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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

The Apollo passive seismic experiment

The completed data set obtained from the 4-station Apollo seismic network includes signals from approximately 11,800 events of various types. Four data sets for use by other investigators, through the NSSDC, are in preparation. Some refinement of the lunar model based on seismic data can be expected, but its gross features remain as presented two years ago. The existence of a small, molten core remains dependent upon the analysis of signals from a single, far-side impact. Analysis of secondary arrivals from other sources may eventually resolve this issue, as well as continued refinement of the magnetic field measurements. Evidence of considerable lateral heterogeneity within the moon continues to build. The mystery of the much meteoroid flux estimate derived from lunar seismic measurements, as compared with earth-based estimates, remains; although, significant correlations between terrestrial and lunar observations are beginning to emerge.

Latham, G. V.↗
NASA NTRS1979

Crustal evolution of the early earth: The role of major impacts

The role of major impact basins (such as those which formed on the moon before 4 billion years ago) is examined to determine the effects of such impacts on the early crustal evolution of the earth. Specifically addressed is the fundamental problem of what is the origin of the earth's fundamental crustal dichotomy of low density continental and high density oceanic crust and its relationship to the superficially similar highlands/maria crustal dichotomies of the moon, Mercury and Mars.

Frey, H.↗
NASA NTRS1979

Silicon web process development

Silicon dendritic web, a single crystal ribbon shaped during growth by crystallographic forces and surface tension (rather than dies), is a highly promising base material for efficient low cost solar cells. The form of the product smooth, flexible strips 100 to 200 microns thick, conserves expensive silicon and facilitates automation of crystal growth and the subsequent manufacturing of solar cells. These characteristics, coupled with the highest demonstrated ribbon solar cell efficiency-15.5%-make silicon web a leading candidate to achieve, or better, the 1986 Low Cost Solar Array (LSA) Project cost objective of 50 cents per peak watt of photovoltaic output power. The main objective of the Web Program, technology development to significantly increase web output rate, and to show the feasibility for simultaneous melt replenishment and growth, have largely been accomplished. Recently, web output rates of 23.6 sq cm/min, nearly three times the 8 sq cm/min maximum rate of a year ago, were achieved. Webs 4 cm wide or greater were grown on a number of occassions.

Duncan, C. S.↗
NASA NTRS1978

Temporal and spatial variations of the interplanetary dust flux

The heliocentric radial and latitudinal distributions of both small and large meteoritic particles appear to demonstrate that these particles have largely derived from comets in short-period orbits. Asteroids are unlikely to be a major source for the dust. There appears to be a spatial density depletion near the orbit of the earth, indicating significant control by the earth over particles or source bodies that come near it. Although many short-term fluctuations of meteoritic activity are observed, the content of the overall interplanetary meteoritic complex has probably been stable to within a factor of 2 within approximately the last 10,000 yr. This conclusion, together with meteoroid impact-pit and solar-flare track data on lunar rocks, suggests that solar flare activity may have been much higher about 10,000 yr ago than the present average rate.

Zook, H. A.↗
NASA NTRS1979

The Shaw meteorite - History of a chondrite consisting of impact-melted and metamorphic lithologies

Three intermingled lithologies are identified in the Shaw L-group chondrite: a light-colored lithology with a poikilitic texture, consisting of olivine and augite crystals surrounded by larger orthopyroxene grains; a dark-colored lithology containing remnant chondrules and exhibiting a microgranular texture; and a gray lithology which appears to be intermediate between the other two. Contrary to published opinions, the Shaw meteorite contains normal L-group chondrite abundances of metal and troilite, though these phases are irregularly distributed. The lithological analyses suggest that 4.52 Byr ago an impact took place on the L-group chondrite parent object of Shaw.

Taylor, G. J.↗
NASA NTRS1979

The terrestrial cratering record. II - The crater production rate

The terrestrial crater production rate is estimated from a compilation of the locations and ages of proven and probable terrestrial impact craters and compared with that calculated from astronomical observations and for other planets. The estimated size-frequency distribution of craters greater than 20 km in diameter formed during the Phanerozoic, a -2 power law, is similar to the distributions of lunar and Martian craters. The North American and East European cratons are estimated to have cratering rates of craters greater than 20 km of 0.36 x 10 to the -14/sq km yr and 0.33 x 10 to the -14/sq km yr, respectively, in good agreement with previous estimates and observations of Apollo bodies. Comparisons with the lunar rate indicate that the lunar and terrestrial rates overlap if the cratering flux had been constant over the last 3.4 billion years, however if a constant rate was not reached until 3.0 to 2.5 billion years ago, the lunar rate would have been half that of the terrestrial rate.

