Results of the Surveyor III sample impact examination conducted at the Manned Spacecraft Center
Apollo 12 returned Surveyor 3 samples examination for meteoroid and lunar ejecta impacts evidence by optical and electron microscopy
Cour-Palais, B. G.↗
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Do some of the sub-micrometer cosmic dust particles come from the sun.
Studies of cosmic dust particles collected at altitudes of 80 to 120 km over White Sands, New Mexico, and at times of noctilucent clouds over Kiruna, Sweden, indicate that an anomalously high atomic weight contribution is present within those particles collected at Kiruna. The elements observed are inconsistent with an origin due to atomic bomb fallout, meteoroidal crumbling, lunar ejecta, or comets. Many of these heavy elements may be stable in particulate form at the relatively high temperatures found in the coolest regions of the solar atmosphere. Some implications of the sun as the source of a significant component of cosmic dust are discussed.
Hemenway, C. L.↗
Do oblique impacts produce Martian meteorites
It is pointed out that several achondritic meteorites, classified as shergottites, nakhlites, and chassignites, have a number of unusual characteristics. Following the suggestion of Wood and Ashwal (1981) these meteorites are collectively referred to as SNC meteorites. The major element compositions of the SNC meteorites are, in general, distinct from those of other meteorites and lunar samples, and similar to certain terrestrial rocks. The geochemical and geochronological characteristics of the SNC meteorites strongly imply that their parent body was on the order of lunar size or larger and geologically active. Serious attention must be given to the hypothesis of a Martian origin of the SNC meteorites and to dynamic processes capable of delivering Martian meteorites to earth. In connection with the present investigation, it is suggested that oblique impacts of large meteoroids can produce ejecta which is entrained with the ricocheting projectile and accelerated to velocities in excess of Martian escape velocity.
Nyquist, L. E.↗
An Astronaut's Risk of Experiencing a Critical Impact from Lunar Ejecta During Lunar EVA
The Moon is under constant bombardment by meteoroids. When the meteoroid is large, the impact craters the surface, launching crater ejecta far from the impact potentially threatening astronauts on the lunar surface. In the early 1960’s, the ejecta impact flux was thought no more than the sporadic meteoroid flux but with speeds one to two orders of magnitude smaller. However, the Lunar Module designers realized by 1965 that meteoroid bumpers do not perform well at the smaller ejecta impact speeds. Their estimates of the Lunar Module risk of penetration by ejecta were 25 to 50% of the total risk. This was in spite of the exposure time to ejecta being only a third of that to sporadic meteoroids. The standard committee based the 1969 NASA SP-8013 lunar ejecta environment on Zook’s 1967 flux analysis and Gault, Shoemaker and Moore’s 1963 test data for impacts into solid basalt targets. However, Zook noted in his 1967 analysis, that if the lunar surface was composed of soil, that the ejected soil particles would be smaller than ejected basalt fragments and that the ejection speeds would be smaller. Both effects contribute to reducing the risk of a critical failure due to lunar ejecta. The authors revised Zook’s analysis to incorporate soil particle size distributions developed from analysis of Apollo lunar soil samples and ejected mass as a function of ejecta speed developed from coupling parameter analyses of soil impact-test data. The authors estimated EVA risk by assuming failure occurs at a critical impact energy. At these impact speeds, this might be true for suit hard and soft goods. However, these speeds are small enough that there may be significant strength effects that require new test data to modify the hypervelocity critical energy failure criterion. With these caveats, Christiansen, Cour-Palais and Freisen list the critical energy of the ISS EMU hard upper torso as 44 J and the helmet and visor as 71 J at hypervelocity. The authors then assumed that the lunar EVA suit fails at 50 J critical energy. This results in a 1,700,000 years mean time to failure using the results of this analysis and a 3,800 years mean time to failure using NASA SP-8013.
