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At least 1,243 records · Page 69
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Decomposition of NO studied by infrared emission and CO laser absorption

A diagnostic technique for monitoring the concentration of NO using absorption of CO laser radiation has been developed and applied in a study of the decomposition kinetics of NO. Simultaneous measurements of infrared emission by NO at 5.3 microns were also made to validate the laser absorption technique. The data were obtained behind incident shocks in NO-N2O-Ar (or Kr) mixtures, with temperatures in the range 2400-4100 K. The rate constant for the dominant reaction of O and NO to yield N and O2 was inferred from comparisons with computer simulations of the reactive flow.

Hanson, R. K.↗
NASA NTRS1976

Highlights in planetary spectroscopy 1962-75

Recent advances in spectroscopic studies of the planets with ground-based telescopes in the photomultiplier and IR spectral ranges are reviewed. Results of spectroscopic observations of Venus and Mars are briefly summarized, noting that the crucial problem confronting the interpretation of the Venusian spectrum is the nature of the clouds and that the outstanding problem in understanding the Martian atmosphere is the N2 or Ar concentration that may be present. Spectroscopic results for Jupiter, Saturn, Uranus, and Neptune are discussed, emphasizing observations of molecular hydrogen, HD, water, (C-13)H4, other hydrocarbons, and deuterated hydrocarbons. IR and visual spectroscopic observations of Titan and Io are reviewed which show that the CH4 bands in Titan's spectrum are pressure broadened and that a flattened ring of sodium is situated around Jupiter in the orbital plane of Io.

Muench, G.↗
NASA NTRS1976

Noble gases and shock effects in the Odessa octahedrite

Noble gas contents and shock effects have been studied in 21 Odessa irons from known geographic locations. Cosmogenic He-3, Ne-21, Ar-38 contents and He-3/Ne-21 ratios vary by factors of 62, 91, 68, and 1.55, respectively, while Ne-22/Ne-21 ratios are virtually constant at 1.07. The samples fall into two groups differing by a factor of 4.1 in exposure age, 1000 in source mass, or some combination of these. Three samples show significant shock effects, two of them to above 130 kbar, probably arising during terrestrial impact from the crater-forming explosion. As in Canyon Diablo plains specimens, noble gas contents do not correlate with siting or shock.

Herzog, G. F.↗
NASA NTRS1976

Comparison of neutral temperatures inferred from instruments on the AE-C satellite

Determinations of neutral thermospheric temperature from data taken with instruments aboard the AE-C spacecraft have been compared during the circular orbit phase in late December 1974 and January 1975 when the satellite altitude was near 260 km. These temperatures are found to be in overall agreement to within about 10% during periods of low magnetic activity. The methods are based on: analysis of the satellite spin modulation of N2 density; analysis of the ion temperature; and the calculation of the temperature needed to match measured N2 and Ar densities assuming fixed boundary conditions at 120 km.

Hedin, A. E.↗
NASA NTRS1976

Status of the Viking missions

A chronology of Viking 1 lander activities is presented for the first 43 sols (Martian days) of surface sampling and analysis. The orbital insertion of the second Viking spacecraft is reviewed along with the search for the second landing site. A general assessment of the planet is made on the basis of the data thus far obtained. Some of the findings reported are that: (1) there is extensive evidence of volcanism, fluvial and aeolian erosion, and deposition over the entire surface; (2) the floor of Vallis Marineris is significantly younger than the planet's surface; (3) the morphology of Martian crater ejecta is indicative of surface flow rather than ballistic deposition; (4) the rocks in the immediate vicinity of the lander are all covered by a layer of fine red dust; (5) the atmosphere is optically thick and well mixed, with suspended particles giving the sky a pink color; (6) the N and Ar isotopic ratios are different from those on earth; (7) atmospheric water vapor varies with both time of day and location; (8) the summer northern polar regions have a high water concentration in the atmosphere; (9) a large fraction of magnetic material resides in the surface; and (10) no complex organic compounds have been detected in the two samples analyzed.

Soffen, G. A.↗
NASA NTRS1977

Low-reflection silicon solar cells

Alteration of surface of silicon solar cell with chemical etchant prior to application of antireflection (AR) coating and encapsulant FEP Teflon, reduces surface reflectivity to 2%. Reduced reflection achieved occurs at all wavelengths resulting in improved short circuit current and spectral response. Improved collection efficiency is also expected.

