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Lunar bases for long-term human habitation are a topic of growing interest to engineers. Structures to be built on the surface of the Moon must be designed to resist extreme environmental hazards such as hard vacuum/no atmosphere, low gravity, ionizing radiation, large temperature variations, moonquakes, and meteoroid impacts. Protective regolith covers may provide adequate shielding from some of these hazards. This paper presents a methodology that utilizes established physics-based models to determine the immediate effects of hypervelocity impacts (HVI), including crater geometry and shock pressure, for engineering design of lunar structures. First, empirical equations and nondimensional scaling laws for computing geometric features of HVI craters are discussed. These damage estimation tools are adopted from the fields of spacecraft design and planetary impact cratering. Next, the planar impact approximation model is discussed, which utilizes one-dimensional shock wave physics and impedance matching conditions to estimate the peak initial pressures generated in HVI. Comprehensive parametric analyses, encompassing a wide range of impact velocities and impactor masses as well as a variety of impactor and target materials, are performed to demonstrate applications of the models to both regolith-shielded and unshielded structures. Crater geometry descriptors and peak shock pressures in HVI scenarios involving various impactor-target combinations are computed with in-house programs and compared with computational results reported in the literature. The analyses indicate that for a given target, the main factors determining cratering damage are impactor mass, impactor density, and impact velocity, while the initial shock pressure is influenced mainly by impact velocity and impactor density. A comparison of impact pressures experienced by monolithic unshielded targets and granular dry sand layers highlights the potential importance of providing regolith-like shielding to attenuate HVI effects. Practical implications of the study are discussed from an engineering design perspective, underscoring the considerable value of such models to practitioners. Practical Applications: A practical methodology for determining cratering and peak shock pressure due to hypervelocity meteoroid impacts on unshielded and regolith-shielded lunar structures is proposed in this work. The methodology utilizes well-established physics-based models of hypervelocity impact effects. These models have several advantages that make them suitable for inclusion in lunar structural design guidelines: (1) the models presented are relatively simple yet realistic, empirical, and analytical models; (2) the models do not rely on computationally expensive numerical methods and have been successfully implemented using a commonly available scientific computing platform; and (3) the models consider several essential aspects of the complex physics of hypervelocity meteoroid impacts, which is essential to ensure accurate prediction of the immediate effects of such impacts for lunar structure design. Additionally, this work also includes a wide-ranging parametric analysis that explores and compares the predictions of the physics-based models from an engineering design perspective, encompassing a variety of impact scenarios and impactor-target combinations. The results highlight the practical importance of providing a protective shield, composed of a regolith-like granular material, to mitigate the peak shock pressure sustained by lunar structures in hypervelocity meteoroid impacts. The models, applications, and results presented herein are of immediate relevance to practicing engineers. [ABSTRACT FROM AUTHOR]

Electromagnetic tethers of hundreds or thousands of meters have been proposed for maneuvring spacecraft in Low Earth Orbit, and in particular, for post-mission disposals. The debate on tether survivability to debris impact is still influencing further advances in the implementation of such technology because of the large area they expose to the debris environment; thin tape geometries have been proposed instead of round ones to increase the survivability to hypervelocity impacts. In this context, this paper introduces a new Ballistic Limit Equation (BLE) for thin tape tethers, derived from experimental results, numerical simulations, and literature data. The resulting equation is non-monotonic with respect to impact angle, presenting a minimum depending on the debris velocity and size; for high obliquities, the debris fragmentation triggered by shock waves propagating into the material reduces the damage. This feature allows to set a minimum particle diameter for risk assessment, excluding a significant part of the debris flux. The proposed BLE confirms the performance of thin tape tethers, with respect to round wires, due to their better ballistic response as well as their reduced cross-section at high-obliquity impacts. [ABSTRACT FROM AUTHOR]

Rubble-pile asteroids may be the type of near-Earth object most likely to threaten Earth in a future collision event. Small-scale impact experiments and numerical simulations for large-scale impacts were conducted to clarify the size ratio of the boulder/projectile diameter effects on ejecta size–velocity distribution. A series of small-scale impact cratering experiments were performed on porous gypsum–basalt targets at velocities of 2.3 to 5.5 km·s−1. Three successive ejection processes were observed by high-speed and ultra-high-speed cameras. The momentum transfer coefficient and cratering size were measured. A three-dimensional numerical model reflecting the random distribution of the interior boulders of the rubble-pile structure asteroid is established. The size ratio (length to diameter) of the boulder size inside the asteroid to the projectile diameter changed from 0.25 to 1.7. We conducted a smoothed particle hydrodynamics numerical simulation in the AUTODYN software to study the boulder size effect on the ejecta size–velocity distribution. Simulation results suggest that the microscopic porosity on regolith affects the propagation of shock waves and reduces the velocity of ejecta. Experiments and numerical simulation results suggest that both excavation flow and spalling ejection mechanism can eject boulders (0.12–0.72 m) out of the rubble-pile asteroid. These experiments and simulation results help us select the potential impact site in a planetary defense scenario and reduce deflection risk. are comprised primarily of boulders of a range of sizes. [ABSTRACT FROM AUTHOR]

One of the most common types of allochthonous impactite produced in hypervelocity impact events is impact breccia that contains melt particles. In numerous terrestrial hypervelocity impact structures such melt‐bearing breccias have been termed “suevite,” after the type locality at the Ries impact structure, Germany. Despite its widespread occurrence, the origin, emplacement, and classification of suevite remains debated. In this contribution, we re‐examine the nature and origin of suevite at the Ries impact structure. The results of new field and laboratory investigations, when combined and synthesized with results from previous studies, lead to a multi‐stage model for the origin and emplacement of allochthonous impactites during the Ries impact event. Following the creation of a transient cavity the so‐called Bunte Breccia and “megablocks” were emplaced via ballistic sedimentation and subsequent radial flow during the excavation stage to form a continuous ejecta blanket. At the end of the excavation stage, a mixture of melt and lithic fragments formed a lining to the transient cavity and it is this material that later became the crater, dike, and outer suevite (OS) units. The crater suevite represents the material from the displaced zone of the transient cavity that was transported and mixed but never left the cavity. The emplacement of dike suevite occurred during the modification stage as the crater suevite was intruded into fractures in the underlying crater floor. The OS and rare impact melt rocks overlying the ballistic (Bunte Breccia) ejecta deposits were emplaced as outwards‐directed ground‐hugging flows largely during the modification stage of crater formation. The OS flows varied both spatially and temporally in terms of the flow characteristics, from being dominated by solid particles and gas (cf. pyroclastic density currents) to a mixture of solid particles, liquid (impact melt), and minor gases (i.e., particulate impact melt‐rich flows). These particulate impact melt‐rich flows dominated by far. Minor “fallback” of material from an ejecta plume is evidenced by accretionary lapilli in the Nördlingen 1973 core. In summary, allochthonous impactites at the Ries impact structure are not unusual but are consistent with observations from other terrestrial and planetary craters, where melt‐rich impactites overly ballistic ejecta deposits both outside and inside crater rims and where melt‐rich impactites occur in crater interiors. [ABSTRACT FROM AUTHOR]

