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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Magnetosheath electrostatic turbulence

The spectrum of electrostatic plasma waves in the terrestrial magnetosheath was studied using the plasma wave experiment on the IMP-6 satellite. Electrostatic plasma wave turbulence is almost continuously present throughout the magnetosheath with broadband (20 Hz- 70 kHz) r.m.s. field intensities typically 0.01 - 1.0 millivolts/m. Peak intensities of about 1.0 millivolts/m near the electron plasma frequency (30 - 60 kHz) were detected occasionally. The components usually identified in the spectrum of magnetosheath electrostatic turbulence include a high frequency ( or = 30 kHz) component peaking at the electron plasma frequency f sub pe, a low frequency component with a broad intensity maximum below the nominal ion plasma frequency f sub pi (approximately f sub pe/43), and a less well defined intermediate component in the range f sub pi f f sub pe. The intensity distribution of magnetosheath electrostatic turbulence clearly shows that the low frequency component is associated with the bow shock, suggesting that the ion heating begun at the shock continues into the downstream magnetosheath.

Rodriquez, P.↗
NASA NTRS1977

Separated-flow unsteady pressures and forces on elastically responding structures

Broadband rms, spectral density, and spatial correlation information that characterizes the fluctuating pressures and forces that cause aircraft buffet is presented. The main theme is to show the effects of elasticity. In order to do so, data are presented that were obtained in regions of separated flow on wings of wind-tunnel models of varying stiffness and on the wing of a full-scale aircraft. Reynolds number effects on the pressure fluctuations are also discussed.

Coke, C. F.↗
NASA NTRS1975

Sensor performance report, volume 4 (S-190A)

A summary of efforts expended to determine the radiometric accuracy and signal to noise ratio achieved by the S190A multispectral camera is reported. The technique used was to computer model the photographic system and to compare theoretical results to known or measured radiometric values. The two sources used as known targets for radiometric evaluation were the film broadband sensitometry and the lunar disc. From the analysis it appears feasible to attain an accuracy of 10% or better in radiometric accuracy. This however is contingent on contemporaneously exposing the target and spectral sensitometry.

Mendlowitz, R. A., Sr.↗
NASA NTRS1971

The 2-8 GHz solar dynamic spectra and polarization measurement feasibility study

The preliminary system design of a Solar Microwave Spectrograph (SMS) is presented. This design resulted from a study to determine the feasibility of measuring solar polarization and dynamic spectra over the range of two to eight GHz, using broadband radio frequency instrumentation and rapid recording equipment in conjunction with radio telescopes. The scientific value of the proposed SMS instrument is discussed, with remarks concerning data reduction and analysis and a presentation of the engineering plan to implement the SMS system.

Haddock, F. T.↗
NASA NTRS1976

Magnetostrictive ultrasonic probes

The principles underlying the design and use of magnetostrictive ultrasonic probes is illustrated by oscillograms and sketches. Attention is given to such concepts as magnetostrictive transduction, broadband pulse shaping, guided wave propagation, wave impedance, reflection, transmission, and attenuation coefficients, coupling methods, and impulse-induced resonance. A number of applications of such probes are discussed including the measurement of elastic moduli, temperature, and acoustic emission and resonance studies.

Lynnworth, L. C.↗
NASA NTRS1976

Stellar model chromospheres. V - Alpha Centauri A /G2 V/ and Alpha Centauri B /K1 V/

Models for the upper photospheres and lower chromospheres of Alpha Centauri A and B are derived from high-dispersion spectrograms of the Ca II K-line emission cores and damping wings. Effective temperatures, surface gravities, and ages consistent with the measured broadband colors, metallicities, and absolute magnitudes are estimated for the two stars. The spectrograms are calibrated by fitting the far-wing K profiles with synthetic fluxes based on radiative-equilibrium models, and the model atmospheres are obtained through a partial-redistribution analysis of the line cores and damping wings. These models are compared with those previously proposed for Procyon, Arcturus, and the sun. Many features in all the models are found to be quite similar, and some evidence suggests that Alpha Cen A may be significantly older and more evolved than the sun, even though both stars exhibit similar chromospheric properties.

