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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Remote sensing of the termination of the solar wind via in situ plasma measurements

Since 1983 the Plasma Wave experiments on the two Voyager spacecraft have detected low frequency radio noise in the outer heliosphere which has been postulated to emanate from the terminal shock of the solar wind or, possibly, from the heliopause itself. The solar wind data from the Plasma Science experiment on the Voyager spacecraft are studied to search for correlations with these radio emissions. It is found that two anomalous high speed streams passed Voyager 2 in late 1982 and early 1983 and it is suggested that the interaction of the streams with the heliospheric terminal shock is responsible for the generation of the most intense radio noise observed later in the same year. If the stream speeds did not decrease in traveling to the interaction region, that region is about 135 AU from the sun. This is consistent with previous estimates of the distance to the inner heliospheric shock.

Mcnutt, R. L., Jr.↗
DOE OSTI2011

Elimination of Radio-Frequency Noise by Identifying and Diverting Large RF Ground Currents

The problem of electromagnetic interference in scientific instruments is compounded for high-power plasma experiments by the large currents and voltages as well as by the broad bandwidths of the instruments. Ground loops are known to allow stray magnetic fields to drive large ground currents that can induce spurious signals and damage electronics. Furthermore, even when a ground loop is broken, capacitive coupling can still permit the flow of radio-frequency current, resulting in high-frequency spurious signals that can overwhelm the desired signal. We present the effects of RF ground loops on the output of vacuum photodiodes used in the Caltech Solar Loop Experiment and demonstrate the elimination of the spurious signals by diverting the ground currents away from the most vulnerable point of the signal line. Techniques for identifying the RF ground loops are also discussed. These techniques should be valuable in many high-power systems where interference from spurious coupling is an issue.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1972

Observed correlations between auroral and vlf emissions.

This paper presents a series of simultaneous observations of very-low-frequency radio noise by the Injun 5 satellite and of visual aurora along the same geomagnetic-field line by the Fort Churchill Auroral Observatory. Seven observations from the period of August 29, 1968, to March 4, 1969, are discussed. In 5 of the 7 events studied vlf hiss is observed in association with auroral-light emissions. These observations typically show the occurrence of vlf hiss in the general region of the auroral arc, with significant changes in the vlf spectrum sometimes observed in the immediate vicinity of the auroral arc. One event for which the associated charged-particle fluxes have been analyzed is investigated in detail. The vlf radio noise intensity for this event is among the largest observed with Injun 5 and is much greater than can presently be explained by an incoherent Cerenkov radiation mechanism.

Mosier, S. R.↗
NASA NTRS1979

Electromagnetic noise and radio wave propagation below 100 kHz in the Jovian atmosphere. I - The equatorial region

The Galileo satellite program includes the delivery of an entry probe to the Jovian equatorial atmosphere in mid-1985. Optical and RF sensors for a lightning detection system are included as a part of the probe experimental payload. In this paper, calculations of the RF wave propagation and reflection characteristics of the equatorial Jovian atmosphere and ionosphere for frequencies less than 100 kHz are presented. It is shown that wave propagation is limited to line-of-sight and one-hop from the ionosphere. Results are also presented of a statistical treatment of the RF wave power densities for the case of a finite number of events and for the case of a uniformly distributed source. The results can be applied to specific RF experiment configurations concerned with establishing the statistical characteristics of Jovian lightning.

Rinnert, K.↗
NASA NTRS1966

Magnetosphere

Diurnal variations of atmospherics, electron density, electric field measurements, and radio noise in magnetosphere

DIURNAL VARIATION↗
NASA NTRS1980

Voyager detection of nonthermal radio emission from Saturn

The detection of bursts of nonthermal radio noise from Saturn by the planetary radio astonomy experiment onboard the Voyager spacecraft is discussed. The emissions occur near 200 kHz with a peak flux density comparable to higher frequency Jovian emissions. The radiation is right-hand polarized and is most likely emitted in the extraordinary magnetoionic mode from Saturn's northern hemisphere. Modulation is apparent in the data which is consistent with a planetary rotation period of 10 hr 39.9 min.

Kaiser, M. L.↗
NASA NTRS1972

Magnetospheric electron density measurements from upper hybrid resonance noise observed by IMP-6

A band of natural radio noise between the local electron plasma frequency and the upper hybrid resonance frequency is observed by the IMP-6 satellite. The band exists over a large range of geocentric radial distances extending from inside the plasmapause boundary to greater than 10 earth radii in the outer magnetosphere. The center frequency of the noise band decreases with increasing radial distance, and changes abruptly at the plasmapause boundary. The broadband electric field strength of this noise is very small, seldom exceeding 10 microvolts/meter, and probably could not be detected without using long electric antennas of IMP-6. It is believed that this noise is produced by incoherent Cerenkov emission from super-thermal electrons. In some cases a second very narrow noise band was observed at a frequency slightly above the second harmonic of the electron gyrofrequency.

Shaw, R. R.↗
DOE OSTI2023

Lightning Interferometry with the Long Wavelength Array

The Long Wavelength Array is a radio telescope array located at the Sevilleta National Wildlife Refuge in La Joya, New Mexico, well suited and situated for the observation of lightning. The array consists of 256 high-sensitivity dual polarization antennas arranged in a 100 m diameter. This paper demonstrates some of the capabilities that the array brings to the study of lightning. Once 32 or more antennas are used to image lightning radio sources, virtually every integration period longer than the impulse response of the array includes at least one identifiable lightning emitter, independent of the integration period used. The use of many antennas also allows multiple simultaneous lightning radio sources to be imaged at sub-microsecond timescales; for the flash examined, 51% of the images contained more than one lightning source. Finally, by using many antennas to image lightning sources, the array is capable of locating sources fainter than the galactic background radio noise level, yielding possibly the most sensitive radio maps of lightning to date. This incredible sensitivity enables, for the first time, the emissions originating from the positive leader tips of natural in-cloud lightning to be detected and located. The tip emission is distinctly different from needle emission and is most likely due to positive breakdown.

Stock, Michael (ORCID:0000000193336790)↗
NASA NTRS1991

Natural noise above 50 MHZ from terrestrial and extraterrestrial sources

This paper offers a brief overview of natural radio noise for frequencies above 50 MHz in terms of brightness temperature as observed from two vantage points. The first is from an Earth station located at 40 degrees north latitude and observing at elevation angles from 0 to 90 degrees with an ideal antenna. The second is a satellite in geostationary orbit communicating with the Earth. Earth station noise at VHF and UHF is dominated by galactic and solar noise. Emission from the atmosphere, gases and hydrometeors, are dominant at EHF and SHF. Radiative transfer theory is invoked in the calculation of brightness temperature from the atmosphere. The situation is not vastly different from geostationary orbit if communications is with the Earth. Emission from the land and sea, even under idealized conditions, enters significantly. Land is a much more effective emitter than sea water, but at frequencies above 30 GHz the differential becomes much less due to the increasing significance of atmospheric emission.

Smith, E. K.↗