Bjorkman, Michael D.↗
Measurement of Primary Ejecta From Normal Incident Hypervelocity Impact on Lunar Regolith Simulant
The National Aeronautics and Space Administration (NASA) continues to make progress toward long-term lunar habitation. Critical to the design of a lunar habitat is an understanding of the lunar surface environment. A subject for further definition is the lunar primary ejecta environment. The document NASA SP-8013 was developed for the Apollo program and is the latest definition of the primary ejecta environment. There is concern that NASA SP-8013 may over-estimate the lunar primary ejecta environment. NASA's Meteoroid Environment Office (MEO) has initiated several tasks to improve the accuracy of our understanding of the lunar surface primary ejecta environment. This paper reports the results of experiments on projectile impact into pumice targets, simulating lunar regolith. The Ames Vertical Gun Range (AVGR) was used to accelerate spherical Pyrex projectiles of 0.29g to velocities ranging between 2.5 km/s and 5.18 km/s. Impact on the pumice target occurred at normal incidence. The ejected particles were detected by thin aluminum foil targets placed around the pumice target in a 0.5 Torr vacuum. A simplistic technique to characterize the ejected particles was formulated. Improvements to this technique will be discussed for implementation in future tests.
Edwards, David L.↗
Size-velocity distribution of large ejecta fragments
The characteristics of three primary extraterrestrial craters and the associated craters were examined to generate a size-velocity distribution for large ejecta fragments. The lunar craters Copernicus and Aristillus and the Martian crater Dv on Olympus Mons were used. Attention was focused on the radial distances between the primary and secondary crater centers and the diameters of the secondaries. The primary craters selected are all relatively young, which avoided contamination of the data from secondaries from other primaries. Attempts were made to account for the speed of the hypervelocity impacts and the elemental compositions of the impactors. An apparent velocity cutoff of about 1 km/sec was observed for the secondaries, which implies that no meteoroid impacts can accelerate ejecta to escape velocities from the moon or Mars.
Vickery, A. M.↗
Lunar ejecta and meteorites experiment
The test equipment installed during the Apollo 17 flight to conduct the lunar ejecta and meteorites (LEAM) investigation is described. The LEAM experiment intercepts ejecta particles created by meteoroid impact on the lunar surface and records information useful in establishing the history of the moon. The deployment of the system in the Taurus-Littrow area and the method for controlling the equipment are explained. The effects of lunar surface temperatures on the operation of the sensors are reported.
Berg, O. E.↗
Ballistic transport in planetary ring systems due to particle erosion mechanisms. I - Theory, numerical methods, and illustrative examples
Ballistic transport, defined as the net radial transport of mass and angular momentum due to exchanges of meteoroid hypersonic-impact ejecta by neighboring planetary ring regions on time-scales orders-of-magnitude shorter than the age of the solar system, is presently considered as a problem in mathematical physics. The preliminary results of a numerical scheme for following the combined effects of ballistic transport and viscous diffusion demonstrate that ballistic transport generates structure near sharp edges already present in the ring-mass distribution; the entire ring system ultimately develops an undulatory structure whose length scale is typically of the order of the radial excursion of the impact ejecta.
Durisen, Richard H.↗
Bombardment of planetary rings by meteoroids - General formulation and effects of Oort Cloud projectiles
A general solution is obtained for the angular distribution of the intensity and velocity of interplanetary projectiles impinging on a planetary ring system. Three significant results emerge from the solution: (1) a variation with orbital longitude is demonstrated in the impact velocity-weighted impact rate of the planetary rings' cometary meteoroids; (2) the angular distribution of ejecta intensity due to the bombardment of a planetary ring by interplanetary meteoroids is determined; and (3) the radial drift velocity due to both simple mass-loading and aberration-induced asymmetry in the impact rate is calculated for a planetary ring of arbitrary optical depth. Attention is given to results for projectiles with Oort Cloud-type orbits.
