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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Compaction as the Origin of the Unusual Craters on the Asteroid Mathilde

Asteroid Mathilde has been pummeled by at least five giant impacts (Figure 1). Previous experience with cratering suggests Mathilde's giant craters should each be surrounded by kilometer-deep blankets of ejecta, i.e. material excavated during the impact events. Curiously, there appears to be very little ejecta around Mathilde's craters; they show no evidence of filling by ejecta from adjacent large craters. A previous explanation for the missing ejecta, based on computer simulations, is that Mathilde's unusually high porosity (50 +/- 20%) confines the deposited impact kinetic energy to a localized volume, and produces excavation velocities so high (greater than approximately 20m/s) that nearly all ejecta escape Mathilde's gravitational field. Here we report on laboratory experiments in a highly porous material that give a different explanation. The crater is formed primarily by compaction, not excavation. The small amount of material that is lofted has velocities and ranges so small that nearly all of it is re-deposited within the crater bowl, thereby sparing neighboring craters from ejecta in-filling. This peculiar style of cratering implies that highly porous asteroids are minor contributors of meteorites, because essentially no ejecta escape these asteroids.

Housen, Kevin R.↗
NASA NTRS1997

The NEAR Spacecraft's Flyby of Asteroid 253 Mathilde

The Terminal navigation of the NEAR spacecraft during its close flyby of asteroid 253 Mathilde involved coordinated efforts first to determine the heliocentric orbits of the spacecraft and Mathilde and then to determine the relative trajectory of the spacecraft with respect to Mathilde.

Asteroid 253 Mathilde↗
NASA NTRS1996

(abstract) Physical Properties of 253 Mathilde from Groundbased Observations

The only physical observations which predate the identifications of 253 Mathilde as a potential flyby target of NEAR were measurements of its absolute magnitude in reflected light and thermal radiometry by IRAS. Mathilde has been revealed to be an unusual object, of a class not previously visited by a spacecraft.

Mathilde 253 IRAS albedo flyby↗
NASA NTRS1997

Plans for Arecibo Radar Investigation of Mathilde

The Near-Earth Asteriod Rendezvous (NEAR) flyby of 253 Mathilde on June 27, 1997, should produce a mass estimate accurate to about 6%. However, a volume determination from flyby imaging may have uncertainties > 75%; anticipated lightcurve data might reduce the volume uncertainty to between 30% and 50%.

Asteriod Arecibo radar Mathilde↗
NASA NTRS2002

Experimental Simulations of Large-Scale Collisions

This report summarizes research on the effects of target porosity on the mechanics of impact cratering. Impact experiments conducted on a centrifuge provide direct simulations of large-scale cratering on porous asteroids. The experiments show that large craters in porous materials form mostly by compaction, with essentially no deposition of material into the ejecta blanket that is a signature of cratering in less-porous materials. The ratio of ejecta mass to crater mass is shown to decrease with increasing crater size or target porosity. These results are consistent with the observation that large closely-packed craters on asteroid Mathilde appear to have formed without degradation to earlier craters.

Housen, Kevin R.↗
NASA NTRS1999

Investigating Atmospheric Effects on Impact Ejecta Morphology: Possible Tool for Determining Past Climate Conditions on Mars?

The combined use of impact crater morphology and mechanics provides important information on the physical conditions of both planetary atmospheres and planetary and asteroid surfaces present during crater formation, while an understanding of the rate of crater production on the surface of asteroids provides information of their surface and spin rate evolution. The research performed with support from this project improves our understanding of (1) the mechanics of impact cratering in order to gain insights on the evolution of these physical surface conditions on planets with atmospheres and asteroids, and (2) how impact flux across an asteroid surface may vary due to anisotropic distribution of impactors in the solar system. As part of this project, we have undertaken three studies. In the first study, we investigate atmospheric effects on the morphology of ejecta excavated during a cratering event in order to determine the atmospheric and target conditions from observed crater morphologies. In the second study, we use the physical and morphological consequences of oblique impacts on an asteroid to understand how the asteroid Mathilde (recently imaged by the Near Earth Asteroid Rendezvous - NEAR- spacecraft) could have survived the formation of five giant craters. In a third study, we use a Monte Carlo method to calculate the impact flux on an asteroid given a distribution of impactors on elliptical orbits. In the following section, we present the result obtained from all three studies.

Appleby, John F.↗
NASA NTRS2003

An Impact Ejecta Behavior Model for Small, Irregular Bodies

In recent years, spacecraft observations of asteroids 951 Gaspra, 243 Ida, 253 Mathilde, and 433 Eros have shown the overriding dominance of impact processes with regard to the structure and surface morphology of these small, irregular bodies. In particular, impact ejecta play an important role in regolith formation, ranging from small particles to large blocks, as well as surface feature modification and obscuration. To investigate these processes, a numerical model has been developed based upon the impact ejecta scaling laws provided by Housen, Schmidt, and Holsapple, and modified to more properly simulate the late-stage ejection velocities and ejecta plume shape changes (ejection angle variations) shown in impact cratering experiments. A target strength parameter has also been added to allow the simulation of strength-dominated cratering events in addition to the more familiar gravity-dominated cratering events. The result is a dynamical simulation which models -- via tracer particles -- the ejecta plume behavior, ejecta blanket placement, and impact crater area resulting from a specified impact on an irregularly shaped target body, which is modeled in 3-dimensional polygon fashion. This target body can be placed in a simple rotation state about one of its principal axes, with the impact site and projectile/target parameters selected by the user. The gravitational force from the irregular target body (on each tracer particle) is determined using the polygonized surface (polyhedron) gravity technique developed by Werner.