Baraona, C. R.↗
NASA NTRS1976

Crystal growth from the vapour phase (ASTP experiment MA-085)

The positive effects of microgravity on crystal quality and fundamental properties of the vapor transport reaction were established by analyzing the results of three transport experiments on multi-component systems performed during the Apollo Soyuz Test Project (ASTP) mission. The systems employed were GeSe(0.99)Te(0.01) - GeI4 (A), GeS(0.98)Se(0.02) - GeCl4 (B), and GeS - GeCl4-Ar (C). The crystallographic analysis is based on a direct comparison of space and ground-based (prototype) crystals, employing X-ray diffraction, microprobe, microscopic, and chemical etching techniques. The results demonstrate a considerable improvement of the space-grown crystals in terms of chemical and crystalline homogeneity, surface morphology, and bulk perfection relative to ground specimens. The confirmation of greater mass transport rates than predicted for micro-gravity by present vapor transport models is of basic scientific and practical importance for the improvement of transport models and techniques on earth and for the development of a transport model for space conditions. The internal consistency and agreement between ASTP and Skylab results obtained for different compounds, transport agents, and temperature gradients strongly support the validity of these observations. The combined findings of improved crystal quality and high mass transport rates are of technological significance for space-processing applications.

Wiedemeier, H.↗
NASA NTRS1977

Crystal growth from the vapor phase. Experiment MA-085

The positive effects of microgravity on crystal quality and the fundamental properties of the vapor transport reaction were established by analyzing the results of three transport experiments on multicomponent systems performed during the Apollo-Soyuz Test Project mission. The systems employed were GeSe0.99Te0.01-GeI4(A), GeS0.98Se0.02-GeCl4(B), and GeS-GeCl4-Ar (C). The crystallographic analysis is based on a direct comparison of space and ground-based (prototype) crystals employing X-ray diffraction, microprobe, microscopic, and chemical etching techniques. The results demonstrate a considerable improvement of the space-grown crystals in terms of chemical and crystalline homogeneity, surface morphology, and bulk perfection relative to ground specimens.

Wiedemeier, H.↗
NASA NTRS1977

Absolute Rayleigh scattering cross sections of gases and freons of stratospheric interest in the visible and ultraviolet regions

The laboratory measurements of absolute Rayleigh scattering cross sections as a function wavelength are reported for gas molecules He, Ne, Ar, N2, H2, O2, CO2, CH4 and for vapors of most commonly used freons CCl2F2, CBrF3, CF4, and CHClf2. These cross sections are determined from the measurements of photon scattering at an angle of 54 deg 44 min which yield the absolute values independent of the value of normal depolarization ratios. The present results show that in the spectral range 6943-3638A deg, the values of the Rayleigh scattering cross section can be extrapolated from one wavelength to the other using 1/lambda (4) law without knowing the values of the polarizabilities. However, such an extrapolation can not be done in the region of shorter wavelengths.

SHARDANAND↗
NASA NTRS1976

Atmospheric, Magnetospheric and Plasmas in Space (AMPS) spacelab payload definition study - program analysis and planning for phase C/D document - Volume 7

Typical missions identified for AMPS flights in the arly 1980's are described. Experiment objectives and typical scientific instruments selected to accomplish these objectives are discussed along with mission requirements and shuttle and Spacelab capabilities assessed to determine any AMPS unique requirements. Preliminary design concepts for the first two AMPS flights form the basis for the Phase C/D program plan. This plan implements flights 1 and 2 and indicates how both the scientific and flight support hardware can be systematically evolved for future AMPS flights.

Keeley, J. T.↗
NASA NTRS1976

Scaling of cross sections for K-electron capture by high-energy protons and alpha-particles from the multielectron atoms

Electron capture by protons from H, He, and the K-shell of Ar, and alpha particles from He are considered. It is shown that when a certain function of the experimental cross sections is plotted versus the inverse of the collision energy, at high energies the function falls on a straight line. At lower energies the function concaves up or down, depending on the charge of the projectile, the effective charge and the ionization potential of the electron that is being captured. The plot can be used to predict cross sections where experimental data are not available, and as a guide in future experiments. High energy scaling formulas for K-electron capture by low-charge projectiles are given.

Omidvar, K.↗
NASA NTRS1977

Energy spectrum of sputtered uranium

The fission track technique for detecting uranium 235 was used in conjunction with a mechanical time-of-flight spectrometer to measure the energy spectrum in the region 1 eV to 1 keV of material sputtered from a 93% enriched U-235 foil by 80 keV Ar-40(+) ions. The spectrum was found to exhibit a peak in the region 2-4 eV and to decrease approximately as E to the -1.77 power for E is approximately greater than 100 eV. The design, construction and resolution of the mechanical spectrometer are discussed and comparisons are made between the data and the predictions of the ramdom collision cascade model of sputtering.

