HYPERVELOCITY ISSUES OF EARTH IMPACT BY ASTEROIDS

Asteroid impact on the Earth is one of the potential threats to human beings. There are a series of complex physical, chemical and mechanical phenomena in the process of asteroids entry to the earth's atmosphere and impacting the earth's surface, such as ablation, disintegration, airburst, fireballs, impact craters, ejecta debris, earthquakes, and tsunamis. In this paper, scientific issues on hypervelocity aerodynamics and hypervelocity impact dynamics behind these phenomena are summarized and discussed. The hypervelocity aerodynamic issues include: aerodynamic forces and trajectory during ultra-high velocity (V =12 ~ 20 km/s) entry, aerodynamic heating and ablation mechanism of asteroids, heat transfer and thermal response of asteroid structure, high-temperature gas effects, physical characteristics of asteroid entry process. The hypervelocity impact dynamics include: cratering and ejecta debris of land impact, ocean impact and tsunamis, earthquake effects caused by impact. Because the entry and impact process of asteroid and man-made hypervelocity flight vehicles are quite different in velocity, material and structure, the existing research methods are insufficient in both ground test and numerical calculation. Finally, based on trajectory equations, mass loss equation, criterion of fragmentation and model of fragmentation, a model for analysis and evaluation of asteroid entry and impact effect is established, and the Chelyabinsk and Tunguska events are analyzed and reconstructed, together with the overpressure and thermal radiation damage caused by fireballs.