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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 NTRS1980

Interferometry of Saturn and its rings at 1.30-cm wavelength

Interferometric observations of Saturn and its rings at a wavelength of 1.30 cm are presented in an attempt to place constraints upon the amount of thermal radiation emitted by the ring particles. Model-fitting and aperture synthesis techniques were used to analyze the data obtained on nine baselines at a frequency of 23 GHz. Ring optical depth is found to be close to that observed at visible wavelengths, while ring brightness temperature is only 7 + or - 1 K, requiring the ring particles to be nearly conservative scatterers at this wavelength and implying an upper limit of 2.4 m to the radius of a typical ring particle with a lower limit of 0.95 to its single scattering albedo. An observed difference between planetary radii observed at 1.30 and 3.71 cm is interpreted in terms of limb darkening and found to be marginally different from the predictions of atmospheric models in which NH3 is the principal source of microwave opacity.

Schloerb, F. P.↗
NASA NTRS1980

Absorption coefficients of solid NH3 from 50 to 7000 per cm

Thin-film spectra of solid NH3 at a resolution of 1 per cm were used to determine its absorption coefficient over the range 50-7000 per cm. The thin films were formed inside a liquid N2 cooled dewar using a variety of substrates and dewar windows. The spectra were recorded with two Fourier spectrometers, one covering the range from 1 to 4 microns and the other from 2.6 to 200 microns. The thickness of the films was measured with a laser interference technique. The absorption coefficients were determined by application of Lambert's law and by a fitting procedure to the observed spectra using thin-film theory. Good agreement was found with the absorption coefficients recently determined by other investigators over a more restricted wavelength range. A metastable phase was observed near a temperature of 90 K and its absorption coefficient is reported. No other major spectral changes with temperature were noted for the range 88-120 K.

Sill, G.↗
NASA NTRS1980

Evidence for live Cm-247 in the early solar system

Variations of the U-238/U-235 ratio in the Allende meteorite, ranging from -35% to +19% are interpreted as evidence of live Cm-247 in the early solar system. The amounts of these and other r-products in the solar system indicate values of (9000 + or - 3000) million years for the age of the Galaxy and approximately 8 million years for the time between the end of nucleosynthesis and the formation of meteoritic grains. Three possible explanations are presented for the different values of the latter time period which are indicated by the decay of products of Cm-247, Al-27, Pu-244, and I-129.

Tatsumoto, M.↗
NASA NTRS1981

Radio maps of Jupiter's radiation belts and planetary disk at lambda 6 cm

Two-dimensional maps of Jupiter's radio emission were made in April 1978 at a frequency of 4885 MHz (6 cm) using the Westerbork telescope in the Netherlands. Pictures in the Stokes parameters I, Q and U have been obtained every 15 deg in longitude, each smeared over 20 deg of the planet's rotation. The half power beam width was approximately 1/6 of the disk diameter in right ascension and approximately 1/2 in declination. The planetary disk shows little or no limb darkening at this wavelength and has a temperature of 220 + or - 8 K. The radiation belts clearly show a kind of plateau or flattening in intensity in the outer part of the belt. A comparison with 21 and 50 cm maps indicate no difference in the width and form of the emission regions with wavelength.

De Pater, I.↗
NASA NTRS1981

Constraints on the composition of the Venus atmosphere from microwave measurements near 1.35 cm wavelength

The determination of the brightness temperature of Venus near 1.35 cm wavelength is reviewed. The observed brightness temperature is compared with models for the microwave emission based on the physical and chemical structure of the atmosphere as obtained from spacecraft. Upper limits are set on the concentrations of microwave-absorbing minor constituents. In particular, upper limits are determined for SO2 (180 ppm) and H2O (0.3%) for a mixing-ratio profile that is uniformly mixed up to the cloud bottom at 50 km and is rapidly depleted (scale height, approximately 1 km) at higher altitudes. The total optical depth of the cloud region at or above 50 km is less than 0.17 at 1.35 cm wavelength. The SO2 upper limit is only in marginal agreement with the spacecraft results, and it may be that the latter have been overestimated, or that the distribution of SO2 is more complex than given by the uniform mixing model.

Janssen, M. A.↗
NASA NTRS1981

Atlas of absorption lines from 0 to 17 900 cm(-1)

Plots of absorption line strength versus line position for wavenumbers from 0 to 17,900 cm(-1) are shown for 20 atmospheric gases (H2O, CO2, O3, N2O, CO, CH4, O2, NO, SO2, NO2, NH3, HNO3, OH, HF, HCl, HBr, HI, ClO, OCS, H2CO). Also shown are similar plots of lower-state energy values for adsorption lines for the strongly adsorbing atmospheric gases (H2O, CO2, O3, and CH4) for wavenumbers from 0 to 5000 cm(-1).

