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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Electrical properties of lunar soil sample 15301,38

Electrical property measurements have been made on an Apollo 15 lunar soil sample in ultrahigh vacuum from room temperature to 827 C for the frequency spectrum from 100 Hz through 1 MHz. The dielectric constant, the total ac loss tangent, and the dc conductivity were measured. The dc conductivity showed no thermal hysteresis, but an irreversible (in vacuum) thermal effect was found in the dielectric loss tangent on heating above 700 C and during the subsequent cooling. This appears to be related to several effects associated with lunar glass above 700 C. The sample also showed characteristic low-frequency dispersion in the dielectric constant with increasing temperature, presumably due to Maxwell-Wagner intergranular effects. The dielectric properties may be fitted to a model involving a Cole-Cole frequency distribution that is relatively temperature-independent below 200 C and follows a Boltzmann temperature distribution with an activation energy of 2.5 eV above 200 C. The dc conductivity is fitted by an exponential temperature distribution and becomes the dominant loss above 700 C.

Olhoeft, G. R.↗
NASA NTRS1974

Propagation of transverse waves in a radially expanding plasma

Investigation of the properties of low-frequency transverse waves in an expanding plasma. The wave vector, the background magnetic field, and the streaming velocity of the plasma are all assumed to lie along the radial direction. Expressions are presented for the radial dependence of the amplitude and phase of left and right circularly polarized waves, correct to first order in the wave frequency divided by the proton cyclotron frequency. Differences in the phase velocities of these two circular polarizations result in a Faraday rotation that can be substantial for typical interplanetary conditions near 1 AU. The implications of these results for a realistic solar wind model with the interplanetary magnetic field along the spiral direction are also considered.

Solodyna, C. V.↗
NASA NTRS1974

Thermal and suprathermal plasma densities in the outer magnetosphere

By using the low-frequency cutoff of electromagnetic noise trapped in the magnetosphere at frequencies above the local plasma frequency, it is now possible to make very accurate electron density measurements in the low density region between the magnetopause and plasmapause. This technique for measuring the total plasma density has been used, together with measurements of the suprathermal proton intensities with the Lepedea instrumentation on the Imp 6 spacecraft, to determine the thermal proton densities in the region between the plasmapause and magnetopause. Usually, the high-energy tail of the thermal proton distribution is sufficient intense to be detected at low energies within the Lepedea energy range. When the high-energy tail of the thermal distribution can be detected, it is possible to determine the temperature of the thermal protons. The temperature in a typical case is found to be 80,000 K. This high temperature for the thermal protons, which are presumably of ionospheric origin, agrees with earlier Ogo 5 measurements reported by Serbu and Maier (1970).

Gurnett, D. A.↗
NASA NTRS1974

Solar longitude dependence of some characteristics of type III radio bursts from metric to hectometric wavelengths

Using the observed data for metric and hectometric type III radio bursts, the dependence of burst characteristics on the solar longitude has been examined over a wide frequency range. It is found that there exists and east-west asymmetry for the extension of metric type III bursts into the hectometric wavelength range. In particular, hectometric bursts are rarely observed for solar flares associated with metric bursts east of 60 E solar longitude. Furthermore, for east longitudes, the low-frequency radio observations show a large dispersion in drift time interval.

Sakurai, K.↗
NASA NTRS1974

Aerodynamic and acoustic performance of ejectors for engine-under-the-wing concepts

Subsonic thrust augmentation, exhaust plume velocity contours and acoustic characteristics of a small-scale, 6-tube mixer nozzle with ejector were obtained with and without a wing. Thrust augmentation up to 30 percent was achieved. Aerodynamic results showed that at a given location, greater downstream velocities are obtained with an ejector than with the baseline nozzle. Ejectors reduce high frequency noise; however, low-frequency noise amplification also occurs. Acoustic reflections off the wing increase the noise level to a ground observer. With an ejector, the acoustic benefits of forward velocity may be significantly reduced compared with the baseline nozzle.

Von Glahn, U.↗
NASA NTRS1974

Ion-ion beam instability in a cylindrical geometry

The ion-ion instability is studied in a cylindrical double-plasma device. Low-frequency cylindrical standing waves are found which are one-dimensional in character with frequency proportional to beam velocity. An approximate dispersion relation for the cylindrical standing waves is derived.

