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Impact Features and Projectile Residues in Aerogel Exposed on Mir
Abstract
Approximately 0.63 m2 of SiO2-based aerogel (0.02 g cm−3) was exposed for 18 months on the Mir Station to capture hypervelocity particles from both man-made and natural sources. Optical inspection revealed two major classes of hypervelocity impact features in the aerogel: (1) long, carrot-shaped tracks, well known from laboratory impact experiments, that exhibit a depth- (t) to-diameter (D) relationship of t/D>10, typically 20–30, and (2) shallow pits (t/D<10; typically 1–3) that have no laboratory analog. Blunt-nosed, yet deep (t/D=5–10), cylindrically shaped cavities suggest the existence of transitional morphologies between these tracks and pits. All tracks contain projectile residues that are unmelted, while pits rarely contain even traces of projectile material. These and other observations suggest that slender tracks form at lower impact velocities than the shallow pits. In addition, we observed that the measured track-length does not systematically correlate with the size of the projectile residue. This renders the reconstruction of encounter velocity and/or projectile mass from measured track dimensions not feasible at present.Recovery of particles from individual tracks is time-consuming, yet readily accomplished by operators familiar with the handling of individual, micrometer-sized particles. Compositional analyses by SEM-EDS identified a variety of man-made and natural particles. A few natural particles were embedded in epoxy, microtomed, and analyzed by TEM. All were polymineralic aggregates that contained olivine exhibiting sharp electron-diffraction spots, and suggesting that the materials had experienced only minimal shock-deformation, if any. One natural particle contained olivine, augite, diopside, troilite, chromite/magnetite, and hercynite, the latter existing as pristine, undeformed octahedral crystals. The olivine in two of the particles were Fo60–70 and Fo39–53, and thus, more equilibrated than olivines in most stratospheric particles (Fo80–100). These results illustrate that particle collections in Earth orbit are highly complementary to ground-based collections of cosmic dust.
... All particles that may have been loose aggregates disaggregated into individual components with the larger, denser components penetrating more deeply into the aerogel, making thin tracks with terminal grains. Individual grains experienced heating effects that ranged widely from excellent preservation to melting; such behavior was expected Hörz et al. 2000;Burchell et al. 2006). It appears that the material deposited along track walls experienced the greatest heating, while the denser grains outran the heated areas as they punched deeper into the aerogel (K. ...
... Wild 2 olivine has an extremely wide composition range, from Fa 0−96 with a pronounced frequency peak at Fa 1 (Fig 3). The presence of significant Fe-rich olivine and lack of a peak at equilibrated olivine compositions (~Fa 40−60 ) suggest that composition changes due to capture heating have been insignificant in the coarse-grained (>0.2 μm) component en masse (Akai 1988;Zolensky and Kinard 1993;Barrett et al. 1993;Hörz et al. 2000;Burchell et al. 2006). Wild 2 olivines include some with very elevated MnO, Al 2 O 3 , and Cr 2 O 3 contents, up to 6.45, 0.71 and 1.46 wt%, respectively (Zolensky et al. 2006). ...
... Flash heating during sample collection may account for the disparity in this particular instance, as olivine equilibrates faster than orthopyroxene under identical circumstances (Ganguly and Tazzoli 1994). We have seen composition equilibration of ferromagnesian minerals in chondritic IDPs during capture in silica aerogel in low-Earth orbit aboard the Mir space station (Hörz et al. 2000). In this situation, we observed that olivines and pyroxenes sometimes equilibrated at compositions in the range (~Fa 60 to Fa 40 ), and sometimes recrystallize into a granular texture. ...
... Two micrometeoroids investigated by transmission electron microscope (TEM) are~5 and~30 μm in the longest dimension. One is composed of Fe-rich olivine (Fo 39-50 ) set in amorphous silicate material, troilite, hercynite, and chromite/magnetite, and the other is composed of Fe-rich olivine (Fo 60-70 ), magnesian high-Ca pyroxene (Wo 50 En 50 Fs 0 to Wo 32 En 61 Fs 7 ), and hercynite (Hörz et al., 2000). On the other hand, anhydrous IDPs, which are considered to be cometary dust, are composed mainly of sub-μmsized components, and are typically characterized by abundant glass with embedded metal and sulfide (GEMS), enstatite whiskers, and low-iron manganese-enriched (LIME) olivine and pyroxene, as well as abundant Ni-poor pyrrhotite, and olivine and pyroxene with various Mg/(Mg + Fe) ratios (Bradley, 2004). ...
... Neither chondrules nor refractory inclusions have been identified among micrometeoroids although they have been found among the terminal captured particles from the Stardust mission to comet 81P/Wild2 (Nakamura et al., 2008;Zolensky et al., 2006) as well as MMs (Genge et al., 2005). It is not understood why the captured micrometeoroids have different mineralogy from IDPs and MMs (Hörz et al., 2000). ...
... However, it is beyond the scope of this paper to discuss the reason why these meteorites contain a higher amount of type II chondrules. As already mentioned, two micrometeoroids captured on the Mir space station are composed of Fe-rich olivine, troilite, two spinels embedded in amorphous silicate material, and of Fe-rich olivine, high-Ca pyroxene, and hercynite (Hörz et al., 2000). If the population of Mir micrometeoroids containing olivine with N 10% molar Fe/(Mg + Fe) were as high as those of the ISS and the Stardust chondrule-like objects, it could be possible that both of the Mir micrometeoroids investigated by TEM (Hörz et al., 2000) contain FeO-bearing olivine. ...
Here we report on the mineralogy, petrography, and oxygen-isotope compositions of a micrometeoroid captured on the international space station. This micrometeoroid has the texture of a porphyritic olivine chondrule. Because hydrated phases were not identified in the micrometeoroid and because Ni-rich sulfide in it does not show exsolution of pentlandite on the TEM scale, the micrometeoroid probably escaped low temperature events such as aqueous alteration on its parent body. However, the mean value and standard deviation of Cr2O3 wt.% in olivine in the micrometeoroid suggest that the micrometeoroid experienced weak thermal metamorphism. Oxygen isotope ratios of pyroxene and olivine in the micrometeoroid are similar to those of chondrule-like objects in comet 81P/Wild2 and coarse-grained crystalline micrometeorites as well as those in chondrules in major types of carbonaceous chondrites. These data suggest that the micrometeoroid is a fragment of a chondrule-like object that was derived from a primitive parent body that experienced thermal metamorphism.
... Since Tsou et al. demonstrated this capability in the late 1980s [2], arrays of silica aerogels have been flown in space and a NASA sample return mission (Stardust) consisting of silica aerogel collectors is expected to return pristine samples of cometary and interstellar dust in 2006 [3]. (LEO), in part to characterize the orbital debris environment , but also with the goal of collecting natural micro- meteorites [4,5]. To date, however, only a handful of extraterrestrial dust particles has been isolated and analyzed in these collectors [5] as most of the captured projectiles are expected to be man-made orbital debris. ...
... (LEO), in part to characterize the orbital debris environment , but also with the goal of collecting natural micro- meteorites [4,5]. To date, however, only a handful of extraterrestrial dust particles has been isolated and analyzed in these collectors [5] as most of the captured projectiles are expected to be man-made orbital debris. The composition and dynamic properties (e.g., spatial density, velocities, and trajectories) of the man-made orbital debris population in LEO is itself of considerable interest to satellite makers and is a field of active research (see e.g., [6]). ...
... Thus, orbital debris that actually impacted at 6 km s À1 could be misidentified to have impacted at greater than 8 km s À1 , assuming that we have underestimated the mass by a factor of 2. However, the point of the calorimetric technique is to rapidly identify collected dust grains that are good candidates for being extraterrestrial on the basis of their impact velocity. A subsequent direct determination of the projectileÕs composition could easily rule in or out the extraterrestrial origins of the dust grain [6,5] . Sophisticated, in situ techniques are currently being developed which are capable of measuring the elemental and total mass compositions of captured projectiles with a resolution of about $20 pg [14]. ...
Silica aerogels have been shown to be superior at capturing hypervelocity projectiles with minimal alteration. On the basis of what is known about the abundance of natural projectiles in low Earth orbit (LEO), aerogel collectors flown in LEO should collect numerous scientifically interesting extraterrestrial dust particles, including interstellar dust grains. However, to date, only a few extraterrestrial dust grains have been found and not a single contemporary interstellar dust grain has ever been identified or analyzed in the laboratory. This lack of success is due to the fact that when using conventional aerogels it is very difficult, if not impossible, to reconstruct the velocity of captured natural projectiles. To address this problem, we are currently developing aerogel collectors/detectors that passively record the kinetic energy of an impacting projectile. In our previous work, we demonstrated that (Gd, Tb)-doped alumina aerogels may transform into a fluorescent phase(s) as a result of the rapid shock heating experienced by the capture of hypervelocity projectiles and that the amount of fluorescence excited, using a UV light source, is an increasing function of the projectile’s kinetic energy. However, our previous work did not demonstrate the accuracy of this ‘calorimetric’ technique in reconstructing the impact velocity of projectiles. In this paper, we report on the production of fluorescent impact cavities in a Ti-doped (5%) SiO2–Al2O3 aerogel monolith that resulted from the capture of 4.37kms−1 20μm glass beads. In addition we demonstrate that the dispersion of the fluorescent response of this aerogel implies that we should be able to reconstruct the velocity of a captured projectile with a resolution of 20% or better.
... Since Tsou et al. demonstrated this capability in the late 1980s [2], arrays of silica aerogels have been flown in space and a NASA sample return mission (Stardust) consisting of silica aerogel collectors is expected to return pristine samples of cometary and interstellar dust in 2006 [3]. Various orbit (LEO), in part to characterize the orbital debris environment, but also with the goal of collecting natural micrometeorites [4,5]. To date, however, only a handful of extraterrestrial dust particles has been isolated and analyzed in these collectors [5] as most of the captured projectiles are expected to be man-made orbital debris. ...
... Various orbit (LEO), in part to characterize the orbital debris environment, but also with the goal of collecting natural micrometeorites [4,5]. To date, however, only a handful of extraterrestrial dust particles has been isolated and analyzed in these collectors [5] as most of the captured projectiles are expected to be man-made orbital debris. ...
... Thus, orbital debris that actually impacted at 6 km s À1 could be misidentified to have impacted at greater than 8 km s À1 , assuming that we have underestimated the mass by a factor of 2. However, the point of the calorimetric technique is to rapidly identify collected dust grains that are good candidates for being extraterrestrial on the basis of their impact velocity. A subsequent direct determination of the projectileÕs composition could easily rule in or out the extraterrestrial origins of the dust grain [6,5]. Sophisticated, in situ techniques are currently being developed which are capable of measuring the elemental and total mass compositions of captured projectiles with a resolution of about $20 pg [14]. ...
The ability of low density silica aerogel collectors to capture partially intact hypervelocity dust grains have made them the material of choice for deployment in space missions. The correlation between the kinetic energy of a captured particle and its track volume (and track length) is poor. This makes estimation of kinetic energy difficult. Motivated by this, we have developed thermally activated fluorescent aerogels that are capable of passively recording a captured dust grain's kinetic energy via the transformation of the amorphous aerogel state into one or more crystalline states that fluoresce efficiently. We will describe our progress in the characterization of the precise relationship between the grain's kinetic energy and track fluorescence.
... Monitoring the dust environment, whether close to Earth or beyond, is therefore important, and there is an extensive history of studies based upon diverse returned spacecraft surfaces (e.g. [1][2][3][4][5][6][7][8][9][10][11]), using progressively more sensitive analytical techniques. Active impact sensors have been deployed on satellites in orbit around Earth and on interplanetary space missions, giving direct measurements of particle size and flux as well as some information about trajectory and velocity, but most have not determined dust composition. ...
... Dedicated capture experiments (e.g. [2][3][4][5]11]) have been used to return materials from space for laboratory analysis, although as with active detectors, sampling of larger dust has been limited by feasible cross-sectional area and exposure duration. In 1990, the return of the large gravity-stabilized long-duration exposure facility (LDEF) [2][3][4][5] after over 5 years in low Earth orbit (LEO) at 331-480 km altitude provided important data on particle impacts. ...