Grieve, R. A. F.↗
NASA NTRS1978

Lead isotope systematics of mare basalt 75075

Uranium, thorium and isotopic lead data are reported for two bulk samples and separated pyroxene, ilmenite and plagioclase from basalt 75075. In a concordia diagram the whole rock, ilmenite and four pyroxene samples define a chord intersecting the concordia curve at approximately 4.25 and 2.8 AE. Three plagioclase samples plot distinctly off the chord. The crystallization age of 75075 is accurately determined at 3.74 AE by Rb-Sr, Sm-Nd and K-Ar measurements from other laboratories. It is not possible to adjust the isotopic composition of initial lead so as to reconcile the U-Pb data with a crystallization age of 3.74 AE. The data therefore indicate some type of post-crystallization disturbance of the U-Pb system that is not detected by the other systems. The 75075 data are one of the few examples of this type of age pattern found on the moon. If the disturbance was a single event, it probably occurred around 2.8 AE ago, the time indicated by the pyroxene, whole rock and ilmenite data.

Chen, J. H.↗
NASA NTRS1978

The Sm-Nd history of KREEP

Sm-Nd whole rock measurements on a variety of KREEP-rich samples from different landing sites are reported. Despite a variation of Nd and Sm concentrations of almost a factor of 3, the Sm-Nd ratios, as well as the Nd-143/Nd-144 values, show an extremely close grouping. No systematic differences between samples from different landing sites are resolved. These results are taken to be indicative of a moon-wide process having been responsible for the generation of the KREEP source reservoir, 4.36 plus or minus 0.06 AE ago, as estimated from model age calculation.

Lugmair, G. W.↗
NASA NTRS1978

Nitrogen isotope systematics of two Apollo 12 soils

Soils 12023 and 12037 were analyzed for nitrogen by step-wise heating. Helium contents, Ar-40/Ar-36 ratios and spallation N-15 ages were determined in addition to nitrogen contents and isotopic compositions. The results for 12023 show it to be a typical lunar soil similar to many Apollo 16 and 17 soils in its nitrogen content and delta N-15 value, with a complex history. Soil 12037 appears to have had a simple, two-stage surface exposure history; one exposure occurring recently for about 10-20 m.y. and the other between about 3 to 4 b.y. ago. The delta N-15 value of nitrogen implanted in the earlier exposure was -125%. This nitrogen may reside in the minor components of 12037 such as the KREEP. If it should reside in the basaltic component of 12037, however, then the variation in the delta N-15 of implanted nitrogen with time probably has been more complex than previously considered.

Becker, R. H.↗
NASA NTRS1978

Carbon-14 in lunar soil and in meteorites

C-14 was measured in grain-size fractions of lunar soil 10084 and in samples of the Bruderheim chondrite and of several meteorites recently found in Antarctica (Allan Hills no. 5, 6, and 8). Temperature-release patterns were investigated. It was found that C-14 is released at temperatures below melting from small soil grains (less than 74 microns), but not from meteorites or from large soil grains. Below-melting C-14 contents increase with decreasing grain size in a manner similar to solar-wind-implanted rare-gas isotope contents (Eberhardt et al., 1970), whereas the C-14 released above melting temperatures is independent of grain size, suggesting that below-melting C-14 is solar-wind-implanted and above-melting C-14 is the result of cosmic ray spallations. The activity of C-14 in lunar samples is half that measured in the Bruderheim meteorite, which fell on May 4, 1970. No C-14 activity was observed in the Allan Hills chondrites; the C-14 limits suggest that these meteorites fell more than 25,000 years ago.

Fireman, E. L.↗
NASA NTRS1978

Petrology of a sequence of pyroclastic rocks from the valley of Taurus-Littrow /Apollo 17 landing site/

Thirteen samples of core 74001/2, collected at Shorty Crater by Apollo 17, have been analyzed. The samples, taken from the core section below 5.5 cm and representing most of the major stratigraphic units described by Nagle (1978), consist entirely of whole and fragmented orange and black droplets. The grain shape, degree of crystallinity, breakage, vesicularity, predominant olivine shapes, and phenocryst content of about 18,000 droplets were investigated. The crystalline droplets were found to contain olivine and ilmenite as major phases and pyroxene, Cr-spinel and metallic Fe as minor phases. The grain shape, degree of crystallization, olivine shape and olivine composition suggest that a wide range of cooling rates is represented. The upper part of the core section (above 5.5 cm) has undergone in situ reworking by micrometeorites. The 74001/2 samples are believed to be from an ultramafic pyroclastic deposit brought to the surface by the Shorty Crater impact and originally formed by a lava fountain active in the Taurus-Littrow valley 3.5 b.y. ago. The sequence represented in the sample was most likely deposited over a very short period of time.

