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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Near-Sun solar wind consequences of solar structure and dynamic phenomena observed by radio scintillation measurements

Since radio propagation measurements using either natural or spacecraft radio signals are used for probing the solar wind in the vicinity of the sun, they represent a key tool for studying the interplanetary consequences of solar structure and dynamic phenomena. New information on the near sun consequences was obtained from radio scintillation observations of coherent spacecraft signals. The results covering density fluctuations, fractional density fluctuations, coronal streamers, heliospheric current sheets, coronal mass ejections and interplanetary shocks are reviewed. A joint ICE S-band (13 cm wavelength) Doppler scintillation measurement with the SOHO white-light coronograph (LASCO) is described.

Woo, Richard↗
NASA NTRS1979

Measurements of turbulence in the Venus atmosphere deduced from Pioneer Venus multiprobe radio scintillations

The 2.3-GHz log-amplitude fluctuations observed in the radio links of the Pioneer Venus entry probes during Venus encounter have been used to study turbulence in the Venus atmosphere. The deduced estimates of the upper bound of the structure constant of the refractive index fluctuations (less than approximately 4 x 10 to the -8th/cu root cm) are inconsistent with similar entry probe measurements by Veneras 4 to 8 but are consistent with the radio occultation measurements by flyby (Mariners 5 and 10) and orbiting (Venera 9) spacecraft. The Pioneer Venus measurements therefore provide a resolution of the long-standing order of magnitude discrepancy between these earlier measurements of the structure constant.

Woo, R.↗
NASA NTRS2019

Orbiters, CubeSats, and radio telescopes, oh my; entry, descent, and landing communications for the 2018 InSight Mars lander mission

The Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport (InSight) Mars lander mission was launched on May 5th, 2018 and its November 26, 2018 entry, descent, and landing sequence was observed by no less than five separate assets. The Mars Reconnaissance Orbiter (MRO) in orbit about Mars, the two Mars Cube One (MarCO) probes flying by, and two radio telescopes back on Earth were all used for this critical event communication coverage. These many paths of communication were enabled via the InSight launch/arrival strategy design, MRO orbital phasing selection, and MarCO trajectory design

Wagner, Sean↗
NASA NTRS1978

Voyager radio occultation investigations at Saturn

Voyager will use dual-frequency 3.5 and 13 cm wavelength radio occultation techniques to study the atmospheres and ionospheres of Saturn and Titan, and the rings of Saturn. At Titan radio occultation is predicted to probe the atmosphere to the surface. The existence of a surface could be confirmed by detection of an obliquely scattered echo. At Saturn the two Voyager encounters will provide occultation measurements of temperate and equatorial regions of the atmosphere and ionosphere, and of the rings. The atmosphere will also be probed in polar regions during the deepest portions of the occultation. Both frequency and intensity data will be collected and jointly analyzed to study temperature-pressure profiles, and to derive information on atmospheric shape, turbulence, and weather. For the rings, Voyager will provide measurements of the complex (amplitude and phase) radio extinction and angular scattering functions of the ring particles as a function of wavelength, polarization, and radial distance from Saturn.

Tyler, G. L.↗
NASA NTRS1989

High stability radio links

Radio telecommunication links are used for communication with deep space probes. These links consist of sinusoidal carrier signals at radio frequencies (RF) modulated with information sent between the spacecraft and the earth. This carrier signal is a very pure and stable sinusoid, typically derived from an atomic frequency standard whose frequency and phase are used to measure the radial velocity of the probe and from this and other data types derive its trajectory. This same observable can be used to search for space-time distortions cased by low frequency (0.1 to 100 MHz) gravitation radiation. How such a system works, what its sensitivity limitations are, and what potential future improvements can be made are discussed.

Kursinski, E. Robert↗
NASA NTRS1986

Communicating from the edge of the solar system

Communication technology for deep-space scientific missions is surveyed, with a focus on systems being developed for Galileo, a NASA orbiter/probe mission to Jupiter. The problems faced in designing the links from the probe (descending into the Jovian atmosphere) to the orbiter and from the orbiter to earth are examined; the technological solutions adopted for Galileo are discussed; the expansion of the Deep Space Network for the mission is described; the advantages and limitations of cm-band communication systems being considered to meet the data-rate requirements of future deep-space missions are outlined; and the potential of optical communication for the 21st century is indicated. Also included are tables listing past and planned deep-space missions and a brief description of the use of spacecraft radio signals by radio and planetary scientists to probe solar-system plasmas and gravitational fields.