Exposure of the Hubble Space Telescope to space in low Earth orbit resulted in numerous hypervelocity impacts by cosmic dust (micrometeoroids) and anthropogenic particles (orbital debris) on the solar arrays and the radiator shield of the Wide Field and Planetary Camera 2, both subsequently returned to Earth. Solar cells preserve residues from smaller cosmic dust (and orbital debris) but give less reliable information from larger particles. Here, we present images and analyses from electron, ion and X-ray fluorescence microscopes for larger impact features (millimetre- to centimetre-scale) on the radiator shield. Validated by laboratory experiments, these allow interpretation of composition, probable origin and likely dimensions of the larger impactors. The majority (~90%) of impacts by grains greater than 50 μm in size were made by micrometeoroids, dominated by magnesium- and iron-rich silicates and iron sulfides, metallic iron-nickel and chromium-rich spinel similar to that in ordinary chondrite meteorites of asteroid origin. Our re-evaluation of the largest impact features shows substantially fewer large orbital debris impacts than reported by earlier authors. Mismatch to the NASA ORDEM and ESA MASTER models of particle populations in orbit may be partly due to model overestimation of orbital debris flux and underestimation of larger micrometeoroid numbers.
This article is part of the theme issue ‘Dust in the Solar System and beyond’.
... Email: duai@tongji.edu.cn sources [6] . In the NASA Stardust mission [7] , silica aerogels were used in the primary instrument to capture fine particles from both Comet 81P/Wild 2 and interstellar particle [8][9][10][11][12] . ...
... The decomposition of particles eventually was split into the forked tracks although the particle remained intact in the initial part of the track (Figure 9(c)). The morphology is the cone-in-cone structure of the terminal section of tracks and the off-axis location of the impactor residue, which is similar to the track in the Orbital Debris Collector [6] . This may arise from shock waves. ...
As an attractive collector medium for hypervelocity particles, combined with outstanding physical properties and suitable compositional characteristics, SiO 2 aerogel has been deployed on outer space missions and laser shock-loaded collection experiments. In this paper, impact experiments were conducted to understand the penetration process of irregular grains, irregular Al 2 O 3 grains with two different sizes and speeds (~110 μm@7 km/s, ~251 μm@2.3 km/s) at various density silica aerogels. By classifying the shapes of projectile residues and tracks, the morphology of tracks was analyzed. It was observed that there were several kinds of typical tracks in the penetration of irregular grains, accompanied by residues with the shapes of near-sphere, polyhedron, streamlined body wedge, and rotator. The rotational behavior was demonstrated by the final status of one flake projectile as direct evidence. In addition, there was no obvious relationship between the track length and experimental parameters, which may be caused by the uncertain interaction between aerogels and irregular particles. In addition, it confirmed the existence of fragmentation, melting situation by observing the shape of the impact entrance hole. At the same time, optical coherence tomography was used to observe the detail of tracks clearly, which provided a method to characterize the tracks nondestructively.
... Aerogels can be utilized in numerous applications and they have first been used as catalysts or insulating materials (sound and temperature) [2,[8][9][10]. More recently, aerogels are employed in the field of the environment [11][12][13], greenhouse gases sensors [16,17] pharmaceuticals [14,15] but also in exotic applications such as cosmic dust and space debris sensors [21][22][23] or nuclear wastes containment materials [18][19][20]. Like any type of material for a defined application, knowledge of their mechanical properties is necessary. ...
... Sintering is a process by which the surface of a material is reduced by mass transport [12,[22][23][24]. The aerogel network is described as an aggregates assembly (~50-200 nm). ...
In this paper, we present the different characterization techniques used to measure the mechanical properties of silica aerogels. The mechanical behavior of aerogels is generally described in terms of elastic and fragile materials (such as glasses or ceramics) but also in terms of plastic media in compression testing. Because of these very different mechanical behaviors, several types of characterization techniques are proposed in the literature. We first describe the dynamic characterization techniques such as ultrasounds, Brillouin scattering, dynamic mechanical analysis (DMA) to measure the elastic properties: Young’s modulus (E), shear modulus (G), Poisson ratio (υ) but also attenuation and internal friction. Thanks to "static" techniques such as three-point bending, uniaxial compression, compression we also access to the elastic modulus (E) and to the rupture strength (σ). The experimental results show that the values of the elastic and fracture moduli measured are several orders of magnitude lower than those of a material without porosity are. With regard to the brittleness characteristics, Weibull's analysis is used to show the statistical nature of the fracture resistance. We also present the SENB (Single Edge Notched Beam) technique to characterize toughness (KIC) and the stress corrosion mechanisms, which are studied in ambient conditions and temperature by the double cleavage drilled compression experiment (DCDC). In the last part of the paper, we show how, during the isostatic compression test, aerogels behave like plastic materials. The data allow calculating the bulk modulus (K), the amplitude of the plastic deformation and the yield strength (σel), which is the boundary between the elastic and plastic domains. These different techniques allow understanding which parameters influence the overall mechanical behavior of aerogels, such as pore volume, but also pore size, internal connectivity and silanol bounds content. It is shown that the pore size plays a very important role; pores can be considered as flaws in the terms of fracture mechanics.
... The Stardust spacecraft carried an aerogel known as a low-density amorphous SiO 2 to decelerate and capture particles intact. The idea of using aerogel for hypervelocity capture and recovery of particles such as interplanetary dust has been previously investigated from the 90s with early studies and development of techniques conducted in a laboratory set up as well as in space (Barrett et al., 1992;Brownlee et al., 1994;Burchell et al., 1998;Hörz et al., 1998;Kitazawa et al., 1999;Hörz and Zolensky, 2000;Westphal et al., 2002Westphal et al., , 2004Tsou et al., 2003). The analysis of the small cometary dust particle by Stardust revealed signatures of diverse suites of cometary organic compounds including simplest form of amino acid glycine Elsila et al., 2009). ...
... This could be due to ionic interactions between silanol moieties of the aerogel and peptides (based on the electrophoretic results, the degree of dissociation of longer migrating species such as Tyr-Glu-Tyr and Tyr-Asp-Tyr was expected to be lower compared with other peptides). Evidence of accretion of compressed aerogel on captured projectiles (Hörz and Zolensky, 2000) may also enhance such selective liquid extraction. Furthermore, extraction from blank aerogel showed a clean CZE profile under UV spectra, suggesting no contamination above the detection limit (Fig. 6, green trace). ...
The in situ detection of organic molecules in space is key to understanding the variety and the distribution of the building blocks of life, and possibly the detection of extraterrestrial life itself. Gas chromatography mass spectrometry (GC-MS) has been the most sensitive analytical strategy for organic analyses in flight, and was used on missions from NASA's Viking, Phoenix, Curiosity missions to ESA's Rosetta space probe. While pyrolysis GC-MS revealed the first organics on Mars, this step alters or degrades certain fragile molecules that are excellent biosignatures including polypeptides, oligonucleotides and polysaccharides, rendering the intact precursors undetectable. We have identified a solution tailored to the detection of biopolymers and other biomarkers by the use of liquid-based capillary electrophoresis and electrochromatography. In this study, we show that a capillary electrochromatography approach using monolithic stationary phases with tailor-made surface chemistry can separate and identify various polycyclic aromatic hydrocarbons, nucleobases and aromatic acids that could be formed under astrophysically relevant conditions. In order to simulate flyby organic sample capture, we conducted hypervelocity impact experiments which consisted of accelerating peptide-soaked montmorillonite particles to a speed of 5.6 km s ⁻¹ , and capturing them in an amorphous silica aerogel of 10 mg cm ⁻³ bulk density. Bulk peptide extraction from aerogel followed by capillary zone electrophoresis led to the detection of only two stereoisomeric peptide peaks. The recovery rates of each step of the extraction procedure after the hypervelocity impact suggest that major peptide loss occurred during the impact. Our study provides initial exploration of feasibility of this approach for capturing intact peptides, and subsequently detecting candidate biomolecules during flight missions that would be missed by GC-MS alone. As the monolith-based electrochromatography technology could be customized to detect specific classes of compounds as well as miniaturized, these results demonstrate the potential of the instrumentation for future astrobiology-related spaceflight missions.
... In order to test the feasibility of these techniques and to develop them for the return of the Stardust collectors, we used a keystone extracted from the Orbital Debris Collection Experiment (ODCE) from NASA (Hö rz et al., 2000). We describe here the analytical procedures and the first results obtained. ...
... Such an experiment that is now currently investigated is the NASA ODCE, that was exposed outside the MIR station for 18 months, in 1996-1997 for the study of the orbital debris environment of the station. Fortunately, the station was hit by a relatively large chondritic particle and the resulting secondary particles were collected by some of ODCE aerogel tiles and are available for analysis (Hö rz et al., 2000). ...
In January 2006, the NASA Stardust mission will return, trapped in aerogel, the first samples of cometary and contemporary interstellar dust origins. Their analyses will require high spatial resolution techniques, among which Synchrotron X-rays MicroFluorescence (SR-XRF) techniques for in-situ identification of the incident grains [1]. In the case of aerogel, it is possible to optically scan the samples and locate the trapped grains, which can then be extracted using techniques developed at Berkeley [2]. Pieces of aerogel a few hundreds of microns large that contain an incident grain and its penetration track, called ``aerogel keystones'', can now be produced self supported on microforklifts [3]. The non-destructive identification of the material distributed inside a keystone by SR-XRF can then be followed by other analyses, like, for instance a spectroscopic identification that can also be partly performed in situ, such as Raman. The extraction of the grain from the aerogel is not always possible if the grain is too small or has disintegrated and has been distributed along the entrance track. In order to test the analytical protocol, we analysed various samples : first keystones containing a dust grain originating from the chondritic swarm identified in the Orbital Debris Collection Experiment (ODCE) that was deployed for 18 months outside the Russian space station MIR [3]. We also analysed a keystone from the COMET99 experiment, that was deployed outside the MIR station, during the crossing of the Earth by the Leonid meteor stream [4]. This study was completed with keystones of aerogel in which were trapped grains of the Murchison meteorite, by use of a dust gun projection. We present here results that indicate a very strong tendency of the incident particles to break up during their slowing down in the aerogel. These non-destructive techniques might be among the only ones to be used for analysing the interstellar grains trapped in the Stardust aerogel and for those cometary grains that might have lost most of their material along the penetration track. References - [1] J. Borg et al. (2002) PSS, 50, 1055-1065. [2] A.J.Westphal et al. (2002) Met. {& Planet. Sci., }37, 6, 855-865. [3] A.J.Westphal et al. (2004) Met. {& Planet. Sci., }submitted. [4] J. Borg PSS 50, 9, 889-894 (2002).
... In order to test the feasibility of these techniques and to develop them for the return of the Stardust collectors, we used a keystone extracted from the Orbital Debris Collection Experiment (ODCE) from NASA (Hö rz et al., 2000). We describe here the analytical procedures and the first results obtained. ...
... Such an experiment that is now currently investigated is the NASA ODCE, that was exposed outside the MIR station for 18 months, in 1996-1997 for the study of the orbital debris environment of the station. Fortunately, the station was hit by a relatively large chondritic particle and the resulting secondary particles were collected by some of ODCE aerogel tiles and are available for analysis (Hö rz et al., 2000). ...
In January 2006, the NASA Stardust mission will return, trapped in aerogel, the first samples of cometary and contemporary interstellar dust. Their analyses will require high spatial resolution techniques. An example is Synchrotron X-ray analysis, which could be useful for in situ identification of the captured grains. In the case of aerogel, it is possible to optically scan the samples and locate the trapped grains, which can then be extracted in pieces of aerogel, called “keystones”, a few hundreds of microns large and self-supported on microforklifts that contain one incident grain and its penetration track. The non-destructive identification of the material distributed inside a keystone can be completed using Synchrotron X-ray microbeams either in the fluorescence or the absorption mode. In order to develop an analytical protocol, we analysed a keystone containing a dust grain originating from the chondritic swarm identified in the Orbital Debris Collection Experiment (ODCE) that was deployed for 18 months outside the Russian space station MIR. The results we present concern μ-fluorescence mappings and XANES at the Fe K-edge measurements. They indicate a very strong tendency of the incident particle to break up into many fragments during the slowing in the aerogel. Furthermore, a structural evolution of the grain is also possible, during the slowing down in the aerogel. These non-destructive techniques might be among the only ones to be used for analysing the interstellar grains trapped in the Stardust aerogel and for those cometary grains that might have lost most of their material along the penetration track.
... At the time, only nine impacts visible with the aid of a magnifying glass were identified, a slightly disappointing yield. However, owing to the relatively small exposure area-time product of the experiment as compared with, for instance, NASA's Orbital Debris Collector, ODC, [2,3] mounted on Mir -only about 5% -we are required to analyse down to much smaller sizes. Table 2 for the Ram and Wake faces, assuming pure ram and wake exposure for the entire 315-day period. ...
... A close-up of this is shown in Fig. 8. This phenomenon has not been observed in earlier aerogel experiments, such as ODC [2,3]. Although some slight evidence of contamination is visible to the naked eye on the other surfaces and the experimental frame, the polyimide cover films still appear pristine. ...