Meteorite impacts have proved to be a significant source of seismic signal on the Moon, and have now been recorded on Mars by InSight seismometers. Understanding how impacts produce seismic signal is key to the interpretation of this unique data, and to improve their identification in continuous seismic records. Here, we use the seismic Representation Theorem, and particularly the stress glut theory, to model the seismic motion resulting from impact cratering. The source is described by equivalent forces, some resulting from the impactor momentum transfer, and others from the stress glut, which represents the mechanical effect of plasticity and non linear processes in the source region. We condense these equivalent forces into a point-source with a time-varying single force and nine-component moment tensor. This analytical representation bridges the gap between the complex dynamics of crater formation, and the linear point-source representation classically used in seismology. Using the multiphysics modelling software HOSS, we develop a method to compute the stress glut of an impact, and the associated point-source from hypervelocity impact simulations. For a vertical and an oblique impact at 1000 m s−1, we show that the moment tensor presents a significant deviatoric component. Hence, the source is not an ideal isotropic explosion contrary to previous assumptions, and draws closer to a double couple for the oblique impact. The contribution of the point force to the seismic signal appears negligible. We verify this model by comparing two signals: (1) HOSS is coupled to SPECFEM3D to propagate the near-source signal elastically to remote seismic stations; (2) the point-source model derived from the stress-glut theory is used to generate displacements at the same distance. The comparison shows that the point-source model is accurately simulating the low-frequency impact seismic waveform, and its seismic moment is in trend with Lunar and Martian impact data. High-frequencies discrepancies exist, which are partly related to finite-source effects, but might be further explained by the difference in mathematical framework between classical seismology and HOSS' numerical modelling. [ABSTRACT FROM AUTHOR]

Achondrites provide an opportunity to examine the igneous processes of differentiated bodies in our solar system. The recent discovery of several silica‐rich achondrites suggests that andesitic crusts were more common among planetesimals than previously thought, though the processes behind their emplacement are not well understood. Here, electron backscatter diffraction (EBSD) is used to investigate the igneous emplacement conditions of Erg Chech 002 (EC 002), a recently discovered ungrouped achondrite representing andesitic magmatism ~2 Myr after the formation of calcium–aluminum‐rich inclusions (CAIs). EBSD analyses of crystallographic preferred orientations (CPOs) for augite and plagioclase feldspar phenocrysts indicate that EC 002 exhibits a weak foliation CPO. Augite misorientation inverse pole figures (mIPF) indicate preferential slip along the (100)[001] system with a distinct shift toward the {0kl}[u0w] system in plastically deformed grains. Our findings support the hypothesis that EC 002 was likely emplaced in the lower regions of a magmatic intrusion. Augite slip signatures suggest that EC 002 crystallization and emplacement were restricted to high temperatures (>800°C) and experienced at least two strain regimes. The distinct shift from a dominant (100)[001] slip system, which corresponds to high temperatures (800–1050°C), to a [0kl][u0w] slip system indicates an increased strain rate due to shock deformation (1–5 GPa) attributed to ejection by hypervelocity impact. [ABSTRACT FROM AUTHOR]

There are likely many undiscovered impact structures on Earth, but several challenges prevent their detection, including possible concealment beneath large ice sheets. In recent years, geophysical, geochemical, and microphysical evidence has mounted for a ca. 58 Ma impact structure under the Hiawatha Glacier, northwest Greenland. Here, we report evidence for a second, much older hypervelocity impact event in this region, recorded in an impact melt rock sample collected from a glaciofluvial deposit in Inglefield Land. Secondary ion mass spectrometry U-Pb analyses of shock metamorphosed zircon grains yielded a previously unrecorded, Proterozoic best estimate impact age of 1039 ± 16 Ma (mean square of weighted deviates = 2.9). Based on Archean-Proterozoic target rock U-Pb ages obtained from unshocked zircon grains and the location of the melt rock sample along the ice margin, we suggest this sample was derived from a hypervelocity impact structure farther inland, concealed by the Greenland Ice Sheet. This study demonstrates the ability to uncover new impact events in some of the most inaccessible areas on Earth and the possibility of sampling multiple impact structures from one location when examining ex situ material. Our results have implications for current and future Martian and lunar returned samples that demonstrably bear complex impact histories. [ABSTRACT FROM AUTHOR]

In this study, a series of hypervelocity impact tests were carried out based on a two-stage light gas gun, and the sequence spectrum and radiation evolution data of the impact products under different impact conditions were obtained. The diameter of the projectile is 3e5 mm, the impact velocity is 3.13e6.58 km/s, and the chamber pressure is 0.56e990 Pa. The spectrum of ejected debris cloud in the 250e310 nm band were obtained using a transient spectral measurement system and a multi-channel radiometer measurement system. The test results reveal that the flash radiation intensity increases as a power function with the kinetic energy of the impact. Furthermore, the peak value of the line spectrum decreases as the chamber vacuum degree increases, while the radiation width gradually expands. The line spectrum in the spectral characterization curve corresponds to the ejected debris clouds splitting phase, which does not produce significant line spectrum during material fragmentation and is dominated by the continuum spectrum produced by blackbody radiation. There will appear one or three characteristic peaks in the flash radiation time curve, the first and second peaks correspond to the penetration phase and the third peak corresponds to the expansion phase of the ejected debris clouds on the time scale, the first and second peaks are more sensitive to the chamber vacuum degree, and when the pressure is higher than 99 Pa, the first and second characteristic peaks will disappear. The radiant heat attenuation of the flash under different impact conditions is significantly different, the attenuation exponent has a power function relationship with the impact velocity and the chamber vacuum degree, while the attenuation exponent has a linear relationship with the diameter of the projectile, the specific expression of the attenuation exponent is obtained by fitting. The findings from this research can serve as a valuable reference for remote diagnostic technologies based on flash radiation characteristics. [ABSTRACT FROM AUTHOR]

Hypervelocity impacts can generate hydrothermal systems, which have been suggested as candidate environments for prebiotic chemistry on the early Earth. The Haughton impact structure (a 23 km diameter crater located on Devon Island, Nunavut, Arctic Canada) displays evidence of water‐rock alteration indicative of a hydrothermal system generated from a cosmic impact. To model the formation of this crater and subsequent hydrothermal alteration, we have successfully developed a new two‐code methodology that utilizes a shock physics code and a hydrothermal code (HYDROTHERM). We can best reproduce the Haughton crater with a ∼700 m diameter projectile with an impact velocity of 14 km/s. With our approach, we were able to match all the major geological constraints observed at the Haughton impact structure. Our models show that the Haughton crater interior could have sustained temperatures ideal for thermophilic and hyperthermophilic life (50–120°C) for more than 50,000 years, indicating that these systems can sustain prebiotic chemistry and life for longer than previously estimated. Plain Language Summary: Impacts of cosmic objects moving at hypervelocity can create high‐temperature hydrothermal systems. These environments have been suggested as possible sites for the formation of prebiotic chemistry on early Earth. The Haughton impact structure on Devon Island, Nunavut, Arctic Canada, has a well‐studied impact‐generated hydrothermal system and offers a unique analog to similar systems on early Earth or Mars. Here, we present a two‐code modeling technique to model the full evolution of the impact‐generated hydrothermal system at Haughton. We were able to match the major geological constraints observed at the Haughton structure. Our models suggest that the Haughton crater interior should have sustained temperatures ideal for early life (50–120°C) for >50,000 years, indicating that these systems can sustain life for longer than previously estimated. Key Points: The Haughton impact structure can be better modeled utilizing a smaller impactor (∼700 m in diameter) than previously estimatedWe successfully match a multitude of observed fluid alterations observed at Haughton with our novel two‐code methodologyOur models show that the Haughton crater interior sustained temperatures ideal for thermophilic and hyperthermophilic life for >50,000 years [ABSTRACT FROM AUTHOR]

