Engineering Papers⌕ Search

Engineering topics

Hoerz, F.

Publications and source records attributed to Hoerz, F..

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Micrometeoroid abrasion of lunar rocks - A Monte Carlo simulation

A Monte Carlo computer model simulating the randomness of the impact process both in space and in time is developed in order to provide insight into lunar rock erosion by single particle abrasion and into bombardment history of fractional surface areas of lunar rocks. Microcrater frequencies derived from lunar rocks are used to calculate magnitude and probability of each cratering event, and experimental cratering results are employed to determine the eroded volumina for individual crater sizes. It is shown that a fractional surface area of a lunar rock sample may have a completely different bombardment history, and that the exposure histories and actual erosion depths of the surfaces vary accordingly and are highly heterogeneous. A minimum erosion rate of 0.3 to 0.6 mm for the past one million years is obtained.

Hoerz, F.↗
NASA NTRS1973

Emplacement of the Cayley formation

Analysis of the effects of ejection of materials from large lunar craters, photogeologic evidence, remote measurements of surface chemistry and petrology of lunar samples are synthesized. Previous theories for emplacement of the Cayley are volcanic ash emplacement and emplacement as ejecta from multiringed basins. Calculations show that materials ejected beyond the continuous deposits of large lunar craters produce secondary impact craters that excavate and deposit masses of local material equal to multiples of the crater ejecta deposited at the same place. It is shown that the main influence of a large cratering event on terrain at distances greater than 50 km from large lunar craters is one of cratering and deposition of local material by secondary craters rather than deposition of ejecta from the large crater.

Oberbeck, V. R.↗
NASA NTRS1973

Debye-Scherrer investigations of experimentally shocked silicates.

Small ballistic ranges were used to perform controlled laboratory shock experiments on 12 selected silicates. Debye-Scherrer investigations of shocked materials revealed a gradual lattice breakdown of crystalline matter under shock. Individual mineral species behave selectively. Sheet silicates break down very easily, followed by tecto-silicates. Chain-, ino- and ortho-silicates are of considerably higher shock resistance. Depending on the mineral species, the first sign of shock damage is evidenced in the long range order at 20-70 kb. At intermediate pressures (100-200 kb) the long range order is essentially destroyed with the short range order heavily disturbed. At pressures exceeding 300 kb tecto-silicates are completely collapsed.

Hoerz, F.↗
NASA NTRS1973

Lunar rocks as meteoroid detectors

About 5000 microcraters on seven lunar rocks recovered during the Apollo 12 mission have been systematically studied using a stereomicroscope. Based on comparisons with laboratory cratering experiments, at least 95 percent of all millimeter sized craters observed were formed by impacts in which the impact velocity exceeded 10 km/s. The dynamics of particle motion near the moon and the distribution of microcraters on the rocks require an extralunar origin for these impacting particles. The microcrater population on at least one side of all rocks studied was in equilibrium for millimeter sized craters; i.e., statistically, craters a few millimeters in diameter and smaller were being removed by the superposition of new craters at the same rate new craters were being formed. The population of craters on such a surface is directly related to the total population of particles impacting that surface. Crater size distribution data together with an experimentally determined relationship between the crater size and the physical parameters of the impacting particle, yield the mass distribution of interplanetary dust at 1 AU.

Hartung, J. B.↗
NASA NTRS1973

Some physical parameters of micrometeoroids

Detailed morphological parameters (depth/diameter ratio, circularity index) of microcraters in the 0.2 to 100 micron diameter range were obtained via SEM techniques for three lunar glass surfaces. The depth/diameter ratios are typically 0.5 to 0.8 with a range of 0.3 to 1.3. The circularity index varies from 0.4 to 1.0 with a pronounced maximum at 0.7 to 0.9. These parameters are compared with microcraters produced in the laboratory via electrostatic particle accelerators. The following conclusions are drawn: The great majority of observed crater depths are compatible with micrometeoroid densities of 2 to 4 g/cu cm; crater depths are incompatible for projectile densities less than 1 g/cu cm and greater than 7 g/cu cm. The circularity index of microcrater pits indicates rather equidimensional, if not spherical, projectiles. Needles, platelets and other highly irregular shapes can be excluded. Less than 5% of all craters observed may offer different conclusions.

