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At least 163 records · Page 9
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NASA NTRSDate not supplied

Lunar Surface Crater Thermal Effects on Lander Radiator Performance

Lunar surface craters smaller than the spatial resolution of surface meshes used in typical Lunar surface thermal models (10 to 60 meters per pixel) may impact the accuracy of thermal model extrema predictions. The goal of this study is to investigate the thermal sensitivity of representative lander systems with realistic thermal surface orientations in bare and cratered terrain environments at relevant Artemis mission locations. This thermal analysis task investigates the impact of lunar surface craters on lander radiator performance by comparing heat rejection capability results between bare and cratered terrain environments. This study examines external body-mounted lander radiator thermal performance across varying lander heights (5.5m, 20m, 50m) and radiator orientations (horizontal, 45º tilted, and vertical) at two representative Artemis mission latitudes (-89.5ºS and -82.5ºS), spanning from the Shackleton Connecting Ridge to Mons Mouton Plateau.

Lunar Surface↗
NASA NTRS1972

Artificial lunar impact craters: Four new identifications, part I

The Apollo 16 panoramic camera photographed the impact locations of the Ranger 7 and 9 spacecraft and the S-4B stage of the Apollo 14 Saturn launch vehicle. Identification of the Ranger craters was very simple because each photographed its target point before impact. Identification of the S-4B impact crater proved to be a simple matter because the impact location, as derived from earth-based tracking, displayed a prominent and unique system of mixed light and dark rays. By using the criterion of a dark ray pattern, a reexamination of the Apollo 14 500 mm Hasselblad sequence taken of the Apollo 13 S-4B impact area was made. This examination quickly led to the discovery of the ray system and the impact crater. The study of artificial lunar impact craters, ejecta blankets, and ray systems provides the long-needed link between the various experimental terrestrial impact and explosion craters, and the naturally occurring impact craters on the moon. This elementary study shows that lunar impact crater diameters are closely predictable from a knowledge of the energies involved, at least in the size range considered, and suggests that parameters, such as velocity, may have a profound effect on crater morphology and ejecta blanket albedo.

Whitaker, E. A.↗
NASA NTRS2013

Lunar Simple Crater Impact Melt Volumes

Impact melt is observed in simple lunar craters having diameters as small as less than 200 m. The presence of ponds of impact melt on the floor of such small craters is interpreted to indicate vertical impacts. Data from the LRO LROC and LOLA experiments allow quantitative estimates of the volume of impact melt in simple crater. Such estimates allow for validation of theoretical models of impact melt generation and examination of target effects. Preliminary data have considerable scatter but are broadly consistent with the models.

Plescia, Jeffrey B.↗
NASA NTRS1986

Lunar and Venusian radar bright rings

Twenty-one lunar craters have radar bright ring appearances which are analogous to eleven complete ring features in the earth-based 12.5 cm observations of Venus. Radar ring diameters and widths for the lunar and Venusian features overlap for sizes from 45 to 100 km. Radar bright areas for the lunar craters are associated with the slopes of the inner and outer rim walls, while level crater floors and level ejecta fields beyond the raised portion of the rim have average radar backscatter. It is proposed that the radar bright areas of the Venusian rings are also associated with the slopes on the rims of craters. The lunar craters have evolved to radar bright rings via mass wasting of crater rim walls and via post-impact flooding of crater floors. Aeolian deposits of fine-grained material on Venusian crater floors may produce radar scattering effects similar to lunar crater floor flooding. These Venusian aeolian deposits may preferentially cover blocky crater floors producing a radar bright ring appearance. It is proposed that the Venusian features with complete bright ring appearances and sizes less than 100 km are impact craters. They have the same sizes as lunar craters and could have evolved to radar bright rings via analogous surface processes.

Thompson, T. W.↗
NASA NTRS1974

Laboratory simulation of the herringbone pattern associated with lunar secondary crater chains

V-shaped ridge components of the herringbone pattern associated with lunar secondary crater chains have been simulated by simultaneous and nearly simultaneous impact of two projectiles near one another. The impact velocities and angles of the projectiles were similar to those of the fragments that produced secondary craters found at various ranges from large lunar craters. Variables found to affect the included angles of the V-shaped ridges are: relative time of impact of the projectiles, impact angle, relative projectile mass, and azimuth angle of the crater chain relative to the projection of the flight line onto the target surface. The functional relationships between the forms of the ridges and many of these variables are similar to those observed for lunar V-shaped ridges. Comparison of the magnitudes of the ridge angles of both laboratory crater pairs and secondary crater chains of the crater Copernicus implies that material was ejected from Copernicus at angles in excess of 60 deg, measured from the normal, to form many of Copernicus' satellite craters.