The National Space Development Agency of Japan (NASDA) have deployed
three sets of two passive experiments on the exterior of the Russian
Service Module on the International Space Station: the Micro-Particles
Capturer and the Space Environment Exposure Device, known collectively
as MPAC&SEED. The MPAC segment of each unit consists mainly of a
front and back face, nominally ram- and wake-pointing, each of which
contains aerogel and polyimide foam tiles for capturing micrometeoroids
and small space debris particles. In addition, the ram face contains a
6061-T6 aluminium witness plate. We provide a description of the MPAC,
summarise the inspection and analysis performed to date, discuss the
results so far achieved, and lay out our plans for the remainder of the
work.
... Another crucial element of NFC aerogels for use as thermal insulation is their barrier property. Due to their excellent thermal barrier qualities, aerogel was previously used by NASA Stardust mission to trap and collect interstellar and comet dust particles from a comet named "Wild 2." But because of the extraordinarily hot environment, they shrank strangely and developed mechanical brittleness (Hörz et al. 2000). Because cellulose-based insulation materials are renewable, recyclable, nontoxic, and sustainable and require straightforward production processes, there is an increasing worry about them (Aditya et al. 2017). ...
Aerogels are highly porous solid-state structures with low density and have numerous properties, such as high absorption activity, low dielectric constant, high sound absorption, and low thermal conductivity. These properties made aerogels worthwhile as acoustic and thermal insulators, pharmaceutical carriers, flexible energy storage devices, and a template for synthesizing inorganic nanomaterials. From an environmental aspect, biodegradable and green aerogels are in light of the research. Cellulose, extracted from various natural sources, is the most abundant and environmentally benign material employed as a starting material for aerogels. This review provides insights into the introduction of cellulose nanofiber aerogels and their fabrication processes using various pre-treatment techniques, such as enzymatic, chemical, or ionic-liquid methods, and several drying methods. Following this, the properties, thermal performance, and morphology that affects the thermal insulation of nano-fibrillated cellulosic aerogels are discussed. Owing to their outstanding thermal insulating properties, nano-fibrillated cellulose aerogels would be a potential choice for insulation in building applications. The steps toward sustainability require such resource-bounded research development.
... Silica aerogels are widely used to capture interplanetary dust particles (IDPs) in the space missions of cosmic dust sample collection, such as Stardust, TANPOPO, and other space missions. [1][2][3][4][5][6][7] This is due to its low density, high porosity, and high light transmission, which are the superior physical properties derived from its nanoporous microstructure. Silica aerogel also possesses other preeminent physical properties, such as low thermal conductivity, low sound velocity, and low refractive index. ...
Porous silica aerogel is an ultra-low-density material with nanostructures that leads to its excellent physio-chemical properties. Considering the characteristics of the material, a micromechanical model to assess the microstructure–property relations is highly demanded. In this study, a cuboctahedron unit cell is proposed as a representative volume element of the silica aerogel to correlate with its density and compressive stress–strain curves. The backbone lattice-structure combined with the dead ends is established to represent the periodic configuration of the aerogel. It is implemented in both the numerical scheme with the finite element method and the analytical model by modifying the Gibson–Ashby model. Furthermore, the crushing behaviors of the material under large deformation are discussed in the numerical study. Due to the features of load-bearing skeletons and non-load-bearing short pillars, the compression process of the silica aerogel exhibits strong nonlinear behaviors. Overall, this computational micromechanics model is capable of accurately simulating the stress–strain curves of silica aerogels with different densities under different loading levels. This work provides a general framework to quantify the microstructure–property relations of porous silica aerogels and also other porous materials.
... In contrast, they switch to mechanically fragile material and experienced unusual shrinkage behavior because of the high-temperature climate [149,150]. However, there are some limitations on the efficient operation of cellulose aerogels, as hornification, moisture sensitivity, density and contraction changes due to drying methodology restrict their applications in lightweight engineering materials and harsh environmental circumstances [151]. ...
... In contrast, they switch to mechanically fragile material and experienced unusual shrinkage behavior because of the high-temperature climate [149,150]. However, there are some limitations on the efficient operation of cellulose aerogels, as hornification, moisture sensitivity, density and contraction changes due to drying methodology restrict their applications in lightweight engineering materials and harsh environmental circumstances [151]. ...
Considering the recent massive usability of plastics that are nonbiodegradable and unsuitable for our environment, our scientists wanted to introduce green technology-based and environmentally friendly products to ensure our global life. In this regard, a most abundant naturally occurring purified plant matter biopolymer, “Nanocellulose,” has been considered for its outstanding properties. It consists of impressive chemical and physical properties, gas inflammable, high infinity to water, biodegradable (not like petroleum), rigid than Kevlar and more robust than steel, it in composites form can be used in electrical and thermally conductive materials. Nanocellulose-based aerogels are one of the attractive fields for researchers because of their extraordinary mechanical properties, low density, large specific surface area, high porosity, low thermal conductivity, and low electrical conductivity. This review consists of structure, source, and method of extraction for nanocellulose, its properties, and applications, as well as the illustration of, in what manner the porous morphology and characteristics of aerogels based on nanocellulose can be adapted for applications such as thermal insulation and energy storage, air filtration, water filtration, precursors of carbon aerogels.
... Some unique properties of aerogels, including low thermal conductivity (k, 0.01-0.03 W/(m·K) at 300 K), low density (ρ, <0.1 g/cm 3 ), and high porosity (φ p , 75%-99%) (Yuan et al., 2012), make aerogels promising candidates for some of most extreme applications, such as laser targets (Fearon et al., 1987;Alon et al., 1995), microelectronic devices (Hrubesh & Poco, 1995;Xiao et al., 2000), magnetic nanocomposites (Casas et al., 2001), acoustic dampening elements (Cross et al., 1989;Forest et al., 2001), micro-particle capturers (Anderson and Ahrens, 1994;Horz et al., 2000), and heat insulators (Alkemper et al., 1995;Kwon et al., 2000;Moner-Girona et al., 2001;Reim et al., 2005;Bardy et al., 2007;Pacheco-Torgal et al., 2018). Most prominently, aerogels are utilized as thermal insulators in the areas of clothing, construction, aerospace, and energy due to their extremely low thermal conductivities. ...
An experimental study was conducted for evaluating the feasibility of using silica aerogel as thermal insulator for combustor liners. Aerogels are a superior material for minimizing heat flux to the metal structure of the combustion liner due to their low thermal conductivity. In this study, a conical natural gas fired swirling-flame combustor was utilized for reproducing the combustion environment. The silica aerogel blanket was attached to the inner side of a perforated combustor liner. Temperature distribution on the outer side of the combustion liner was measured using a calibrated IR camera. To create a protective cooling film over the aerogel surface, cooling air was supplied from the back side of the perforated metal liner and was allowed to penetrate the silica aerogel blanket to be discharged to the combustor. As the combustor was operated at a fixed equivalence ratio of 0.83, cooling air flow rates were varied to evaluate the effectiveness of transpiration cooling on the aerogel blanket as various cooling flow rates. The measured evolution of temperature distribution confirmed thermal equilibriums for every test condition with transpiration cooling. The measured temperature distribution of metal liner demonstrated superior thermal insulation of aerogel blanket under the protection of cooling film with a temperature difference as high as 1580 K between combustion products temperature and the metal liner temperature on the back side. In addition, silica aerogel samples were examined before and after the combustion tests to understand their material degradation exposing to a typical gas turbine combustor environment using high-resolution scanning electron microscope (SEM). Test results suggest multiple degradation mechanisms to the silica aerogel blanket samples from the combustion tests. Improvements can be made to the silica aerogel blankets for a more resilient thermal insulator, for example, by replacing glass fibers in silica aerogels.
... Some unique properties of aerogels, including low thermal conductivity (k, 0.01-0.03 W/(m·K) at 300K), low density (ρ, <0.1 g/cm3), and high porosity (φp, 75%-99%) (Yuan et al, 2012), make aerogels promising candidates for some of most extreme applications, such as laser targets (Fearon et al, 1987, Alon et al, 1995, microelectronic devices (Hrubesh et al, 1995, Xiao et al, 2000, magnetic nanocomposites (Casas et al, 2001), acoustic dampening elements (Cross et al, 1989, Forest et al, 2001, micro-particle capturers (Anderson et al, 1994, Horz et al, 2000, and heat insulators (Alkemper et al, 1995, Moner-Girona et al, 2001, Kwon et al, 2000, Reim et al, 2005, Bardy et al, 2007, Pacheco-Torgal et al, 2018. Most prominently, aerogels are utilized as thermal insulators in the areas of clothing, construction, aerospace, and energy due to their extremely low thermal conductivities. ...
An experimental study was conducted for evaluating the feasibility of using silica aerogel as thermal insulator for combustor liners. Aerogels are a superior material for minimizing heat flux to the metal structure of the combustion liner due to their low thermal conductivity. In this study, a conical natural gas fired swirling-flame combustor was utilized for reproducing the combustion environment that's typical to a gas turbine combustor. The silica aerogel blanket was attached to the inner side of a perforated combustor liner. Temperature distribution on the outer side of the combustion liner was measured using a calibrated thermal infrared (IR) camera. To minimize the uncertainty in steel surface emissivity due to surface oxidation at elevated temperatures, designated areas on the metal surface were coated with a ceramic cement whose emissivity was carefully determined. To create a protective cooling film over the aerogel surface, cooling air was supplied from the back side of the perforated metal liner and was allowed to penetrate the silica aerogel blanket to be discharged to the combustor. As the combustor was operated at a fixed equivalence ratio of 0.83, cooling air flow rates were varied to evaluate the effectiveness of transpiration cooling on the aerogel blanket as various cooling flow rates.
The measured evolutions of temperature distribution confirmed thermal equilibriums for every test condition with transpiration cooling. The measured temperature distribution of metal liner demonstrated superior thermal insulation of aerogel blanket under the protection of cooling film with a temperature difference as high as 1580 K between combustion products temperature and the metal liner temperature on the back side. In addition, silica aerogel samples were examined before and after the combustion tests to understand their material degradation exposing to a typical gas turbine combustor environment using high-resolution scanning electron microscope (SEM). Test results suggest multiple degradation mechanisms to the silica aerogel blanket samples from the combustion tests. The material analysis suggests that improvements can be made to the silica aerogel blankets for a more resilient thermal insulator, for example, by replacing glass fibers in silica aerogels.
... Previously, the Stardust mission of NASA utilized aerogel to arrest and collect interstellar and comet dust particles from a comet "Wild 2 " because of their high thermal barrier properties. However, due to an extremely high-temperature environment, they became mechanically brittle and experienced unusual shrinkage behavior [184] . Thus, there is an emerging concern in cellulose-based insulation materials because of their renewability, recyclability, non-toxicity, sustainability and require simplistic routes for production [185] . ...
With the depletion of fossil fuel and increasing environmental concerns, the modernized era of technology is urgently in need for sustainable and eco-friendly materials. The industrial sector certainly possesses enough resources for the production of available cost-effective, renewable, reusable, and sustainable raw materials. Ultralight, eco-friendly and renewable cellulosic aerogels are one of the most accentuated materials in the polymer research field due to their highly abundant and inexpensive raw material, biocompatibility, high specific surface area and other feasible properties. This review summarizes the recent progress in cellulosic aerogels, their main processing route, including a detailed description of versatile new solvents along with some essential properties of cellulosic aerogels and illustrate how their variety of chemical functionalities can be adjusted for applications in the fields of thermal insulation, fire retardant, antibacterial, CO2 capture and energy storage systems. A detailed morphological analysis has been elaborated and effect of processing route, solvent medium and drying procedure on the morphology of cellulosic aerogels is also decribed. Finally, we propose some suggestions to the functionalization such as silanized cellulosic aerogels and their applications in antibacterial activity yet they are still in progress and need further study for future research.
... Excavated materials are ejected at much lower velocities and higher ejection angles, so that a minimum amount of materials would be ejected beyond the crater interior. As solid foam is very weakly resistant to projectile penetration, craters tend to be much smaller in diameter and deeper than a similar impact into solid basalt or typical regolith (Figures S23a and S23b), as evidenced by numerous laboratory and numerical simulation impact experiments (e.g., Figure S23, Collins et al., 2011;Flynn et al., 2015;Hörz et al., 2000;Housen & Holsapple, 2003Michikami et al., 2007;Schultz et al., 2002;Wünnemann et al., 2006Wünnemann et al., , 2012Wünnemann et al., , 2011 and spacecraft observations at highly porous asteroids (e.g., Housen et al., 1999). Such high aspect ratios will decrease rapidly due to filling with crushed materials, producing shallower depressions. ...
