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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1970

Geology - Craters

Lunar crater size and shape characteristics from Surveyor missions, discussing rimless shallow and cup shaped craters

Morris, E. C.↗
NASA NTRS1993

The size of complex craters

Lunar craters larger than about 15 km and terrestrial craters larger than about 3 km in diameter presumably underwent gravity-driven, 'late-stage' collapse that modified an initial transient bowl-shaped 'simple' crater into the flat-floored complex craters observed. These same mechanisms were operative for the larger craters on other solar system bodies, at a threshold size inversely proportional to gravity. This paper presents a new look at the scaling relations for these complex craters.

Holsapple, K. A.↗
NASA NTRS1984

Morphologic studies of the Moon and planets

The impact, volcanic, and tectonic history of the Moon and planets were investigated over an eight year period. Research on the following topics is discussed: lunar craters, lunar basins, lunar volcanoes, correlation of Apollo geochemical data, lunar geology, Mars desert landforms, and Mars impact basins.

El-Baz, F.↗
NASA NTRS1976

Large scale cratering of the lunar highlands - Some Monte Carlo model considerations

In an attempt to understand the scale and intensity of the moon's early, large scale meteoritic bombardment, a Monte Carlo computer model simulated the effects of all lunar craters greater than 800 m in diameter, for example, the number of times and depths specific fractions of the entire lunar surface were cratered. The model used observed crater size frequencies and crater-geometries compatible with the suggestions of Pike (1974) and Dence (1973); it simulated bombardment histories up to a factor of 10 more intense than those reflected by the present-day crater number density of the lunar highlands. For the present-day cratering record the model yields the following: approximately 25% of the entire lunar surface has not been cratered deeper than 100 m; 50% may have been cratered to 2-3 km depth; less than 5% of the surface has been cratered deeper than about 15 km. A typical highland site has suffered 1-2 impacts. Corresponding values for more intense bombardment histories are also presented, though it must remain uncertain what the absolute intensity of the moon's early meteorite bombardment was.

Hoerz, F.↗
NASA NTRS2011

Direct Solar Wind Proton Access into Permanently Shadowed Lunar Polar Craters

Recent analyses of Lunar Prospector neutron spectrometer (LPNS) data have suggested that high abundances of hydrogen exist within cold traps at the lunar poles, and it has often been assumed that hydrogen-bearing volatiles sequestered in permanent shadow are topographically shielded from sputtering by solar wind protons. However, recent simulation results are presented showing that solar wind protons clearly access the floor of an idealized, shadowed lunar crater through a combination of thermal and ambipolar processes, in effect creating a plasma "miniwake". These simulations are the first to model the mini-wake environment in two spatial dimensions with a self-consistent lunar surface-plasma interaction. Progress is reported on constraining the nonzero particle fluxes and energies incident on kilometer-scale shadowed topography, such as a small crater embedded within a larger one. The importance of direct solar wind proton bombardment is discussed within the context of understanding the stability and inventory of hydrogen-bearing volatiles in shadow at the lunar poles. The support of the National Lunar Science institute, the DREAM institute, LPROPS, and the NASA Postdoctoral Program at NASA Goddard Space Flight Center administered by ORAU are gratefully acknowledged.

Zimmerman, M. I.↗
NASA NTRS1964

Lunar impact craters

Topography and evolution of lunar craters - meteoritic impact - selenography

TOPOGRAPHY↗
NASA NTRS1979

Large lunar secondary craters - Size-range relationships

The relationship between primary crater diameter and mean maximum secondary crater diameter for lunar craters is essentially linear for primary diameters from 0.5 to 260 km. The mean range from the primary to the largest secondary craters is also nearly linearly related to primary diameter. Extrapolation of these results to lunar basin scale supports the contention that basin secondaries of large diameter are to be found across much of the moon.

Allen, C. C.↗
NASA NTRS1973

The environmental heat flux routine, version 4 (EHFR-4) and Multiple Reflections Routine (MRR), volume 1

The environmental heat flux routine version 4, (EHFR-4) is a generalized computer program which calculates the steady state and/or transient thermal environments experienced by a space system during lunar surface, deep space, or thermal vacuum chamber operation. The specific environments possible for EHFR analysis include: lunar plain, lunar crater, combined lunar plain and crater, lunar plain in the region of spacecraft surfaces, intervehicular, deep space in the region of spacecraft surfaces, and thermal vacuum chamber generation. The EHFR was used for Extra Vehicular Mobility Unit environment analysis of the Apollo 11-17 missions, EMU manned and unmanned thermal vacuum qualification testing, and EMU-LRV interface environmental analyses.