Weller, R. A.↗
NASA NTRS1976

Production of Mg and Al Auger electrons by noble gas ion bombardment of Mg and Al surfaces

Relative production efficiencies of Mg and Al Auger electrons by He, Ne, Ar, Kr, and Xe ion bombardment are reported as a function of ion energy for energies not exceeding 3 keV. The experimental apparatus employed consisted of a LEED-Auger system equipped with an ion gun and a four-grid retarding-potential analyzer. It is found that: (1) the shape of the ion-excited Auger signal was independent of the rare gas and quite symmetric; (2) the Al signal was about an order of magnitude smaller than the Mg signal for a given bombarding species and ion-gun voltage; (3) no signal was observed for He(+) bombardment under any of the experimental conditions; (4) signal strengths were independent of temperature and ion dose; (5) the Auger production efficiencies differed by no more than a factor of two among the different gases - except for He(+) - on a given metal; (6) all the signal strengths increased with increasing ion-gun voltage, with no maximum exhibited; and (7) the apparent threshold energy for the Al signal was higher than that for the Mg signal. The differences between the results for the two metals are attributed to the fact that the Al 2p orbital lies deeper in energy and closer to the nucleus than the corresponding Mg orbital.

Ferrante, J.↗
NASA NTRS1976

Direct measurements of neutral wave characteristics in the thermosphere

The elliptical and circular phases of the Atmosphere Explorer-C satellite have provided the basis for a study of the neutral wave characteristics in the thermosphere using data collected by the open source mass spectrometer used to measure both reactive (O,N) and nonreactive (O2, N2, He, Ar) constituents. The phase relationships between the constituents are discussed and the results of a wave occurrence and amplitude survey covering 338 despun orbits in which the local time and latitude characteristics of the waves are presented are discussed. Conclusions based on this survey are tested in a study of waves measured at high latitudes during a geomagnetic storm.

Potter, W. E.↗
NASA NTRS1976

A two-satellite study of the neutral atmosphere response to a major geomagnetic storm

Simultaneous measurements of neutral composition from both Esro 4 and Aeros-A have provided a complementary set of data for studying the temporal and spatial characteristics of the thermosphere during a major geomagnetic storm. From the correlative studies of Ar and N2 number densities, the magnetic index Aps, and ground-based magnetograms, it is found that the Ap index only reflects the gross features of atmospheric disturbances. Superposed on the global component are localized regions of 'hot spots' which appear correlated with ground-based magnetograms. Because of these localized disturbances, the interpretation of the atmospheric response to geomagnetic storms becomes ambiguous.

Trinks, H.↗
NASA NTRS1976

Thermospheric storms and related ionospheric effects

A comparative study of thermospheric storms for equinox and winter conditions is presented based on neutral-composition measurements from the Aeros-A neutral-atmosphere temperature experiment. The main features of the two storms as inferred from changes in N2, Ar, He, and O are described, and their implications for current theories of thermospheric storms are discussed. On the basis of the study of the F-region critical frequency measured from a chain of ground-based ionospheric stations during the two storm periods, the general characteristics of the ionospheric storms and the traveling ionospheric disturbances are described. It is suggested that the positive and negative phases of ionospheric storms are different manifestations of thermospheric storms.

Chandra, S.↗
NASA NTRS1976

Double-quantum vibrational energy transfer in the O3-CO and O3-OCS systems

Using the CO2 laser induced fluorescence technique at 298 K for excitation of the P(30) transition in O3 or the P(22) transition in OCS, double-quantum vibrational energy transfer was studied in the O3-CO and O3-OCS binary gas systems. Rapid rates were observed for energy transfer from the CO (nu = 1) to the coupled O3(200), O3(101), and O3(002) levels, as well as for the transfer from the coupled O3(001) and O3(100) levels to the OCS(020) level. Deactivation of OCS by N2, Ar, and OCS was studied and deactivation rate constants were measured. The experimental results are compared with those calculated using the first order perturbation theory of dipole transition-moment interactions (Sharma and Brau, 1969) as modified by Tam (1972). An attempt is made to interpret the obtained results.

Hui, K.-K.↗
NASA NTRS1977

Diogenite exposure ages

He, Ne and Ar isotopes have been measured in six, and Al-26 in two diogenites. Cosmic-ray exposure ages corrected for shielding effects using Ne-22/Ne-21 ratios are generally concordant. Five diogenites have a group age of 14 Myr and three others may have a group age of 24 Myr, implying that two collisions may have produced 8 of the 9 diogenites.

Herzog, G. F.↗