Ina, a distinctive ~2 × 3 km D‐shaped depression, is composed of unusual bulbous‐shaped mounds surrounded by optically immature hummocky/blocky floor units. The crisp appearance, optical immaturity, and low number of superposed impact craters combine to strongly suggest a geologically recent formation for Ina, but the specific formation mechanism remains controversial. We reconfirm that Ina is a summit pit crater/vent on a small shield volcano ~3.5 billion years old. Following detailed characterization, we interpret the range of Ina characteristics to be consistent with a two‐component model of origin during the waning stages of summit pit eruption activities. The Ina pit crater floor is interpreted to be dominated by the products of late‐stage, low‐rise rate magmatic dike emplacement. Magma in the dike underwent significant shallow degassing and vesicle formation, followed by continued degassing below the solidified and highly microvesicular and macrovesicular lava lake crust, resulting in cracking of the crust and extrusion of gas‐rich magmatic foams onto the lava lake crust to form the mounds. These unique substrate characteristics (highly porous aerogel‐like foam mounds and floor terrains with large vesicles and void space) exert important effects on subsequent impact crater characteristics and populations, influencing (1) optical maturation processes, (2) regolith development, and (3) landscape evolution by modifying the nature and evolution of superposed impact craters and thus producing anomalously young crater retention ages. Accounting for these effects results in a shift of crater size‐frequency distribution model ages from <100 million years to ~3.5 billion years, contemporaneous with the underlying ancient shield volcano.
... The physical attributes of low density aerogel make it one of the most useful particle collector media [5]. Prior to Stardust, aerogel blocks were exposed in low Earth orbit (LEO) aboard Mir [6,7]. Numerous impact tracks were collected, some subsequently sent out to laboratories around the world to help develop sample preparation and analytical methods appropriate for Stardust (e.g. ...
In the last two decades, experimental hypervelocity impacts (HVI) using light gas gun (LGG) shots have answered numerous questions about how comet dust can be captured, and have repeatedly provided explanations for phenomena encountered during study of samples returned from comet Wild 2 by the NASA JPL-Caltech Stardust mission. LGG experiments were carried out in several laboratories, especially in NASA, in Japan, and at the University of Kent (Canterbury, UK). Analogue materials were produced for testing and calibration of novel and diverse microanalysis methods in research institutions around the world. Impact tracks on low density silica aerogel and craters on Al alloy foils gave calibration in determination of size and composition for Wild 2 particles, and experimental HVI features revealed how internal grain size and structure of comet dust grains can be interpreted from detailed shapes of impact structures. Firing of analogue mineral materials helped us to understand how specific mineral components are preserved, how crystal structure and composition are altered during capture, and how this may limit interpretation of collected grains. In this review, I explain the range of studies performed so far, and suggest new experiments are needed to help understand: preservation, alteration and loss of subtle internal grain structures; modification of elemental and isotopic signatures in relatively fragile materials (e.g. organic matter); and the size of particles making bulbous aerogel tracks.
... While these 39 collections include particles exhibiting different degrees of thermal alteration (ranging from 40 unmelted particles to cosmic spherules) and weathering, it has been possible to establish 41 their general properties before aerobraking (Jessberger, et al., 2001, Kohout, et al., 2014, 42 Taylor, et al., 2012. IDPs size and composition have also been investigated by particle 43 detectors on board orbital spacecraft such as the Long Duration Exposure Facility (LDEF) 44 (Love and Brownlee, 1993) and the MIR Space Station (Hörz, et al., 2000), where the major 45 difficulty has been characterising the effect of the high speed impacts (v >11 km s -1 ) on the 46 exposed materials (e.g. aluminium, aerogel). ...
Analogues have been developed and characterised for both interplanetary dust and meteoric smoke particles. These include amorphous materials with elemental compositions similar to the olivine mineral solid solution series, a variety of iron oxides, undifferentiated meteorites (chondrites) and minerals which can be considered good terrestrial proxies to some phases present in meteorites. The products have been subjected to a suite of analytical techniques to demonstrate their suitability as analogues for the target materials.
... Low-density aerogel can reduce the damage caused by impact. Aerogels have been used in space experiments to capture artificial debris and interplanetary dust particles (Yano and McDonnell, 1994;Hörz et al., 2000;Kitazawa et al., 2000;Brownlee et al., 2006). Our silica aerogel block has two layers, one 0.01 g/cc is the lowest-density aerogel ever used in space. ...
Unlabelled:
The Tanpopo mission will address fundamental questions on the origin of terrestrial life. The main goal is to test the panspermia hypothesis. Panspermia is a long-standing hypothesis suggesting the interplanetary transport of microbes. Another goal is to test the possible origin of organic compounds carried from space by micrometeorites before the terrestrial origin of life. To investigate the panspermia hypothesis and the possible space origin of organic compounds, we performed space experiments at the Exposed Facility (EF) of the Japanese Experiment Module (JEM) of the International Space Station (ISS). The mission was named Tanpopo, which in Japanese means dandelion. We capture any orbiting microparticles, such as micrometeorites, space debris, and terrestrial particles carrying microbes as bioaerosols, by using blocks of silica aerogel. We also test the survival of microbial species and organic compounds in the space environment for up to 3 years. The goal of this review is to introduce an overview of the Tanpopo mission with particular emphasis on the investigation of the interplanetary transfer of microbes. The Exposed Experiment Handrail Attachment Mechanism with aluminum Capture Panels (CPs) and Exposure Panels (EPs) was exposed on the EF-JEM on May 26, 2015. The first CPs and EPs will be returned to the ground in mid-2016. Possible escape of terrestrial microbes from Earth to space will be evaluated by investigating the upper limit of terrestrial microbes by the capture experiment. Possible mechanisms for transfer of microbes over the stratosphere and an investigation of the effect of the microbial cell-aggregate size on survivability in space will also be discussed.
Key words:
Panspermia-Astrobiology-Low-Earth orbit. Astrobiology 16, 363-376.
... A method of referring to the major morphological components of a track, e.g., cavity, styli etc. was developed by Hörz et al. (1998Hörz et al. ( , 2000 and is illustrated on a Stardust track in Fig. 1. Also shown in Fig. 1 is a top view of the same track which shows a complex structure. ...
The capture of 81P/Wild 2 cometary particles in aerogel with a well-defined impact velocity (6.1 km s(-1)) has provided a wealth of data concerning the composition of Jupiter-family comets. To interpret this data we must understand the capture processes in the aerogel. A major category of tracks are those with bulbous cavities lined with particle fragments. We present a new model to account for the production of these "turnip"-shaped impact cavities. The model uses a thermodynamic approach in order to account for the likely expansion of vapors from particles rich in volatile species. Volume measurements of some of the largest Stardust tracks analysed so far, together with theoretical considerations, indicate that for the majority of Stardust cometary aggregate particle impacts, fragmentation of relatively weak impactors (combined with radial expansion of the resulting subgrains) is the leading cause of bulbous track production, while volatile release of vapors played a secondary role.
... Low-density aerogel can reduce the damage caused by impact. Aerogels have been used in space experiments to capture artificial debris and interplanetary dust particles (Yano and McDonnell, 1994;Hörz et al., 2000;Kitazawa et al., 2000;Brownlee et al., 2006). Our silica aerogel block has two layers, one 0.01 g/cc is the lowest-density aerogel ever used in space. ...
The mechanical thermometer using a bimetallic strip coil was developed for the Tanpopo mission. The Tanpopo mission is a multi-year passive exposure experiment for astrobiology exposure and micrometeoroid capture onboard the Exposed Experiment Handrail Attachment Mechanism (ExHAM) at the Japanese Experiment Module ‘Kibo’ (JEM) Exposed Facility (EF) on the International Space Station (ISS). The Tanpopo mission apparatuses were launched by the SpaceX-6 Dragon CRS-6 on April 14 2015, from the Cape Canaveral Air Force Station in the U.S.A. Since its microbial exposure experiment requires recording the maximum temperature that the Tanpopo exposure panel experiences, we have developed a mechanical thermometer with no electric power supplied from the ExHAM. At a given time and orbital position of the ISS, the thermometer indicator was video-imaged by the extravehicular video camera attached to the Kibo-EF and controlled from the ground. With these images analyzed, we were able to derive the maximum temperature of the Tanpopo exposure panels on the space pointing face of the ExHAM as 23.9±5 °C. Now this passive and mechanical thermometer is available to other space missions with no electric supplies required and thus highly expands the possibility of new extravehicular experiments and explorations for both human and robotic missions.
... L'impact laser de 1,18 TW/cm 2 induit dans la cible solide une pression maximale de 27,5 GPa. La figure III.49 présente des observations par microscopie optique à travers le collecteur des fragments d'or récupérés dans le varagel. Ces observations nous permettent de distinguer deux types de fragments : (i) les fragments "liquides" et (ii) les fragments "solides". ...
The irradiation of a metallic target by a high power laser pulse induces a shock wave in the material. Under some conditions, it leads to the production of high velocity ejecta which can damage the optical environment (lenses, mirrors, windows, etc.). With the ongoing development of high energy laser facilities designed to achieve inertial confinement fusion, such as the Laser MégaJoule in France or the National Ignition Facility in the USA, the question of debris ejection from metallic samples subjected to intense laser irradiation has become a key issue. It is necessary to understand fragmentation processes induced by laser shock, and to anticipate and quantify generated fragments, in order to design suitable protections and experiments, and to preserve laser facilities. The main fragmentation processes which can occur in a laser-shock-loaded metallic target and generate high velocity ejecta are : (i) microjetting, which occurs upon reflection of the incident compressive front from the free surface, (ii) spallation, which is due to the later interaction of the release wave reflected from that surface with the incident unloading wave and (iii) dynamic punching of thin targets. Experimental campaigns have been performed on high energy laser facilities in the Centre d'Études Scientifiques et Techniques d'Aquitaine (CESTA, CEA, Alisé facility) and in the Laboratoire pour l'Utilisation des Lasers Intenses (LULI, École Polytechnique, LULI 2000 facility). Gold and aluminium have been mainly studied because they are the two main metallic components of the target which will be used to achieved the inertial confinement fusion. Specific diagnostics have been developed and used during these experiments to study the dynamic fragmentation : transverse shadowgraphy, free surface velocity measurement and recovery of generated fragments. Experimental results have been compared with numerical predictions obtained with a bi-dimensional hydrodynamic code, where a specific numerical model has been implemented. The ability of simulations to reproduce dynamic fragmentation of laser shock-loaded metallic targets have been verified.
... However, aerogel could not yield reliable dynamic data for each particle, including chronological information about the collisions. Nevertheless, the unique ability of aerogel to preserve and trap unmolten residues at relatively high velocities in low-Earth orbit was confirmed compared to traditional nonporous media; those threshold velocities for vaporization were much smaller than aerogel [105,107]. ...
Aerogels are highly porous structures prepared via a sol-gel process and supercritical drying technology. Among the classes of aerogels, silica aerogel exhibits the most remarkable physical properties, possessing lower density, thermal conductivity, refractive index, and dielectric constant than any solids. Its acoustical property is such that it can absorb the sound waves reducing speed to 100 m/s compared to 332 m/s for air. However, when it comes to commercialization, the result is not as expected. It seems that mass production, particularly in the aerospace industry, has dawdled behind. This paper highlights the evolution of aerogels in general and discusses the functions and significances of silica aerogel in previous astronautical applications. Future outer-space applications have been proposed as per the current research trend. Finally, the implementation of conventional silica aerogel in aeronautics is argued with an alternative known as Maerogel.
... This means that the sprayed materials may be removed by washing without destroying the detector, and can also be studied separately. Aerogels have been used by NASA [39] and then on NIF [21] to study debris, but the debris stay embedded in the porous silica material that composes the aerogel. Therefore this could especially be of interest on facilities such as NIF where we will be able to access a new range of parameters in the laboratory and where new materials will be created. ...
Proton radiography is a very powerful diagnostic but in some high debris environments it may be challenging to get a good signal-to-noise ratio radiograph to gain insights into the electric and magnetic field topology, and thus the basic physics. Such environments are produced for example on z-pinches and also on lasers such as the National Ignition Facility. We demonstrate here the feasibility of clean, very high signal-to-noise ratio proton radiographs in extremely hostile environments.
... A method of referring to the major morphological components of a track, e.g., cavity, styli etc. was developed by Hörz et al. (1998Hörz et al. ( , 2000 and is illustrated on a Stardust track in Fig. 1. Also shown in Fig. 1 is a top view of the same track which shows a complex structure. ...
