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At least 199 records · Page 11

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NASA NTRS1979

Pyroxenes in Serra de Mage - Cooling history in comparison with Moama and Moore County

Thin sections and single grains of pyroxenes from the Serra de Mage feldspar cumulate eucrites were studied by X-ray crystallography, electron microprobe and optical techniques. It was concluded that the pyroxene crystallized as pigeonite. On cooling augite was exsolved along (001) and inverted to hypersthene, with exsolution of (100) augite from hypersthene during continued slow cooling. The estimated original bulk composition of the pigeonite pyroxene is Wo10En51Fs39. The compositional data, textural relations, and existence of P2 sub 1 ca hypersthene suggest very low cooling (about 0.0004 deg C/year) below 800 deg. The Serra de Mage augite lamellae were found to be as thick or thicker than those of Moore County and Moama meteorites.

Harlow, G. E.↗

NASA NTRS1979

Ionosphere of Venus - First observations of day-night variations of the ion composition

Preliminary observations of day-night variations in the ion composition of the ionosphere of Venus, obtained by the Pioneer Venus Orbiter ion mass spectrometer experiment, are reported. A remarkable abundance and extent of ionization in the deep regions of the nightside ionosphere was observed, in spite of the long Venus night. A comparison of dayside and nightside ion distributions reveals a nightside composition similar in several respects to that of the dayside, with the ions O(+) and O2(+) forming the nightside F 2 and F 1 regions, respectively, as in the dayside. Important differences include a greater abundance of low-latitude ionization in the nightside, a significant increase of H(+) and NO(+) ions with increasing solar zenith angle, and extreme dynamic variability of the nightside region above 160 km. Ion composition data support the view that the nightside ionosphere can be maintained by the transport of ionization from the dayside.

Taylor, H. A., Jr.↗

NASA NTRS1979

The prediction of AE, ap, and Dst at time lags between 0 and 30 hours

The magnetic activity indexes AE, ap, and Dst are correlated with approximately 35,000 hours of interplanetary plasma and magnetic field measurements acquired near the Earth (assembled by NASA/NSSDC into a composite data sat). Lag times between the indexes and solar wind parameters ranged from 0 to 30 hours. Correlations at lags less than 6 hours yield results in agreement with previous studies. At greater lags, the correlation coefficients between the solar wind parameters and AE and ap approach these parameters' autocorrelation (persistence) values. For Dst the correlation with solar wind parameters is lower than that with AE and ap in the 3 to 4 hour lag range whereas the autocorrelation of Dst is significantly higher over the entire 0 to 30 hour lag range. The implications of these differences between AE, ap, and Dst are discussed in terms of persistence of solar wind structure.

Smart, D. F.↗

NASA NTRS1980

Process modifications for improved carbon fiber composites: Alleviation of the electrical hazards problem

Attempts to alleviate carbon-fiber-composite electrical hazards during airplane crash fires through fiber gasification are described. Thermogravimetric and differential scanning calorimetric experiments found several catalysts that caused fibers to combust when composites were exposed to test fires. Composites were tested in the 'Burn-Bang' apparatus and in high voltage electrical detection grid apparatus. In a standard three minute burn test modified composites released no fibers, while state-of-the-art composites released several hundred fiber fragments. Expected service life with and without catalytic modification was studied and electron microscopy and X-ray microanalysis furnished physical appearance and chemical composition data. An acrylic acid polymer fiber coating was developed that wet the carbon fiber surface uniformly with the catalyst, providing a marked contrast with the uneven coats obtained by solution-dipping.

Ramohalli, K.↗

NASA NTRS1979

Characterization of submicron matrix phyllosilicates from Murray and Nogoya carbonaceous chondrites

The combined techniques of high-resolution transmission electron microscopy and energy-dispersive X-ray analysis have been used to study dispersed, submicron phyllosilicates and the 'poorly characterized phase' of C2 matrix material. Morphologies and structure types observed are similar to terrestrial chrysotile. Distinctive morphologies and 7.3-A characteristic basal spacings combined with composition information rule out phyllosilicates other than serpentine group minerals as the predominant phyllosilicate material. The 'poorly characterized phase' is composed of chemically similar very fine-grained phyllosilicate and amorphous material. The observation of interstratified phyllosilicate material sheds additional doubt on compositional data which is not accompanied by structural data from the same particle.

Mckee, T. R.↗

NASA NTRS1980

Solar flux variation of the thermospheric molecular oxygen density

The paper presents measurements of the thermospheric molecular oxygen density obtained from the Atmosphere Explorer (AE) satellites and composition data obtained from rocket-based experiments which provide information on the distribution of O2 between 120 and 200 km as a function of solar flux. The rocket experiment data can be analyzed for long-term variations, which show that the O2 density at 200 km shows little variation but at 120 km decreases approximately 30% for the F sub 10.7-cm flux.