Oberbeck, V. R.↗
NASA NTRS1979

The role of rim slumping in the modification of lunar impact craters

The role of rim slumping in the formation of terraces on interior crater walls and consequent modifications of the shapes of large lunar impact craters is evaluated. Impact excavation cavities were reconstructed by means of a terrace restoration model for twelve lunar craters ranging in diameter from 19 to 137 km. For craters up to 30 km, reconstructed cavity depths are comparable to or greater than cavity depths extrapolated from nonterraced smaller craters, and in the 30 to 70 km diameter range, the reconstructed cavity depths are significantly greater. For craters larger than 70 km, however, the reconstructed cavity depths are consistently less than those predicted from small crater morphometry, indicating a significant additional contribution from ejecta fallback and basement rebound to the modification of the shape of impact craters greater than 70 km.

Settle, M.↗
NASA NTRS1972

Lunar secondary craters, part K

Formation of V-shaped structures surrounding the fresh Copernicus Crater and its secondary craters are reviewed, and preliminary observations of the more extensively eroded secondary crater field of Theophilus are presented. Results of laboratory simulation of secondary lunar craters to examine their effects on V-shaped ridges are also described.

Overbeck, V. R.↗
NASA NTRS1978

A composition and thickness model for lunar impact crater and basin deposits

A model was developed for determining the composition and thicknesses of continuous deposits of large lunar impact craters and basins. Results of a photogeologic study and topographic analysis of continuous deposits of the lunar crater Delisle, which support the model, show that numerous secondary craters and crater chains with concentric dunes on their uprange rims occur well within the mapped deposits. At any given radius from Delisle, the secondary craters are of equal freshness and not vastly different in size, but with increasing radius they become better defined. The upper surface of the continuous deposits reaches the level of the pre-existing mare surface well within the mapped boundary of the deposits.

Morrison, R. H.↗
NASA NTRS1979

Geology of the lunar farside crater Necho

The ejecta morphology and distribution as well as the interior materials of the 30-km-diameter, Necho lunar crater is discussed and the effects of regional preimpact topography on the formation structure and modification of the crater are described. Three types of ejecta: hummocky, lineated, and smooth, that are concentrated in a band extending from the rim crest to a distance of less than one crater diameter are examined. The crater's interior, divided into floor units of textured, bubbled, and smooth material is analyzed and hypotheses of their origin are presented. The last area of study is the preimpact setting, characterized by a series of large, degraded, pre-Nectarian craters. Results showed that the Necho, in comparison with surrounding craters, was the freshest, insuring that the data from its excavation was preserved without a significant amount of degradation.

Gifford, A. W.↗
NASA NTRS1993

Twenty-fourth Lunar and Planetary Science Conference. Part 1: A-F

The topics covered include the following: petrology, petrography, meteoritic composition, planetary geology, atmospheric composition, astronomical spectroscopy, lunar geology, Mars (planet), Mars composition, Mars surface, volcanology, Mars volcanoes, Mars craters, lunar craters, mineralogy, mineral deposits, lithology, asteroids, impact melts, planetary composition, planetary atmospheres, planetary mapping, cosmic dust, photogeology, stratigraphy, lunar craters, lunar exploration, space exploration, geochronology, tectonics, atmospheric chemistry, astronomical models, and geochemistry.

Source record↗
NASA NTRS1977

Topographic analysis of lunar secondary craters of Copernicus and implications

An analysis is conducted of the topography of lunar secondary craters and the associated herringbone pattern observed on lunar topophotomaps. The topography and the patterns are compared with those of crater pairs produced in the laboratory. The results are used to identify secondaries on the lunar uplands. The chain of craters that was selected for mapping and which is described is known to be a secondary impact crater chain produced by material ejected from Copernicus Crater because it lies on a well-developed ray system of Copernicus. Oberbeck et al. (1977) had hypothesized that most lunar areas exhibit more craters smaller than 50 km than are observed on Mars and Mercury because lower lunar gravity permitted more widespread distribution of secondaries for the moon. After removal of basin secondaries it is found that the surfaces of the lunar uplands are only sparsely populated by craters between 5 and 50 km. The lunar uplands appear then similar to the Mercurian terrain.

Oberbeck, V. R.↗
NASA NTRS1980

Small impact craters in the lunar regolith - Their morphologies, relative ages, and rates of formation

The size frequency distributions, relative ages, and absolute age determination of lunar impact craters ranging in diameter from 1 to 100 m are discussed in relation to present-day and past impact rates. The size frequency distributions of craters produced by impacts on the lunar surface and of craters remaining after degradation with time and later impacts are examined, together with the steady state frequency curves for various crater morphologies. Relations between the relative ages of craters, their morphologies and their diameters are discussed, and the calibration of this kind of relationship with absolute crater ages by the location of individual craters with known absolute ages, diameters and frequency distribution statistics is considered. Estimates of present and past cratering rates based on crater size-frequency distributions are presented which suggest that the rate of impacting objects producing small lunar craters could have been constant over the last 100 million years.

Moore, H. J.↗