The capture of 81P/Wild 2 cometary particles in aerogel with a
well-defined impact velocity (6.1 km s-1) has provided a wealth of
data concerning the composition of Jupiter-family comets. To interpret
this data we must understand the capture processes in the aerogel. A
major category of tracks are those with bulbous cavities lined with
particle fragments. We present a new model to account for the production
of these “turnip”-shaped impact cavities. The model uses a
thermodynamic approach in order to account for the likely expansion of
vapors from particles rich in volatile species. Volume measurements of
some of the largest Stardust tracks analysed so far, together with
theoretical considerations, indicate that for the majority of Stardust
cometary aggregate particle impacts, fragmentation of relatively weak
impactors (combined with radial expansion of the resulting subgrains) is
the leading cause of bulbous track production, while volatile release of
vapors played a secondary role.
... Low-density aerogel can reduce the damage caused by impact. Aerogels have been used in space experiments to capture artificial debris and interplanetary dust particles (Yano and McDonnell, 1994; Hörz et al., 2000; Kitazawa et al., 2000; Brownlee et al., 2006). Our silica aerogel block has two layers, one 0.01 g/cc is the lowest-density aerogel ever used in space. ...
Microbes have been collected from high altitude using balloons, aircraft and meteorological rockets since 1936. Spore forming fungi and Bacilli, and Micrococci (probably Deinococci) have been isolated in these experiments. These spores and Deinococci are known by their extremely high resistance against UV, gamma ray, and other radiation. We have also collected microorganisms at high altitude by using an aircraft and balloons. We collected two novel species of the genus Deinococcus, one from top of troposphere (D. aerius) and the other from bottom of stratosphere (D. aetherius). These two species showed high resistance comparable with D. radiodurans R1 to the UV and radiation such as gamma ray. If microbes could be found present even at the higher altitude of low earth orbit (400km), the fact would endorse the possible interplanetary migration of terrestrial life. Indeed, to explain how organisms on the Earth were originated at the quite early stage of the history of Earth, panspermia hypothesis was proposed. Recent findings of the Martian meteorite suggested possible existence of extraterrestrial life, and interplanetary migration of life as well. We proposed the "Tanpopo" mission to examine possible interplanetary migration of microbes, and organic compounds on Japan Experimental Module (JEM) of the International Space Station (ISS). Two of six subthemes in Tanpopo are on the possible interplanetary migration of microbes --- capture experiment of microbes at the ISS orbit and space exposure experiment of microbes. In this paper, we focus on the space exposure experiment of microbes. In our proposal, microbes will be exposed to the space environment with/without model-clay materials that might protect microbes from vacuum UV and cosmic rays. Spore of Bacillus sp., and vegetative cells of D. radiodurans and our novel deinococcal species isolated from high altitude are candidates for the exposure experiment. In preliminary experiments, clay-materials tend to increase survivability of microorganisms under irradiation of heavy ion beam and other radiation. In this paper, we discuss current status of exposure experiment of microorganisms defined for the Tanpopo mission.
... Analytical SEM has already proven a very useful tool in the location and examination of materials trapped in aerogel (e.g., Hörz et al. 2000. The suite of essentially nondestructive imaging and analysis methods that can be supported on a SEM allow rapid examination of broken and cut surfaces of aerogel, and the location of impacting particle remnants in situ within impact tracks and their analysis (Graham et al. 2004b). ...
Aerogel is an ultra-low-density material that can be used to capture small particles incident upon it at speeds in excess of 1 km s−1. This permits capture of cosmic dust in space where the high speeds usually result in destructive impact events. The performance of aerogel in laboratory impact tests is described. Completely intact capture is rare; most studies show that between 10% to 100% of the incident particle's mass is captured. However, in all cases unaltered domains were found in the particles captured in the laboratory at speeds up to 6 or 7 km s−1. Several analytic techniques can be applied in situ to particles captured in aerogel, yielding data on the preimpact composition of the particle. Extraction techniques for removing small particles from aerogel are described, and after extraction, handling and analysis in the laboratory can proceed as for any small-sized particle. Coupled with the survival of intact regions in the captured particles, this allows detailed identification of the com...
This chapter discusses the emerging and promising field of environmental applications of aerogels. Due to their large pore volume, specific surface area, and diverse range of tailorable solid-phase and surface chemistries, aerogel materials are interesting candidates for addressing many challenging environmental remediation objectives. Herein we review the use of silicate, non-silicate, and allophane-clay-based aerogels in several challenging environmental remediation applications including the removal of air pollutants, water remediation, oil spill reclamation, heavy metal capture, CO2 sequestration, trapping of pesticides, immobilization of nuclear waste, and capture of orbital space debris.
In this handbook, we explore the diverse class of porous materials called aerogels – what they are, how they are made, how they are characterized, materials properties they can exhibit, their applications, and their increasing role in commerce. In this chapter, we provide the reader with a general introduction to the topic of aerogels and an overview of their history.
NASA has used aerogel in several space exploration missions over the last two decades. Aerogel has been used as a hypervelocity particle capture medium (Stardust) and as thermal insulation for the Mars Pathfinder, Mars Exploration Rovers, and Mars Science Laboratory. Future applications of aerogel are also discussed and include the proposed use of aerogel as a sample collection medium to return upper atmosphere particles from Mars to Earth and as thermal insulation in thermal-to-electric generators for future space missions and terrestrial waste-heat recovery technology.
This review (in Japanese) highlights the results on the Stardust mission organics preliminary examination of the returned Comet 81P/Wild 2 particles, based on the Science article published in December 15, 2006. The recent developments of studies on organics in chondritic meteorites and/or interstellar dust particles using modern instruments are also described for seeking relations of organic characteristics among the three extraterrestrial samples. In addition, potential chemistry for which cometary and meteoritic organics were responsible as a source of exogenous delivery to the early Earth is discussed.
In this study, we present results from hypervelocity impacts of iron particles onto smooth surfaces under shallow incidence. For the first time, the submicron fragments of the projectiles were measured using a delay-line detector combined with a multichannel plate. Micron-sized spherical iron particles with speeds between 4 - 40 km/s are fired by a dust accelerator facility and impact on an optical mirror target at grazing angles of 2°, 4°, and 6° from the horizontal. Individual fragments generated in each impact event have been measured and analyzed including their speeds, masses, and trajectories. The total mass and momentum of fragments are comparable to their parent projectile. It is observed that most fragments have speeds exceeding 80% of pre-impact velocities. Fragments generated at incident angle of 2° leave the target surface with even lower elevation angles of around 1°. The majority of impact fragments generated under incident angles of 4° and 6° form a spatial distribution centered an axis of 5° elevation, which increases with increasing impact speed. Furthermore, azimuthal scattering occurs with a distribution concentrated within ±10°.
The decade of the 2020s promises to be when humanity returns to space beyond Earth orbit, with several nations trying to place astronauts on the Moon, before going further into deep space. As part of such a programme, NASA and partner organisations, propose to build a Deep Space Gateway in lunar orbit by the mid-2020s. This would be visited regularly and offer a platform for science as well as for human activity. Payloads that can be mounted externally on the Gateway offer the chance to, amongst other scientific goals, monitor and observe the dust flux in the vicinity of the Moon. This paper looks at relevant technologies to measure dust which will impact the exposed surface at high speed. Flux estimates and a model payload of detectors are described. It is predicted that the flux is sufficient to permit studies of cometary vs. asteroidal dust and their composition, and to sample interstellar dust streams. This may also be the last opportunity to measure the natural dust flux near the Moon before the current, relatively pristine environment, is contaminated by debris, as humanity’s interest in the Moon generates increased activity in that vicinity in coming decades.
I have been studying mineralogy and petrology of various kinds of extraterrestrial samples: meteorites, Antarctic micrometeorites (AMMs), interplanetary dust particles (IDPs), and fine-grained samples returned from Moon, asteroid (25143) Itokawa, comet 81P/Wild 2, and international space station (ISS). Here I introduce some of my mineralogical studies of extraterrestrial materials by using transmission electron microscope (TEM). I began my meteorite studies during a graduate student, which led me to electron petrography of the extraterrestrial materials by TEM. Next, I describe how I introduced ultramicrotomy to the studies of extraterrestrial materials in Japan. Then, I show some of my studies of AMMs; they are (1) the mineralogy of the vast majority of hydrated AMMs, which is not similar to that of CM chondrites but that of chondritic smooth (CS) IDPs and that of Tagish Lake ungrouped C chondrite, (2) GEMS and enstatite whisker and platelet-bearing highly porous AMMs, which give us another opportunity to investigate samples originated from comets and comet-like icy bodies, and (3) GEMS-bearing AMMs experienced various degrees of aqueous alteration, which shed light on the relationships between CP IDPs and CS IDPs. Then, I introduce micrometeoroids captured at the ISS. A large micrometeoroid revealed similarity to chondrule-like objects recovered from comet 81P/Wild 2 on the standpoint of mineralogy and oxygen isotopic ratios of ferromagnesian silicates. Finally, I show TEM studies of surface modification (space weathering) of Itokawa grains. TEM observation revealed that solar wind is the major cause of the space weathering of the asteorid Itokawa. Some Itokawa grains show blistering on their surfaces, which resulted from the segregation of gaseous species such as H and He near the surface in the space weathering rims.
In a consortium analysis of a large particle captured from the coma of comet 81P/Wild 2 by the Stardust spacecraft, we report the discovery of a field of fine‐grained material (FGM) in contact with a large sulfide particle. The FGM was partially located in an embayment in the sulfide. As a consequence, some of the FGM appears to have been protected from damage during hypervelocity capture in aerogel. Some of the FGM particles are indistinguishable in their characteristics from common components of chondritic‐porous interplanetary dust particles, including glass with embedded metals and sulfides and equilibrated aggregates. The sulfide exhibits surprising Ni‐rich lamellae, which may indicate that this particle experienced a long‐duration heating event after its formation but before incorporation into Wild 2.
The unique physical properties of aerogels have provided enabling technologies to a variety of both flight and proposed space science missions. The extremely low values of the density and corresponding high values of the porosity of aerogels make them suitable for stopping high velocity particles, as highly efficient thermal barriers and as a porous medium for the containment of cryogenic fluids. The use of silica aerogel as a hypervelocity particle capture and return medium for the Stardust Mission, which launched in 1999 and returned to earth in 2006, has drawn the attention of the scientific community, as well as the public, to these fascinating materials. Aerogels are currently being used as the thermal insulation material in the 2003 Mars Exploration Rovers and will be used on the 2009 Mars Science Laboratory rover, as well. The SCIM (Sample Collection for the Investigation of Mars) and the STEP (Satellite Test of the Equivalence Principle) Missions are proposed scientific missions, in which the use of aerogel is critical to their overall design and success. Composite materials comprised of silica aerogel and oxide powders are currently under development for use in a new generation of thermoelectric devices that are planned for use in future mission designs. Work is ongoing in the development and production of non-silicate and composite aerogels to extend the range of useful physical properties, and thus, the applications of aerogels in future space science missions.
NASA has used aerogel in several space exploration missions over the last two decades. Aerogel has been used as a hypervelocity particle capture medium (Stardust) and as thermal insulation for the Mars Pathfinder, Mars Exploration Rovers, and Mars Science Lander. Future applications of aerogel are also discussed and include the proposed use of aerogel as a sample collection medium to return upper atmosphere particles from Mars to earth and as thermal insulation in thermal-to-electric generators for future space missions and terrestrial waste-heat recovery technology.
We discuss the inherent difficulties that arise during "ground truth" characterization of the Stardust interstellar dust collector. The challenge of identifying contemporary interstellar dust impact tracks in aerogel is described within the context of background spacecraft secondaries and possible interplanetary dust particles and beta-meteoroids. In addition, the extraction of microscopic dust embedded in aerogel is technically challenging. Specifically, we provide a detailed description of the sample preparation techniques developed to address the unique goals and restrictions of the Interstellar Preliminary Exam. These sample preparation requirements and the scarcity of candidate interstellar impact tracks exacerbate the difficulties. We also illustrate the role of initial optical imaging with critically important examples, and summarize the overall processing of the collection to date.
Spitzer Infrared Spectrograph observations of the Deep Impact experiment in July 2005 have created a new paradigm for understanding the infrared spectroscopy of primitive solar nebular (PSN) material-the ejecta spectrum is the most detailed ever observed in cometary material. Here we take the composition model for the material excavated from Comet 9P/Tempel 1's interior and successfully apply it to Infrared Space Observatory spectra of material emitted from Comet C/1995 O1 (Hale-Bopp) and the circumstellar material found around the young stellar object HD 100546. Comparison of our results with analyses of the cometary material returned by the Stardust spacecraft from Comet 81P/Wild 2, the in situ Halley flyby measurements, and the Deep Impact data return provides a fundamental cross-check for the spectral decomposition models presented here. We find similar emission signatures due to silicates, carbonates, phyllosilicates, water ice, amorphous carbon, and sulfides in the two ISO-observed systems but there are significant differences as well. Compared to Tempel 1, no Fe-rich olivines and few crystalline pyroxenes are found in Hale-Bopp and HD 100546. The YSO also lacks amorphous olivine, while being super-rich in amorphous pyroxene. All three systems show substantial emission due to polycyclic aromatic hydrocarbons. The silicate and PAH material in Hale-Bopp is clearly less processed than in Tempel 1, indicating an earlier age of formation for Hale-Bopp. The observed material around HD 100546 is located similar to 13 AU from the central source, and demonstrates an unusual composition due to either a very different, non-solar starting mix of silicates or due to disk material processing during formation of the interior disk cavity and planet(s) in the system. (c) 2006 Elsevier Inc. All rights reserved.
