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Employing the finite element and computational fluid dynamics methods, we have determined the conditions for the fragmentation of space bodies or preservation of their integrity when they penetrate into the Earth's atmosphere. The origin of forces contributing to the fragmentation of space iron bodies during the passage through the dense layers of the planetary atmosphere has been studied. It was shown that the irregular shape of the surface can produce transverse aerodynamic forces capable of causing deformation stress in the body exceeding the tensile strength threshold of iron.

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We have studied the conditions of through passage of asteroids with diameters 200, 100, and 50 m, consisting of three types of materials-iron, stone, and water ice, across the Earth's atmosphere with a minimum trajectory altitude in the range 10-15 km. The conditions of this passage with a subsequent exit into outer space with the preservation of a substantial fraction of the initial mass have been found. The results obtained support our idea explaining one of the long-standing problems of astronomy-the Tunguska phenomenon, which has not received reasonable and comprehensive interpretations to date. We argue that the Tunguska event was caused by an iron asteroid body, which passed through the Earth's atmosphere and continued to the near-solar orbit.
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Asteroids populations are highly diverse, ranging from coherent monoliths to loosely bound rubble piles, with a broad range of material and compositional properties. These different structures and properties could significantly affect how an asteroid breaks up and deposits energy in the atmosphere, and how much ground damage may occur from resulting blast waves. We have previously developed a fragment-cloud model (FCM) for assessing the atmospheric breakup and energy deposition of asteroids striking Earth. The approach represents ranges of breakup characteristics by combining progressive fragmentation with releases of variable fractions of debris and larger discrete fragments. In this work, we have extended the FCM to also represent asteroids with varied initial structures, such as rubble piles or fractured bodies. We have used the extended FCM to model the Chelyabinsk, Benešov, Košice, and Tagish Lake meteors, and have obtained excellent matches to energy deposition profiles derived from their light curves. These matches provide validation for the FCM approach, help guide further model refinements, and enable inferences about pre-entry structure and breakup behavior. Results highlight differences in the amount of small debris vs. discrete fragments in matching the various flare characteristics of each meteor. The Chelyabinsk flares were best represented using relatively high debris fractions, while Košice and Benešov cases were more notably driven by their discrete fragmentation characteristics, perhaps indicating more cohesive initial structures. Tagish Lake exhibited a combination of these characteristics, with lower-debris fragmentation at high altitudes followed by sudden disintegration into small debris in the lower flares. Results from all cases also suggest that lower ablation coefficients and debris spread rates may be more appropriate for the way in which debris clouds are represented in FCM, offering an avenue for future model refinement.
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Conclusion As follows from the above, data and theoretical calculations of the entry of large meteoroids into the earth’s atmosphere available at present are scanty and incomplete as yet; however they provide an idea of the main processes occurring and make it possible to assess the basic parameters. Further accumulation of observational data and their analysis as well as the development of theoretical models and calculations by them, primarily to compare with observational data and to analyze new effects not investigated in detail earlier (for example, electro- and magnetohydrodynamic disturbances), are required.
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An overview of the basics of radio astronomy is presented as well as a short history of the development of radio interferometry. The underlying relationships of interferometry are discussed with consideration given to the coordinate systems and parameters that are required to describe synthesis mapping and the configurations of antennas for multielement synthesis arrays. Other topics include the response of the receiving system, digital signal processing, VLBI, calibration and Fourier transformation of visibility data, interferometer techniques for astrometry and geodesy, propagation effects, and radio interference.
Near-Earth asteroid (NEA) 1566 Icarus ($a=1.08$ au, $e=0.83$, $i=22.8^{\circ}$) made a close approach to Earth in June 2015 at 22 lunar distances (LD). Its detection during the 1968 approach (16 LD) was the first in the history of asteroid radar astronomy. A subsequent approach in 1996 (40 LD) did not yield radar images. We describe analyses of our 2015 radar observations of Icarus obtained at the Arecibo Observatory and the DSS-14 antenna at Goldstone. These data show that the asteroid has an equivalent diameter of 1.44 km with 18\% uncertainties, resolving long-standing questions about the asteroid size. We also solve for Icarus' spin axis orientation ($\lambda=270^{\circ}\pm10^{\circ}, \beta=-81^{\circ}\pm10^{\circ}$), which is not consistent with the estimates based on the 1968 lightcurve observations. Icarus has a strongly specular scattering behavior, among the highest ever measured in asteroid radar observations, and a radar albedo of $\sim$2\%, among the lowest ever measured in asteroid radar observations. The low cross-section suggests a high-porosity surface, presumably related to Icarus' cratering, spin, and thermal histories. Finally, we present the first use of our orbit determination software for the generation of observational ephemerides, and we demonstrate its ability to determine subtle perturbations on NEA orbits by measuring Icarus' orbit-averaged drift in semi-major axis ($(-4.62\pm0.48) \times 10^{-4}$ au/My, or $\sim$60 m per revolution). Our Yarkovsky rate measurement resolves a discrepancy between two published rates that did not include the 2015 radar astrometry.
