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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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

The cone structure and focusing of the electric field of VLF and LF waves at high altitudes of the ionosphere

This paper presents a short review of the frequency and angle dependencies of the electric field radiated by an electric dipole E = E(sub 0)cos(omega)t in a magnetoplasma and detailed results of numerical calculations of (E) in the VLF and LF frequency bands 0.02f(sub b) is less than or equal to F is less than or equal to 0.5f(sub b) in the ionosphere and magnetosphere in the altitude region Z = (800 - 6000) km (F is approximately (4 - 500) kHz and f(sub b) is approximately equal to (1.1 to 0.2) MHz is the electron gyro-frequency). The amplitudes of the electric field have large maxima in four regions: close to the direction of the Earth magnetic field line B(sub 0) (it is the so called Axis field E(sub 0); in the Storey E(sub St); Reversed Storey E(sub RevSt); and Resonance E(sub Res) Cones. The maximal values of E(sub 0), E(sub Res), and E(sub Rev ST) are the most pronounced close to the low hybrid frequency, F is approximately F(sub L). The flux of the electric field is concentrated in very narrow regions, with the apexes angles of the cones delta(beta) is approximately (0.1 - 1) degree. The enhancement and focusing of the electric field increases with altitude starting at Z is greater than 800 km. At Z is greater than or equal to 1000 up to 6000 km, the relative value of E, in comparison with its value at Z equals 800 km is about (10(exp 2) to 10(exp 10)) times larger. Thus, the flux of VLF and LF electromagnetic waves in the Earth magnetoplasma produces and is guided by very narrow pencil beams, similar, let us say, to laser beams.

Alpert, Y. L.↗
NASA NTRS2009

Observations of a Unique Type of ULF Waves by Low-altitude ST5 Satellites

We report a unique type of ULF waves observed by low-altitude Space Technology 5 (ST5) constellation mission. ST5 is a three micro-satellite constellation deployed into a 300 x 4500 lan, dawn-dusk, and sun synchronous polar orbit with 105.6 inclination angle. Even though the spacecraft are in a high-inclination orbit, the combined effects of the Earth's rotation and dipole tilt allow the spacecraft's dawn-dusk orbit track to reach subauroral latitudes on the day side. Whenever the spacecraft traverse across the dayside closed field line region at sub auroral latitudes they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pc 2-3 frequency range. These Pc 2-3 waves appear as wave packets with durations of the order of 5-10 minutes. As the maximum separations of the ST5 spacecraft are around 10 minutes, the three ST5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. Coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc 2-3 band; instead, the waves appear to be the common Pc 4-5 waves associated with field line resonances. We suggest that this unique Pc 2-3 waves seen by ST5 are in fact high azimuthal wave number Pc 4-5 waves Doppler-shifted to higher frequencies by the rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. These unique low altitude observations, where the spacecraft motion is mainly azimuthal at subauroral latitudes, reveal the azimuthal wave-number characteristics of the field-aligned resonance signals.

Le, G.↗
NASA NTRS2015

An MHD Code for the Study of Magnetic Structures in the Solar Wind

We have developed a 2.5D MHD code designed to study how the solar wind influences the evolution of transient events in the solar corona and inner heliosphere. The code includes thermal conduction, coronal heating and radiative cooling. Thermal conduction is assumed to be magnetic field-aligned in the inner corona and transitions to a collisionless formulation in the outer corona. We have developed a stable method to handle field-aligned conduction around magnetic null points. The inner boundary is placed in the upper transition region, and the mass flux across the boundary is determined from 1D field-aligned characteristics and a 'radiative energy balance' condition. The 2.5D nature of this code makes it ideal for parameter studies not yet possible with 3D codes. We have made this code publicly available as a tool for the community. To this end we have developed a graphical interface to aid in the selection of appropriate options and a graphical interface that can process and visualize the data produced by the simulation. As an example, we show a simulation of a dipole field stretched into a helmet streamer by the solar wind. Plasmoids periodically erupt from the streamer, and we perform a parameter study of how the frequency and location of these eruptions changed in response to different levels of coronal heating. As a further example, we show the solar wind stretching a compact multi-polar flux system. This flux system will be used to study breakout coronal mass ejections in the presence of the solar wind.

corona↗
NASA NTRS1971

New results and techniques in space radio astronomy.

The methods and results of early space radioastronomy experiments are reviewed, with emphasis on the RAE 1 spacecraft which was designed specifically and exclusively for radio astronomical studies. The RAE 1 carries two gravity-gradient-stabilized 229-m traveling-wave V-antennas, a 37-m dipole antenna, and a number of radiometer systems to provide measurements over the 0.2 to 9.2 MHz frequency range with a time resolution of 0.5 sec and an absolute accuracy of plus or minus 25%. Observations of solar bursts at frequencies down to 0.2 MHz provide new information on the density, plasma velocity, and dynamics of coronal streamers out to distances greater than 50 solar radii. New information on the distribution of the ionized component of the interstellar medium is being obtained from galactic continuum background maps at frequencies around 4 MHz. Cosmic noise background spectra measured down to 0.5 MHz produce new estimates on the interstellar flux of cosmic rays, on magnetic fields in the galactic halo, and on distant extragalactic radio sources.