We have proposed an experiment (the Tanpopo mission) to capture microbes on the Japan Experimental Module of the International Space Station. An ultra low-density silica aerogel will be exposed to space for more than 1 year. After retrieving the aerogel, particle tracks and particles found in it will be visualized by fluorescence microscopy after staining it with a DNA-specific fluorescence dye. In preparation for this study, we simulated particle trapping in an aerogel so that methods could be developed to visualize the particles and their tracks. During the Tanpopo mission, particles that have an orbital velocity of ~8 km/s are expected to collide with the aerogel. To simulate these collisions, we shot Deinococcus radiodurans-containing Lucentite particles into the aerogel from a two-stage light-gas gun (acceleration 4.2 km/s). The shapes of the captured particles, and their tracks and entrance holes were recorded with a microscope/camera system for further analysis. The size distribution of the captured particles was smaller than the original distribution, suggesting that the particles had fragmented. We were able to distinguish between microbial DNA and inorganic compounds after staining the aerogel with the DNA-specific fluorescence dye SYBR green I as the fluorescence of the stained DNA and the autofluorescence of the inorganic particles decay at different rates. The developed methods are suitable to determine if microbes exist at the International Space Station altitude.
The Stardust collector shows diverse aerogel track shapes created by
impacts of cometary dust. Tracks have been classified into three broad
types (A, B, and C), based on relative dimensions of the elongate
"stylus" (in Type A "carrots") and broad "bulb" regions (Types B and C),
with occurrence of smaller "styli" in Type B. From our experiments,
using a diverse suite of projectile particles shot under Stardust
cometary encounter conditions onto similar aerogel targets, we describe
differences in impactor behavior and aerogel response resulting in the
observed range of Stardust track shapes. We compare tracks made by
mineral grains, natural and artificial aggregates of differing subgrain
sizes, and diverse organic materials. Impacts of glasses and robust
mineral grains generate elongate, narrow Type A tracks (as expected),
but with differing levels of abrasion and lateral branch creation.
Aggregate particles, both natural and artificial, of a wide range of
compositions and volatile contents produce diverse Type B or C shapes.
Creation of bulbous tracks is dependent upon impactor internal
structure, grain size distribution, and strength, rather than overall
grain density or content of volatile components. Nevertheless, pure
organic particles do create Type C, or squat Type A* tracks, with length
to width ratios dependent upon both specific organic composition and
impactor grain size. From comparison with the published shape data for
Stardust aerogel tracks, we conclude that the abundant larger Type B
tracks on the Stardust collector represent impacts by particles similar
to our carbonaceous chondrite meteorite powders.
We report transmission electron microscopy (TEM) investigations of
micro-craters that originated from hypervelocity impacts of comet
81P/Wild 2 dust particles on the aluminium foil of the Stardust
collector. The craters were selected by scanning electron microscopy
(SEM) and then prepared by focused ion beam (FIB) milling techniques in
order to provide electron transparent crosssections for TEM studies. The
crater residues contain both amorphous and crystalline materials in
varying proportions and compositions. The amorphous component is
interpreted as resulting from shock melting during the impact and the
crystalline phases as relict minerals. The latter show evidence for
shock metamorphism. Based on the residue morphology and the
compositional variation, the impacting particles are inferred to have
been dominated by mixtures of submicron olivine, pyroxene and Fe sulfide
grains, in agreement with prior results of relatively coarse-grained
mineral assemblages in the aerogel collector.
We surveyed craters on a space-exposed surface from the Genesis solar wind sample return mission to find new constraints on the population of micrometeoroids at the edge of the Earth's gravitational sphere of influence. The target was made of 6061-T6 aluminum, identical to the composition of the space-facing end of the Long Duration Exposure Facility satellite, which recorded micrometeoroid impacts in low Earth orbit. We use data from both locations to compare crater frequency as a function of size, with and without gravitational focussing by the Earth. We find that the cratering flux near the Earth–Sun L1 libration point is indistinguishable, within the ∼40%∼40% uncertainty of this study, from that in low Earth orbit. The small degree of gravitational focussing between the two locations indicates that particles with geocentric free-space velocities less than a few kilometers per second comprise no more than a few percent of the interplanetary dust complex.
The NASA Johnson Space Center Astromaterials Acquisition and Curation Office has the unique responsibility to curate NASA's extraterrestrial samples – from past and forthcoming missions – into the indefinite future. Presently curation includes documentation, preservation, preparation, and distribution of samples from the Moon, asteroids, comets, the solar wind, and the planet Mars. Each of these sample sets has a unique history and comes from a unique environment. The curation laboratories and procedures developed over forty years have proven both necessary and sufficient to serve the evolving needs of a worldwide research community. A new generation of sample return missions is being planned and proposed to destinations across the solar system. Curation must evolve to meet the increased challenges of these new samples.
Cosmic dust grains are the abundant, fine-grained end-member of a range of extraterrestrial materials travelling through space. These particles can impact orbiting space vehicles (e.g. satellites and the International Space Station) at velocities ranging from 10 to 72 kms-1. Impact damage resulting from such a collision could potentially disable or limit the operational use of a spacecraft. There is great commercial interest from the satellite companies and space agencies to understand the nature and proportion of impacts that are caused by cosmic dust particles to assist in risk management studies and for protective shielding optimization. The successful recovery of any surface that has been exposed to the near-Earth environment offers an excellent opportunity to search for micrometre-scaled impact features and the associated projectile residues using scanning electron microscopy and X-ray microanalysis.
Microbiology at the high altitude atmosphere i s i m p o r t a n t f o r a s s e s s i n g t h e c h a n c e s and limits of microbial transfe r from the earth to extraterrestrial bodies. Among the microorganisms isolate d from the high -atmospheric samples, spore formers and vegetative Deinococci were highly resistant against harsh environment at high altitude. From limited knowledge available to date, it is suggested that terrestrial microorganisms may have had chances to be ejected and transferred to outer space. Survival of these organisms during their space travel and proliferation on other planets might be also feasible. Directed Panspermia from Earth to extraterrestrial bodies is discussed on the basis of findings reported in literatures. ©2009 Jpn. Soc. Biol. Sci.
With the development of high energy laser facilities dedicated to inertial confinement fusion, the question of debris ejection from metallic shells subjected to intense laser irradiation has become a key issue. We have used two diagnostics to investigate fragmentation processes. Recovery of ejected fragments has been performed in a highly transparent gel of density 0.9 g/cm3. Fragments sizes, shapes, and penetration depths, can be easily observed with a spatial resolution of micrometer-order. Complementary data are provided by transverse shadowgraphy which allows to obtain quasi-instantaneous, successive pictures of the debris clouds and mean ejection velocities.
It is a fundamental goal of interplanetary dust particle (IDP) research
to determine the sources and histories of these primitive
extraterrestrial materials. Chondritic IDPs have been divided into
anhydrous and hydrous varieties. The presumption is that hydrated IDPs
experienced aqueous alteration on parent bodies (hydrous asteroids or
possibly comets). We wish to discover whether the anhydrous IDPs were
the initial raw materials for these reactions. We report here analyses
of olivines and pyroxenes from 22 large (>15 micrometers) chondritic
IDPs: 11 anhydrous and 11 hydrous. We find there exists no significant
difference in the compositions of olivines from olivine vs. pyroxene
dominated IDPs. The degree of heterogeneity of these olivine
compositions from anhydrous IDPs (Fo44-100) is great, significantly
exceeding that of the olivines from the hydrous IDPs (Fo76-100) we
examined. We observe the same relationship for orthopyroxenes (En57-100
for anhydrous, En79-100 for hydrous). Interestingly, we encountered true
diopsides predominantly in pyroxene-dominated hydrous IDPs. Some
anhydrous IDPs also displayed restricted compositional ranges for
olivines and pyroxenes. For sulfate- containing anhydrous IDPs, olivines
and orthopyroxenes had the ranges Fo91-100 and En94-100; for melted
(atmospherically ablated) IDPs these ranges were Fo90-100 and En91-94.
Are hydrous and anhydrous IDPs genetically related? With the exception
of some from the serpentine class (Bradley and Brownlee, 1991), all
chondritic IDPs have nearly identical mineralogies (Zolensky and
Lindstrom, 1992). The compositional ranges of olivines and pyroxenes in
these materials are quite dissimilar, with those from hydrous IDPs being
relatively magnesium-rich; however this could be explained by a
relatively greater ease of destruction of iron-rich silicates during
aqueous alteration. It is known that increasing the Fe^2+ content of
olivine decreases the temperature at which serpentinization occurs (Deer
et al., 1982). This is apparently due to greater dislocation densities
for Fe-rich olivines, and oxidation of Fe^2+. If a similar phenomenon
affects alteration of pyroxenes and olivines to smectite, then the
genetic relation of hydrous to anhydrous IDPs is permitted by our
results. We have already reported that the Mg-Fe compositional range
exhibited by phyllosilicates in hydrated IDPs is nearly identical to
that of olivines and pyroxenes in anhydrous IDPs (Zolensky and
Lindstrom, 1992); this observation also permits a genetic link between
these IDP types. However, it is also possible that hydrous are not
genetically related to anhydrous IDPs. We note that the relatively
Mg-rich compositions of olivines and orthopyroxenes in
sulfate-containing IDPs can also be explained by preferential
destruction of Fe-rich olivines by oxidation of Fe^2+. The ablated IDPs
are merely showing the results of equilibration. Are chondritic IDPs
merely small samples of the parent bodies of chondritic meteorites?
Aside from differences in bulk composition and physical properties, IDPs
differ from all chondritic meteorites except CIs and CMs in the
compositional ranges of olivines and pyroxenes (for olivines: CV3-
Fo40-60; CO3- Fo40-70; H3, L3 and LL3- Fo30-80; Scott et al., 1988;
Dodd, 1981). Although a few hydrous IDPs (a subset of the serpentine
class particles) are apparently related to CMs (Zolensky and Lindstrom,
1992), the majority are mineralogically dissimilar. Small carbonaceous
clasts contained within certain meteorites (e.g., CR chondrites, the
Bholghati howardite, LEW 85300 polymict eucrite and Kaidun carbonaceous
breccia) have similar mineralogies to some IDPs (Zolensky et al., 1992),
although more detailed analyses of these materials are still required.
In summary, most chondritic IDPs are compositionally and mineralogically
distinct from chondritic meteorites, but have apparently experienced
similar conditions of origin and evolution both in the solar nebula and
on parent bodies. References: Bradley and Brownlee (1991) Science 251,
549; Deer, Howie, and Zussman (1982) Rock-Forming Minerals, p. 77; Dodd
(1981) Meteorites, A Petrologic-Chemical Synthesis, p. 45; Scott et al.
(1988) in Meteorites and the Early Solar System, 721; Zolensky and
Lindstrom (1992) Proc. Lunar and Planet. Sci. Conf. 22, 161; Zolensky et
al. (1992) Lunar and Planet. Sci. XXIV, 1587.
The Chemistry of Micrometeoroids Experiment (LDEF instrument A0187-1)
exposed witness plates of high-purity gold (greater than 99.99 percent
Au) and commercial aluminum (greater than 99 percent Al) with the
objective of analyzing the residues of cosmic-dust and orbital-debris
particles associated with hypervelocity impact craters. The gold
substrates were located approximately 8 deg off LDEF's trailing edge
(Bay A03), while the aluminum surfaces resided in Bay A11, approximately
52 deg from LDEF's leading edge. SEM-EDX techniques were employed to
analyze the residues associated with 199 impacts on the gold and 415
impacts on the aluminum surfaces. The residues that could be analyzed
represent natural or man-made materials. The natural particles dominate
at all particle sizes less than 5 micron. It is possible to subdivide
both particle populations into subclasses. Chondritic compositions
dominate the natural impactors (71 percent), followed by monomineralic,
mafic-silicate compositions (26 percent), and by Fe-Ni rich sulfides
(approximately 3 percent). Approximately 30 percent of all craters on
the gold collectors were caused by man-made debris such as aluminum,
paint flakes, and other disintegrated, structural and electronic
components. Equations-of-state and associated calculations of shock
stresses for typical LDEF impacts into the gold and aluminum substrates
suggest that substantial vaporization may have occurred during many of
the impacts and is the reason why approximately 50 percent of all
craters did not contain sufficient residue to permit analysis by the
SEM-EDX technique. After converting the crater diameters into projectile
sizes using encounter speeds typical for the trailing-edge and
forward-facing (Row 11) directions, and accounting for normalized
exposure conditions of the CME collectors, we derived the absolute and
relative fluxes of specific projectile classes. The natural impactors
encounter all LDEF pointing directions with comparable, modal
frequencies suggesting compositional (and dynamic) homogeneity of the
interplanetary-dust environment in near-Earth orbit.
