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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

A comparative Rb-Sr, Sm-Nd, and K-Ar study of shocked norite 78236 - Evidence of slow cooling in the lunar crust

The sample 78236 was chipped from the top of a norite boulder at Station 8 by the Apollo 17 landing team. Jackson et al. (1975) concluded that this rock formed at a depth of 8-30 km in the lunar crust and suggested that it was excavated by a large basin-forming impact event. A petrographic description of the boulder is provided, and isotopic analyses are discussed. Attention is given to a chronology for 78236 which seems to be most consistent with radiometric and other evidence. It is proposed that cumulate norite 78236 formed deep in the lunar crust approximately 4.4 AE ago. The rock cooled slowly in the crust until it was excavated by a major basin-forming event. Excavation may have occurred about 4.2 AE ago, but the time of this event is not well constrained.

Nyquist, L. E.↗
NASA NTRS1982

Age and provenance of the target materials for tektites and possible impactites as inferred from Sm-Nd and Rb-Sr systematics

Chemical, trace element, and isotopic compositions of tektites are consistent with production by melting of sediments derived from the old terrestrial continental crust. Each tektite group is characterized by a uniform Nd model age, interpreted as the time of formation of the crustal segment which weathered to form the parent sediment for the tektites. Sr model ages are variable within each group, reflecting Rb-Sr fractionation, and, in the favorable limit of very high Rb/Sr ratios, approach the time of sedimentation of the parent material which melted to form the tektites. Unlike tektites, which are dense homogeneous objects, sanidine spherules are porous, fine grained inhomogeneous objects. The leaching experiment employed by the present study shows that the sanidine spherules could have been formed by an oceanic impact involving basaltic crust and overlying sediments or seawater.

Shaw, H. F.↗
NASA NTRS1983

Al-Sm-Eu-Sr systematics of eucrites and moon rocks Implications for planetary bulk compositions

Constraints are placed on the bulk compositions of the eucrite parent body (EPB) and the moon through analysis of the Eu and Sr 'anomalies' of eucrites and lunar rooks. It is noted that the elements Al, REE, and Sr are incompatible with the major minerals of these small, low-f(O2) bodies,except for plagioclase. Predictions can be derived about the concentrations of Al, REE, and Sr in samples affected by plagioclase fractionation, based on the hypothesis that these elements in the EPB and moon are all in proportions close to those in the bulk solar system. It is determined that the predictions are almost idealy fulfilled by eucrites and lunar samples. For the EPB, the ratios REE/Al, Sr/Al, and Sr/REE are found to be constrained probably within 10 percent of the chondritic ratios. For the moon, the constraints are found to be less precise: REE/Al is very probably within 25 percent of chondritic; Sr/Al and Sr/REE are probably within 35 percent of chondritic; Sr/Al and Sr/REE are probably within 35 percent of chondritic. It is concluded that there is a very strong similarity between the bulk compositions of the planets and the compositions of chondritic meteorites.

Warren, P. H.↗
NASA NTRS1986

Significance of the Sm-Nd isotopic systematics of the Akilia Association

Samarium-Neodymium analyses were carried out on fourteen samples of basic to ultrabasic metavolcanics from several enclaves of the Amitsoq gneisses (T = to or approximately 3,700 Ma). Field observations suggest that all the analyzed rocks belong to the pre-Amitsoq Akilia Association. Consequently, a minimum age of 3,700 Ma is postulated for the emplacement of their protoliths. When all the data points are put together in a conventional isochron diagram, no clear isochron relationship can be discerned. However, the points seem to fall within a band broadly corresponding to an age of 3,600 Ma. The isotopic results are difficult to interpret satisfactorily. Two contrasting interpretations are offered and summarized: (1) data scatter as a result of open system behavior; and (2) data scatter due to a melange of data sets defining two distinct isochrons.

Gruau, G.↗
NASA NTRS1986

Duty cycle testing and performance evaluation of the SM-229 teleoperator

The first known experimental studies and analyses of teleoperator performance for specific duty cycles are discussed. The results are presented in two distinct areas as position usage patterns, and as three-dimensional power grids. The position usage patterns are a valuable means to assess the available motion range. The power grids are a unique concept for evaluating joint performance. Final conclusions contain recommendations to upgrade the teleoperator for optimum performance.