Alexander, J. K.↗
NASA NTRS1987

The plasma and magnetic field properties of coronal loops observed at high spatial resolution

Two data sets are analyzed in order to improve understanding of the plasma and magnetic field properties of active region coronal loops. Each set consists of coaligned, high spatial resolution soft X-ray, microwave, and magnetogram images that are used to compare observations of coronal loops and their feet in the photosphere and to constrain possible microwave emission mechanisms. The loops are found to have plasma parameters typical of quiescent active region loops. Each loop has a compact microwave source with peak brightness temperature T(b) = 1-2.5 x 10 to the 6th K cospatial with or near the loop apex. No complete loops are imaged in microwaves. The loop emission observed at 4.9 GHz is best described by fourth harmonic gyroresonance emission from a dipole loop model, but with less field variation along the loop than in the models of Holman and Kundu (1985).

Webb, D. F.↗
NASA NTRS2011

Observations of a Unique Type of ULF Wave by Low-Altitude Space Technology 5 Satellites

We report a unique type of ULF waves observed by low-altitude Space Technology 5 (ST-5) constellation mission. ST-5 is a three-microsatellite constellation deployed into a 300 x 4500 km dawn-dusk and Sun-synchronous polar orbit with 105.6deg inclination angle. Because of the Earth's rotation and the dipole tilt effect, the spacecraft's dawn-dusk orbit track can reach as low as subauroral latitudes during the course of a day. Whenever the spacecraft traverse the dayside closed field line region at subauroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pc2-3 frequency range. These Pc2-3 waves appear as wave packets with durations in the order of 5-10 min. As the maximum separations of the ST-5 spacecraft are in the order of 10 min, the three ST-5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc2-3 band; instead, the waves appear to be the common Pc4-5 waves associated with field line resonances. We suggest that these unique Pc2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-dusk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field line resonances.

Le, G.↗
NASA NTRS1984

The far-infrared laser magnetic resonance spectrum of the SiH radical and determination of ground state parameters

The far-infrared laser magnetic resonance spectrum of the SiH radical in the v = O level of its X2Pi state has been recorded. The signals are rather weak. The molecules were generated in the reaction between fluorine atoms and SiH4. Rotational transitions have been detected in both 2Pi1/2 and 2Pi3/2 spin components but no fine structure transitions between the spin components were observed. Proton hyperfine splittings were resolved on some lines. The measurements have been analyzed, subjected to a least-squares fit using an effective Hamiltonian, and the appropriate molecular parameters determined. The weakness of the spectrum and the failure of attempts to power saturate favorable lines are both consistent with a small value for the electric dipole moment for SiH.

Brown, J. M.↗
NASA NTRS2010

Observations of Field Line Resonances by Low-Altitude ST-5 Satellites

Space Technology 5 (ST-5) mission is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, and sun synchronous polar orbit with 105.6deg inclination angle. Due to the Earth's rotation and the dipole tilt effect, the spacecraft's dawn-dusk orbit track can reach as low as subauroral latitudes during the course of a day. Whenever the spacecraft traverse across the dayside closed field line region at subauroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pe 2-3 frequency range. These Pc 2-3 waves appear as wave packets with durations in the order of 5-10 minutes. As the maximum separations of the ST-5 spacecraft are in the order of 10 minutes, the three ST-5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc 2- 3 band; instead, the waves appear to be the common Pc 4-5 waves associated with field line resonances. We suggest that this unique Pc 2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc 4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-disk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field-aligned resonances.

Le, G.↗
NASA NTRS2011

Observations of a Unique Type of ULF Waves by Low-Latitude Space Technology 5 Satellites

We report a unique type of ULF waves observed by low-altitude Space Technology 5 (ST-5) constellation mission. ST-5 is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, and sun synchronous polar orbit with 105.6deg inclination angle. Due to the Earth s rotation and the dipole tilt effect, the spacecraft s dawn-dusk orbit track can reach as low as subauroral latitudes during the course of a day. Whenever the spacecraft traverse across the dayside closed field line region at subauroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pc 2-3 frequency range. These Pc 2-3 waves appear as wave packets with durations in the order of 5-10 minutes. As the maximum separations of the ST-5 spacecraft are in the order of 10 minutes, the three ST-5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc 2-3 band; instead, the waves appear to be the common Pc 4-5 waves associated with field line resonances. We suggest that this unique Pc 2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc 4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-disk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field-aligned resonances.