Potentially hazardous asteroid (185851) 2000 DP107 was the first binary near-Earth asteroid to be imaged. Radar observations in 2000 provided images at 75 m resolution that revealed the shape, orbit, and spin-up formation mechanism of the binary. The asteroid made a more favorable flyby of the Earth in 2008, yielding images at 30 m resolution. We used these data to obtain shape models for the two components and to improve the estimates of the mutual orbit, component masses, and spin periods. The primary has a sidereal spin period of 2.7745 +/- 0.0007 h and is roughly spheroidal with an equivalent diameter of 863 m +/- 5%. It has a mass of 4.656 +/- 0.56 x 10^11 kg and a density of 1381 +/- 268 kg/m^3. It exhibits an equatorial ridge similar to the (66391) 1999 KW4 primary, however the equatorial ridge in this case is not as regular and has a ~300 m diameter concavity on one side. The secondary has a sidereal spin period of 1.77 +/- 0.02 days commensurate with the orbital period. The secondary is slightly elongated and has overall dimensions of 377 x 314 x 268 m (6% uncertainties). Its mass is 0.178 +/- 0.021 x 10^11 kg and its density is 1047 +/- 230 kg/m^3. The mutual orbit has a semi-major axis of 2.659 +/- 0.08 km, an eccentricity of 0.019 +/- 0.01, and a period of 1.7556 +/- 0.0015 days. The normalized total angular momentum of this system exceeds the amount required for the expected spin-up formation mechanism. An increase of angular momentum from non-gravitational forces after binary formation is a possible explanation.
Contents: Elements of gas dynamics and classical theory of shock waves; thermal radiation and radiant heat exchange in a medium; thermodynamic properties of gases at high temperatures; shock tubes; absorption and emission of radiation in gases at high temperatures; speed of relaxation processes in gases; structure of front of shock waves in gases; physico-chemical kinetics in hydrodynamic processes; light phenomena in shock waves and during strong explosion in air; thermal waves; shock waves in solids; certain self-similar processes in gas dynamics.
The work examines phenomena associated with the entry of meteoroids into the earth's atmosphere. Attention is given to the simple physical theory of meteoroids, including processes of meteoroid drag and ablation in the atmosphere, and the associated shock-wave formation. The study of meteoroid luminescence and spectra, the determination of meteoroid mass and density from photographs, the fragmentation of meteoroids, and the problem of meteor trails are also considered.
The motion of fragments following disintegration of a meteoroid during its flight through the Earth's atmosphere is investiated. Shock wave configurations, aerodynamical forces and moments acting on each fragment and the trajectories of the pieces are determined for hypothetical initial configurations. The results of numerical simulations show that a meteoroid's breakup may lead to both increase and decrease of the total cross section, drag forces and energy release in the atmosphere. As a consequence the emitted radiation varies.
A review is presented of the mechanical properties of meteorites and meteorite constituents. Scientific literature data on the strength of stony and iron meteorites are extremely limited. The average mechanically-measured stony meteorite compressive strength is 200 MPa, while the average iron meteorite compressive strength is 430 MPa. However, the best current estimate of the strength of stony bodies in space may be in the range of only 1–5 MPa, based on observations of meteorite fragmentation due to dynamic atmospheric loading upon Earth entry. Mechanical property and behavior information on both iron-nickel alloy and mineral meteorite constituents is also surprisingly limited in the metallurgical, rock mechanics, and ceramics literature.
The stopping powers of 11 solid media have been measured for 20–80 MeV/u Ar and 80 MeV/u Ca ions from the French GANIL accelerator. The energy measurements were made using the LISE magnetic spectrometer. The accuracy in stopping power determinations is of ± 1–2%. Several charge state distributions for Ar ions exiting relatively thick targets of Be, Al, Au have also been determined. The stopping power data have been compared with semi-empirical values from the literature, and with a scaling relative to He ion stopping powers, assuming fully stripped ions inside the degraders. The best agreement is obtained with the values from Ziegler (Pergamon 1980) over the whole energy range; the tabulation of Hubert et al. (Ann. Phys. Fr. 5 supp. (1980)) leads to a fair agreement with the data for degraders heavier than C. but overestimates the stopping powers of Be and C by 10–15%; the simple scaling method gives results in agreement with all data above .
Disintegration of large meteoroids, 1 m to 1 km in size, when affected by aerodynamic forces in flight is considered in this paper. Arguments are adduced that ablation is of secondary importance in comparison with mechanical processes of deformation and fragmentation. 2D hydrodynamic simulations using the free-Lagrangian method and the Eulerian method with a volume-of-fluid front tracking procedure have been carried out. The cosmic body was treated as a fluid, with the equation of state of water, moving through gas of appropriate density. We find that disintegration is more complex than simple models based on the estimate of lateral expansion due to differential ram pressure across a meteoroid make it. Rayleigh-Taylor instabilities strongly deform the body and it breaks up in the center. The outer radius of an originally spherical or cylindrical body agrees with the analytic models of spreading. However, a body of accidentally aerodynamic shape does not have its cross section significantly enlarged.A sandbag model has been developed in which a heavily dispersed meteoroid is represented as a conglomeration of noncolliding particles moving through the atmosphere. The particles transfer energy and impulse to the atmosphere and are enclosed by a single bow shock. Calculations show that a spherical swarm of particles takes a conical form but lateral expansion agrees with the above-mentioned simple theoretical models.The approximate analytical approach of a spreading fragmented impactor has got additional support: integration of the drag, ablation, and radiation equations produces results which are in a good agreement with light flashes registered by DoD satellites.
The mechanisms involved in the formation of impact craters are examined theoretically, reviewing the results of recent investigations. Topics addressed include crater morphology, stress waves in solids, the contact and compression stage, the excavation stage, and ejecta deposits. Consideration is given to the scaling of crater dimensions, the crater modification stage, multiring basins, cratered landscapes, atmospheric interactions, and the implications of impact cratering for planetary evolution. Extensive diagrams, graphs, tables, and images of typical craters are provided.
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