Park, J. H.↗
NASA NTRS1982

A calibration line list for 807-1167 cm -1 from high resolution Fourier spectroscopy of the 14NH3 nu sub 2 band

A calibration list of 295 lines observed over the 800 to 1170 cm to the -1 power region is presented. This list is intended for use as a calibration reference for calibrating diode laser spectra. The transition frequencies were calibrated against the well established laser frequencies of CO2. The estimated uncertainty in the corrected frequencies is + or - 1x.0001 cm to the -1 power.

Hillman, J. J.↗
NASA NTRS1981

Stratospheric measurements of continuous absorption near 2400 per cm

Measurements of continuous absorption near 2400 per cm by N2 and CO2 over long path lengths in the lower stratosphere are presented. The continua were measured in a stratospheric solar spectrum obtained during sunset with a balloon-borne Michelson interferometer in the 2380-2500 per cm region, and transmittances were calculated by ratioing the amplitudes to those of a high-sun spectrum in order to eliminate the wavelength dependence of the measured flux. Comparison of the measured transmittances with those calculated for a multilayered atmospheric model using laboratory absorption measurements results in a fair agreement, and reveals the primary component of the absorption throughout most of the range to be N2, with the CO2 contribution equal to that of N2 only at the CO2 band head. In this region, the shape of the continuum is very sensitive to the sub-Lorentzian line shape assumed in the calculations, and so, if the shape of the N2 continuum at low temperatures can be determined through laboratory measurements, may be used to infer air-broadened far-wing CO2 line shape.

Rinsland, C. P.↗
NASA NTRS1982

High-accuracy linear and circular polarization measurements at 21 cm

New high-accuracy linear and circular polarization measurements have been obtained for 27 small-diameter radio sources, using the Westerbork Synthesis Radio Telescope at 21 cm (1415 MHz). From these and other observed properties of the sources, estimates of the average internal magnetic field strengths in the sources are made by applying the uniform synchrotron emission model to the measured circular polarization and by using equipartition arguments. These two values are compared and found to be in agreement to within an order of magnitude, as was previously found by Weiler and de Pater (1980). Also, the magnetic fields estimated from circular polarization measurements at two different wavelengths (49 and 21 cm) are compared and found to be in rough agreement, but with indications of differences between variable and nonvariable sources. A comparison of the magnitudes of linear and circular polarization in sources shows no correlations.

De Pater, I.↗
NASA NTRS1982

VLA observations of Saturn at 1.3, 2, and 6 cm

Radio maps with a resolution of 1.5 arcsec were made of Saturn at 1.3, 2, and 6 cm. The inclination of the ring plane was -5.4 deg. A fraction of 0.49 + or - 0.08 of Saturn's emitted light is transmitted through the rings at 2 and 6 cm. This value converts to an effective head-on or normal optical depth of 0.07 + or - 0.02. The transparency at this small inclination angle must be provided entirely by the regions of very low optical depth, e.g., the Cassini and Encke's Divisions, and to achieve the desired number this requires either a relatively large fraction of gaps or a strong forward scattering by the ring particles. The planetary disk appears to be much less limb darkened in the N-S than the E-W direction, while cuts across the planet, averaged over all directions, agree with the theoretical limb-darkening curves for a planet with a uniform atmosphere and solar abundances for all chemical elements.

De Pater, I.↗
NASA NTRS1981

Extended Performance 8-cm Mercury Ion Thruster

A slightly modified 8-cm Hg ion thruster demonstrated significant increase in performance. Thrust was increased by almost a factor of five over that of the baseline thruster. Thruster operation with various three grid ion optics configurations; thruster performance as a function of accelerator grid open area, cathode baffle, and cathode orifice size; and a life test of 614 hours at a beam current of 250 mA (17.5 mN thrust) are discussed. Highest thruster efficiency was obtained with the smallest open area accelerator grid. The benefits in efficiency from the low neutral loss grids were mitigated, however, by the limitation such grids place on attainable ion beam current densities. The thruster components suffered negligible weight losses during a life test, which indicated that operation of the 8-cm thruster at extended levels of thrust and power is possible with no significant loss of lifetime.