Le, G.↗
NASA NTRS2011

Observations of a Unique Type of ULF Waves by Low-Latitude Space Technology Five Mission

We report a unique type of ULF waves observed by low-altitude Space Technology 5 (ST-5) constellation mission. ST-5 is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, and sun synchronous polar orbit with 105.6deg inclination angle. Due to the Earth s rotation and the dipole tilt effect, the spacecraft s dawn-dusk orbit track can reach as low as subauroral latitudes during the course of a day. Whenever the spacecraft traverse across the dayside closed field line region at subauroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pc 2-3 frequency range. These Pc 2-3 waves appear as wave packets with durations in the order of 5-10 minutes. As the maximum separations of the ST-5 spacecraft are in the order of 10 minutes, the three ST-5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc 2-3 band; instead, the waves appear to be the common Pc 4-5 waves associated with field line resonances. We suggest that these unique Pc 2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc 4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-disk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field-aligned resonances.

Le, G.↗
NASA NTRS2010

Observations of a Unique Type of ULF Waves by Low-Latitude Space Technology 5 Mission

We report a unique type of ULF waves observed by low-altitude Space Technology 5 (ST-5) constellation mission. ST-5 is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, and sun synchronous polar orbit with 105.6 degree inclination angle. Due to the Earth's rotation and the dipole tilt effect, the spacecraft's dawn-dusk orbit track can reach as low as subauroral latitudes during the course of a day. Whenever the spacecraft traverse across the dayside closed field line region at sub auroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pc 2-3 frequency range. These Pc 2-3 waves appear as wave packets with durations in the order of 5-10 minutes. As the maximum separations of the ST-5 spacecraft are in the order of 10 minutes, the three ST-5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc 2-3 band; instead, the waves appear to be the common Pc 4-5 waves associated with field line resonances. We suggest that these unique Pc 2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc 4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-disk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field-aligned resonances.

Le, G.↗
NASA NTRS2011

Observations of a Unique Type of ULF Waves by Low-Latitude Space Technology 5 Mission

We report a unique type of ULF waves observed by low-altitude Space Technology 5 (ST-5) constellation mission. ST-5 is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, and sun synchronous polar orbit with 105.6 inclination angle. Due to the Earth's rotation and the dipole tilt effect, the spacecraft's dawn-dusk orbit track can reach as low as sub auroral latitudes during the course of a day. Whenever the spacecraft traverse across the dayside closed field line region at sub auroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pc 2-3 frequency range. These Pc 2-3 waves appear as wave packets with durations in the order of 5-10 minutes. As the maximum separations of the ST-5 spacecraft are in the order of 10 minutes, the three ST -5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc 2-3 band; instead, the waves appear to be the common Pc 4-5 waves associated with field line resonances. We suggest that these unique Pc 2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc 4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-disk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field-aligned resonances.

Le, Guan↗
NASA NTRS1981

Magnetic space-based field measurements

Because the near Earth magnetic field is a complex combination of fields from outside the Earth of fields from its core and of fields from its crust, measurements from space prove to be the only practical way to obtain timely, global surveys. Due to difficulty in making accurate vector measurements, early satellites such as Sputnik and Vanguard measured only the magnitude survey. The attitude accuracy was 20 arc sec. Both the Earth's core fields and the fields arising from its crust were mapped from satellite data. The standard model of the core consists of a scalar potential represented by a spherical harmonics series. Models of the crustal field are relatively new. Mathematical representation is achieved in localized areas by arrays of dipoles appropriately located in the Earth's crust. Measurements of the Earth's field are used in navigation, to map charged particles in the magnetosphere, to study fluid properties in the Earth's core, to infer conductivity of the upper mantels, and to delineate regional scale geological features.

Langel, R. A.↗
NASA NTRS1992

Investigation of the structure of the electromagnetic field and related phenomena, generated by the active satellite

A short review is given for the general frequency and angle distribution of the electric field radiated by an electric dipole E = E(sub 0)cos(omega)t, in a magnetoplasma. Detailed results of numerical calculations of (E) were made in the Very Low Frequency (VLF) and the Low Frequency (LF) bands 0.02f(sub b) is less than or equal to F is less than or equal to 0.5f(sub b) (F is approximately (4-500) kHz) in the ionosphere and magnetosphere in the altitude region Z = (800-6000) km; f(sub b) is the electron gyro-frequency of the plasmas in the discussed region f(sub b) is approximately equal to (1.1 to 0.2) MHz. The amplitudes of the electric field have large maxima in four regions: close to the direction of the Earth's magnetic field line (B(sub 0)), it is the so called Axis field (E(sub 0)) and in the Storey (E(sub St)), Reversed Storey (E(sub RevSt)), and Resonance (E(sub Res)) Cones. The maximal values of E(sub 0), E(sub Res), and E(sub RevSt) are very pronounced close to the low hybrid frequency, F approximately F(sub L). The flux of the electric field is concentrated in very narrow regions, the apex angles of the cones delta(beta) is approximately equal to (0.1 - 1) degree. The enhancement and focusing of the electric field is growing up, especially quickly at Z greater than 800 km. At Z is greater than 1000 up to 6000 km, the relative value of (E), in comparison with its value at Z = 800 km is about (10(exp 2) to 10(exp 4)) times larger. Thus, the flux of VLF and LF electromagnetic waves in the Earth magnetoplasma produces and is guided by very narrow pencil beams, similar, let us say, to laser beams.