Astrobiology studies are a top priority in answering one of the most fundamental questions in planetary science: Is there life beyond Earth? Saturns icy moon Enceladus is a prime target in the search for life in our solar system, identified by NASA as the second-highest priority site for a flagship mission in the next decade. The orbital sampling technique of impact ionization mass spectrometry indicated the presence of complex organics in the small icy plume particles ejected by Enceladus encountered previously by Cassini. However, high interaction velocities caused ambiguity as to the origin and identity of the organics. Laboratory validation of this technique is needed to show that biosignature molecules can survive an impact at hypervelocity speeds for detection. Here, we present results on the hypervelocity impact of organic-laden submicron ice grains for in situ mass spectrometric characterization with the first technique to accurately replicate this plume sampling scenario: the Hypervelocity Ice Grain Impact Mass Spectrometer. Our results show good agreement with Cassini data at comparable compositions. We show that amino acids entrained in ice grains can be detected intact after impact at speeds up to 4.2 km/s and that salt reduces their detectability, validating the predictions from other model systems. Our results provide a benchmark for this orbital sampling method to successfully detect signs of life and for the interpretation of past and future data. This work has implications not only for a potential Enceladus mission but also for the forthcoming Europa Clipper mission.

A series of small-scale impact cratering experiments were performed on basalt at velocities of 3.5–6.0 km s−1. The formation and motion process of ejecta were observed by high-speed and ultra-high-speed cameras. The momentum transfer coefficient values and cratering size were measured. Hydrodynamic simulations in 2D were carried out to replicate the impact conditions of the basalt and calibrate model parameters. The contribution of jet, central cratering, and spalling ejection to momentum enhancement was quantitatively analyzed by simulation. Simulation results show that: the mass and the momentum of the jet are less than 1 % of the projectile mass, and the initial momentum, can be ignored. For craters in small-sized basalt, the momentum enhancement mainly comes from the spall region ejecta. The formation mechanism of ejecta at different stages was analyzed based on the shock wave and jet theory. An analytical model is developed for estimating the velocity and motion of ejecta formation at different stages. The model calculation results of the speed of the ejecta formed in different stages are consistent with the numerical results. The maximum velocity of the ejecta formed in the jet and cratering stage depends on the initial impact velocity and the Hugoniot parameters of the projectile/target material. The minimum velocity of the spallation ejecta is linearly related to the spalling strength of the target. The model provides a fast and simple method to calculate the ejecta velocity and estimate the influence range of ejecta under different impact conditions. • The speed of the jet is greater than the initial impact speed. • The contribution of jet to momentum enhancement can be ignored. • For craters in small-sized, the momentum enhancement and mass mainly come from the spall region ejecta. • A model was developed for estimating the velocity and motion of ejecta. [ABSTRACT FROM AUTHOR]

There is growing momentum, as articulated through the visions of space agencies, to establish permanent settlements on planetary bodies such as the Moon and Mars. One key hazard that structures will be subjected to will be hypervelocity impacts of micrometeoroids and orbital debris. Shielding against such impacts is essential to ensure the safety of structures and their human inhabitants. There has, however, been limited research on such shields and no field applications to date. In order to inform the composition and design of protective shields for planetary structures, recourse can be made to protective shields utilised in spacecraft and space stations that have benefitted from years of research and development. This paper reviews the existing shielding practices for spacecraft and space stations as a starting point for the shielding of planetary structures. Shield configurations are firstly introduced. Both experimental tests and numerical simulations required to evaluate the performance of the shields are then discussed. Analytical prediction models for shields are reviewed, and the predictions of these models are compared with test results of corresponding shields from the literature. Finally, the effect of parameters such as projectile diameter, impact velocity, impact angle, and shield geometry on the overall shield performance is analysed. This paper ultimately provides technical knowledge about the shielding systems for spacecraft and space stations that can be used as a point of reference for scientists and engineers to develop shields for structures on planetary bodies. • Review of shielding systems on spacecraft and ISS for MMOD protection. • Analysis of theoretical models for predicting protective shield performance. • Recommendations provided for shielding systems of Lunar and Martian structures. [ABSTRACT FROM AUTHOR]

• An optimisation methodology is proposed for shielding against Orbital Debris. • Hypervelocity impact models are developed to capture damage/fracture mechanisms. • The proposed models are validated against hypervelocity impact experiments. • The optimised configuration maximises protection and minimises areal density. Advancements in space exploration over the last few decades have led to a sharp increase in Micro-Meteoroid and Orbital Debris (MMOD), with the associated increased risk of hypervelocity impact on satellites and space structures. The Whipple shield can mitigate the effects of such impacts and current research is exploring further developments towards effective lightweight passive shielding technology to counter the damaging effects of MMOD. With the increase in MMOD and the prospect of increased space travel in the coming years and decades, it is vital that more research is conducted and improvements are made in the development and design of efficient, lightweight shielding technology to protect both unmanned and manned spacecraft against hypervelocity impacts (HVI). The optimisation of shield design for HVI is a high dimensionality problem, suited to advanced computational approaches. Key variables in HVI shield design that should inform the focus on optimisation include: impact velocity, rear wall thickness, projectile diameter and bumper thickness. A hybrid shield configuration and numerical model are proposed and validated, with alternating layers of aluminium (AL2024) and carbon fibre composites (CFRP, T300 woven-fabric) to form a 5 mm thick target plate consisting of 5 plies. The adaptive coupled FEM-SPH method is used to model the target plates. The proposed hypervelocity shield design optimisation methodology is based on Direct Simulation-based Genetic Algorithm (DSGA) optimisation and is implemented to optimise a multi-variable shield design space. Objective weightings are used to analyse and discuss results, referring to the ratio of the kinetic energy to the shield areal density objectives. A clear transition in the impact behaviour of the optimised MMOD shields is observed in the transition region from high-velocity to hypervelocity impact, where significant levels of kinetic energy dissipation are observed below the transition region, and lower energy dissipation at hypervelocity. The shield design optimisation results show that with a weighted kinetic energy to mass objective of 90:10, the kinetic energy of the back shield plate decreases significantly (62.7%) and the areal density can be reduced by more than 18%. Alternative configurations displayed sub-optimal results based on a trade-off between objective functions. [ABSTRACT FROM AUTHOR]