Ayres, T. R.↗
NASA NTRS1976

Martian north pole summer temperatures - Dirty water ice

Broadband thermal and reflectance observations of the Martian north polar region in late summer yield temperatures for the residual polar cap near 205 K with albedos near 43 percent. The residual cap and several outlying smaller deposits are water ice with included dirt; there is no evidence for any permanent carbon dioxide polar cap.

Kieffer, H. H.↗
NASA NTRS1976

Magnetospheric chorus - Occurrence patterns and normalized frequency

Over 400 hours of continuous broadband data obtained by the OGO 3 satellite are analyzed to provide a statistically accurate description of band-limited (magnetospheric) chorus. Certain aspects of the chorus frequency distribution are interpreted in terms of a gyroresonant electron feedback model of generation. An example of high chorus activity during an outbound pass through the noon magnetosphere is examined in detail, the spectral complexity of some chorus is illustrated, and the diurnal variation of chorus occurrence is investigated. The frequency and bandwidth distributions of chorus are analyzed. The results indicate that chorus occurrence depends strongly on local time and dipole latitude, the general region of maximum chorus occurrence approximates the previously reported zone of 'hard' electron precipitation, and the normalized chorus frequency is strongly dependent on dipole latitude. It is shown how a change in the curvature of the whistler-mode refractive-index surface affects focusing of radiation along magnetic field lines and how interference can occur between modes with slightly different ray velocities. It is concluded that most magnetospheric chorus consists of rising emissions which are probably generated by gyroresonant electrons slightly off the equator.

Burtis, W. J.↗
NASA NTRS1976

Plasma waves in the distant magnetotail

The results of an extensive study of plasma waves in the distant magnetotail on the basis of measurements from the Imp 8 spacecraft are discussed. The plasma measurements are compared with plasma and magnetic field measurements described by Frank et al. (1976) to study the relationship of the plasma waves to the various plasma regimes found in the distant magnetotail. Three distinctly different types of plasma wave turbulence in the distant magnetotail are detected. The first, most frequently occurring type of turbulence, consists of broadband electrostatic noise at frequencies between 10 Hz and a few kHz. The second, less frequent type of plasma wave turbulence consists of intense (100 milligamma) bursts of low frequency (10 to 300 Hz) magnetic noise. The third, least frequent type of turbulence consists of electrostatic waves near harmonics of the electron gyrofrequency.

Gurnett, D. A.↗
NASA NTRS1977

VLF emissions associated with enhanced magnetospheric electrons

VLF emissions and enhancements of low-energy electrons have been simultaneously observed during periods of geomagnetic disturbances by the equatorial orbiting Explorer 45 satellite. These events are characterized by the following: (1) the VLF emissions occur outside the plasmasphere in the nightside of the magnetosphere, (2) the emissions consist of two frequency regimes, one below the local electron gyrofrequency, and the other above it, (3) the emissions below the gyrofrequency are relatively broadband whistler waves characteristic of chorus, (4) the emissions above the gyrofrequency are electrostatic and typically have components near 3/2 the gyrofrequency, (5) the onset of emissions coincides with abrupt increases outside the plasmasphere in 1-10 keV electrons to intensities of the order of 10 to the 8th el/sq cm/s/sr/keV, and (6) the cessation of the emissions coincides with a drop in the electron intensities to their preenhancement levels, which are of the order of 10 to the 6th el/sq cm/s/sr/keV or less.

Anderson, R. R.↗
NASA NTRS1976

Determination of the energy or pressure of a solar X-ray structure using X-ray filtergrams from a single filter

While the X-ray fluxes measured through two different broadband filters can be used to derive the temperatures and emission measures of solar plasmas, it is generally assumed that no plasma parameters can be measured quantitatively with a single filtergram alone. It is shown that the thermal energy density (or pressure) of a solar plasma can be measured with an ideal single filtergram. Calculations have been done to compare the properties of the Skylab S-054 X-ray telescope filters with those of the ideal filter.

