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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Edge Stabilized Ribbon (ESR); Stress, Dislocation Density and Electronic Performance

The edge stabilized ribbon (ESR) silicon ribbon was grown in widths of 1, 2.2 and 4.0 inches at speeds ranging from .6 to 7 in/min, which result in ribbon thicknesses of 5 to 400 microns. One of the primary problems remaining in ESR growth is that of thermally induced mechanical stresses. This problem is manifested as ribbon with a high degree of residual stress or as ribbon with buckled ribbon. Thermal stresses result in a high dislocation density in the grown material, resulting in compromised electronic performance. Improvements in ribbon flatness were accomplished by modification of the ribbon cooling profile. Ribbon flatness and other experimental observations of ESR ribbon are discussed. Laser scanner measurements show a good correlation between diffusion length and dislocation density which indicates that the high dislocation densities are the primary cause of the poor current performance of ESR materials. Dislocation densities were reduced and improved electronic performance resulted. Laser scanner data on new and old material are presented.

Sachs, E. M.↗
NASA NTRS1989

Ionization from soft electron precipitation in the auroral F region

Rocket-borne instrumentation, launched into the morning sector auroral zone from Sondre Stromfjord, Greenland, detects electron density enhancements correlated with enhancements in the flux of soft (less than 1 keV) downgoing electrons. These electron density enhancements seem most likely to have been generated by direct production of ionization at F region altitudes. Model calculations of the electron impact ionization rate, based on the measured electron spectrum, lend support to this hypothesis.

Labelle, J.↗
NASA NTRS1973

An experimental investigation of mesospheric ionization

Mesospheric ionization and its variability are examined. Data were obtained primarily by the parachute-borne blunt probe technique conducted in coordinated rocket experiments at White Sands Missile Range, New Mexico and Wallops Island, Virginia. Electrical conductivity measurements and deduced charge density values from ten rocket launches are presented and discussed. Positive ion conductivity and electron density were found to be relatively invariant with height between 45 and 60 km. Variations in positive conductivity of a factor of two and enhancements in negative conductivity by as much as a factor of four were measured by the blunt probe. A simple lumped parameter ion chemistry model is shown to satisfactorily explain the charge density values for the undisturbed lower D-region. Implications of the data in terms of this model are considered. The principal loss mechanism for positive ions in the 45 to 60 km. region is concluded to be dissociative recombination. Electron densities deduced from the conductivity data are explained by detachment involving a minor neutral constituent which is mixed between 65 and 45 km. and then cuts off sharply below 45 km. A correlation study involving blunt probe measurements shows relatively good agreement between variations in positive conductivity and temperature.

Mitchell, J. D.↗
NASA NTRS1998

GPS, Earthquakes, the Ionosphere, and the Space Shuttle

Sources such as atmospheric or buried explosions and shallow earthquakes producing strong vertical ground displacements are known to produce infrasonic pressure waves in the atmosphere. Because of the coupling between neutral particles and electrons at ionospheric altitudes, these acoustic waves induce variations of the ionospheric electron density. The Global Positioning System provides a way of directly measuring the Total Electron Content in the ionosphere and, therefore. of detecting such perturbations in the upper atmosphere. In this work, we demonstrate the capabilities of the GPS technique to detect ionospheric perturbations caused by the January 17. 1994, M (sub w) =6.7, Northridge earthquake and the STS-58 Space Shuttle ascent. In both cases, we observe a perturbation of the ionospheric electron density lasting for about 30 m, with periods less than 10 m. The perturbation is complex and shows two sub-events separated by about 15 m. The phase velocities and waveform characteristics of the two sub-events lead us to interpret the first arrival as the direct propagation of 2 free wave, followed by oscillatory guided waves propagating along horizontal atmospheric interfaces at 120 km altitude and below.