The LDEF Meteoroid and Debris Special Investigation Group (hereafter M&D SIG) was formed to maximize the data harvest from LDEF by permitting the characterization of the meteoroid and space debris impact record of the entire satellite. Thus, our work is complementary to that of the various M&D PIs, all of whom are members of the SIG. This presentation will summarize recent results and discussions concerning five critical SIG goals: (1) Classification of impactors based upon composition of residues; (2) Small impact (microimpact) features; (3) Impact cratering and penetration data to derive projectile sizes and masses; (4) Particulate flux estimates in low-Earth orbit; (5) The LDEF Meteoroid and Debris database.
Small-scale impact craters (5-7 mm in diameter) were produced with a light gas gun in high purity Au and Cu targets using soda lime glass (SL) and man-made basalt glass (BG) as projectiles. Maximum impact velocity was 6.4 km/s resulting in peak pressures of approximately 120-150 GPa. Copious amounts of projectile melts are preserved as thin glass liners draping the entire crater cavity; some of this liner may be lost by spallation, however. SEM investigations reveal complex surface textures including multistage flow phenomena and distinct temporal deposition sequences of small droplets. Inasmuch as some of the melts were generated at peak pressures greater than 120 GPa, these glasses represent the most severely shocked silicates recovered from laboratory experiments to date. Major element analyses reveal partial loss of alkalis; Na2O loss of 10-15 percent is observed, while K2O loss may be as high as 30-50 percent. Although the observed volatile loss in these projectile melts is significant, it still remains uncertain whether target melts produced on planetary surfaces are severely fractionated by selective volatilization processes.
Small-scale impact craters (5-7 mm in diameter) were produced within a light gas gun in high purity Au and Cu targets using soda lime glass (SL) and man-made basalt glass (BG) as projectiles. Maximum impact velocity was 6. 4 km/s resulting in peak pressures of approximately 120-150 GPa. Copious amounts of projectile melts are preserved as thin glass liners draping the entire crater cavity; some of this liner may be lost by spallation, however. SEM investigations reveal complex surface textures including multistage flow phenomena and distinct temporal deposition sequences of small droplets. Inasmuch as some of the melts were generated at peak pressures greater than 120 GPa, these glasses represent the most severely shocked silicates recovered from laboratory experiments to date. Major element analyses reveal partial loss of alkalis; Na//2O loss of 10-15% is observed, while K//2O loss may be as high as 30-50%.
This paper provides equations defining the performance capability of various types of meteoroid and debris shielding systems. These equations have been developed at the NASA Johnson Space Center (JSC) Hypervelocity Impact Test Facility (HIT-F). Equations are included that are applicable for aluminum Whipple shields, Nextel(R) Multi-Shock (MS) shields, hybrid Nextel(R)/Aluminum MS shields, and Mesh Double-Bumper (MDB) shields. The MS and MDB shields are advanced shields with demonstrated weight and performance advantages over conventional Whipple shields.
The sharp rise in reports of child abuse has led to efforts to protect children in family courts in child protective proceedings. Hearsay evidence of a child's prior statements may be admitted in child protective proceedings, but such evidence is legally insufficient to support an adjudication of abuse without corroborative evidence. Courts have admitted expert psychological, psychiatric or social work testimony about the child sex abuse syndrome as sufficient corroborative evidence. The testimony is called “validation” testimony. The scientific basis for such validation testimony in the absence of a disclosure by the child is very weak. Courts have also tended to accept the most minimal evidence as corroboration of the child's out-of-court statements, including other hearsay evidence. The socially valuable policy of protecting children by admitting weak evidence, such as validation testimony, or other hearsay, should be reviewed to ensure the evidence meets criteria of reliability in order to minimize erroneous determinations.
Using optical microscopy, scanning electron microscopy (SEM), electron
microprobe analysis (EPMA) and transmitted electron microscopy (TEM), we
studied several chondrules and isolated forsterite grains in a Type A/B
Allende dark inclusion 5a2. All chondrules and isolated forsterite
grains in this dark inclusion show various degrees of replacement by
fayalitic olivine which occurs in two textural types: compact rims
around forsterite grains and plate-like euhedral and subhedral olivine
grains surrounded by finer-grained olivine, chromite, hercynite, Fe-Ni
sulfides, nepheline and sodalite. We found that plate-like fayalitic
olivines in the Allende dark inclusion contain abundant lozenge-shaped
voids and planar dislocations which are characteristic for olivine
grains produced by dehydration of phyllosilicates. Based on these
observations we conclude that Allende dark inclusions experienced
various degrees of aqueous alteration and subsequent thermal
metamorphism which produced fayalitic olivine rims and plate-like
fayalitic olivines and their interstitial mineral assemblage.
Most impacts occur obliquely rather than vertically as typically modeled. Laboratory experiments permit documenting the effects of impact angle on energy partitioning and related phenomena. Three results have particular significance for understanding the possible global atmospheric and biospheric response to a major impact. First, at low impact angles (<30° from the horizontal) the original impactor disrupts and ricochets downrange at a significant fraction of the original impact velocity. Results for different projectile/target combinations lead to a general disruption law such that sufficiently low impact angles (<5°) can result in nearly intact ricochet of the projectile with velocities close to the original impact velocity. More probable impact angles (5 to 15°) result in disruption dominated by 5 to 10 large fragments retaining about 50 percent of the original impact velocity. Scaling relations incorporating strain rate and possible weakening with size indicate that a 10-km object impacting at 10° with a velocity of 20 km/s could ricochet numerous 0.1 to 1-km-diameter fragments at hypervelocities, thereby producing a global swarm of Tr.nguska-scale events and enhancing environmental stress. Craters produced by oblique impacts on the Moon and Mars exhibit many of the same features as observed in the laboratory, including downrange impacts by ricocheted fragments. This observation provides evidence that basic phenomena observed at laboratory scales can be extended to much broader scales. Second, our experiments reveal that energy partitioned to target heating surprisingly increases as cos2θ for impact angles between 45° and 15°. This contrasts with peak stress levels, which decrease as sin2θ, and reflects the effect of shear heating along the projectile/target interface. As a consequence, vaporization of easily volatized materials (water, carbonates) can occur without initially large energy densities, thereby potentially adding to-rather than escaping from-the atmosphere. Thus, nitrate production from such a swarm could greatly exceed that from a single vertical impactor not only due to the greater ionization efficiency by numerous small objects and their much longer cumulative atmospheric path lengths but also due to increased coupling with the atmosphere. Third, the ricochet component appears to be embedded in an expanding vapor cloud sufficient to drive gases away from the downrange trajectory. For a major collision, this process would substantially increase the zone and duration of biomass incineration in a downrange "fireline," as well as providing a mechanism for inserting substantial material into orbit. A potential consequence of orbital insertion is the possible development of a temporary debris ring. Such a ring might substantially prolong the climatic response to an impact through the reduced solar constant and through strong thermal gradients created by the ring shadow. Moreover, impact debris, including the cosmic signature, may be titrated into the geologic record well after the initial collision (<10 m.y.).
Light gas gun studies have shown that 6 km/s solid mineral and glass
test particles can be successively captured in 0.05 g cm-3
aerogel without severe heating or fragmentation. In spite of this work,
there has been uncertainty in the performance of aerogel for
hypervelocity capture of real meteoroids. Natural impacts differ from
simulations in that the particles are likely to be structurally weak and
they typically impact at higher velocity that can be simulated in the
laboratory. We are fortunate now to have had two successful capture
experiments using aerogel exposed in space. These experiments provide
fundamental data for the assessment of the value of silica aerogel for
capture of hypervelocity meteoroids from spacecraft. The first
experiment used 0.02 g cm-3 aerogel flown on the lid of a
Shuttle Get Away Special canister. During its 9 day exposure, the 0.165
m2 of aerogel in this Sample Return Experiment (SRE) captured
two long 'carrot-shaped' tracks and one highly fractured bowl shaped
'crater'. The second collection was with 0.04 m2 of 0.05 g
cm-3 aerogel exposed on ESA's Eureca freeflying spacecraft
that was exposed for 11 months before recovery by the Shuttle. The
Eureca aerogel exposure consisted of four 10x10 cm module trays that
were part of the TiCCE meteoroid collector built by the University of
Kent at Canterbury. To date we have found ten 'carrot-shaped' tracks and
two 'craters' on this experiment. The longest tracks in both exposures
are over 2 mm long. Two of the TiCCE modules had a 0.1 micron Al film
suspended a millimeter above the aerogel. On these modules several of
the projectiles fragmented during passage through the film producing
fields of carrot shaped tracks from the resulting miniature 'meteor'
shower. Most of the tracks in these showers have observable particles at
their ends. We have extracted one of the carrot track meteoroids and
mounted it in epoxy for sectioning. So far the examination of these 14
impacts suggests that low density aerogel is a magic and highly
effective media for intact capture of hypervelocity particles in space.
The debris plumes resulting from penetration experiments using soda-lime glass projectiles (3.2 mm diameter; at 6 km/s) and aluminum 1100-0 targets (1.0 and 0.8 mm thick) were intercepted with blued Cu-witness plates some 6, 12 and 49 cm from the target's rear. Scanning Electron Microprobe (SEM) methods and associated Energy Dispersive X-Ray Spectroscopy (EDS) were used to detail the morphology of the witness-plate features and to determine chemically which features were caused by target- or projectile-derived plume components. The projectile suffered complete melting and almost the entire melt volume dispersed into an intricate, three-dimensional network of melt-ribbons and stringers that form a highly regular and reproducible web-like pattern in the central portion of the witness-plate spray. In contrast, the aluminum debris remained solid and was largely concentrated in the peripheral parts of the plume. These experiments also produced prominent circles of closely spaced craters, previously described as “hole-saw rings”. EDS analysis reveals that such rings are caused by either projectile-derived materials or from fragments dislodged from the target.
Empirical formulae are presented for calculating the displaced mass, depth, diameter, and effects of oblique trajectories
for impact craters formed in dense crystalline rocks. The formulae are applicable to craters with diameters from approximately
10−3–103 cm that require, respectively, impact kinetic energies of approximately 10 to 1016 ergs for their formation. The experimental results are in poor agreement with Öpik’s theoretical calculations and raise questions
on the validity of his theoretical model.
Projectile/target behavior for 1100 Al/Cu, soda-lime glass/Cu, soda-lime glass/1100 Al, ferritic stainless steel/Cu, and ferritic stainless steel/1100 Al for spherical (3.18 mm diameter) projectiles at impact velocities ranging from 0.8 to ∼6 km s−1 has been examined by light metallography, SEM, and TEM. At a reference velocity of 1 km s−1, the crater depth/crater diameter ratio (p/Dc) is observed to be linearly related to bulk density ratios (ρp/ρt)1/2 and elastic modulus ratios (Ep/Et)(ρp/ρt)1/2, and to vary from about 0.2 to 2.95. The hypervelocity (uo>5 km s−1) threshold value for p/Dc is also shown to be linearly related to these functionalities and ranges from p/Dc=0.4 for the 1100 Al/Cu system and 0.85 for the ferritic stainless steel/1100 Al system. The residual crater microstructures are all characterized by a zone of dynamic recrystallization at the crater wall (which thickens with impact velocity), and decreasing dislocation density beyond this zone; consistent with residual hardness profiles whose amplitudes decrease with distance from the crater wall. Computer simulations and validation of these simulations utilizing the ranges of experimentally measured crater geometries with impact velocity were developed which fairly accurately represented residual crater shapes and related features. These results also demonstrate the importance of appropriate projectile/target strength ratios in computer simulations; and illustrate the potential for extrapolations to new systems, and for impact velocities well beyond those achievable in the laboratory.
An experimental impact simulation program is currently performed with respect to Columbus hull components. The main objectives are to establish a data base for an optimum design of meteoroid/debris protection shields (MDPS) as well as viewport components, and to obtain input data for numerical models which describe the penetration and perforation processes of meteoroid bumper and viewport systems.As expected, it has been experimentally demonstrated that protection against particles in the order of 1 cm, at relatively low impact velocities (around 3 km/s), is extremely problematic.Applying usual dual-plate Al bumper techniques would require unrealistically thick and heavy systems in order to safety stop such particles, which are expected to occur within the low earth orbit space debris complex.Preliminary results obtained with multiplate Al targets as well as hybrid target systems (Al-ceramics, Al-Kevlar) indicate that the situation can be considerably improved with respect to the shielding efficiency at a given areal material density.These investigations are still in progress. Results of the test series performed with Al dual-plate systems and with laminated glass targets as viewport components are reported and discussed.