Richardson, J. E.↗
NASA NTRS2004

The Seismic Effect of Impacts on Asteroid Surface Morphology: Early Modeling Results

In recent years, spacecraft observations of asteroids 951 Gaspra, 243 Ida, 253 Mathilde, and 433 Eros have shown the overriding dominance of impact processes with regard to the structure and appearance of these small, irregular bodies. One currently unanswered question is: to what degree does seismic shaking from impacts affect the surface morphology of these bodies? Through detailed modeling, we begin to address this question.

Richardson, J. E.↗
NASA NTRS2004

Generation of an Ordinary-Chondrite 'Regolith' by Repetitive Impact

Analyses of meteorites and remote sensing studies for years have suggested the presence of regolith on asteroids, yet detailed observations of asteroid regoliths have been possible only recently with the flybys of 951 Gaspra, 243 Ida, and 253 Mathilde, and with the orbiting of and landing on 433 Eros by the NEAR Shoemaker spacecraft. Virtually all investigations into the generation and evolution of asteroid regoliths to date have been theoretical in nature. These have been guided mainly by observations of the lunar regolith, using what meager experimental data exist for terrestrial materials as substitutes for their asteroidal counterparts. As part of a program to evaluate the behavior of an ordinary chondrite under impact conditions, about 460 g of the L6 chondrite ALH85017 were subjected to 50 consecutive impacts, sufficient to reduce the target from a mean grain size of 11 mm to 0.5 mm. Some of the details of these experiments are presented here.

Cintala, M. J.↗
NASA NTRS2005

A Stochastic Cratering Model for Asteroid Surfaces

The observed cratering records on asteroid surfaces (four so far: Gaspra, Ida, Mathilde, and Eros [1-4]) provide us with important clues to their past bombardment histories. Previous efforts toward interpreting these records have led to two basic modeling styles for reproducing the statistics of the observed crater populations. The first, and most direct, method is to use Monte Carlo techniques [5] to stochastically populate a matrix-model test surface with craters as a function of time [6,7]. The second method is to use a more general, parameterized approach to duplicate the statistics of the observed crater population [8,9]. In both methods, several factors must be included beyond the simple superposing of circular features: (1) crater erosion by subsequent impacts, (2) infilling of craters by impact ejecta, and (3) crater degradation and era- sure due to the seismic effects of subsequent impacts. Here we present an updated Monte Carlo (stochastic) modeling approach, designed specifically with small- to medium-sized asteroids in mind.

Richardson, J. E.↗
NASA NTRS2012

Craters Without Ejecta

A significant portion of the Solar System's population of minor bodies may be quite porous. A unique aspect of crater formation in porous bodies is that large craters may form without the ejecta deposits that are associated with craters on less porous bodies. In this paper. laboratory experiments and scaling theories are used to identify the conditions under which ejecta deposits are suppressed. The results are consistent with the interpretation that large craters on asteroid Mathilde (porosity approx. 50%) and Saturn's moon Hyperion (porosity >40%) apparently formed without producing Significant ejecta deposits. while smaller bodies do have notable regoliths.

Housen, Kevin R.↗
NASA NTRS2012

Multiple NEO Rendezvous Using Solar Sail Propulsion

The NASA Marshall Space Flight Center (MSFC) Advanced Concepts Office performed an assessment of the feasibility of using a near-term solar sail propulsion system to enable a single spacecraft to perform serial rendezvous operations at multiple Near Earth Objects (NEOs) within six years of launch on a small-to-moderate launch vehicle. The study baselined the use of the sail technology demonstrated in the mid-2000 s by the NASA In-Space Propulsion Technology Project and is scheduled to be demonstrated in space by 2014 as part of the NASA Technology Demonstration Mission Program. The study ground rules required that the solar sail be the only new technology on the flight; all other spacecraft systems and instruments must have had previous space test and qualification. The resulting mission concept uses an 80-m X 80-m 3-axis stabilized solar sail launched by an Athena-II rocket in 2017 to rendezvous with 1999 AO10, Apophis and 2001 QJ142. In each rendezvous, the spacecraft will perform proximity operations for approximately 30 days. The spacecraft science payload is simple and lightweight; it will consist of only the multispectral imager flown on the Near Earth Asteroid Rendezvous (NEAR) mission to 433 Eros and 253 Mathilde. Most non-sail spacecraft systems are based on the Messenger mission spacecraft. This paper will describe the objectives of the proposed mission, the solar sail technology to be employed, the spacecraft system and subsystems, as well as the overall mission profile.

Johnson, Les↗