Posner, E. C.↗
NASA NTRS1984

Radio Science

Radio science experiments use electromagnetic waves to probe or study the solar system. Three major research areas were identified within this discipline: radio astronomy, radar astronomy, and celestial mechanics. Radio astronomy (or radiometry) is the detection and measurement of naturally produced radio frequency emissions. Sources include surfaces, atmospheres, rings, and plasmas. Radar astronomy is the observation of man-made signals after their interaction with a target. Both imaging and non-imaging results. Celestial mechanics includes all studies related to the motions of (and gravity fields of) bodies within the solar system. These should not be considered rigid separations, but aid in the discussion of the data sets.

Source record↗
NASA NTRS2000

Langmuir Probe Measurements in an Inductively Coupled Ar/CF4 Plasmas

Technological advancement in the microelectronics industry requires an understanding of the physical and chemical processes occurring in plasmas of fluorocarbon gases, such as carbon tetrafluoride (CF4) which is commonly used as an etchant, and their mixtures to optimize various operating parameters. In this paper we report data on electron number density (ne), electron temperature'(Te), electron energy distribution function (EEDF), mean electron energy, ion number density (ni), and plasma potential (Vp) measured by using Langmuir probe in an inductively coupled 13.56 MHz radio frequency plasmas generated in 50%Ar:50%CF4 mixture in the GEC cell. The probe data were recorded at various radial positions providing radial profiles of these plasma parameters at 10-50 mTorr pressures and 200 W and 300 W of RF power. Present measurements indicate that the electron and ion number densities increase with increase in pressure and power. Whereas the plasma potential and electron temperature decrease with increase in pressure, and they weakly depend on RF power. The radial profiles exhibit that the electron and ion number densities and the plasma potential peak at the center of the plasma with an exponential fall away from it, while the electron temperature has a minimum at the center and it increases steadily towards the electrode edge. The EEDFs have a characteristic drop near the low energy end at all pressures and pressures and their shapes represent non-Maxwellian plasma and exhibit more like Druyvesteyn energy distribution.v

Rao, M. V. V. S.↗
DOE OSTI2023

Diffuse sources, clustering, and the excess anisotropy of the radio synchrotron background

ABSTRACT We present the largest low frequency (120 MHz) arcminute resolution image of the radio synchrotron background (RSB) to date, and its corresponding angular power spectrum of anisotropies (APS) with angular scales ranging from 3° to 0.3 arcmin. We show that the RSB around the north celestial pole has a significant excess anisotropy power at all scales over a model of unclustered point sources based on source counts of known source classes. This anisotropy excess, which does not seem attributable to the diffuse Galactic emission, could be linked to the surface brightness excess of the RSB. To better understand the information contained within the measured APS, we model the RSB varying the brightness distribution, size, and angular clustering of potential sources. We show that the observed APS could be produced by a population of faint clustered point sources only if the clustering is extreme and the size of the Gaussian clusters is ≲1 arcmin. We also show that the observed APS could be produced by a population of faint diffuse sources with sizes ≲1 arcmin, and this is supported by features present in our image. Both of these cases would also cause an associated surface brightness excess. These classes of sources are in a parameter space not well probed by even the deepest radio surveys to date.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1986

First results from the Giotto radio-science experiment

A definite deceleration of the comet probe Giotto due to drag in the comet Halley atmosphere has been noted by means of Doppler and ranging measurements based on the radio signals of the Giotto spacecraft. The total radial velocity change is 16.7 cm/s over a 100-s interval; this corresponds to a Doppler frequency of 4.7 Hz. This velocity change is used to estimate a total cometary mass striking the spacecraft of between 0.1 and 1.0 g.