Mantenieks, M. A.↗
NASA NTRS1982

Inert gas test of two 12-cm magnetostatic thrusters

Comparative performance tests were conducted with 12 cm line and ring magnetic cusp thrusters. Shell anode and magnetoelectrostatic containment boundary anode configurations were evaluated with each magnet array. The best performance was achieved with the 12-cm ring cusp-shell anode configuration. Argon operation of this configuration produced 65-81 percent mass utilization efficiency at 170-208 watts/single-charged-equivalent (SCE) ampere beam. Xenon test results showed 75-95 percent utilization at 162-188 watts/SCE ampere beam.

Ramsey, W. D.↗
NASA NTRS1982

Frequency of gamma-ray bursts greater than 3 x 10 to the -6th erg/sq cm

Results are presented for gamma-ray burst observations with the Large Area Sky Survey instrument on HEAO-1. It is noted that during the time HEAO-1 was operational, the instrument detected at least 12 confirmed gamma-ray bursts with intensities greater than 3 microerg/sq cm and identified six additional unconfirmed bursts. The rates of gamma-ray bursts are estimated to be about 125 per yr for intensities greater than 3 microerg/sq cm and approximately 50 per yr for intensities greater than 10 microerg/yr. The data are shown to yield a log N - log S relation for gamma-ray bursts that is consistent with a spherical distribution of sources within the Galaxy and having a broad range of intrinsic luminosities.

Share, G. H.↗
NASA NTRS1984

A search for formic acid in the upper troposphere - A tentative identification of the 1105-per cm nu-6 band Q branch in high-resolution balloon-borne solar absorption spectra

Infrared solar absorption spectra recorded at 0.02-per cm resolution during a balloon flight from Alamogordo, NM (33 deg N), on March 23, 1981, have been analyzed for the possible presence of absorption by formic acid (HCOOH). An absorption feature at 1105 per cm has been tentatively identified in upper tropospheric spectra as due to the nu-6 band Q branch. A preliminary analysis indicates a concentration of about 0.6 ppbv and 0.4 ppbv near 8 and 10 km, respectively.

Goldman, A.↗
NASA NTRS1984

Hydrothermal alteration of CM carbonaceous chondrites: Implications of the identification of tochilinite as one type of meteoritic PCP

Poorly characterized phases (PCP's) constitute up to 30 volume percent of some CM carbonaceous chondrites, and are therefore an important key to an understanding of the physico-chemical conditions attending matrix evolution. An iron rich form of the terrestrial phase tochilinite was recently identified as a common type of PCP. Tochilinite has the general formula 6Fe(0.9)S.5(Mg,Fe)(OH)2 and consists of alternating machinawite (FeS) and brucite ((Mg,Fe)(OH)2) sheets, with iron vacancies in the sulfide sheets. In iron rich tochilinite, ferrous hydroxide, called amakinite, replaces brucite. If CM carbonaceous kchondrites have underdone hydrothermal alteration, iron rich tochilinite, at least, probably grew from aqueous solutions characterized by low FO2, high FS2, pH 10 to 12, and at a temperature at or below 170 C.

Zolensky, M. E.↗
NASA NTRS1985

Growth of the 889 per cm infrared band in annealed electron-irradiated silicon

Isothermal annealing of electron-irradiated Czochralski silicon has been studied at four different temperatures ranging from 304 to 350 C using infrared spectroscopy. At annealing temperatures above 300 C the irradiation-induced band at 830 per cm, usually attributed to a vacancy-oxygen complex (the A center), disappears and a new band at 889 per cm grows up. Within the experimental accuracy, the activation energy for the growth of this band is found to be identical with the value given by Stavola et al. for 'anomalous' oxygen diffusion in silicon. Also the frequency factors for the two processes are in reasonable agreement. The results show that a vacancy-assisted process may provide an explanation for enhanced motion of oxygen in silicon.

Svensson, B. G.↗
NASA NTRS1986

VLA observations of coronal bright points at 6 and 20 cm wavelengths

Prior to and during the Spacelab-2 operation, observations were made at 6 and 20 cm of solar coronal bright points, using the Very Large Array (VLA) in the C-configuration. The ultraviolet coverage ranged from 200 to 18,000 wavelengths. The maps were convolved with beams of 18 x 18 inches at 20 km and 4 x 4 inches at 6 cm. Only the preliminary results from July 15 and July 31, 1985 observations.

Kundu, M. R.↗
NASA NTRS1986

Quantification of HCl from high-resolution, ground-based, infrared solar spectra in the 3000 per cm region

Recent ground-based infrared solar spectra at 0.02 per cm resolution in the 3000 per cm region have been analyzed for the atmospheric content of HCl. Nonlinear spectral least-squares fitting applied to spectra obtained at several zenith angles shows little sensitivity of the results to tropospheric HCl but provides an accurate measurement of the total column amount.

Goldman, A.↗