Brownlee, D. E.↗
NASA NTRS1973

Crater populations on lunar rocks

Approximately 10,000 microcraters were investigated using binocular microscope techniques on fifteen Apollo 16 rocks: crystalline rocks 60315, 60335, 61156, 62235, 62295, and 68415; breccias 60016, 61015, 61175, 66075, and 69935; and glass surfaces 60015, 60095, 60135, and 64455. Diameter measurements of the central glass-lined pits and surrounding spall zones were made. Ratios of spall to pit diameters may range from 3.0 to 4.5 for different rock surfaces. Crater size distributions obtained for production surfaces confirm and extend to larger crater sizes data published previously. The crater size distribution on lunar rocks in the pit diameter range, 10 to 1000 microns, is shown to depend on the average angle of impact which is a function of the exposure geometry. In contrast to results of earlier studies, a wide range of crater densities was observed on relatively heavily cratered surfaces.

Neukum, G.↗
NASA NTRS1972

Abrasion and catastrophic rupture of lunar rocks - Some implications to the micrometeoroid flux at 1 AU.

Results from laboratory studies of hypervelocity impact against crystalline rocks, combined with estimates of the micrometeoroid flux at the lunar surface, provide a basis for calculating abrasion rates and survival times before catastrophic rupture of rocks on the lunar surface. The surface residence times observed for lunar rocks of the order of 10 m.y. (derived from the track densities of iron group nuclei) restrict the mass range of impacting particles of interest to masses less than about 1.01 gram. Extrapolation downward to smaller masses following flux distributions suggested by early satellite data and photographic meteor observations leads to absurd rates of abrasion. Consistent with the observed crater populations on the lunar rocks and with the Pegasus, Explorer, and Pioneer satellite data, the slope of the mass-flux distribution must decrease markedly for masses below 1 to .1 microgram.

Gault, D. E.↗
NASA NTRS1972

The surface orientation of some Apollo 14 rocks.

Detailed stereomicroscopic studies of the distribution of microcraters, soil covers, and glass coatings were performed to reconstruct the most recent surface orientations of selected Apollo 14 rocks. Surface orientations could be established for rocks 14053, 14073, 14301, 14303, 14307, 14310, and 14311 (which includes rock 14308). A tentative orientation of rock 14055 is suggested, and comments concerning the surface history of rocks 14302, 14305, and 14318 are presented. The examination of rocks 14066, 14306, and 14321 indicates that these specimens have complicated surface histories that prevent reconstruction of their orientation by the criteria that were established in these stereomicroscopic studies.

Hoerz, F.↗
NASA NTRS1972

Microcraters on lunar rocks.

Lunar microcraters may consist of a central, glass-lined pit, a halo of microfractured material surrounding the pit and a larger, generally concentric, spall area. A classification of microcraters is based on the presence or absence of a pit and a spall. The change from one crater type to another is gradational. Comparison with laboratory experiments indicates that a primary microcrater may be identified by the presence of melted host rock associated with the crater. Most microcraters are the result of the high-speed impact of primary, extralunar particles. Microcratering represents the small-scale end of a continuum of impact cratering as a process.

Hartung, J. B.↗
NASA NTRS1972

Apollo 16 special samples, part B

Information is presented concerning special samples which were collected for specific investigations. The methods of sample collection are described along with fillet and core samples.

Hoerz, F.↗
NASA NTRS1972

Effects of microcratering on the lunar surface.

Based on new laboratory impact data and current best estimates of the lunar micrometeoroid flux, calculations have been made of (1) the survival times of rocks on the lunar surface before they are catastrophically ruptured by meteoritic impacts; and (2) the rate of mass wasting by single particle abrasion. The calculated results are in systematic disagreement with observations in a direction suggesting that the current micrometeoroid flux may be greater than the long-term average integrated over the past several tens of millions of years. Most of the mass in the micrometeoroid flux is concentrated in particles with masses between .01 and 100 micrograms.

Gault, D. E.↗
NASA NTRS1972

Lunar microcraters and interplanetary dust.

The ratio of spall to pit diameter of lunar microcraters decreases with decreasing crater size. The trend from micron-sized to cm-sized craters involves a transition of crater types from pit-only to pit-plus-spall craters. Some spall-only craters may have possessed a pit originally. Most microcraters are formed by the impact of primary interplanetary dust particles because melting occurred during their formation. According to experimental and theoretical data such melting phenomena require impact velocities which are consistent only with the velocity distribution of extralunar particles.

Hartung, J. B.↗
NASA NTRS1971

A classification of impact craters

Planetary and lunar meteorite craters classification according to radius logarithm to base ten, covering diameter size from 2 microns to 2000 km

Hoerz, F.↗