Edenhofer, P.↗
DOE OSTI2022

Simulation of Plasma Emission in Magnetized Plasmas

The recent Parker Solar Probe observations of type III radio bursts show that the effects of the finite background magnetic field can be an important factor in the interpretation of data. In the present paper, the effects of the background magnetic field on the plasma-emission process, which is believed to be the main emission mechanism for solar coronal and interplanetary type III radio bursts, are investigated by means of the particle-in-cell simulation method. The effects of the ambient magnetic field are systematically surveyed by varying the ratio of plasma frequency to electron gyrofrequency. The present study shows that for a sufficiently strong ambient magnetic field, the wave–particle interaction processes lead to a highly field-aligned longitudinal mode excitation and anisotropic electron velocity distribution function, accompanied by a significantly enhanced plasma emission at the second-harmonic plasma frequency. For such a case, the polarization of the harmonic emission is almost entirely in the sense of extraordinary mode. On the other hand, for moderate strengths of the ambient magnetic field, the interpretation of the simulation result is less clear. The underlying nonlinear-mode coupling processes indicate that to properly understand and interpret the simulation results requires sophisticated analyses involving interactions among magnetized plasma normal modes, including the two transverse modes of the magneto-active plasma, namely, the extraordinary and ordinary modes, as well as electron-cyclotron-whistler, plasma oscillation, and upper-hybrid modes. At present, a nonlinear theory suitable for quantitatively analyzing such complex-mode coupling processes in magnetized plasmas is incomplete, which calls for further theoretical research, but the present simulation results could provide a guide for future theoretical efforts.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

Remote sensing of atmospheric and surface temperatures with microwaves.

Solids, liquids, and gases emit at microwave wavelengths measurable amounts of black-body thermal radiation. Receiver sensitivities readily approach 0.01 K, and permit accurate measurements of land, sea, and atmospheric temperatures. Sea and land temperature measurements must be corrected for the effects of surface emissivity, but these effects can often be measured or estimated. Observations near the 5 mm wavelength 02 resonances can yield atmospheric temperature profiles with an approximate accuracy of 2 K for altitudes 0-80 km. Such measurements from balloons and aircraft suggest that the planned earth-orbital satellite experiments will yield data valuable for numerical weather prediction. Ground-based radio telescopes and planetary-probes have yielded similar information about the surfaces and atmospheres of other planets.

Staelin, D. H.↗
NASA NTRS1976

Gravity fields

Detailed results on internal mass distribution have been obtained via earth-based Doppler radio tracking of deep space probes in the case of Mars, the earth's moon, Venus, Mercury, and Jupiter. Global gravity fields show close correlation with topography in the case of the moon and Mars, as data from orbiting spacecraft indicate. Some data are available on Jovian satellites. The gravity measuring instrumentation and data reduction techniques are described. Gravity profiles referable to lunar frontside mascons, craters, and mountain chains have been acquired from low-altitude (15-20 km) orbit surveys. Theoretically based cross sections through the moon and Jupiter are presented.

Sjogren, W. L.↗
NASA NTRS1982

Small-scale turbulence in the atmosphere of Venus

Pioneer Venus data on the morphology of the 45 and 65 km altitude scintillation regions were analyzed. A poleward decrease in the 65 km scintillations was detected, together with a peak at 60-70 deg latitude. Poleward increases in refractive index fluctuations and temperature fluctuations from previous observations displayed a peak near 70 deg latitude, with greater turbulence near the pole. The same fluctuations were an order of magnitude lower at 45 km altitude, with turbulence considerably lower than at 60 km. The favorable comparison of the scintillation measurements with the in-situ velocity and temperature measurements validates the radio measurement technique as a probe of small scale turbulence in a planetary atmosphere. Particular success is noted in identification of small scale temperature fluctuations as a result of shear generated turbulence.

Woo, R.↗
NASA NTRS1985

Waves In Space Plasmas (WISP)

Waves in space plasmas (WISP) utilizes powerful radio transmitters and sensitive receivers to probe the secrets of the magnetosphere, ionosphere and atmosphere. The scientific objective is to achieve a better understanding of the physical processes occurring in these regions. For example, audio frequency radio waves will be radiated from the long WISP antenna, will travel to the outer reaches of the magnetosphere, and will interact with Van Allen belt particles, releasing some of their energy which amplifies the waves. Study of this interaction will give us a better understanding of a major magnetospheric process, wave particle interactions. Radio waves from WISP at higher frequencies (AM radio and beyond) will be reflected by the ionosphere and will, for example, advance our understanding of bubbles in the equatorial ionosphere which affect satellite communications.

Taylor, W. W. L.↗