Cuzzi, Jeffrey N.↗
Corvid meteoroids and a Giordano Bruno ray are genetically related
Both Corvid meteoroids and the Giordano Bruno (GB) crater are products of recent events. On June 25, or 26, 1178, Corvid meteoroids and a portion of GB ejecta were at the same place in the Solar System and moved in the same direction (right ascension = 12 degrees and declination = +19 degrees). The ground track of this direction is the same as that of the most prominant GB ray (azimuth = 237 degrees). These 'coincidences' could not have occurred by change and, therefore, support the conclusions that the GB impact occurred on June 26, 1178, and that Corvid meteoroids are high-velocity ejecta fragments from that impact. Finally, those fragments ejected with somewhat lower velocities failed to escape from the Earth-Moon system and produced the prominant ray extending southwest from the GB crater. Between June 25 and July 2, 1937, a Corvid meteor shower was observed. The apparent lack of Corvid showers in other years suggests that Corvids are the product of a recent break-up event. The right ascension and declination, corrected for zenith attraction, of 192 degrees and -19 degrees were reported for the radiant of this shower. This corresponds to a right ascension and declination of the direction of motion of Corvid meteoroids of 12 degrees and +19 degrees. In ecliptic coordinates the celestial longitude and latitude of this direction are 18 degrees and +13 degrees.
Hartung, Jack B.↗
Micrometeoroid and Orbital Debris (MMOD) Testing, Ballistic Limit Equation Definition and Risk Assessment of the Exploration Extravehicular Mobility Unit (XEMU)
A well-known hazard associated with exposure to the space environment is the risk of failure due to an impact from a micrometeoroid and orbital debris (MMOD) particle. As NASA prepares to return astronauts to the moon with the Artemis program, the next generation of spacesuit is in development to support future extravehicular activities (EVAs). An MMOD impact to the spacesuit is of great concern as a large leak could prevent an astronaut from safely reaching an airlock in time resulting in a loss of life. The exploration extravehicular mobility unit (xEMU) must meet MMOD requirements for multiple environments including those in low earth orbit (LEO) as well as the meteoroid and secondary lunar regolith ejecta environments found on the lunar surface. The subject of this paper is an MMOD risk assessment of the internal xEMU configuration design developed by NASA Johnson Space Center (JSC) personnel. Assessment of the MMOD risk for an 8-hour, 2-person EVA in both LEO and on the lunar surface showed that the xEMU spacesuit meets the program technical requirement of 1 in 2500 failure odds.
Micrometeoroid↗
Effects of meteoroids and space debris on the particulate environment for space station
A large orbiting platform such as Space Station will be subjected to numerous impacts by meteoroids and space debris fragments. These hypervelocity impacts will produce clouds of ejected structural material in the vicinity of the Station. The development of a preliminary model for impact-generated ejecta production which combines the fluxes of meteoroids and space debris fragments with a description of the number of ejecta particles produced by hypervelocity impacts is reported. Modeling results give mean ejecta densities from 30 to 100 percent of the present particulate background limitation of 1 particle 5 microns and larger per orbit per 1 x 10(-5) sr field-of-view as seen by a 1-m-diameter aperture telescope in the 1990's time frame. Projected increases in the space debris flux raise this density to 300 percent of this limitation after 2010. The model is also applied to estimate the vulnerability of metallic claddings on composite structural members to penetration by hypervelocity projectiles, thereby exposing the substrate to atomic oxygen. The estimated annual number of penetrations is from 4 to 8 per square meter of cross-sectional area in the mid 1990's, increasing to more than 40 penetrations per square meter after 2010.
Seebaugh, W. R.↗
Constraining the Ratio of Micrometeoroids from Short- and Long-Period Comets at 1 AU from LADEE Observations of the Lunar Dust Cloud
We interpret recent observations of the secondary dust ejecta cloud around the Moon from the Lunar Dust Experiment (LDEX) on board the NASA Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft with help from dynamical models of meteoroids. Results suggest that in order to match the spatial structure of observed ejecta profiles, the flux of meteoroids on the Moon must be primarily provided by short-period comets with an excess ratio of at least 1.3:1 compared to long-period comets. This ratio increases significantly if the dependence of the ejecta yield on impactor velocity is stronger than generally believed. The model accounts for the orbital geometry of LADEE and shows no indication of a large asymmetry in the meteoroid flux impacting from the Helion and Anti-Helion directions.