Calais, Eric↗
NASA NTRS1975

Doppler measurements of the ionosphere on the occasion of the Apollo-Soyuz test project. Part 1: Computer simulation of ionospheric-induced Doppler shifts

A computer simulation of the ionospheric experiment of the Apollo-Soyuz Test Project (ASTP) was performed. ASTP is the first example of USA/USSR cooperation in space and is scheduled for summer 1975. The experiment consists of performing dual-frequency Doppler measurements (at 162 and 324 MHz) between the Apollo Command Service Module (CSM) and the ASTP Docking Module (DM), both orbiting at 221-km height and at a relative distance of 300 km. The computer simulation showed that, with the Doppler measurement resolution of approximately 3 mHz provided by the instrumentation (in 10-sec integration time), ionospheric-induced Doppler shifts will be measurable accurately at all times, with some rare exceptions occurring when the radio path crosses regions of minimum ionospheric density. The computer simulation evaluated the ability of the experiment to measure changes of columnar electron content between CSM and DM (from which horizontal gradients of electron density at 221-km height can be obtained) and to measure variations in DM-to-ground columnar content (from which an averaged columnar content and the electron density at the DM can be deduced, under some simplifying assumptions).

Grossi, M. D.↗
NASA NTRS1971

Ceramic wiring board increases packaging density of electronic modules

Ceramic multilayer wiring board interconnects large scale integration /LSI/ modules which dissipate nearly 2W/cc. Extremely high packaging density is possible by application of alumina cover hermetically sealed to board. Signal interconnections are completely dependent on transfer heat between layers.

Hamley, L. D.↗
NASA NTRS1984

Effect of hot electrons on the polar wind

A semikinetic model is used to describe the steady state collisionless flow of H(+), O(+), and electrons along diverging geomagnetic field lines in the high-latitude topside ionosphere. The effect that hot electron populations have on the polar wind is emphasized. Several such populations are considered, including the polar rain, polar showers, and polar squall. Hot electron densities and temperatures are calculated from the characteristic energy and flux measurements. The results indicate that the hot/cold electron temperature ratio varies from 10 to 10,000 and that the hot/cold electron density ratio varies from 0.001 to 0.1 at the baropause. For higher hot electron temperatures and a greater percentage of hot electrons, there is a discontinuity in the kinetic solution, which indicates the presence of a sharp transition corresponding to a contact surface between the hot and cold electrons. Along this surface, a double-layer potential barrier exists which reflects the cold ionospheric electrons and prevents their penetrations to higher altitudes.

Barakat, A. R.↗
NASA NTRS1995

Interplanetary Scintillation

Interplanetary scintillation (IPS) has been used as a diagnostic of solar wind speed and interplanetary plasma turbulence, allowing inference of speed and electron density power spectrum close to the Sun and out of the ecliptic. In that context, IPS is 'signal' and provides scientifically interesting data. IPS is also of interest because amplitude and phase perturbations imposed on radio waves are 'noise' for telemetry and precision Doppler tracking of deep space probes and for some radio astronomical observations. This paper briefly reviews the connection between scattering observables and the electron density power spectrum. Interplanetary phase scintillation on time scales of 100 to 10 000 seconds is an important noise in mass determinations of small solar system bodies during space-probe fly-bys and in searches for low-frequency gravitational radiation.

waves deep space probes electron density power spe↗
NASA NTRS1993

Evidence for two different structuring and scattering mechanisms and the associated role of aerosols in the polar summer mesosphere

A Super Arcas rocket, MISTI B, was launched as part of the Polar Mesospheric Summer Echoes (PMSE) salvo to measure electron density irregularities using rf and dc probes. Large and small scale structures in the electron density were measured on rocket ascent and descent at the altitudes of 86.5 and 88.5 +/- .5 km. Since the rocket apogee was 89 km, the rocket was in the height range 88.5 +/- .5 km for 30 seconds giving us an unusual measurement of horizontal structure over a distance of 5.5 km. A power spectrum of the fluctuations for the upper layer gives further evidence that turbulent mixing is an important process in PMSE. The power spectrum of the lower layer, however, gives evidence that this layer is characterized by a form of partial or Fresnel scattering. Both spectra are in excellent agreement with similar analysis of electron fluctuation spectra measured in the same layers on the TURBO-B rocket flown 12 minutes later and the analysis of Cornell University Portable Radar Interferometer (CUPRI) data by Cho et al., 1993A. Thus two different structuring and scattering mechanisms exist at altitudes only 1 km apart. Using the simultaneous dc and rf probe measurements of electron depletions and sharp gradients in the lower layer, we speculate on the role of aerosols in creating these depletions and gradients.

