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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Combined observations of meteors by image-orthicon television camera and multi-station radar

Observations from multiple sites of a radar network and by television of 29 individual meteors from February 1969 through June 1970 are reported. Only 12 of the meteors did not appear to fragment over all the observed portion of their trajectories. From these 12, the relation for the radar magnitude to the panchromatic absolute magnitude was found in terms of velocity of the meteor. A very tentative fit to the data on the duration of long enduring echoes versus visual absolute magnitude is made. The exponential decay characteristics of the later parts of several of the light curves are pointed out as possible evidence of mutual coalescence of droplets into which the meteoroid has completely broken.

Cook, A. F.↗
NASA NTRS1974

Study of structure defect interactions in aluminum by the acoustic method

Using echo pulse and resonance rod methods, internal friction in pure aluminum was studied as a function of frequency, hardening temperature, time (internal friction relaxation) and impurity content. These studies led to the conclusion that internal friction in these materials depends strongly on dislocation structure and on elastic interactions between structure defects. It was found experimentally that internal friction relaxation depends on the cooling rate and on the impurity content. Some parameters of the dislocation structure and of the diffusion process were determined. It is shown that the dislocated dependence of internal friction can be used as a method of nondestructive testing of the impurity content of high-purity materials.

Nicolaescu, I. I.↗
NASA NTRS1974

Contribution to the acoustic study of theater auditoriums transformable for different types of productions

The auditorium of the Bucharest National Theater has been equipped with devices permitting it to be transformed into three functional types of rooms for different types of productions. In view of the purpose of the room (spoken theater) and the volume of the room (3,000-3,600 cu m 3) the optimum reverberation time is 0.95 sec at a frequency of 1,000 Hz. By applying the different types of acoustic treatment, a reverberation time ranging from 0.96 to 1.06 sec was obtained. The problem of flutter echoes in the arena was solved by applying semispherical bodies to the fixed ceiling. The level of noise transmitted to the auditorium was reduced down to the Cz25 curve.

Belea, R.↗
NASA NTRS1974

Computer program for thin-wire structures in a homogeneous conducting medium

A computer program is presented for thin-wire antennas and scatters in a homogeneous conducting medium. The anaylsis is performed in the real or complex frequency domain. The program handles insulated and bare wires with finite conductivity and lumped loads. The output data includes the current distribution, impedance, radiation efficiency, gain, absorption cross section, scattering cross section, echo area and the polarization scattering matrix. The program uses sinusoidal bases and Galerkin's method.

Richmond, J. H.↗
NASA NTRS1974

Collection and processing of data from a phase-coherent meteor radar

An analysis of the measurement accuracy requirement of a high resolution meteor radar for observing short period, atmospheric waves is presented, and a system which satisfies the requirements is described. A medium scale, real time computer is programmed to perform all echo recognition and coordinate measurement functions. The measurement algorithms are exercised on noisy data generated by a program which simulates the hardware system, in order to find the effects of noise on the measurement accuracies.

Backof, C. A., Jr.↗
NASA NTRS1974

Digital ionosonde studies of F-region waves

Accurate fixed-frequency virtual height data collected on a digital ionosonde are analyzed to measure speed and direction of traveling ionospheric disturbances by matching the experimental data with virtual height and echo amplitude obtained from a simple model of the disturbed ionosphere. Several data records analyzed in this manner indicate speeds of 400 to 680 m/sec and a direction of propagation from north to south. The digital ionosonde collects virtual height data with a time resolution of 10 sec and a height resolution of less than 300 m.

Harper, R. M.↗
NASA NTRS1973

Grain size analysis and high frequency electrical properties of Apollo 15 and 16 samples

The particle size distribution of eleven surface fines samples collected by Apollo 15 and 16 was determined by the method of measuring the sedimentation rate in a column of water. The fact that the grain size distribution in the core samples shows significant differences within a few centimeters variation of depth is important for the understanding of the surface transportation processes which are responsible for the deposition of thin layers of different physical and/or chemical origin. The variation with density of the absorption length is plotted, and results would indicate that for the case of meter wavelength radar waves, reflections from depths of more than 100 meters generally contribute significantly to the radar echoes obtained.

Gold, T.↗
NASA NTRS1974

Mare Serenitatis - A preliminary definition of surface units by remote observations

Mare Serenitatis is a ringed mare about 600 km in diameter situated in the northeast quadrant of the moon. The floor of the mare is comprised of several units. Remote observations of Mare Serenitatis are presented. Color difference photographs were produced by photographing the moon at two wavelength bands. Radar images were obtained by delay-Doppler mapping of radar echoes. The definition of surface units is discussed together with surface properties obtained from remote observations.

