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At least 883 records · Page 49

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NASA NTRS1975

Exposure histories of Bench Crater rocks

A description is presented of the results of mass spectrometric analyses of the noble gases krypton and xenon, in eight Apollo 12 basaltic rocks. The significance of the results is evaluated. It is concluded that the Bench Crater rocks are not what they appear to be in their field relationships. They are not fragments ejected from bedrock by the Bench impact. Most, if not all, have had a previous history of regolith residence prior to the Bench impact. In retrospect, sampling of fresh ejecta from lunar craters during the Apollo missions turned out to be surprisingly difficult. Sampling was successful for Cone and North Ray craters where large boulders were available, but fresh South Ray ejecta was surprisingly elusive. The reported investigation shows that fresh ejecta was not obtained from Bench, and moreover, that the concept of 'radial sampling', in which the rocks sampled from a crater rim are supposed to represent the deepest material excavated, fails very badly for Bench.

Burnett, D. S.↗

NASA NTRS1975

The simulated depth history of dust grains in the lunar regolith

Trajectories giving the individual depth variations of lunar dust grains with time are randomly generated by a Monte Carlo code, where the variables are the mass and speed distribution of meteorites at the lunar surface and the geometrical shape of impact craters. A statistical analysis of a great number of such trajectories is then used to define the 'average' depth history of lunar dust grains for two grain radii: 1 and 50 microns. This yields: (1) estimates for time constants involved during the dynamic evolution of the regolith, (2) a model for the layering of the regolith, and (3) a better understanding of the basic dust-grain mechanisms responsible for the formation of the most mature lunar soil samples. The validity of various soil models proposed for the dynamic evolution of the regolith is discussed in terms of experimental constraints on the models.

Duraud, J. P.↗

NASA NTRS1979

Time history solution program, L225 (TEV126). Volume 1: Engineering and usage

Volume 1 of a two volume document is presented. The usage of the convolution program L225 (TEV 126) is described. The program calculates the time response of a linear system by convoluting the impulsive response function with the time-dependent excitation function. The convolution is performed as a multiplication in the frequency domain. Fast Fourier transform techniques are used to transform the product back into the time domain to obtain response time histories. A brief description of the analysis used is presented.

Kroll, R. I.↗

NASA NTRS1978

Thermal history of the Abee enstatite chondrite

Constraints are reported on the thermal history of the constituents of the Abee enstatite chondrite. From thermal experiments on laboratory-prepared alloys, and on actual samples of the meteorite, it is concluded that the metal phase of Abee cooled from above 700 C to room temperature in less than ten hours.

Herndon, J. M.↗

NASA NTRS1978

Regional stratigraphy and geologic history of Mare Crisium

Remote sensing and Luna 24 sample data are used to develop a summary of the regional stratigraphy and geologic history of Mare Crisium. Laboratory spectra of Luna 24 samples, telescopic reflectance spectra in the 0.3 to 1.1 micron range and orbital X-ray data have identified three major basalt groups in the region. Group I soil is derived from iron- and magnesium-rich titaniferous basalts and was apparently emplaced over the majority of the basin, however is presently exposed as a shelf in the southwest part. Group II soils, derived from very low titanium ferrobasalts, were emplaced in two stages subsequent to Group I emplacement and now appear as part of the outer shelf and topographic annulus. Subsidence of the basin interior preceded and continued after the emplacement of the third basalt group, a soil derived from a low titanium ferrobasalt. The Luna 24 site is found to be within a patch of Group II material.

Head, J. W., III↗

NASA NTRS1978

Lunar surface processes and cosmic ray histories over the past several million years

Measurements of the Al-26 and Mn-53 in interior portions of lunar rocks have shown that lunar surface processes which move a significant fraction of kilogram size rocks on the lunar surface occur on time scales of a few million years. These measurements, together with noble gas age dating have made it possible to define the history for nine rock samples selected from whole rock counting data because of anomalously low Al-26 relative to Na-22. Six of the rocks from the Apollo 15 and 16 missions showed evidence of movement during the past five million years. Of these six, only two are of an age consistent with their origin from the South Ray Crater Event. In addition, our measurements of Na-22 and Al-26 in Apollo 17 double drive tube 74001-74002 suggest that one to two cm of soil is missing from the top of this core tube. Even with this loss, at least two cm of gardening is indicated in the top portion of 74002.