The selected ice nanoparticle accelerator, SELINA, was used to prepare beams of single ice particles with positive or negative charge. Positively charged particles were prepared from deionized water and 0.05–0.2 molar solutions of sodium chloride in water, and negatively charged ice particles were generated from water without salt. Depending on the electrospray source configuration, the measured particles vary from 50 to 1000 nm in diameter. The kinetic energy per charge for all particles was set to 200 eV by the collisional equilibration in quadrupoles, which resulted in primary velocities up to 600 m/s for the lowest m/z particles. The electrospray ionization and thus particle formation from SELINA become less efficient with increasing salt concentration, resulting in a lower detected particle frequency and size. Good instrument operation is achievable for concentrations below 0.2 M. After we have verified and characterized positively and negatively charged ice particles, we have combined SELINA with a target and time-of-flight spectrometer for a 'proof-of-principle' post acceleration of 120 nm particles towards hypervelocity (v ~ 3000 m/s) and detection of fragments from the particle impact (SELINA-HIMS). General conditions are discussed for the acceleration of particles between 50 and 1000 nm to velocities well above 3000 m/s with SELINA-HIMS instrument. This article is part of the theme issue 'Dust in the Solar System and beyond'. [ABSTRACT FROM AUTHOR]

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'. [ABSTRACT FROM AUTHOR]

To investigate the damage characteristics of spacecraft structures caused by external impacts and propose protective measures, this study utilizes two-stage light gas gun launcher with detonation capability. Hypervelocity impact experiments are conducted on composite laminates that incorporate varying proportions of shear stiffening gel (SSG). Polyvinylidene fluoride (PVDF) sensors are employed to collect response signals from the front corners, rear corners, and rear edges of the laminate, enabling an assessment of its behavior under impact conditions. By analyzing the signals acquired from the Polyvinylidene fluoride sensor, the study obtains the time-frequency response characteristics of the signals at various positions with different proportions of shear stiffening gel. The correlation between these response characteristics and the damage of the laminate is investigated. The analysis reveals that the vibration response at various positions of the laminate provides a comprehensive indication of internal delamination and surface damage. Moreover, this response is linked to the level of fragmentation of the projectile. The incorporation of shear stiffening gel in the laminate enhances its impact resistance and helps mitigate damage at the connection between the laminate and other components. Interestingly, the impact resistance does not follow a monotonic trend with respect to the proportion of shear stiffening gel. Based on the experimental results discussed in this article, the optimal proportion of shear stiffening gel is determined to be 5 %. • Impact experiments were conducted on laminates containing varying proportions of shear stiffening gel. • The addition of shear stiffening gel effectively suppresses vibrations within the specified range. • Following impact, the corners of the laminate experience more pronounced vibrations compared to the edges. • Excessive proportion of shear stiffening gel may alter the internal phase and interface morphology. [ABSTRACT FROM AUTHOR]

The Discrete Element Method is uniquely suited to modeling the extreme fragmentation typical of impact-induced satellite breakups. In this paper, we introduce a discrete orthotropic material model for simulating carbon fiber reinforced polymers (CFRP). We calibrate and validate the CFRP model with hypervelocity impact experiments performed at Fraunhofer EMI on thin CFRP face sheets. We demonstrate the suitability of the model for simulating spacecraft breakups by comparing simulation results to a ground-based experiment of a 15 x 15 × 15 cm CFRP micro-satellite from literature. Fragment size distributions show excellent agreement between experiment and literature. Comparisons are also made with the NASA breakup model. • Introduce a discrete material model for simulating carbon fiber reinforced polymers. • Calibrate and validate the model with hypervelocity impact experiments. • Simulate the breakup of a 15 x 15 × 15 cm CFRP microsatellite. • Compare the simulation results to experimental fragmentation results from literature and NASA breakup model. • Simulation and experiment show excellent agreement. [ABSTRACT FROM AUTHOR]

For impact velocities larger than a threshold velocity of 3 km/s, aluminium Whipple Shields present an enhanced protection capability with respect to monolithic protections with the same areal density. In particular, in the range between 3 and 7 km/s the projectile partially fragments and melts after impacting the bumper; modelling this transition might be complex due to the high number of parameters affecting the collision. In particular, limited data is available in literature with a systematic evaluation of such parameters. In this context, a campaign of 22 experiments was performed to assess the response of aluminium Whipple Shields to normal impacts of aluminium projectiles in the transition range up to 5 km/s. In the tests, the projectile diameter was fixed at 2.9 mm and the bumper thickness and impact velocity were systematically varied respectively at 1, 1.5, and 2 mm and between 2.6 and 5 km/s. Collected data included high-velocity videos of the debris cloud generated by the impacts at both low resolution (for all shots) and high resolution (for 19 out of 22 tests); in addition, for 10 experiments high-resolution images of both the bumper and the wall were acquired after the tests. In this paper, the experimental campaign is described and the main collected results are presented; in particular, the influence of the different impact parameters is discussed. Experimental results are finally compared with numerical simulations conducted with a smoothed particle hydrodynamics method available in IMPETUS Solver. • 22 impact experiments were performed on Aluminium Whipple Shields. • The projectile diameter was fixed at 2.9 mm for all tests. • Bumper thickness and impact velocity varied in the ranges 1–2 mm and 2.6–5 km/s. • The influence of the different impact parameters is discussed. • Experimental results are compared with numerical SPH simulations. [ABSTRACT FROM AUTHOR]

Micrometeoroids and Orbital Debris (MMOD) travelling at extremely high velocities in space are a threat to the structural integrity of spacecrafts in the Low Earth Orbit. Whipple shield, consisting of a Bumper and a Rear Wall, with a stand-off distance in between, is widely used to protect spacecrafts from hypervelocity MMOD impacts. In this paper, we present numerical simulations of a set of well-known hypervelocity impact (HVI) experiments on aluminium-based Whipple shields reported in the literature. These simulations are conducted using the three-dimensional Lagrangian Finite Element Method in ABAQUS/Explicit software. In six out of the seven tests reported in the literature, the Whipple shield failed due to a detached spall from the back surface of the Rear Wall, while in the seventh test, the spall was not detached. The present work successfully replicates and favourably compares the failure mechanisms observed in these Whipple shields to the corresponding experimental results. Various critical aspects of the Whipple shield's failure mechanics and mechanisms are investigated. These include impact pressure on the projectile, Bumper and Rear Wall, Bumper hole diameter, temperature rise, and residual velocity of debris particles and spalled fragments. The predicted ballistic limit of the Whipple shield falls between 2.54 mm and 3.18 mm of Rear Wall thickness in excellent agreement with the experimental results reported in the literature. The present work provides valuable insights into Whipple shield performance. The developed methodology could be employed to optimize shield design through predictive simulations, thereby improving spacecraft protection. [ABSTRACT FROM AUTHOR]

The space debris in Earth's orbit has increased drastically due to the failure of spacecraft, rocket bodies, and mission-related objects. These objects in orbit increase the space waste and challenge other flying objects such as spacecraft. A hypervelocity impact of space debris on spacecraft structures can have a range of effects (mechanical damage and functional failure), raising significant concerns about spacecraft safety. This paper reviews the different studies on the performance and development of the Whipple shield against the hypervelocity impact of space debris. The study focuses on the impact mechanism, dynamic Fragmentation of materials, strength models, Equation of state, characteristics, and model of the debris cloud. The strength models (Steinberg–Guinan and Johnson–Cook) and Mie–Gruneisen equation of state, primarily used for hypervelocity impact applications, are thoroughly covered in this study. The study also reported the various experimental and numerical techniques for high and hypervelocity impact. The study concluded that mesh-based, mesh-free, and hybrid finite element methods are reliable for analyzing Whipple shield targets to resist hypervelocity impact. The study also observed that the two-stage light gas gun technique investigates most experimental analyses of hypervelocity impact on the Whipple shield. Alongside reviewing the abovementioned aspects, this paper also underlines the future scope of study in this paradigm. The authors strongly believe that this study provides more insights into the fundamentals and perceptions of the Whipple shield to protect the spacecraft against the hypervelocity impact of space debris. [ABSTRACT FROM AUTHOR]