Heiken, G.↗
NASA NTRS1978

Depositional and irradiational history and noble gas contents of orange-black droplets in the 74002/1 core from Shorty Crater

Isotopic concentrations of noble gases were assessed in grain size separates of 14 soils from a 67-cm section of lunar regolith taken on the rim of Shorty Crater. The orange-black droplets in this section were probably formed from pyroclastic eruptions about 3.6 billion years ago; they give little indication of surface exposure. The isotopic concentrations suggest that cosmic ray irradiation of the core occurred in two stages and that the core stratigraphy was inverted between stages. The first irradiation stage may have taken place immediately after pyroclastic deposition of the droplets and could have lasted about 20 million years.

Bogard, D. D.↗
NASA NTRS1978

Is there any record of meteorite impact in the Archean rocks of North America

Current speculations on the early impact history of the earth between 4.5 and 3.0 billion years ago range from simple analogies between mare basalts and Archean terrestrial greenstones to casual dismissal. The latter is based on the view that the high rate of convection in the Archean would have obliterated the effects of impact via plate tectonic processes. In the present paper it is suggested that the impact process may have been the prime control on localizing the convection process. The Superior Province and basin-in-basin structure within it may be a record of such localized convection.

Weiblen, P. W.↗
NASA NTRS1978

Age of graben systems on the moon

The study focuses on the time of formation of the graben. An attempt is made to determine whether the graben are restricted to geologic units of certain ages, and whether and at what time graben formation ceased. It is shown that (1) most preserved graben formed considerably later than the impacts that formed the basins; (2) graben are faults that are reactivated along older basin concentric and radial structures and lunar grid directions; (3) graben formation ceased about 3.6 + or - 0.2 b.y. ago; and (4) graben formation reflects a tensile stress fields that obtained during part of early lunar history. Other features of graben systems on the moon are also identified.

Lucchitta, B. K.↗
NASA NTRS1979

How tidal heating in Io drives the Galilean orbital resonance locks

The mechanisms by which orbital resonance locks are maintained among Io, Europa and Ganymede are analyzed, and the effects of the dissipative tides in Jupiter and Io on their establishment and evolution are considered. According to the proposed model, initially all three satellites are in orbits far from the 2:1 commensurabilities or the three body lock. The tide raised on Io damps down the free eccentricity; only modest tidal heating occurs. Subsequently the dissipative tide raised on Jupiter by Io causes Io's orbit to spiral outwards; Io approaches the 2:1 commensurability with Europa. Io's forced eccentricity increases rapidly to a critical value, and thereafter the resonant interaction causes Europa's orbit to expand at half that of Io's orbit. A fluid core is probably formed as the result of tidal heating. Finally Europa approaches the 2:1 commensurability, angular momentum is transferred from Europa's orbit to Ganymede's, and a steady state is attained. On the basis of the observed three-body resonance amplitude (0.066 deg), it is concluded that three-body resonance may have formed less than 500 million years ago; a measurement of the rate of tidal heating in Io may determine the Q value of both Io and Jupiter. Upper and lower limits for the Jovian Q value of 2 million and 20,000 are suggested.

Yoder, C. F.↗
NASA NTRS1979

Comment on the mechanism of operation of the impregnated tungsten cathode

Recent life-test measurements, over 20,000-30,000 h, on impregnated tungsten cathodes in tubes employing an open-type electron-gun structure, show emission current degradation with time. This is in contrast to those recently published by Rittner on B-type cathodes, run in close-spaced diodes, taken some years ago. These more recent life-test results are consistent with the model suggested by Forman and disputed by Rittner that the barium coverage on an impregnated cathode is less than a monolayer for most of its life and decreases with time.

Forman, R.↗
NASA NTRS1979

Sulfur volcanoes on Io

Widespread volcanism on Jupiter's satellite Io, if it occurred over the age of the solar system, would quickly reduce the inventory of most common volatiles needed to drive such volcanism. One exception is the volatile element sulfur. It is therefore postulated that sulfur is the driving volatile for Ionian volcanism. Its presence is consistent with a carbonaceous-chondrite-like bulk composition for the original material that formed Io 4.5 billion years ago. The ubiquity of sulfur on Io today demonstrates the importance of this element in the processes that formed its surface.

Consolmagno, G. J.↗