Kahler, S.↗
NASA NTRS1977

Observations of Jupiter and Saturn at 5-8 micron

Moderate-resolution spectrophotometry (about 0.015) has shown the effects of known atmospheric constituents (NH3, CH4, C2H6) on the 5-8 micron spectrum of Jupiter. Broadband observations of Saturn at 6.5 micron are also reported.

Russell, R. W.↗
NASA NTRS1977

A region of intense plasma wave turbulence on auroral field lines

Plasma wave measurements from the Hawkeye 1 and Imp 6 satellites show that a region of intense plasma wave turbulence occurs on high-latitude auroral field lines at altitudes ranging from a few thousand kilometers in the ionosphere to greater than 40 R-E in the distant magnetotail. Two distinct components are evident in the spectrum of this turbulence: (1) an intense quasi-electrostatic component called broadband electrostatic noise and (2) a weak whistler mode electromagnetic component called magnetic noise bursts. It is suggested that the plasma wave turbulence occurs on magnetic field lines which connect with regions of intense inverted V electron precipitation at low altitudes and with regions of intense earthward plasma flow in the distant magnetotail.

Gurnett, D. A.↗
NASA NTRS1977

Ultraviolet response of InGaAsP photocathodes

Three type VPM 164 photomultiplier tubes with III-IV compound InGaAsP reflective photocathodes were developed for use in ground-based and space-borne astronomical detectors. Although the achieved response of about 0.02% quantum efficiency at 1.083 microns fell short of the goal of 1% quantum efficiency, the broadband characteristics are still considerably better than those of the S-1 photocathode.

Feibelman, W. A.↗
NASA NTRS1977

Far-infrared and submillimeter observations of the planets

Broadband observations in several passbands between 30 and 500 microns of Mercury, Venus, Mars, Jupiter, Saturn, and Uranus are presented. The best agreement between the data and various thermal models of Mars, Jupiter, and Uranus is obtained with a slightly cooler absolute temperature scale than that previously adopted by Armstrong et al. (1972). The effective temperature of Uranus is 58 + or - 2 K, which is in agreement with its solar equilibrium temperature. The existence of an internal energy source for Saturn has been reconfirmed; its output must lie within the range of 0.9 to 3.2 times the absorbed solar flux. A depression exists in the spectra of Jupiter, Saturn, and Uranus between 80 and 300 microns, which may be a result of NH3 opacity.

Loewenstein, R. F.↗
NASA NTRS1977

Longitudinal variations of very-low-frequency chorus activity in the magnetosphere - Evidence of excitation by electrical power transmission lines

The distribution of VLF chorus in the high-altitude magnetosphere as detected by the Ogo 3 satellite was investigated. Chorus occurrence frequency over 4,668 samples of 5 min of broadband data was computed for Northern Hemisphere bins of 10 deg by 10 deg in dipole invariant latitude and longitude. Peaks in activity were noted over Alaska, the eastern U.S. and Canada, western Europe, and western Siberia, and were shown not to be the result of biased sampling. It is suggested that power line radiation of only about 1 W or less at a given harmonic frequency may be sufficient to stimulate the observed chorus activity and that such power levels can be expected in industrial areas or from large distribution networks. Preliminary results show that chorus starting frequencies are highly correlated with 60 Hz harmonics in the American sector and with 50 Hz harmonics in the European sector.

Luette, J. P.↗
NASA NTRS1977

The S-054 X-ray telescope experiment on Skylab

A description of the S-054 X-ray telescope on Skylab is presented with a discussion of the experimental objectives, observing program, data reduction and analysis. Some results from the Skylab mission are given. The telescope photographically records high-resolution images of the solar corona in several broadband regions of the soft X-ray spectrum. It includes an objective grating used to study the line spectrum. The spatial resolution, sensitivity, dynamic range and time resolution of the instrument were chosen to survey a wide variety of solar phenomena. It embodies improvements in design, fabrication, and calibration techniques which were developed over a ten-year period. The observing program was devised to optimize the use of the instrument and to provide studies on a wide range of time scales. The data analysis program includes morphological studies and quantitative analysis using digitized images. A small sample of the data obtained in the mission is presented to demonstrate the type of information that is available and the kinds of results that can be obtained from it.

Vaiana, G. S.↗