Stoughton, Robert S.↗
NASA NTRS1991

Reflectance spectra of some fractions of Migei and Murchison SM chondrites in the range of 0.3-2.6 microns

The reddening observed in CM chondrites is not understood. Johnson and Fanale observed that, as CM chondrites are more finely powdered, their spectra become more reddened. In the process of meteorite crushing, the chondrules are broken up. Those authors suggested that in this case the silicate components of the chondrules (mainly olivine), which have higher IR reflectivities, were able to contribute more to the overall spectrum. Gaffey and McCord proposed two possible physical mechanisms which could produce such an effect. But it is also possible that the presence of the organic polymers in the matrix material results in the reddening of the CM spectra. To test these two hypotheses, the matrix material and the material enriched in olivines were separated from Migei and Murchison CM chondrites using a binocular microscope. The spectra of these fractions were compared with the spectra of the bulk samples of Migei and Murchison. The spectra of the most 'clean' Migei matrix fractions indicate that the reddish slopes of CM spectral curves in the near infrared are due to the enhanced olivine feature, rather than to organic matter. The authors propose that the red slope of the spectra of some C-type asteroids may indirectly suggest the presence of olivine in the surface material. At the same time, the red sloped spectra of more distant D-type asteroids seem to be due to the presence of organic materials. If so, then the chemical or physical form of this organic matter must be quite different from the organic materials which would be on the surfaces of the parent bodies of CM chondrites (most likely C-type asteroids). It is also possible that the content of organic components in the CM matrix is too low to change the slope of the spectra.

Moroz, L. V.↗
NASA NTRS1991

The RadioSat (sm) network

The RadioSat network under development by radio Satellite Corporation will use mobile satellite (MSAT) technology to provide diverse personal communications, broadcast, and navigation services. The network will support these services simultaneously for integrated mobile radios throughout Canada and the United States. The RadioSat network takes advantage of several technological breakthroughs, all coming to fruition by the time the first MSAT satellite is launched in 1994. The most important of these breakthroughs is the enormous radiated power of each MSAT spacecraft - orders of magnitude greater than the radiated power of previous L-band spacecraft. Another important breakthrough is the development of advanced digital audio compression algorithms, enabling the transmission of broadcast quality music at moderate data rates. Finally, continuing dramatic increases in VLSI capabilities permit the production of complex, multi-function mobile satellite radios in very large quantities at prices little more than those of conventional car radios. In addition to performance breakthroughs and their economic implications to RadioSat, the design of the RadioSat network is reviewed.

Noreen, Gary K.↗
NASA NTRS2004

Rb-Sr and Sm-Nd Isotope Systematics of Shergottite NWA 856: Crystallization Age and Implications for Alteration of Hot Desert SNC Meteorites

Nakhlite NWA 998 was discovered in Algeria in 2001, and is unique among the six known members of this group of Martian meteorites in containing significant modal orthopyroxene. Initial petrologic and isotopic data were reported by Irving et al. This 456 gram stone consists mainly of sub-calcic augite with subordinate olivine and minor orthopyroxene, titanomagnetite, pyrrhotite, chlorapatite, and intercumulus An(sub 35) plagioclase. We report here preliminary results of radiogenic isotopic analyses conducted on fragmental material from the main mass.

Brandon, A. D.↗
NASA NTRS2006

Sm-Nd Age and Nd- and Sr- Isotopic Evidence for the Petrogenesis of Dhofar 378

Dhofar 378 (hereafter Dho 378) is one of the most ferroan lithologies among martian meteorites, resembling the Los Angeles basaltic shergottite in lithology and mineral chemistry, although it is more highly shocked than Los Angeles. All plagioclase (Pl) grains in the original lithology were melted by an intense shock in the range 55-75 GPa. Clinopyroxenes (Cpx) sometimes show mosaic extinction under a microscope showing that they, too, experienced intense shock. Nevertheless, they zone from magnesian cores to ferroan rims, reflecting the original lithology. Cpx grains also often contain exsolution lamellae, showing that the original lithology cooled slowly enough for the lamellae to form. Because all plagioclase grains were melted by the intense shock and subsequently quenched, the main plagioclase component is glass (Pl-glass) rather than maskelynite. Like Los Angeles, but unlike most basaltic shergottites, Dho 378 contains approximately equal modal abundances of Cpx and Pl-glass. The grain sizes of the original minerals were comparatively large (approximately 1 mm). The original plagioclase zoning has been severely modified. Following shock melting, the plagioclase melts crystallized from the outside inward, first forming outer rims of Cpx-Pl intergrowths (approximately 10 micrometers) followed by inner rims (10's to 100 micrometers) of An(sub 40-50) feldspar, and finally Pl-gl cores of compositions An(sub 33-50) with orthoclase compositions up to Or(sub 12).

Nyquist, L. E.↗