Context. Hypervelocity stars (HVSs) unbound to the Galaxy can be formed with extreme stellar interactions, for example close encounters with supermassive black holes or in massive star clusters, supernova explosions in binary systems, or the stripping of dwarf galaxies. Observational evidence comes from measurements of radial velocities (RVs) of objects crossing the outer Galactic halo and of tangential velocities based on high proper motions (HPMs) and distances of relatively nearby stars. Aims. I searched for new nearby HVS candidates and reviewed known objects using their Gaia astrometric measurements. Methods. Candidates were selected with significant Gaia parallaxes of >0.1mas, proper motions of >20 mas yr−1, and computed galactocentric tangential velocities vtan_g>500 km s−1. The DR2 and DR3 samples of several thousand HVS candidates were studied with respect to their proper motions, sky distribution, number of observations, location in crowded fields, colour-magnitude diagrams, selection effects with magnitude, and RVs in DR3. The 72 most extreme (vtan_g>700 km s−1) and nearest (within 4kpc) DR3 HVS candidates were investigated with respect to detected close neighbours, flags, and astrometric quality parameters of objects of similar magnitudes in DR3. The quality checks involved HPM objects in a global comparison and all objects in the vicinity of each target. Results. Spurious HPMs in the Galactic centre region led to false HVS interpretations in Gaia DR2 and are still present in DR3, although to a lesser extent. Otherwise there is good agreement between the HPMs of HVS candidates in DR2 and DR3. However, HVS candidates selected from DR2 tend to have larger parallaxes, and hence lower tangential velocities in DR3. Most DR3 RVs are much lower than the tangential velocities, indicating that the DR3 HVS candidates are still affected by underestimated parallaxes. None of the 72 extreme nearby DR3 HVS candidates, including three D6 stars, passed all the quality checks. Their tangential velocities may turn out to be lower, but at least some of them still appear unbound to the Galaxy. [ABSTRACT FROM AUTHOR]

The debris cloud generated by the hypervelocity impact (HVI) of orbiting space debris directly threatens the spacecraft. A full understanding of the damage mechanism of rear plate is useful for the optimal design of protective structures. In this study, the hypervelocity yaw impact of a cylindrical aluminum projectile on a double-layer aluminum plate is simulated by the FE-SPH adaptive method, and the damage process of the rear plate under the impact of the debris cloud is analyzed based on the debris cloud structure. The damage process can be divided into the main impact stage of the debris cloud and the structural response of the rear plate. The main impact stage lasts a short time and is the basis of the rear plate damage. In the stage of structure response, the continuous deformation and inertial motion of the rear plate dominate the perforation of the rear plate.We further analyze the damage mechanism and damage distribution characteristics of the rear plate in detail. Moreover, the connection between velocity space and position space of the debris cloud is established, which promotes the general analysis of the damage law of debris cloud. Based on the relationship, the features of typical damage areas are identified by the localized fine analysis. Both the cumulative effect and structural response cause the perforation of rear plate; in the non-perforated area, cratering by the impact of hazardous fragments is the main damage mode of the rear plate. [ABSTRACT FROM AUTHOR]

Recent Gaia observations suggest that some hypervelocity stars (HVSs) might originate from outside the Galaxy. We ask whether these HVSs could come from as far as Andromeda. Therefore, we simulate HVSs originating in Andromeda with initial conditions based on attributes of high-velocity stars measured in the Milky Way and a simple model for the gravitational potential of Andromeda and the Milky Way. We evaluate the validity of this scenario based on the simulation results. While we expect that the vast majority of HVSs in our Galaxy will originate here, we expect the number of stars present from Andromeda at any one time to be between 12 and 3910, depending upon model assumptions. Further, we analyse the properties of HVSs that are able to reach the Milky Way. We discuss whether they could be detected experimentally based on recent constraints set on the ejection rate of HVSs from the Milky Way centre. [ABSTRACT FROM AUTHOR]

In order to study the impact initiation process and mechanism of hypervelocity PTFE/Al composite structure reactive fragments on a shielded charge, first, an existing PTFE/Al reactive fragment hypervelocity collision experiment was numerically simulated using the SPH algorithm in ANSYS/AUTODYN 17.0 software. Then, the Lee–Tarver model was verified to describe the detonation reaction behavior and explosion damage effect of reactive materials. A numerical simulation analysis of the impact of two kinds of ultra-high-speed PTFE/Al composite-structure reactive fragments on a shielded charge was carried out using the SPH algorithm. These were steel-coated PTFE/Al and steel-semi-coated PTFE/Al fragments, and they were compared with the impact of steel fragments. The results indicate that the threshold velocities of the impact initiation of the two composite-structure reactive fragments on the shielded charge were both 2.6 km/s, while the threshold velocity of the steel fragment was 2.7 km/s. Under the threshold velocity condition, the two composite-structure reactive fragments increase the time and intensity of the compressed shock wave pulse in the explosive due to the impact energy release effect of the reactive materials, causing the shielded charge to detonate under the continuous long-term pulse loads. However, the mechanism of the steel fragment on the shielded charge belongs to the shock–detonation transition. The research results can provide scientific references for the design of hypervelocity reactive fragments and the study of their damage mechanism. [ABSTRACT FROM AUTHOR]

In this study, the finite element and smoothed-particle hydrodynamics (FE-SPH) adaptive method was used to reproduce experiments on DebriSat under hypervelocity impact. The development and stabilization process of the debris cloud, as well as the damage and response process of the satellite, were reproduced. Compared with the experimental results, although the cumulative number of fragments is relatively small, the trend of the quantity distribution is consistent with the experiment. In addition, the area-to-mass ratio distribution of the fragments shows good agreement with the experimental results and theoretical prediction. The damage, destruction, and failure process of the satellite can be divided into two stages: material and structural response stages. In the material response stage, the satellite is directly destructed by the debris cloud, with worse damage caused by the Domino Effect. The failure modes in this stage include perforation, bending, and bucking of satellite components. The structural response stage is mainly caused by the inertial motion of satellite components, with failure modes primarily involving the connection failure between components and the bending deformation of internal components. In this stage, the overall structure of the satellite is stretched or compressed, resulting in the final disintegration. It was found that the FE-SPH adaptive method is suitable for the full-scale simulation of complex satellites, and the real shape of fragment features can be obtained, providing new ideas for studying the satellite breakup mechanism. The results indicate that the material response primarily causes damage to the satellite components, while the structural response is the main factor of the damage to the overall satellite structure. • The breakup process of the DebriSat is analyzed using FE-SPH adaptive method. • The Domino Effect of the impacts is clarified, which causes much worse damage to the satellite. • A critical time is proposed to distinguish the satellite's material response and structural response stage. [ABSTRACT FROM AUTHOR]