Ulwick, J. C.↗
NASA NTRS1995

Sensitivity of the 6300 A twilight airglow to neutral composition

The field line interhemispheric plasma (FLIP) model is used to study the 6300 A line intensity measured during three morning twilights from the McDonald Observatory in Texas. The Imaging Spectrometric Observatory (ISO) measured the 6300 A intensity during the winter of 1987 and the spring and summer of 1988. The FLIP model reproduces the measured intensity and its variation through the twilight well on each day using neutral densities from the MSIS-86 empirical model. This is in spite of the fact that different component sources dominate the integrated volume emission rate on each of the days analyzed. The sensitivity of the intensity to neutral composition is computed by varying the N2, O2, and O densities in the FLIP model and comparing to the intensity computed with the unmodified MSIS-86 densities. The ion densities change self-consistently. Thus the change in neutral composition also changes the electron density. The F2 peak height is unchanged in the model runs for a given day. The intensity changes near 100 deg SZA are comparable to within 10% when either (O2), (N2), or (O) is changed, regardless of which component source is dominant. There is strong sensitivity to changes in (N2) when dissociative recombination is dominant, virtually no change in the nighttime (SZA greater than or equal to 108 deg) intensity with (O2) doubled, and sensitivity of over 50% to doubling or halving (O) at night. When excitation by conjugate photoelectrons is the dominant nighttime component source, the relative intensity change with (O) doubled or halved is very small. This study shows the strong need for simultaneous measurements of electron density and of emissions proportional to photoelectron fluxes if the 6300 A twilight airglow is to be used to retrieve neutral densities.

Melendez-Alvira, D. J.↗
NASA NTRS1990

Interstellar absorption along the line of sight to Sigma Scorpii using Copernicus observations

From Copernicus observations of Sigma Sco, 57 individual lines of 11 elements plus the molecular species H2 and CO were identified. By using a profile-fitting technique, rather than curves of growth, it was possible to obtain column densities and Doppler b values for up to four separate components along this line of sight. Electron density in the major H I component was derived from the photoionization equilibrium of sulfur, obtaining, n(e) of about 0.3/cu cm. The neutral hydrogen density in the same component was also derived using fine-structure excitation of O I. An H II component is also present in which the electron density was n(e) about 20/cu cm. As a by-product of this analysis, previously undetermined oscillator strengths for two Mn II lines were obtained: for 1162.-017 A, f about 0.023 and for 1164.211 A, f about 0.0086.

Allen, M. M.↗
NASA NTRS1973

Jovian ionospheric models

This paper reports results obtained on ionosphere formation in the Jovian upper atmosphere with special reference to some of the recently available reaction rates, and to recent models of the Jovian neutral atmosphere based on the possibility of a warmer mesopause. In the older models of the Jovian ionosphere, the major ions were H+ which were lost only by pure radiative recombination. This led to high electron densities and practically no diurnal change. In contrast, recent models have relatively much smaller electron densities, especially in lower regions, and may be susceptible to significant diurnal variation.

Capone, L. A.↗
NASA NTRS1998

Interpretation of Solar Wind Ion Composition Measurements from Ulysses

The ion compositions measured in situ in the solar wind are important since the ion fractions carry information on the plasma conditions in the inner corona. The conditions in the inner corona define the properties of the solar wind plasma flow. Thus, if the ion fraction measurements can be used to unravel some of the plasma parameters in the inner corona, they will provide a valuable contribution to solving the heating and acceleration problem of the solar wind. The ion charge states in the solar wind carry information on electron temperature, electron density and ion flow speed. They are also sensitive to the shape of the electron distribution function. Through carefully modeling the solar wind and calculating the ion fractions predicted for different solar wind conditions, constraints on the electron temperature and ion flow speeds can be placed if the electron density is measured using polarization brightness measurements.

