the epitaxial growth. When the heterojunctions are formed by the usual LPE method, the junction boundaries become irregular in the case for the lasers with wavelengths of over 10 micrometers at 77K. The mechanism by which the heterojunction boundaries become irregular is cleared and a new LPE method which prevents the irregularity is explained. The lasers prepared from the wafers grown by the new method have demonstrated CW operation at wavelengths longer than 10 micrometers above liquid nitrogen temperature.

Shinohara, K.↗
NASA NTRS1981

The case of the noisy derivatives - Evidence for a spacecraft-plasma interaction

Data from the retarding potential analyzers on Atmosphere Explorers C and D indicate the existence of 2-m irregularities in the ion flux to the satellite. These irregularities are seen only occasionally, and usually very near the magnetic dip equator. They occur both in sunlight and eclipse and span at least two decades of ion concentration. They tend to be present when the spacecraft is moving nearly parallel to the magnetic field vector and are not seen at all from the low latitude AE-E orbit. It is believed that the irregularities, whose amplitude is of the order of 1% of the background ion flux, are the result of a spacecraft interaction with the ionospheric plasma. A mechanism for producing this interaction that utilizes a fast beam of ambient ions reflected upstream from the satellite to produce a two-stream instability is examined in some detail.

Hanson, W. B.↗
NASA NTRS1983

Mesospheric scatter and its microstructure

The difference in character between mesospheric returns from about 70 and about 80 km was noted. The 69-km echo is characterized by a single return with about .1 Hz width, while the 82.5 km return extends over more than 3 Hz bandwidth; this difference is also perceptible, but to a lesser degree, on the fading curves. The conclusion seems inescapable that internal random velocities of a few m/s are present within the scattering volume for the 82.5-km echo. The most likely source for these rather large velocities is convective instability arising from deformations of the temperature profile by breaking gravity waves. The distinction between the two types of scatter at these altitudes probably accounts for the behavior with frequency of the nightime fading period at low and very low frequencies. The fading period of D-region reflections at night was constant at about 7 min from 16 to 43 kHz, but that at frequencies of 70 kHz and above, the fading period decreased in such a way as to indicate the presence of irregularities smaller than about 1 km in size. This suggests that frequencies of 48 kHz and above, the fading period decreased in such a way as to indicate the presence of irregularities smaller than about 1 km in size. This suggests that frequencies of 48 kHz and below were reflected primarily from the region below 80 km where the narrow spectral irregularities dominate.

Bowhill, S. A.↗
NASA NTRS1984

Magnetic field orientations in Saturn's upper ionosphere inferred from Voyager radio occultations

The radio scintillations observed during occultations of Voyagers 1 and 2 by Saturn are analyzed to determine the morphology of plasma irregularities and hence the magnetic field orientation in Saturn's upper atmosphere. The measurement techniques, the weak scattering theory, and the method used to relate the observed radio scintillations to physical properties of the ionospheric irregularities are briefly described. Results on the spatial characteristics of the irregularities are presented, and the magnetic field orientation in Saturn's ionosphere is inferred. Although the occultation measurements generally confirm the accuracy of the Saturnian magnetic field model of Connerney et al. (1982), it is found that a small adjustment of the coefficients in that model's zonal harmonic expansion would remove the discrepancy between the model predictions and the measurements. A strategy for obtaining improved measurements of Saturn's magnetic field from radio occultation observations of scintillations and Faraday rotation using an orbiting spacecraft is briefly discussed.

Hinson, D. P.↗
NASA NTRS1983

Radio scintillations observed during atmospheric occultations of Voyager: Internal gravity waves at Titan and magnetic field orientations at Jupiter and Saturn

The refractive index of planetary atmospheres at microwave frequencies is discussed. Physical models proposed for the refractive irregularities in the ionosphere and neutral atmosphere serve to characterize the atmospheric scattering structures, and are used subsequently to compute theoretical scintillation spectra for comparison with the Voyager occultation measurements. A technique for systematically analyzing and interpreting the signal fluctuations observed during planetary occultations is presented and applied to process the dual-wavelength data from the Voyager radio occultations by Jupiter, Saturn, and Titan. Results concerning the plasma irregularities in the upper ionospheres of Jupiter and Saturn are reported. The measured orientation of the irregularities is used to infer the magnetic field direction at several locations in the ionospheres of these two planets; the occultation measurements conflict with the predictions of Jovian magnetic field models, but generally confirm current models of Saturn's field. Wave parameters, including the vertical fluxes of energy and momentum, are estimated, and the source of the internal gravity waves discovered in Titan's upper atmosphere is considered.

Hinson, D. P.↗
NASA NTRS1986

A morphological study of waves in the thermosphere using DE-2 observations

Theoretical model and data analysis of DE-2 observations for determining the correlation between the neutral wave activity and plasma irregularities have been presented. The relationships between the observed structure of the sources, precipitation and joule heating, and the fluctuations in neutral and plasma parameters are obtained by analyzing two measurements of neutral atmospheric wave activity and plasma irregularities by DE-2 during perigee passes at an altitude on the order of 300 to 350 km over the polar cap. A theoretical model based on thermal nonlinearity (joule heating) to give mode-mode coupling is developed to explore the role of neutral disturbance (winds and gravity waves) on the generation of plasma irregularities.

Gross, S. H.↗
NASA NTRS1986

Photometry of resolved galaxies. V - NGC 6822

Three-color CCD frames of the local group irregular galaxy NGC 6822 have been reduced to GRI photometry for 3475 stars using RICHFLD point-spread function fitting techniques. The data are compared with earlier work on this galaxy, particularly with Kayser (1966) on a star-by-star basis. Color-magnitude diagrams are constructed from the data and compared with both theoretical stellar model tracks and the expected foreground star contamination. A luminosity function for the blue stars is derived; comparison of this luminosity function with those of 10 other irregular galaxies indicates that NGC 6822 has a typical young star population. The stellar birthrate and initial mass function are estimated for this galaxy. The slope at the bright end of the mass function looks similar to recent results for the Galaxy, the Magellanic Clouds, and the irregular galaxy Sextans A. NGC 6822 appears to be presently forming stars at a slower rate for its mass than Sextans A or the Magellanic Clouds.

Hoessel, J. G.↗
NASA NTRS1987

Measuring star formation rates in blue galaxies

The problems associated with measurements of star formation rates in galaxies are briefly reviewed, and specific models are presented for determinations of current star formation rates from H alpha and Far Infrared (FIR) luminosities. The models are applied to a sample of optically blue irregular galaxies, and the results are discussed in terms of star forming histories. It appears likely that typical irregular galaxies are forming stars at nearly constant rates, although a few examples of systems with enhanced star forming activity are found among HII regions and luminous irregular galaxies.

Gallagher, John S., III↗