Hershkowitz, N.↗
NASA NTRS1974

Physics of compact nonthermal sources. II Determination of physical parameters

A set of restrictions upon the magnetic field and visible angular size of a canonical nonthermal source (one whose emission is incoherent electron synchrotron) has been obtained in another paper. The degree of electron anisotropy and magnetic field disordering were left as free parameters. In the present paper these restrictions are applied to the variable compact radio sources 3C 84, 3C 120, 3C 273, 3C 279, 3C 454.3, CTA 102, 3C 446, PKS 2134 + 004, VRO 42.22.01, and OJ 287. The theoretically derived angular sizes for these sources are in reasonable agreement with published VLBI sizes, provided that the characteristic pitch angles are not extremely small. The magnetic field strengths determined from the degree of circular polarization are generally compatible with field strengths derived from the self-absorption and synchrotron self-Compton conditions, again provided that the pitch angles are not too small. It is argued that the self-absorption optical depth cannot be much less than unity near the low-frequency turnovers; otherwise, serious discrepancies with observation result.

Jones, T. W.↗
NASA NTRS1974

Plasma wave turbulence at distant crossings of the plasma sheet boundaries and the neutral sheet

The orbit of IMP 7 frequently takes the spacecraft across the neutral sheet in the geomagnetic tail at a downstream distance of about 35 earth radii. This preliminary report discusses the detection of strong low-frequency electromagnetic signals and moderate electrostatic noise enhancements near local midnight. Data used were obtained during a substorm period on Oct. 28, 1972, when there were multiple crossings of the neutral sheet and the boundary of the plasma sheet.

Scarf, F. L.↗
NASA NTRS1974

A motion-constraint logic for moving-base simulators based on variable filter parameters

A motion-constraint logic for moving-base simulators has been developed that is a modification to the linear second-order filters generally employed in conventional constraints. In the modified constraint logic, the filter parameters are not constant but vary with the instantaneous motion-base position to increase the constraint as the system approaches the positional limits. With the modified constraint logic, accelerations larger than originally expected are limited while conventional linear filters would result in automatic shutdown of the motion base. In addition, the modified washout logic has frequency-response characteristics that are an improvement over conventional linear filters with braking for low-frequency pilot inputs. During simulated landing approaches of an externally blown flap short take-off and landing (STOL) transport using decoupled longitudinal controls, the pilots were unable to detect much difference between the modified constraint logic and the logic based on linear filters with braking.

Miller, G. K., Jr.↗
NASA NTRS1974

Interim prediction method for low frequency core engine noise

A literature survey on low-frequency core engine noise is presented. Possible sources of low frequency internally generated noise in core engines are discussed with emphasis on combustion and component scrubbing noise. An interim method is recommended for predicting low frequency core engine noise that is dominant when jet velocities are low. Suggestions are made for future research on low frequency core engine noise that will aid in improving the prediction method and help define possible additional internal noise sources.

Huff, R. G.↗
NASA NTRS1970

Data user's notes of the radio astronomy experiment aboard the OGO-V spacecraft

General information concerning the low-frequency radiometer, instrument package launching and operation, and scientific objectives of the flight are provided. Calibration curves and correction factors, with general and detailed information on the preflight calibration procedure are included. The data acquisition methods and the format of the data reduction, both on 35 mm film and on incremental computer plots, are described.

Haddock, F. T.↗
NASA NTRS1974

Comparison of the acoustic characteristics of large-scale models of several propulsive-lift concepts

Wind-tunnel acoustic investigations were performed to determine the acoustic characteristics and the effect of forward speed on the over-the-wing externally blown jet flap (OTW), the under-the-wing externally blown jet flap (UTW), the internally blown jet flap (IBF), and the augmentor wing (AW). The data presented represent the basic noise generated by the powered-lift system without acoustic treatment, assuming all other noise sources, such as the turbofan compressor noise, have been suppressed. Under these conditions, when scaled to a 100,000-lb aircraft, the OTW concept exhibited the lowest perceived noise levels, because of dominant low-frequency noise and wing shielding of the high-frequency noise. The AW was the loudest configuration, because of dominant high-frequency noise created by the high jet velocities and small nozzle dimensions. All four configurations emitted noise 10 to 15 PNdB higher than the noise goal of 95 PNdB at 500 ft.