Fruchter, J. S.↗

NASA NTRS1978

Depositional and surface exposure history of the Shorty Crater core 74001/2 - FMR and magnetic studies

Surface exposure (maturity) indices and concentrations of FeO and metallic iron were determined at 0.5-cm intervals of the Apollo 17 core section, which sampled a pyroclastic deposit on the rim of Shorty Crater. The determinations showed that all of the soil in the core is extremely immature. An exposure history of the core is proposed: accumulation (about 3.6 billion years ago), shallow burial (during the first 20 million years), deep burial (till about 10-15 million years ago), followed by excavation (10-15 million years ago), and in situ reworking (till the present).

Morris, R. V.↗

NASA NTRS1978

Lunar KREEP volcanism - Geologic evidence for history and mode of emplacement

The history of KREEP basalt emplacement in the Fra Mauro and Imbrium basin regions was investigated on the basis of the petrologic and geochemical characteristics of Apollo 14 and 15 samples and data from photogeologic, site geology and remote sensing studies. Results suggest that KREEP emplacement began after the excavation of the South Imbrium basin more than 4.0 to 4.1 billion years ago, continued into early to mid-Imbrium, and was in part sychronous with mare volcanism. Surface KREEP activity appears to be concentrated in a triangular area bounded by the Apollo 15 site, southern Procellarum and the Aristarchus region. Most of the Apollo 15 igneous KREEP basalts are products of post-Imbrium KREEP volcanism within the Imbrium basis, whereas the Apollo 14 KREEP-rich breccias represent extensively reworked KREEP volcanics extruded prior to about 4.0 to 4.1 billion years ago.

Hawke, B. R.↗

NASA NTRS1979

Formation, history and energetics of cores in the terrestrial planets

The size, evolution and energetics of the earth's core and the probable central, metalic cores of Mercury, Venus, the moon and Mars are discussed. The cores of Mercury, Mars and the earth are considered likely to decrease in relative mass and volume with distance from the sun; the moon does not fit this sequence and data from Venus are insufficient. Core formation is concluded to have occurred early (prior to four billion years ago) on the earth and Mercury, while that on the moon would have occurred over a longer interval and the core of Mars would have formed much later. Of the possible energy sources in planetary cores able to maintain a molten state and drive magnetic dynamos, the energy of core formation was probably spent too early in planetary history to provide much present power, and the energy gained from freezing an inner core in the earth and Mercury are considered at best marginally able to match conductive heat loss. Future measurements proposed to improve the quantitative understanding of core properties include a better documentation of the magnetic fields of Venus and Mars and the seismometry of Mars.

Solomon, S. C.↗

NASA NTRS1979

Comet Halley and history

A history of Halley's Comet is presented. Comets Kohoutek and Ikeya-Seki are discussed.

Marsden, B. G.↗

NASA NTRS1979

A history of Mars atmospheric opacity in the southern hemisphere during the Viking extended mission

A history of developing opacity in the Mars southern hemisphere during the Viking extended mission has been compiled using orbiter images obtained at high altitude. Observations of changing contrasts under similar viewing conditions have been modeled by multiple-scattering intensity transfer equations that have produced a temporal description of changes in optical depth and particle-scattering properties within a network of control points. The results are presented in the form of Mercator and perspective plots for various dates.

Thorpe, T. E.↗

NASA NTRS1979

Consortium breccia 73255 - Genesis and history of two coarse-grained 'norite' clasts

A study of two clasts of coarse-grained anorthositic-noritic-troctolitic-suite norites from the fragment-laden melt rock 73255 is presented. Both clasts are igneous rocks crystallized from melts that were probably internally generated; clast 27,80 is a cumulate, and the parent magmas of both rocks probably crystallized below the lunar surface. Despite similar history, the parent rocks of the two clasts appear to be derived from distinct magma types: the 27,80 is characterized by plagioclase and orthopyroxene as the major constituents and by a high K, Nb, and Zr content, while the 27,45 type also contains augite and has a low content of K, Nb, and Zr.

James, O. B.↗

NASA NTRS1979

Characterization and depositional and evolutionary history of the Apollo 17 deep drill core

With a depth resolution of about 0.5 cm, the stratigraphy of the approximately 3 m Apollo 17 deep drill core by measurement of the total FeO concentration is characterized along with the FMR surface exposure (maturity) index Is/FeO, the metallic iron concentration Fe-vsm, and the FMR linewidth delta-H. For stratigraphic characterization, the first two parameters are the most important. Most of the core is characterized by a FeO concentration of approximately 15.5 wt. %; there is a more mafic zone in the upper approximately 75 cm where the maximum FeO concentration is approximately 18.5 wt. %, and a more felsic zone between approximately 225 and 260 cm where the minimum FeO concentration is approximately 14.0%. As indicated by Is/FeO, most of the soil in the core is submature to mature; the only immature zone is located between approximately 20 and 60 cm and is one of the most distinctive features in the core. A two stage model for the depositional and evolutionary history of the Apollo 17 deep drill core is proposed: (1) deposition by one event approximately 110 m.y. ago or deposition by a sequence of closely spaced events initating a maximum of approximately 200 m.y. ago and terminating approximately 110 m.y. ago, (2) in situ reworking (gardening) to a depth of approximately 26 cm in the period between approximately 110 m.y. ago and the present day.