We have investigated in the laboratory the capture in aerogel (density 92.5±0.5 kg m−3) of small particles travelling at (5.1±0.2) km s−1. The particles used were soda glass spheres and irregularly shaped olivine and iron particles, with mean diameters in the range 75–355 microns. We have measured the impact site for each particle, characterised by the mean diameter of the entrance hole in the aerogel, the minimum and maximum radii of the damaged region in the surface of the aerogel around the entrance hole, the length of the track in the aerogel caused by passage of the particle into the aerogels interior, and the diameter of the captured particle (if seen) found near the end of the track. For each type of particle we establish relationships between the observed parameters and the pre-impact particle size. We find that the processes resulting in the observed surface features and the capture of the particles in the interior of the aerogel are different. We also find that the particle shape (spherical/irregular) does not unduly influence penetration depths in the aerogel. We have studied the effects of non-normal incidence on the observed impact features and find that the angle of incidence can be reconstructed to within ±2°.We compare the laboratory obtained data with that measured for four particles captured in a sample of aerogel flown in a Low Earth Orbit on board the EuReCa spacecraft. The density of one of the particles is predicted to be (1776±346) km m−3. Using the ability to reconstruct impact direction the probable nature of the particles is shown to be micrometeoroids with retrograde trajectory.
We have measured the depths, average diameters and circularity indices of over 600 micrometeoroid and space debris impact craters formed in surfaces exposed to space aboard the Long Duration Exposure Facility satellite. The target surfaces had a variety of orientations and physical properties. The average depth-diameter ratio of craters formed in aluminum targets by nearly normal impacts is between 0.56 and 0.60, higher than the canonical and widely accepted value of 0.50 which corresponds to a hemispherical shape. The depth-diameter ratio does not change significantly with target Brinell hardness values between 40 and 90, or with average impact velocity above 5 km s−1. The depth-diameter ratio is found to vary as roughly the one-tenth power of target density. Less than 10% of the craters examined had major-to-minor axis ratios higher than 1.5, consistent with the production of shallow, elongated craters exclusively by grazing impacts. The variation in depth-diameter ratio for circular craters most likely results from variation in projectile shapes.
The mesostructure of silica aerogel resembles strings of pearls, ranging in size from 10 to 100 Å. This fine mesostructure transmits nearly 90% of incident light in the visible, while providing sufficiently gentle dissipation of the kinetic energy of hypervelocity cosmic dust particles to permit their intact capture. In 1987, silica aerogel was introduced as a capture medium to take advantage of its low density, fine mesostructure and, most importantly, its transparency, allowing optical location of captured micron sized particles. Without this feature, locating such captured particles in an opaque medium, e.g., polymer foams, is nearly impossible. The capture of hypervelocity particles has been extensively simulated in the laboratory. At the time of this symposium, more than 2.4 m2 of 20 mg/ml silica aerogel will have been flown on Space Shuttle (STS-47, STS-57, STS-60, STS-64 and STS-68). Demonstration of capturing hypervelocity particles ushers in a new, simple avenue to science in capturing intact cosmic dust from space. Since our introduction of aerogel for intact capture of cosmic dust, many useful features unique to aerogel have been identified.
Detailed petrographic descriptions and results of electron microprobe analyses are presented for impact glasses as well as shocked and unshocked minerals associated with individual lunar microcraters (diameters of 0.4 to 4.4 mm). Rocks of four typical lunar lithologies are studied: anorthosite, anorthositic norite, ophitic basalt, and polymict breccia. Textures, mineralogies, and chemical compositions are examined along a radial traverse through each microcrater; i.e., across the impact glasses lining the crater wall, the shock-metamorphosed zone immediately underlying the glass liner, and the unshocked host rock. The microcraters are discussed in a sequence of increasing mineralogical complexity of the host rock (from anorthosite to polymict breccia) in order to distinguish shock effects among mineral types. The shock metamorphic features observed are found to be comparable to those reported in shocked basalt from Lonar Crater, India, and are categorized into five shock-intensity classes with pressures experimentally calibrated.
A logical place to search for surviving pristine nebular material is in the fine-grained matrices of ordinary and carbonaceous chondrites of petrographic type 3. Unfortunately, many of these chondrites have experienced brecciation, thermal metamorphism, and aqueous alteration, so that interpreting individual features in terms of specific nebular conditions and/or processes is difficult. It follows that the origin and evolutionary history of such matrix phases are controversial, and a consensus is difficult to define. In this chapter, therefore, after summarizing the salient mineralogical, petrographic, chemical, and isotopic features of matrix in apparently primitive chondrites, an attempt is made to provide an overview both of areas of agreement and of topics that are currently in dispute.
The current status of the University of Chicago Polyvinylidene Fluoride (PVDF) flux/mass/velocity/trajectory instrumentation is summarized. The particle response and thermal stability characteristics of pure PVDF and PVDF copolymer sensors are described, as well as the characteristics of specially constructed two-dimensional position-sensing PVDF sensors. The performance of high-flux systems and of velocity/trajectory systems using these sensors is discussed, and the objectives and designs of a PVDF velocity/trajectory dust instrument for launch on the Advanced Research and Global Observation Satellite (ARGOS) in 1995 and of a high-flux dust instrument for launch on the Cassini spacecraft to Saturn in 1997 are summarized.
Because of spacecraft motion, a much higher flux of meteoroids is expected to strike the leading (apex) surface of a spacecraft than is expected to strike the trailing (antapex) surface. The ratio of fluxes (apex to antapex) depends on the velocity distribution of meteoroids entering the Earth's atmosphere. The ratio ranges from 5.7 to 9.2 at constant meteoroid mass for the three velocity distributions examined. The velocity of impact is also greater, on average, on the apex surface than on the antapex surface, and the impacts tend to be more normal to the surface. This means that the meteoroids that make a crater of a given diameter are less massive than those that strike the antapex surface. These effects further increase the apex-antapex abundance ratio at constant crater diameter compared to that at constant mass. For craters 100 microns in diameter on 6061 T6 aluminum on the Long Duration Exposure Facility, the ratios obtained on various surfaces are given in tabular form.
Results are presented from a computer simulation in which dust grains of three different sizes were released at perihelion passage from each of (1) 15 main belt asteroids, (2) 15 short-period comets with perihelion greater than 1 AU, and (3) 5 such comets with perihelion less than 1 AU. The evolving-orbit calculations for each of the dust rains include the effects of solar and planetary gravity, radiation pressure, Poynting-Robertson drag, and solar wind drag. It is noted that when dust grains evolve to intersection with the earth's orbit, they retain orbital characteristics indicative of their origins.
A workshop on particle capture, recovery, and velocity/trajectory measurement technologies was held. The primary areas covered were: (1) parent-daughter orbit divergence; (2) trajectory sensing; (3) capture medium development: laboratory experiments, and (4) future flight opportunities.
The ability to capture projectiles intact at hypervelocities opens new applications in science and technology that would either not be possible or would be very costly by other means. This capability has been demonstrated in the laboratory for aluminum projectiles of 1.6 mm diameter, captured at 6 km/s, in one unmelted piece, and retaining up to 95% of the original mass. Furthermore, capture was accomplished passively using microcellular underdense polymer foam. Another advantage of capturing projectiles in an underdense medium is the ability of such a medium to preserve a record of the projectile's original velocity components of speed and direction. A survey of these experimental results is described in terms of a dozen parameters which characterize the amount of capture and the effect on the projectile due to different capture media.
We report here analyses of olivines and pyroxenes, and petrofabrics of 27 chondritic interplanetary dust particles (IDPs), comparing those from anhydrous and hydrous types. Approximately 40% of the hydrous particles contain diopside, a probable indicator of parent body thermal metamorphism, while this mineral is rarely present in the anhydrous particles. Based on this evidence, we find that hydrous and anhydrous IDPs are, in general, not directly related, and we conclude that olivine and pyroxene major-element compositions can be used to help discriminate between IDPs that are (1) predominantly nebular condensates, and lately resided in anhydrous or icy (no liquids) primitive parent bodies, and (2) those originating from more geochemically active parent bodies (probably hydrous and anhydrous asteroids).
The physics of hypervelocity impacts into foams is of interest because of the possible application to interplanetary dust particle (IDP) capture by spacecraft. We present a model for the phenomena occurring in such impacts into low-density organic polymer foams. Particles smaller than foam cells behave as if the foam is a series of solid slabs and are fragmented and, at higher velocities, thermally altered. Particles much larger than the foam cells behave as if the foam were a continuum, allowing the use of a continuum mechanics model to describe the effects of drag and ablation. Fragmentation is expected to be a major process, especially for aggregates of small grains. Calculations based on these arguments accurately predict experimental data and, for hypothetical IDPs, indicate that recovery of organic materials will be low for encounter velocities greater than 5 km/s. For an organic particle 100 micrometers in diameter, approx. 35% of the original mass would be collected in an impact at 5 km/s, dropping to approx. 10% at 10 km/s and approx. 0% at 15 km/s. For the same velocities the recovery ratios for troilite (FeS) are approx. 95%, 65%, and 50%, and for olivine (Mg2SiO4) they are approx. 98%, 80%, and 65%, demonstrating that inorganic materials are much more easily collected. The density of the collector material has only a second-order effect, changing the recovered mass by less than 10% of the original mass.
Results of recent materials flight experiments: POSA I and II and ESEM
- H G Pippin
Pippin, H. G. 1998. Results of recent materials flight experiments: POSA I and II and ESEM. In Proceedings Space Environment Effects Workshop, June 23–25, NASA Marshall Space Flight Center, Huntsville.
EuReCa! Aerogel capture of meteoroids in space. Lunar Planetary Sci
- D E Brownlee
- F Hö
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- J A M Mcdonnell
- P Tsou
- J Williams
Brownlee, D. E., F. Hö, L. Hrubesh, J. A. M. McDonnell, P. Tsou, and J. Williams 1994. EuReCa! Aerogel capture of meteoroids in space. Lunar Planetary Sci. 24th, 183–184.
Intact hypervelocity capture in aerogel in the laboratory In Shock Compression of Condensed Matter-1995
- M J Burchell
- R Thomson
Burchell, M. J., and R. Thomson 1996. Intact hypervelocity capture in aerogel in the laboratory. In Shock Compression of Condensed Matter-1995 (S. C. Schmidt and W. C. Tao, Eds). AIP Conf. Proc., Vol. 370, Part 2, pp. 1155– 1158, AIP Press, Woodbury.
The polished plate meteoroid detector experiment
- W H Kinard
Kinard, W. H. 1998. The polished plate meteoroid detector experiment. In Pro-ceedings Space Environment Effects Workshop, June 23–25, NASA Marshall Space Flight Center, Huntsville.
Highly transparent and rugged sensor for velocity determinations of cosmic dust particles Lunar and Planetary Institute Suitability of SiO 2 aerogel as a capture medium for interplanetary dust
- S Auer
- F Von Bun Barrett
- M E Zolensky
- F Hö
- D Lindstrom
- E K Gibson
Auer, S., and F. von Bun 1994. Highly transparent and rugged sensor for velocity determinations of cosmic dust particles. In Workshop on Particle Capture, Re-covery and Velocity/Trajectory Measurement Technologies (M. E. Zolensky, Ed.), pp. 25–29. Lunar and Planetary Institute, Houston. Barrett, R. A., M. E. Zolensky, F. Hö, D. Lindstrom, and E. K. Gibson 1992. Suitability of SiO 2 aerogel as a capture medium for interplanetary dust. Proc. Lunar Planet. Sci. Conf. 22nd, 203–212.
LDEF Meteoroid and Debris Special Investigation Group in-vestigations and activities at the Johnson Space Center
- Univ See
- M E Zolensky
- R P Bernhard
- J L Warren
- C A Sapp
- C B Dardano
Univ. of Arizona Press, Tucson. See, T. H., M. E. Zolensky, R. P. Bernhard, J. L. Warren, C. A. Sapp, and C. B. Dardano 1993. LDEF Meteoroid and Debris Special Investigation Group in-vestigations and activities at the Johnson Space Center. In LDEF— 69 Months in Space, Proceedings of the Second Post Retrieval Symposium, NASA CP 3194 (A. S. Levine, A. S, Ed.), pp. 257–274. NASA Langley Research Cen-ter, Hampton.