Kayser, D. C.↗

NASA NTRS1980

Satellite studies of N/D-2/ emission and ion chemistry in aurorae

The incident particle flux ion and neutral composition data taken on the AE-D satellite have been used to investigate the quantal emission of N2(plus) at 4278 A, N(D-2) at 5200 A, and the ion chemistry in aurorae. The results of a time dependent auroral model have been compared to the data. The calculated 4278 A emission of N2(plus), the 5200 A emission of N(D-2), the densities of O2(plus), NO(plus), N2(plus), O(plus), and the electron density are generally in agreement with the measured values. These results are consistent with the branching ratios and quenching rates deduced from previous studies of the N(D-2) densities in the day-time, mid-latitude ionosphere. It is found that in an auroral arc, the measured atomic oxygen density is lower than predicted by the MSIS model.

Rusch, D. W.↗

NASA NTRS1981

An analytic formulation for heating source memory in the thermospheric composition

Numerical calculations from a spectral circulation model are utilized to construct an analytic Green's function formulation describing the meridional, time-dependent thermospheric composition and temperature response during magnetic storms. The purpose is to develop a formulation that embodies source memory while being sufficiently simple to serve as a heuristic guide for empirical modeling. By passing from the discrete Fourier series representation, utilized for the numerical circulation model, to a continuous Fourier integral representation, explicit waves are obtained for the thermospheric response times. The response times are altitude and species dependent and can exceed two days below 200 km. Thus, for certain storm scenarios, pronounced source memory signatures for the composition and temperature are predicted. Response times obtained from the formulation are shown to give a response consistent with previously published neutral composition data from AE-C for the February 1974 storm when an ap dependent heat source is employed.

Porter, H. S.↗

NASA NTRS1980

Chemistry of Apollo 11 low-K mare basalts

A reexamination of the bulk major and trace element geochemistry of Apollo 11 low-K mare basalts is presented. New analyses are given for seven previously unanalyzed samples (10003, 10020, 10044, 10047, 10050, 10058, and 10062) and for two low-K basalts (10029 and 10092) and one high-K basalt (10071) for which comprehensive compositional data were previously lacking. The data show that three distinct magma types have been sampled, as proposed by Beaty and Albee (1978), and that these magma types are unrelated by near-surface crystal fractionation. Each magma type is characterized by distinctive magmaphile element ratios, which enable previously unclassified samples (10050 and 10062) to be assigned to an appropriate magma type.

Rhodes, J. M.↗

NASA NTRS1983

The response of thermospheric atomic nitrogen to magnetic storms

Neutral composition data obtained by the open-source neutral-mass spectrometer on the polar orbiting Atmosphere Explorer D satellite during the periods October 31 to November 15, 1975, and January 5 to 15, 1976, are used to characterize the response of thermospheric atomic nitrogen densities to geomagnetic activity. These periods provided nearly simultaneous polar and low-latitude data coverage. At low and middle latitudes near dawn and at all latitudes on the dayside, N densities at 400 km appear to vary like those of a species of atomic mass 14: N is observed to increase with increasing geomagnetic activity in a manner similar to that of O. At auroral latitudes near dawn, however, there is a more complex dependence on the amplitude of the disturbance. For substorm-scale activity, N tends to increase during periods of auroral heating but exhibits a sharp temporary decrease afterward. During large storms there is a significant but short-lived increase of N at auroral latitudes. The present results support current models showing that N is produced and transported out of the auroral zone during geomagnetic disturbances.

Engebretson, M. J.↗

NASA NTRS1983

Solar cycle variations in the interplanetary magnetic field

ISEE 3 interplanetary magnetic field measurements have been used to extend the NSSDC hourly averaged IMF composite data set through mid-1982. Most of sunspot cycle 20 (start:1964) and the first half of cycle 21 (start:1976) are now covered. The average magnitude of the field was relatively constant over cycle 20 with approx. 5-10% decreases in 1969 and 1971, when the Sun's polar regions changed polarity, and a 20% decrease in 1975-6 around solar minimum. Since the start of the new cycle, the total field strength has risen with the mean for the first third of 1982 being about 40% greater than the cycle 20 average. As during the previous cycle, an approx. 10% drop in IMF magnitude accompanied the 1980 reversal of the solar magnetic field. While the interplanetary magnetic field is clearly stronger during the present solar cycle, another 5-7 years of observations will be needed to determine if cycle 21 exhibits the same modest variations as the last cycle. Accordingly, it appears at this time that intercycle changes in IMF magnitude may be much larger than the intracycle variations.