Raman spectroscopy is a non-destructive analytical technique for characterizing organic and inorganic materials with spatial resolution in the micrometer range. This makes it a method of choice for space-mission sample characterization, whether on return or in situ. To enhance its sensitivity, we use signal amplification via interaction with plasmonic silver-based colloids, which corresponds to surface-enhanced Raman scattering (SERS). In this study, we focus on the analysis of biomolecules of prebiotic interest on extraterrestrial dust trapped in silica aerogel, jointly with the Japanese Tanpopo mission. The aim is twofold: to prepare samples as close as possible to the real ones, and to optimize analysis by SERS for this specific context. Serpentinite was chosen as the inorganic matrix and adenine as the target biomolecule. The dust was projected at high velocity into the trapping aerogel and then mechanically extracted. A quantitative study shows effective detection even for adenine doping from a 5·10−9mol/L solution. After the dust has been expelled from the aerogel using a solvent, SERS mapping enables unambiguous adenine detection over the entire dust surface. This study shows the potential of SERS as a key technique not only for return samples, but also for upcoming new explorations. [ABSTRACT FROM AUTHOR]

In operando studies of high explosives involve dynamic extreme conditions produced as a shock wave travels through the explosive to produce a detonation. Here, we describe a method to safely produce detonations and dynamic extreme conditions in high explosives and in inert solids and liquids on a tabletop in a high-throughput format. This method uses a shock compression microscope, a microscope with a pulsed laser that can launch a hypervelocity flyer plate along with a velocimeter, an optical pyrometer, and a nanosecond camera that together can measure pressures, densities, and temperatures with high time and space resolution (2 ns and 2 µm). We discuss how a detonation builds up in liquid nitromethane and show that we can produce and study detonations in sample volumes close to the theoretical minimum. We then discuss how a detonation builds up from a shock in a plastic-bonded explosive (PBX) based on HMX (1,3,5,7-Tetranitro-1,3,5,7-tetrazocane), where the initial steps are hotspot formation and deflagration growth in the shocked microstructure. A method is demonstrated where we can measure thermal emission from high-temperature reactions in every HMX crystal in the PBX, with the intent of determining which configurations produce the critical hot spots that grow and ignite the entire PBX. [ABSTRACT FROM AUTHOR]

We search for high-velocity stars in the inner region of the Galactic bulge using a selected sample of red clump stars. Some of those stars might be considered hypervelocity stars (HVSs). Even though the HVSs ejection relies on an interaction with the supermassive black hole (SMBH) at the centre of the Galaxy, there are no confirmed detections of HVSs in the inner region of our Galaxy. With the detection of HVSs, ejection mechanism models can be constrained by exploring the stellar dynamics in the Galactic centre through a recent stellar interaction with the SMBH. Based on a previously developed methodology by our group, we searched with a sample of preliminary data from version 2 of the Vista Variables in the Via Lactea (VVV) Infrared Astrometric Catalogue (VIRAC2) and Gaia DR3 data, including accurate optical and near-infrared proper motions. This search resulted in a sample of 46 stars with transverse velocities larger than the local escape velocity within the Galactic bulge, of which four are prime candidate HVSs with high-proper motions consistent with being ejections from the Galactic centre. Adding to that, we studied a sample of reddened stars without a Gaia DR3 counterpart and found 481 stars with transverse velocities larger than the local escape velocity, from which 65 stars have proper motions pointing out of the Galactic centre and are candidate HVSs. In total, we found 69 candidate HVSs pointing away from the Galactic centre with transverse velocities larger than the local escape velocity. [ABSTRACT FROM AUTHOR]

An atomistic pathway for a strain-induced subsolidus martensitic transition between quartz and coesite was found by computing the set of the smallest atomic displacements required to transform a quartz structure into a coesite structure. A minimal transformation cell with 24 SiO 2 formula units is sufficient to describe the diffusionless martensitic transition from quartz to coesite. We identified two families of invariant shear planes during the martensitic transition, near the {10 1 ¯ 1} and {12 3 ¯ 2} set of planes, in agreement with the orientation of planar defect structures observed in quartz samples which experienced hypervelocity impacts. We calculated the reaction barrier using density functional theory and found that the barrier of 150 meV/atom is pressure invariant from ambient pressure up to 5 GPa, while the mean principal stress limiting the stability of strained quartz is ≈ 2 GPa. The model calculations quantitatively confirm that coesite can be formed in strained quartz at pressures significantly below the hydrostatic equilibrium transition pressure. [ABSTRACT FROM AUTHOR]

Investigating the hypervelocity impact process on rubble-pile asteroids is crucial for understanding the formation and evolution of small celestial bodies, and has important implications for planetary defence. In recent years, numerical simulations have been widely used to model asteroid impacts, as a complement to experimental and theoretical approaches. In particular, the hybrid SPH–DEM framework has been introduced to describe the multistage dynamics involving shock propagation and gravitational re-accumulation. However, the tension between modelling accuracy and computational costs poses significant challenges in rubble-pile impact simulations. In this study, we introduce two distinct particle configurations, i.e. multiple layers of similar-sized surface contact particles and a set of different-sized gravity particles, to efficiently describe the large irregular boulders during long-term evolution. Accordingly, the new transition algorithms are implemented to convert the smoothed particle hydrodynamics (SPH) results into the desired discrete-element method (DEM) configurations. With the proposed method, the complexity of contact computation is reduced from |$\mathcal {O}(N)$| to |$\mathcal {O}(N^{2/3})$|⁠ , and the gravity computation is accelerated by about one hundred times while maintaining the same level of resolution. The method is then used to simulate the double asteroid redirection test impact on the rubble-pile asteroid Dimorphos. Our numerical simulations have reproduced the observation results regarding momentum transfer and mass ejection. Moreover, we predict that the impact event will form a final crater larger than 45–68 m in diameter and lead to global resurfacing of the target. The renewed surface and fresh interior will be accessible to the upcoming Hera mission, providing new perspectives on the formation and evolution of the rubble-pile binary asteroids. [ABSTRACT FROM AUTHOR]

Dust plasma readily forms during hypervelocity impact, which serves as a source of plasma macroscopic charge separation and strong electromagnetic fields. In this study, we examine the dynamic evolution of surface charging of aluminum dust grains with micrometer or submicrometer sizes in a hypervelocity impact plasma environment based on the theory of orbital motion limited. As dust grains traverse the expanding plasma, plasma density and temperature decrease with increasing distance from the impact point. This leads to longer relaxation times for charging equilibrium (ranging from picoseconds to microseconds) and reduced equilibrium charges. The model incorporates thermionic and secondary electron emission effects on dust grain charging processes while also examining the impacts of five heating and cooling mechanisms on the thermal equilibrium temperatures of dust grains. Near the impact point, thermal equilibrium temperatures exceed aluminum's boiling point, which results in phase transition ablation processes. As dust grain temperatures increase, thermionic emission currents may dominate charging dynamics and influence final equilibrium charge numbers. High-temperature dust grains tend to acquire positive charges. Moreover, we observe that the radius of dust grains considerably affects charging processes, and smaller grain radii correspond to low equilibrium charges and longer relaxation times. [ABSTRACT FROM AUTHOR]