Falarski, M. D.↗
NASA NTRS1974

Dekametric and hectometric observations of Jupiter from the RAE-1 satellite

Analysis of RAE-1 satellite data has revealed the presence of radio bursts from Jupiter in the frequency range from 4700 kHz to 450 kHz. Variations in the activity with respect to the planet's system III longitude are presented at seven frequencies. A merge of ground-based and satellite-acquired data indicates that the long-sought-for peak in Jupiter's low-frequency flux spectrum occurs at about 8 MHz.

Desch, M. D.↗
NASA NTRS1974

Cross correlation between cosmic-ray fluctuations and interplanetary magnetic-field fluctuations

Study of the cross-correlation between cosmic-ray intensity fluctuations and the interplanetary magnetic field, using the low-frequency limit of the theory of the interplanetary scintillations of cosmic rays. Cross-spectral analysis of the flux of the Alert neutron monitor and simultaneous values of the interplanetary magnetic field components are presented which support the theory. A model of cosmic-ray fluctuations is described, with effects of gradients and interplanetary sector structure dominating for very low frequencies (less than or about equal to .000005 Hz) and magnetic-field induced interplanetary scintillations of cosmic rays dominating for higher frequencies.

Jokipii, J. R.↗
NASA NTRS1974

Electrical conductivity of lunar surface rocks - Laboratory measurements and implications for lunar interior temperatures

Results are reported for laboratory measurements of the dc and low-frequency ac electrical conductivity of three lunar rocks with ferrous iron contents of 5 to 26 wt %. The measurements were made at temperatures ranging from 20 to 1000 C, and Mossbauer spectroscopy was used to determine the dependence of electrical conductivity on furnace atmosphere. It is found that the magnitude of electrical conductivity generally increases with increasing iron content. A comparison of the data on these samples with data on terrestrial olivines and pyroxenes shows that the electrical conductivity of anhydrous silicate minerals is influenced primarily by the concentration, oxidation state, and distribution of iron, while the silicate crystal structure is only of secondary importance. Lunar interior temperatures are deduced from experimental lunar conductivity profiles, and the resulting temperature-depth profiles are found to be consistent with those calculated for two different lunar evolutionary models as well as with various experimental constraints.

Schwerer, F. C.↗
NASA NTRS1948

Transonic-flutter Investigation of Wings Attached to Two Low-acceleration Rocket-propelled Vehicles

Two low-acceleration transonic-flutter vehicles were launched and flown. The first carried two test wings, one of which fluttered at M = 0.92 at a frequency of 61.4 cycles per second. The reference flutter speed determined from two-dimensional theory for an unswept wing in incompressible flow is conservative when compared to the experimental flutter speed. The second vehicle carried two test wings, one of which failed at M = 0.71 because of low-frequency divergent oscillation. Since this failure was not caused by conventional flexure-torsion flutter, no comparison with a reference flutter speed can be made.

MISSILES, SPECIFIC TYPES↗
NASA NTRS1961

Balancing Vanguard Satellites

The Vanguard satellites and component parts were balanced within the specified limits by using a Gisholt Type-S balancer in combination with a portable International Research and Development vibration analyzer and filter, with low-frequency pickups. Equipment and procedures used for balancing are described; and the determination of residual imbalance is accomplished by two methods: calculation, and graphical interpretation. Between-the-bearings balancing is recommended for future balancing of payloads.

Simkovich, A.↗
NASA NTRS1959

Analysis of of Injection-Velocity Effects on Rocket Motor Dynamics and Stability

A concept of combustion time lag that includes dependency on injection velocity is introduced. The concept is used in the formulation of chamber transfer functions and in an analysis of low-frequency combustion instability. Theoretical frequency responses and stability boundaries are compared with those obtained when the injection-velocity effect on the time lag to be an important consideration, in the theory of chamber dynamics and combustion instability

Hurrell, Herbert G.↗