Janches, Diego↗
The lunar micrometeoroid experiment, L033
Use of Pioneer 7 and 8 cosmic dust detectors in Apollo 17 lunar ejecta and micrometeorite experiment to measure meteoroid fluxes on moon
Dohnanyi, J. S.↗
The interplanetary micrometeoroid flux and lunar primary and secondary microcraters
It is proposed that considerable care is required to properly interpret either spacecraft in situ data or lunar crater data as well as near-earth data; in the case of the former, complications may arise which may be attributed to secondary lunar ejecta impacts, in the latter, they may result from impacting earth-orbiting debris. Experimental evidence suggests that most impact pits on lunar rocks with pit diameters smaller than 7 micrometers have been generated by lunar secondary ejecta impacts and not by primary meteoroid impacts. It is also found that lunar crater production rates are more accurate when deduced from meteoroid space experiments and not from solar flare track ages. It is concluded that in so far as all of the above qualifications are taken into account, a self-consistent meteoroid flux versus mass distribution is obtained.
Zook, H. A.↗
Venus geology
The Magellan mission to Venus is reviewed. The scientific investigations conducted by 243-day cycles encompass mapping with a constant incidence angle for the radar, observing surface changes from one cycle to the next, and targeting young-looking volcanos. The topography of Venus is defined by the upper boundary of the crust and upwelling from lower domains. Tectonic features such as rift zones, linear mountain belts, ridge belts, and tesserae are described. The zones of tesserae are unique to the planet. Volcanism accounts for about 80 percent of the observed surface, the remainder being volcanic deposits which have been reworked by tectonism or impacts. Magellan data reveal about 900 impact craters with flow-like ejecta resulting from the fall of meteoroids. It is concluded that the age of the Venusian surface varies between 0 and 800 million years. Tectonic and volcanic activities dominate the formation of the Venus topography; such processes as weathering and erosion are relatively unimportant on Venus.
Mclaughlin, W. I.↗
Venus impact craters: Implications for atmospheric and resurfacing processes from Magellan observations
Observations of impact craters on Venus by Magellan yield important insights into: (1) atmospheric effects on the formation of impact craters and their attendant ejecta deposits and (2) the resurfacing history of the planet. Most craters smaller than 15 km are classified as irregular; they possess irregularly shaped rims, and multiple hummocky floors. The irregular nature of these craters is interpreted to be the consequence of breakup and dispersion of incoming meteoroids by the dense atmosphere. Two major ejecta facies of venusian impact craters are hummocky ejecta and outer ejecta. A number of craters documented in the Magellan images possess often non-radial, flow-like ejecta indicative of a low viscosity materials. Approximately half of the impact craters observed with the Magellan radar are partially or wholly surrounded by areas with low radar backscatter cross sections.
Phillips, Roger J.↗
An Analytic Formulation of Ejecta Distributions over Airless Bodies
With recent plans to revisit the Moon by robotic and crewed spacecraft, there has been a renewed interest in understanding the ejecta environment on the Moon and other airless bodies. Meteoroid and asteroid impacts can excavate large amounts of material from the surface and, above an airless body, can send this material long distances on (essentially) ballistic orbits. This ejecta, while typically traveling slower than the impactor, can nevertheless achieve high enough speeds to endanger surface operations. Accurate knowledge of this phenomenon is necessary in order to design appropriate shielding for human activities, both for activities on the surface of the Moon and for orbiters in near-lunar space. This phenomenon is also important in the transport of particles above other Solar System objects, such as Jovian satellites, where this ejecta creates a kind of ever-present “halo” of particles around the gravitating body. While Monte Carlo techniques have been successfully used to model this environment, there are useful analytic expressions, developed for use in modeling the meteoroid environment, that can be used to describe this environment as well. Such analytic tools can shed light on the altitude, velocity, and directionality of these ejecta environments.
Mark Matney↗