Slavin, J. A.↗

NASA NTRS1984

Response of Inconel 617 superalloy to combined ground-based and STS reentry exposure

Inconel 617 is a nickel-based superalloy which is being considered for heat-shield applications because of its high-temperature strength, good oxidation resistance and high emittance of oxidized surfaces. While the effects of simulated reentry conditions on emittance and oxidation of Inconel 617 have been studied, the combined effects of the ground-based environment with sea salt exposure and the reentry environment have not been evaluated. Experimental results are presented to show the effects of environmental simulation including ground-based and reentry exposure on the emittance and oxidation of Inconel 617. Specimens were exposed to simulated reentry at a surface temperature of 2000 F in the Langley Research Center Hypersonic Materials Environmental Test System (HYMETS) Facility with and without alternate exposures to an atmospheric seashore environment or a laboratory sea salt environment. This paper presents emittance, mass loss, oxide chemistry, and alloy composition data for the specimens.

Clark, R. K.↗

NASA NTRS1984

Rapid discrimination of granitic rock compositions by low-resolution near-infrared reflectance

The slopes of near-infrared spectra between approximately 1 and 2 microns from quartz-bearing plutonic rocks are strongly correlated with rock chemistry determined by X-ray spectrometry. The empirically derived predictive equations provide compositional data of adequate precision and resolution to discern patterns of regional geochemical variation in granitic batholithic rocks of southern California. As an analytical method, infrared spectrometry is rapid and inexpensive, and the method has potential in applications to direct field measurements and to data from aircraft and spacecraft scanner systems of relatively low spectral and spatial resolution, provided vegetative cover and surface alteration are not prohibitively masking.

Baird, A. K.↗

NASA NTRS1984

Response of Inconel 617 superalloy to combined ground-based and STS reentry exposure

Clark, R. K.↗

NASA NTRS1984

Origin of the plasma in a cross-polar cap auroral feature (theta aurora)

Ion composition data obtained from a particularly well observed cross-polar cap auroral feature (theta aurora) are presented. Two components of the hot plasma are identified, one from the ionosphere below and the second from the distant plasma sheet. These observations provide strong support for the conclusion that the cross-polar cap auroral feature occurs on field lines closing through the distant plasma sheet or plasma sheet boundary layer. Taken together with the previously published observations, these new results establish substantial constraints on models for the overall polar cap topology. However, they do not unambiguously favor either of the two principal topologies discussed in the literature.

Peterson, W. K.↗

NASA NTRS1984

The Origin and Evolution of Uranus and Neptune

The present state of understanding of the origin and evolution of the planets Uranus and Neptune is briefly reviewed. Emphasis is placed on the need for improved physical and composition data on both planets, particularly those data needed to resolve certain major inconsistencies in the present data set.

J S Lewis↗

NASA NTRS1984

The bulk-Moon MgO/FeO ratio: A highlands perspective

Compositional data for nonmare (highlands) samples suggest that the Moon's mg ratio (MgO/FeO) is higher than general estimates. Geochemically representative highlands soils have mg ratios of 0.66 (Apollo 16), 0.69 (Luna 20) and 0.73 (ALHA81005). These soils are mixtures of unrelated pristine nonmare rocks, of which there are at least three groups: Mg-rich rocks, ferroan anorthosites, and KREEP. Other than Mg-rich rocks, virtually all pristine rocks have mg 0.65. Thus, assuming the mixing process that sampled Mg-rich materials was random, the average mg of Mg-rich parent magmas was probably at least 0.70. More direct evidence can be derived from the Mg-rich rocks themselves. Nine of them have bulk-rock mg 0.87. Two (15445 A and 67435 PST) contain Fo(92) olivine. Production of melts that crystallized Fo(92) olivine implies that the mg ratios of source regions in lunar mantle were commensurably high. A quantification of this constraint is developed assuming that the parent melts formed by equilibrium (batch) partial melting. Implications of the model are discussed.

Warren, P. H.↗

NASA NTRS1985

Relationships between chondritic meteorites and planets

Chondrites formed in the solar nebula prior to the formation of planets; they probably constituted the bulk of preplanetary solids in the inner solar system. In the highly reduced enstatite chondrites 10% of Si is metallic; in the highly oxidized CM and CI chondrites 20-30% of Fe is in the +3 state. The high density of Mercury implies that nebular Fe was reduced, whereas the low density of Mars indicates that a large fraction was oxidized. Most rare gases in the terrestrial planets seem to have accreted trapped in grains; Venusian interelement ratios resemble those in enstatite chondrites; Earth and Mars ratios are more like those in ordinary or carbonaceous chondrites. These observations imply that enstatite chondrites formed near the Sun (near Venus?), the carbonaceous chondrites formed far from the Sun, the ordinary chondrites at an intermediate location. Compositional data on Mercury, comets, an asteroidal fragment, and the moons of Mars are badly needed.

Wasson, J. T.↗