Alpert, Yakov L.↗
NASA NTRS1986

The warped neutral sheet and plasma sheet in the near-earth geomagnetic tail

An analysis of ISEE 2 plasma and magnetic field data indicates that the plasma sheet and neutral sheet in the near-earth magnetotail are warped in such a manner that in summer (winter) the neutral sheet rises above (dips below) the solar magnetospheric equatorial plane near the center of the tail, but dips below (rises above) the equatorial plane along the tail flanks. In the near tail, the neutral sheet crosses the equatorial plane at about 12 earth radii from the aberrated X axis, considerably closer to the center of the tail than has been inferred from data obtained farther downstream. This increase in the warp with decreasing distance from the earth is consistent with theoretical predictions. In the near tail, the warp is sufficiently strong when the dipole tilt angle is large that even in quiet times the upper or lower edge of the plasma sheet can be found close to the solar magnetospheric equatorial plane along the tail flanks. The seasonal dependence of the warp can produce certain dawn-dusk asymmetries in satellite data which are more apparent than real.

Gosling, J. T.↗
NASA NTRS1976

The magnetosphere of Venus - Evidence for a boundary layer and a magnetotail

Mariner 5 magnetic field data collected during its flyby of Venus are evaluated in the light of reexamination of Venera data and in the context of present knowledge on the interaction of the solar wind with the earth. Attention is focused on an analysis of 4 phenomenological regions: magnetosheath, boundary layer, tail, and upstream waves. Enough evidence is revealed for a boundary layer beginning in the dayside ionosphere. The study affirms the possibility that Venus has an intrinsic magnetotail; the key elements of this identification are the positions of the Mariner 5, Venera 4 and Venera 9 magnetopause crossings and the agreements of the polarity of the field during the Mariner 5 and Venera 9 wake traversals with the direction of the implied Venera 4 dipole moment.

Russell, C. T.↗
NASA NTRS1975

Saturn radio emission near 1 MHz

Radio emissions from the direction of Saturn are analyzed which were observed by IMP-6 at 15 frequencies between 375 and 2200 kHz from April 1971 to October 1972. The radio bursts are identified in the IMP-6 data by a phase analysis of the spin-modulated signal from the spacecraft's dipole antenna, and approximately 12 storms are isolated whose occurrence corresponded to times when the spacecraft had an unobstructed view in the direction of Saturn. The spectral character of the radiation is found to be analogous to that of Jupiter, and a power-spectral analysis of the storm occurrence times indicates a weak periodicity for some of the observing frequencies. The Saturnian emission most similar to Jupiter's decametric emission is found to be strongest at 1100 kHz with a bandwidth of about 1000 kHz. A secondary spectral peak may exist at 400 kHz, which is similar to that observed for Earth and Jupiter. The detection of this nonthermal radio emission is shown to be the first direct evidence for the existence of a Saturnian magnetic field containing energetic particles.

Brown, L. W.↗
NASA NTRS1985

Futher identifications of hydrogen in Grw +708247

Numerous spectra of the magnetic white dwarf Grw +70 8247 were obtained with the double CCD spectrograph at Palomar with signal-to-noise ratio above 100. Five weak absorptions in the blue and four in the red are produced by hydrogen in a strong magnetic field. New, precise, multiparameter, variational energy levels yielding intensity and wavelength, from 100 to 600 MG are presented. A search for those Zeeman components with wavelengths nearly constant with field is carried out. Two such Zeeman components which are relatively sharp and strong Pi transitions, explain the Minkowski band, 4137 A (known since 1938), as the 2s0-4f0 and the 5855 A band as the 2s0-3p0. Both have minimum wavelengths at B of about 300 MG. Their absorptions resemble band heads degraded to the red, as observed. The mixed nature of the 4f0 level results in an intensity ratio (2s0-4f0)/(2s0-3p0) = 0.58 at 280 MG, high for a line forbidden at zero field. Profiles computed for a pole-on dipole, near log Bp = 8.5, fit the two observed lines. Other hydrogen transitions (including the core of Ly-alpha) are consistent with the field strength. Six models with a variety of Bp and inclination are illustrated to show the quality of fit to the observations.

Greenstein, J. L.↗