Thompson, T. W.↗
NASA NTRS1974

Comment on radar scattering from Saturn's rings

Strong 12.5 cm-wavelength radar echoes from Saturn's rings have been observed recently. The observed radar cross section of 0.62 (plus or minus 0.15) times the geometric area occupied by the optically observed A, B, and C rings seems too high based on radar experience with the terrestrial planets and the asteroids Icarus and Toro. An explanation of this phenomenon is proposed, based on the fact that backscattering from transparent spheres can show considerable gain over the simple external reflection from the front surface of an equivalent dielectric sphere. It is shown that only 10% of the optically observed material in the A, B, and C rings need consist of smooth ice fragments larger than 8 cm in radius to yield the radar results.

Pettengill, G. H.↗
NASA NTRS1974

Observations of radiation from an electron beam artificially injected into the ionosphere

This paper reports the observations of waves generated by a controlled beam of particles artificially injected into the ionosphere and magnetosphere. The measurements were made during the Electron Echo 1 experiment, in which an electron accelerator was carried to a height of 350 km in the ionosphere from Wallops Island, Virginia, on an Aerobee 350 sounding rocket. It injected into the earth's magnetic field over 3000 16-ms pulses of electrons with 40-keV energy and a current of 70 mA at pitch angles between 70 and 110 deg. The ejected fiber glass nose cone carried antennas and receivers to measure the electric field of waves generated by the beam. Associated with the electron beam was radiation detected at frequencies near the electron plasma frequency of the background ionosphere, near twice the electron cyclotron frequency in the whistler mode, and near zero frequency. Associated with the operation of an argon plasma generator used to keep the accelerator neutralized were continuous emissions detected at frequencies near the lower-hybrid resonance (LHR).

Cartwright, D. G.↗
NASA NTRS1974

Radar map of Venus at 3.8 cm wavelength

Radar echoes from Venus have been mapped at a wavelength of 3.8 cm from approximately 270 deg to 10 deg in longitude and -50 deg to +50 deg in latitude during the inferior conjunctions of 1969 and 1972. Observations made in April 1969 and again in June 1972 both show the same regions of high reflectivity as well as several large regions of low reflectivity.

Rogers, A. E. E.↗
NASA NTRS1974

The mapping of lunar radar scattering characteristics

This is the first of four articles describing a comprehensive series of radar maps of the entire visible lunar hemisphere carried out at wavelengths of 3.8 and 70 cm and analyzing the echoes in both orthogonal senses of circular polarization. In this paper, the basic techniques of delay-Doppler mapping by radar are developed, and the particular steps employed in mapping the moon are outlined. Succeeding articles present the results obtained and discuss the way in which these results relate to other, nonradar measurements as well as to the actual lunar surface properties.

Pettengill, G. H.↗
NASA NTRS1974

Clear air convection - A close look at its evolution and structure

A unique experiment using advanced remote and direct sensing techniques was designed to investigate the detailed evolution and structure of clear-air convection. The measurements involved a high-power, narrow-beam pulse radar, a frequency modulated, continuous wave radar, an acoustic echo sounder, and instrumented aircraft. The various probing methods when used together complement each other and give a compatible and comprehensive description of the spatial and temporal evolution of clear-air convection.

Richter, J. H.↗
NASA NTRS1974

Geoscience instrumentation

Geoscience instrumentation systems are considered along with questions of geoscience environment, signal processing, data processing, and design problems. Instrument platforms are examined, taking into account ground platforms, airborne platforms, ocean platforms, and space platforms. In situ and laboratory sensors described include acoustic wave sensors, age sensors, atmospheric constituent sensors, biological sensors, cloud particle sensors, electric field sensors, electromagnetic field sensors, precision geodetic sensors, gravity sensors, ground constituent sensors, horizon sensors, humidity sensors, ion and electron sensors, magnetic field sensors, tide sensors, and wind sensors. Remote sensors are discussed, giving attention to sensing techniques, acoustic echo-sounders, gamma ray sensors, optical sensors, radar sensors, and microwave radiometric sensors.

Wolff, E. A.↗
NASA NTRS1975

Buffer control unit for computer communications

Unit provides character echoing for keyboard display, parity and syndrome generation (error detection), half or full data-packet generation, automatic retransmission of packets, and keyboard lock-up.

Okinaka, A. K.↗
NASA NTRS1974

Optical transfer function of NTS-1 retroreflector array

An optical transfer function was computed for the retroreflector array carried by the NTS-1 satellite. Range corrections are presented for extrapolating laser range measurements to the center of mass of the satellite. The gain function of the array was computed for use in estimating laser-echo signal strengths.

Arnold, D. A.↗
NASA NTRS1974

Analysis of the backscatter spectrum in an ionospheric modification experiment

Predictions of the backscatter spectrum, including effects of ionospheric inhomogeneity, are compared with experimental observations of incoherent backscatter from an artificially heated region. Our calculations show that the strongest backscatter echo received is not from the reflection level, but from a region some distance below. Certain asymmetrical features are explained of the up-shifted and down-shifted plasma lines in the backscatter spectrum, and the several satellite peaks accompanying them.

Kim, H.↗