Dietz, J. B.↗
NASA NTRS2011

Impact Melt in Small Lunar Highlands Craters

Impact-melt deposits are a typical characteristic of complex impact craters, occurring as thick pools on the crater floor, ponds on wall terraces, veneers on the walls, and flows outside and inside the rim. Studies of the distribution of impact melt suggested that such deposits are rare to absent in and around small (km to sub-km), simple impact craters. noted that the smallest lunar crater observed with impact melt was approximately 750 m in diameter. Similarly, theoretical models suggest that the amount of melt formed is a tiny fraction (<1%) of the total crater volume and thus significant deposits would not be expected for small lunar craters. LRO LROC images show that impact-melt deposits can be recognized associated with many simple craters to diameters down to approximately 200 m. The melt forms pools on the crater floor, veneer on the crater walls or ejecta outside the crater. Such melt deposits are relatively rare, and can be recognized only in some fresh craters. These observations indicate that identifiable quantities of impact melt can be produced in small impacts and the presence of such deposits shows that the material can be aggregated into recognizable deposits. Further, the present of such melt indicates that small craters could be reliably radiometrically dated helping to constrain the recent impact flux.

Plescia, J. B.↗
NASA NTRS2012

Locating the LCROSS Impact Craters

The Lunar CRater Observations and Sensing Satellite (LCROSS) mission impacted a spent Centaur rocket stage into a permanently shadowed region near the lunar south pole. The Sheperding Spacecraft (SSC) separated approx. 9 hours before impact and performed a small braking maneuver in order to observe the Centaur impact plume, looking for evidence of water and other volatiles, before impacting itself. This paper describes the registration of imagery of the LCROSS impact region from the mid- and near-infrared cameras onboard the SSC, as well as from the Goldstone radar. We compare the Centaur impact features, positively identified in the first two, and with a consistent feature in the third, which are interpreted as a 20 m diameter crater surrounded by a 160 m diameter ejecta region. The images are registered to Lunar Reconnaisance Orbiter (LRO) topographical data which allows determination of the impact location. This location is compared with the impact location derived from ground-based tracking and propagation of the spacecraft's trajectory and with locations derived from two hybrid imagery/trajectory methods. The four methods give a weighted average Centaur impact location of −84.6796 deg, −48.7093 deg, with a 1σ uncertainty of 115 m along latitude, and 44 m along longitude, just 146 m from the target impact site. Meanwhile, the trajectory-derived SSC impact location is −84.719 deg, −49.61 deg, with a 1 alpha uncertainty of 3 m along the Earth vector and 75 m orthogonal to that, 766 m from the target location and 2.803 km south-west of the Centaur impact. We also detail the Centaur impact angle and SSC instrument pointing errors. Six high-level LCROSS mission requirements are shown to be met by wide margins. We hope that these results facilitate further analyses of the LCROSS experiment data and follow-up observations of the impact region

LCROSS↗
NASA NTRS2011

Solar Wind Access to Lunar Polar Craters: Feedback Between Surface Charging and Plasma Expansion

Determining the plasma environment within permanently shadowed lunar craters is critical to understanding local processes such as surface charging, electrostatic dust transport, volatile sequestration, and space weathering. In order to investigate the nature of this plasma environment, the first two-dimensional kinetic simulations of solar wind expansion into a lunar crater with a self-consistent plasma-surface interaction have been undertaken. The present results reveal how the plasma expansion into a crater couples with the electrically-charged lunar surface to produce a quasi-steady wake structure. In particular, there is a negative feedback between surface charging and ambipolar wake potential that allows an equilibrium to be achieved, with secondary electron emission strongly moderating the process. A range of secondary electron yields is explored, and two distinct limits are highlighted in which either surface charging or ambipoiar expansion is responsible for determining the overall wake structure.

Zimmerman, M. I.↗
NASA NTRS1979

Blocky craters - Implications about the lunar megaregolith

Radar, IR, and photogeologic properties of some 1310 lunar craters that have been catalogued as radar or IR anomalies, or both, are studied to determine whether a systematic difference in blocky craters exists between the lunar maria and terrae and whether this difference might be caused by a deep magaregolith of pulverized material forming the terra surface. Examination of Apollo orbital photography confirms that the radar and IR anomalies are correlated with blocky rubble around the craters, and analysis of the radar and IR data indicates systematic terra-mare differences. The data are interpreted by postulating that the maria are rock layers where craters eject boulder fields, that the terrae are covered by a relatively pulverized megaregolith at least 2 km deep, and that the terra craters eject less rocky rubble. It is concluded that blocky rubble, in the form of either actual rocks or partly consolidated blocks, contributes to the radar and IR signatures of the craters.

Thompson, T. W.↗