Morris, R. V.↗

NASA NTRS1979

Stratigraphy and depositional history of the Apollo 17 drill core

Lithologic abundances obtained from modal analyses of a continuous string of polished thin sections indicate that the Apollo 17 deep drill core can be divided into three main zones: An upper zone (0-19 cm depth) characterized by high abundances of agglutinates (30%) and a high ratio of mare to non-mare lithic fragments (less than 0.8); a coarse-grained layer (24-56 cm) rich in fragments of high-Ti mare basalts and mineral fragments derived from them, and poor in agglutinates (6%); and a lower zone (56-285 cm) characterized by variable but generally high agglutinate abundances (25%) and a low ratio of mare to nonmare lithic fragments (0.6). Using observations of the geology of the landing site, the principles of cratering dynamics, and the vast amount of data collected on the core, the following depositional history for the section of regolith sampled by the Apollo 17 drill core: was devised.

Taylor, G. J.↗

NASA NTRS1979

History of the Apollo 17 deep drill string during the past few million years

Measurements of the cosmogenic radionuclides 22-Na, 26-Al and 53-Mn in the Apollo 17 deep drill string 70002-70009 have shown that this core sample was taken in an area of considerable recent surface activity. Measurements of 22-Na indicate that the core had not been significantly altered during its collection and subsequent handling, while measurements of the 26-Al and 53-Mn showed a very substantial excess in these isotopes in the top 25 cm and a depletion below about 50 cm. The analysis of the data indicates that a crater excavation occurred to a depth of 50 to 60 cm at the site of the deep drill string no longer that 0.5 m.y. ago, and probably 0.3 m.y. ago. Since that time, the crater has filled to a depth of about 25 cm with near-surface material which contains high concentrations of 26-Al and 53-Mn. This recent activity at the site of the Apollo 17 drill string places firm time constraints on the models developed by other investigators which describe the history of this site.

Fruchter, J. S.↗

NASA NTRS1979

Impact melting early in lunar history

The total amount of impact melt produced during early lunar history is examined in light of theoretically and experimentally determined relations between crater diameter (D) and impact melt volume. The time dependence of the melt production is given by the time dependent impact rate as derived from cratering statistics for two different crater-size classes. Results show that small scale cratering (D less than or equal to 30 km) leads to melt volumes which fit selected observations specifying the amount of impact melt contained in the lunar regolith and in craters with diameters less than 10 km. Larger craters (D greater than 30 km) are capable of forming the abundant impact melt breccias found on the lunar surface. The group of large craters (D greater than 30 km) produces nearly 10 times as much impact melt as all the smaller craters, and thus, the large impacts dominate the modification of the lunar surface. A contradiction between the distribution of radiometric rock ages and a model of exponentially decreasing cratering rate going back to 4.5 b.y. is reflected in uncertainty in the distribution of impact melt as a function of time on the moon.

Lange, M. A.↗

NASA NTRS1980

Tangential mode combustion instability of solid propellant rocket motors. 2: Pressure, frequency, and burning rate histories

The relationships among excursions of mean chamber pressure, high frequency pressure oscillations and accelerations associated with tangential mode combustion instability are considered. A data reduction procedure was devised to utilize the precise pressure time data as input to a numerical solution of the chamber mass balance relationships. The results indicate that both elevated burning rate induced by the tangential wave motions and variable nozzle blockage due to passage of vortical flow through the nozzle throat must act together to generate the large mean pressure peaks observed in the tests. There is strong correlation between the amplitude of wave motions and the level of mean pressure rise. Evidence for the presence of traveling tangential waves at the time of the D.C. shift was found by use of dual Kistler pressure transducers mounted at the head end of the burner. A very unusual frequency history was found to accompany the high amplitude disturbances. This was consistent from test to test and may represent an additional source of information regarding the complicated flow combustion interactions within the propellant burning zone.

Flandro, G. A.↗

NASA NTRS1980

The History of the Development of the Rectenna

The history of the development of the rectenna is reviewed through its early conceptual developmental phases. Some selective aspects of the current solar power satellite rectenna development are examined.

Brown, W. C.↗