Esser, Ruth↗
NASA NTRS2005

Cassini Radio and Plasma Wave Observations at Saturn

Results are presented from the Cassini radio and plasma wave instrument during the approach and first few orbits around Saturn. During the approach the intensity modulation of Saturn Kilometric Radiation (SKR) showed that the radio rotation period of Saturn has increased to 10 hr 45 min plus or minus 36 sec, about 6 min longer than measured by Voyager in 1980-81. Also, many intense impulsive radio signals called Saturn Electrostatic Discharges (SEDs) were detected from saturnian lightning, starting as far as 1.08 AU from Saturn, much farther than terrestrial lightning can be detected from Earth. Some of the SED episodes have been linked to cloud systems observed in Saturn s atmosphere by the Cassini imaging system. Within the magnetosphere plasma wave emissions have been used to construct an electron density profile through the inner region of the magnetosphere. With decreasing radial distance the electron density increases gradually to a peak of about 100 per cubic centimeter near the outer edge of the A ring, and then drops precipitously to values as low as .03 per cubic centimeter over the rings. Numerous nearly monochromatic whistler-mode emissions were observed as the spacecraft passed over the rings that are believed to be produced by meteoroid impacts on the rings. Whistlermode emissions, similar to terrestrial auroral hiss were also observed over the rings, indicating that an electrodynamic interaction, similar to auroral particle acceleration, may be occurring in or near the rings. During the Titan flybys Langmuir probe and plasma wave measurements provided observations of the density and temperature in Titan's ionosphere.

Gurnett, D. A.↗
NASA NTRS1994

Results of critical velocity experiments with barium, strontium, and calcium releases from CRRES satellite

As part of the NASA Combined Release and Radiation Effects Satellite (CRRES) chemical release program in September 1990, two Ba and also one each Sr and Ca canisters of a boron-titanium thermite mixture, which vaporizes the element on ignition, were released near perigee after dusk in the South Pacific to study the critical velocity effect proposed by Alfven. The critical velocities of these three elements are 2.7, 3.5, and 5.4 km/s respectively, all well below the orbital velocity of 9.4 km/s. On September 10, 1990, a Sr and Ba pair (G-13, or critical ionization velocity (CIV) I) was released near Rarotonga at approximately 515 km altitude in a background electron density of 3.4 x 10(exp 6)/cu cm. On September 14, 1990, G-14 or CIV II released a Ca and Ba pair west of New Caledonia near 595 km at an electron density of 1.5 x 10(exp 6)/cu cm. Ions of all three elements were observed with low-light level imagers from two aircraft after they had transited up the magnetic field lines into the sunlight. Emissions from the spherically expanding neutral gas shells below the solar terminator, observed with cameras filtered for the Ba(+) ion line at 4554 A and also in unfiltered imagers for approximately 15 s after release, are probably due to excitation by hot electrons created in the CIV process. The ions created clearly lost much of their energy, which we now show can be explained by elastic collisions: Ba(+) + O. Inventories of the observed ions indicate yields of 0.15% and 1.84% for Ba in the first and second experiments, 0.02% for Sr and 0.27% for Ca. Ionization from all the releases continued along the satellite trajectory much longer (greater than 45 s) than expected for a CIV process. The ion production along the satellite track versus time typically shows a rapid rise to a peak in a few seconds followed by an exponential decrease to a level essentially constant rate. The characteristic distances for CIV I and II are 47 and 62 km, respectively. We interpret the early time rise and exponential fall to be due to CIV ionization, of 0.014% (CIV I) and 0.40% (CIV II) for the Ba releases. The later ions produced at a constant rate probably have origins from other such processes as stripping and associative ionization collisions with atmospheric constituents primarily O, and charge exchange with O(+), He(+), and H(+). We suggest that the much larger Ba ionization rate in CIV II than CIV I is due to the fact that the release occurred in the peak Ca density where hot electrons were already present.

Wescott, E. M.↗
NASA NTRS1985

Universal time dependence of nighttime F region densities at high latitudes

Coincident auroral-zone experiments using three incoherent-scatter radars at widely spaced longitudes are reported. The observational results demonstrate that, during the night, the F layer electron density is strongly dependent on the longitude of the observing site. Ionization patches were observed in the nighttime F region from the Chatanika and EISCAT radars, while densities observed from the Millstone radar were substantially smaller. The electron density within these maxima is larger at EISCAT than at Chatanika. When observed in the midnight sector auroral zone, these densities had a peak density at a high altitude of 360-475 km. The density was maximum when EISCAT was in the midnight sector and minimum when Millstone was in the midnight sector. A minimum in insolation in the auroral zone occurs at the UT when Millstone is in the midnight sector.

De La Beaujardiere, O.↗