The effects of projectile/target impedance matching and projectile shape on energy, momentum transfer and projectile melting during collisions are investigated by numerical simulation. By comparing the computation results with the experimental results, the correctness of the calculation and the statistical method of momentum transfer coefficient is verified. Different shapes of aluminum, copper and heavy tungsten alloy projectiles striking aluminum, basalt, and pumice target for impacts up to 10 km/s are simulated. The influence mechanism of the shape of the projectile and projectile/target density on the momentum transfer was obtained. With an increase in projectile density and length-diameter ratio, the energy transfer time between the projectile and targets is prolonged. The projectile decelerates slowly, resulting in a larger cratering depth. The energy consumed by the projectile in the excavation stage increased, resulting in lower mass-velocity of ejecta and momentum transfer coefficient. The numerical simulation results demonstrated that for different projectile/target combinations, the higher the wave impedance of the projectile, the higher the initial phase transition velocity and the smaller the mass of phase transition. The results can provide theoretical guidance for kinetic impactor design and material selection. [ABSTRACT FROM AUTHOR]

In this study, hypervelocity impact (HVI) simulations between a space object and space structure using various shielding systems are conducted. A nonlinear structural dynamics analysis code, LS-DYNA, is used. The space object at 6.910 km/s is modeled as an Al2017-T4 sphere with a diameter of 2 mm. The four types of space sandwich structures with the same mass of 0.0121 kg are considered to investigate the shielding performances and are modeled as honeycomb core sandwich panel (HCSP), lattice core sandwich panel (LCSP), LC/HCSP, and HC/LCSP. The shielding performances and final failure shapes of the space structures are studied through the HVI simulations on the space structure using various shielding systems. The HCSP fails to protect due to the channeling effect, resulting in failure to the rear wall. The three types of the shielding systems using the LC successfully protect the space structure from the HVI with the space object as the debris cloud is distributed by the multishock effect. [ABSTRACT FROM AUTHOR]

A large fraction of spacecraft external surfaces or appendages often consists of solar arrays, which can be subjected to space debris impacts as in the case of the Sentinel 1 A event of August 2016. Therefore, it is of interest to understand how solar arrays respond to hypervelocity impacts and to investigate the generated fragments population. In this context, the University of Padova performed an impact experiment on a solar array consisting in a composite sandwich panel, coated with a Kapton layer, and provided with solar cells: a nylon cylinder of 0.039 g collided with the solar panel at a velocity of 4.86 km/s with an impact angle of 45 deg, detaching a solar cell and damaging the panel structure. More than 4500 fragments larger than 0.2 mm were collected and classified after the impact. In this paper the impact experiment is described and the fragments analysis is presented in terms of size and shape distributions; a comparison with a test on a composite sandwich panel shows that the distributions are strongly affected by material and manufacturing choices, in particular regarding the fragments generated by delamination. • An impact experiment was performed on a solar array sample. • More than 4500 fragments larger than 0.2 mm were collected and classified. • Fragments size and shape distributions were obtained and compared with older experiments. • Distributions are strongly affected by material and manufacturing choices. [ABSTRACT FROM AUTHOR]

Experimental studies of the collision phenomena of submicrometer particles is a developing field. This review examines the range of phenomena that can be observed with new experimental approaches. The primary focus is on single-particle impact studies enabled by charge detection mass spectrometry (CDMS) implemented using the Aerosol Impact Spectrometer (AIS) at the University of California, San Diego. The AIS combines electrospray ionization, aerodynamic lens techniques, CDMS, and an electrostatic linear accelerator to study the dynamics of particle impact over a wide range of incident velocities. The AIS has been used for single-particle impact experiments on positively charged particles of diverse composition, including polystyrene latex spheres, tin particles, and ice grains, over a wide range of impact velocities. Detection schemes based on induced charge measurements and time-of-flight mass spectrometry have enabled measurements of the impact inelasticity through the determination of the coefficient of restitution, measurements of the angular distributions of scattered submicrometer particles, and the chemical composition and dissociation of solute molecules in hypervelocity ice grain impacts. [ABSTRACT FROM AUTHOR]

Ground-based tests are important for studying hypervelocity impact (HVI) damage to spacecraft pressure vessels in the orbital debris environment. We analyzed the damage to composite overwrapped pressure vessels (COPVs) in the HVI tests and classified the damage into non-catastrophic damage and catastrophic damage. We proposed a numerical simulation method to further study non-catastrophic damage and revealed the characteristics and mechanisms of non-catastrophic damage affected by impact conditions and internal pressures. The fragments of the catastrophically damaged COPVs were collected after the tests. The crack distribution and propagation process of the catastrophic ruptures of the COPVs were analyzed. Our findings contribute to understanding the damage characteristics and mechanisms of COPVs by HVIs. [ABSTRACT FROM AUTHOR]

Based on the dynamic shock response of the material and structure, the hypervelocity impact processes and mechanisms of long composite rods with axial density/impedance gradients penetration into four-layer targets were studied through experiments and numerical simulation methods. The propagation law of the shock waves, together with the structural responses of the projectiles and targets, the formation and evolution of the fragment groups formed during the processes and their distributions were described. The damage of each target plate was quantitatively analysed by comparing the results of the experiment and numerical simulation. The results showed that the axial density/impedance gradient projectiles could decrease the impact pressure to a certain extent, and the degree of damage to the target plate decreased layer by layer when the head density/impedance of the projectile was high. When the head density/impedance of the projectile was low, the degree of target damage first increased layer by layer until the projectile was completely eroded and then it decreased. The results can provide a reference for the design and application of long rods with axial composite structure for velocities ranging from 6 to 10 Ma or greater.

In shockwave experiments, the launch velocity of flyer is a crucial parameter for determining the physical quantities in sample under dynamic compression. Magnet velocity induction system is used to determine the velocity of flyer which can work under hypervelocity conditions. Based on finite element method, ANSYS Electromagnetics Suite module was used to establish a three-dimensional model and the launch process of flyer was simulated. The simulated results well reproduce the experimental signals. Comparing to the experimental results, the relative error of simulated amplitude of induced electromotive force (AIEMF) is 1.1%, lower than the system error of 2.0%. The relative error for flyer velocity determined by simulation is less than 0.4%, also lower than the measurement system error of 0.9%. The dependence of AIEMF with the thickness, radius, tilt angle, launch velocity of flyer and the diameter of pick-up coils is analyzed. The simulation result provides a reference for better signal acquisition in shockwave experiments. [ABSTRACT FROM AUTHOR]

The present work reports on the first evidence of a possible hypervelocity impact crater in the Sultanate of Oman. The impact origin of the structure is determined based on field observations, microscopic observations of shatter cones, planar fractures (PFs) and feather features (FFs) in quartz, calcite, and feldspar, and melt-bearing polymict breccias with various types of melts. The structure consists of an elliptical bowl-shaped ridge 750 m long and 550 m wide, oriented roughly north-northeast to south-southwest. The elliptical shape and relief asymmetry indicate an oblique collision. The precursor target lithologies include local late Proterozoic Masirah Bay siliciclastic formations, carbonate and acidic volcanic rocks of the late Precambrian Halfayn Formation, and basement rocks. The crater rim, up to 15–20 m above ground, is composed of quartzite, jasper, agate, monomict siliceous and hematite breccia, and metamorphosed shale (hornfels). An ejecta blanket composed of target rocks covers the floor, outer rim, and the area extending to the immediate northeast and east of the structure. Quaternary aeolian sand covers most of the crater surface, including the 1 to 2 m thick melt-rich polymict breccia found in the crater center. The planar fractures (PFs) and feather features (FFS) in quartz and feldspar suggest a low shock pressure between 5 and 14 GPa. Our observations are consistent with set criterions for impact crater identification, confirming the possible impact origin of the Mahout structure. [ABSTRACT FROM AUTHOR]

Hypervelocity impact (HVI) on carbon fiber reinforced plastics (CFRPs) is associated with extreme impulse response of material as well as complex characteristics of the composites. It is a challenging task to predict the physical process of CFRP-HVI problems accurately. We apply a GPU-accelerated smoothed particle hydrodynamics (SPH) method which incorporates the composite material model and the decoupled finite particle method to simulate the CFRP-HVI processes. The presented SPH model is validated by simulating the processes of aluminum spheres impacting metallic plates. The simulation results agree well with available experimental and numerical results, and the GPU parallelization technique significantly improves the simulation efficiency (350 times faster than an equivalent serial SPH model). With such computational accuracy and efficiency, the model is extended to simulate CFRP laminate impact problems, and a particle convergence analysis is performed. It is shown that the model can obtain convergent results when modeling each CFRP layer with three SPH particles in the thickness direction and correspondingly using about twenty million particles in total. The simulation can be completed within several hours, and the dominant mechanisms of the CFRP-HVI can be captured quantitatively. To further investigate the protective performance of CFRP structures, HVI on a well-known shielding structure Whipple bumper is investigated numerically. The dynamic response of the structure is well reproduced, and the results show that the CFRP pressure wall is more effective than the metallic one. These simulation results demonstrate that the presented SPH model can model the CFRP-HVI problems accurately and efficiently. [ABSTRACT FROM AUTHOR]

Diogenites are thought to have originated from asteroid 4 Vesta asteroid, and it has been previously shown that they mostly consist of orthopyroxene, chromite, and olivine minerals. In this study, the Aioun El Atrouss (AAT‐1) diogenite was analyzed by vibrational spectroscopic (FT‐IR and micro‐Raman), EDXRF, and XRD techniques. AAT‐001 is mainly composed of pyroxene and with lesser olivine. XRD investigation confirmed magnetite, kamacite, ilmenite, and albite. A troilite‐orthopyroxene intergrowth was revealed by XRF. The olivine composition was estimated to be approximately Fo66 by Raman olivine characteristic doublets. Pyroxenes in AAT‐01 were found to be En80Fs20. Finally, approximate peak shock pressure of more than 86 GPa for AAT‐1 was suggested based on previous hypervelocity impact experiments on olivine. [ABSTRACT FROM AUTHOR]

We consider a scenario in which Sgr A* is in a massive black hole binary (MBHB) with an as-of-yet undetected supermassive or intermediate-mass black hole companion. Dynamical encounters between this MBHB and single stars in its immediate vicinity would eject hypervelocity stars (HVSs) with velocities beyond the Galactic escape velocity of the Galaxy. In this work, we use existing HVS observations to constrain for the first time the existence of a companion to Sgr A*. We simulate the ejection of HVSs via the 'MBHB slingshot' scenario and show that the population of HVSs detectable today depends strongly on the companion mass and the separation of the MBHB. We demonstrate that the lack of uncontroversial HVS candidates in Gaia Data Release 3 places a firm upper limit on the mass of a possible Sgr A* companion. Within one milliparsec of Sgr A*, our results exclude a companion more massive than |$2000 \, \mathrm{M_\odot }$|⁠. If Sgr A* recently merged with a companion black hole, our findings indicate that unless this companion was less massive than |$500 \, \mathrm{M_\odot }$|⁠ , this merger must have occurred at least 10 Myr ago. These results complement and improve upon existing independent constraints on a companion to Sgr A* and show that large regions of its parameter space can now be ruled out. [ABSTRACT FROM AUTHOR]

The dynamic of hypervelocity projectile impacting inflatable multilayer flexible membrane structure is studied in this paper. The velocity increment of the inflatable multilayer flexible membrane structure under hypervelocity impact comes from two parts. One is the acceleration caused by the pulling of the membrane when the hypervelocity projectile is in direct contact with the membrane, and the other is the acceleration provided by the reverse impulse caused by the gas leakage in the inflatable structure. The hypervelocity projectile will be decelerated in the impact process, and finally fly with the accelerated multilayer flexible membrane structure at the same velocity, which means that the projectile is captured by the membrane structure. According to the above process, the influence of the mechanical property parameters of the flexible membrane on the structural parameters of the multi-layer flexible membrane can be calculated, which can be used to guide the engineering design. Finally, the hypervelocity impact process is verified by the numerical simulation. • Space soft capture method achieved through flexible inflatable membrane structure. • Hypervelocity impact dynamics of flexible inflatable membrane structure. • Verify the dynamic process of hypervelocity impact using numerical simulation. • The influence of membrane mechanical properties on the parameters of the structure. [ABSTRACT FROM AUTHOR]

We have been conducting hypervelocity impact tests and numerical simulations to develop a Japanese spacecraft design guideline for the protection of satellites from a certain degree of M/OD impacts. A working group is formed by members of JAXA, spacecraft manufacturers, experts, and researchers in the field of hypervelocity impacts to investigate the effects of M/OD impacts on satellite critical parts and bumpers by hypervelocity impact (HVI) tests and analysis. The knowledge acquired is now being reflected in the spacecraft design guidelines. We investigated the effect of hypervelocity impacts of micrometeoroids and small-scale space debris on space structures by comparing numerical simulation results obtained using the AUTODYN-2D hydrocode with the results of experiments using a two-stage light gas gun since 2005. We will consider the case of a satellite hydrazine fuel tank and the consequences of a hypervelocity impact from space debris. The final purpose of this study is to better understand the mechanisms of detonation of hydrazine vapor during a hypervelocity impact on a low-pressure reservoir. As part of this effort and an initial study, the response of a Ti–6Al–4V plate which is used tank material to 6 km/s high-velocity impacts is shown and discussed. It was found that the ballistic limit of the titanium tank material for both curved and flat plates was generally predictable using the existing ballistic limit equation. The effect of curvature on the impact scar size of flat (t = 1.2 mm) and curved plates was examined, and no significant difference was found. • We introduced our achievements and plans overview related protection for small debris and meteoroid related space in Japan. • The ballistic limit of the titanium tank material of spacecraft was predictable using the existing ballistic limit equation. • The effect of curvature on the size of the hiper-velocity impact scar was examined, but no significant difference was found. [ABSTRACT FROM AUTHOR]

Impact craters are formed by collisions of cosmic bodies moving with hypervelocity. The formation of these features is not restricted to the distant geological past; new structures are constantly being created and at least 13 confirmed impact craters and crater fields have formed during the Holocene alone. This short review paper: (1) introduces the basics of the impact cratering process to physical geographers and Quaternary geologists; (2) provides a short description of representative examples of such features (Morasko, Kaali, Kamil, Ilumetsa); and (3) discusses the similarities and differences among very small craters, and contrasts these with larger impact structures. This manuscript may be useful to researchers planning to test whether a small Quaternary depression in the ground may be of impact origin. [ABSTRACT FROM AUTHOR]