Abstract:

Ablation is one of the most important phenomenon when an asteroid enters the earth atmosphere at hypervelocity, which largely determines the mass loss, flight trajectory, and even radiation characteristics of the asteroid. To research the typical ablation process of asteroids when entering the earth atmosphere, experiments were conducted in an arc heater to simulate the typical conditions (velocity: 6 km/s, height: 17 km, diameter: 1 m) of Chelyabinsk asteroid event. The blunt-shaped test samples with the head radius of 20mm were made by carbon steel and basalt. In this work, the ablation process of test samples were clearly recorded, in which the melt flow of two different materials and the spallation of fragments as well as vaporization of basalt were observed. The evolutions of emission spectroscopy, recession profile and surface temperature profile during the whole process were acquired. The results indicate that the ablation phenomenon and the mechanism of mass loss of two materials are obviously different: Under the impact of the high-temperature flow, the carbon steel was sputtering into mass of tiny droplets which were washed away by the flow rapidly, while the mass loss of basalt were the shear flow of molten matter with small amount of massive spalling and evaporation spraying. All samples were exposed for four seconds in the plasma stream, mass loss and recession of the basalt and carbon steel were [37.9 g, 7.3 mm] and [72.7 g, 13.1 mm] respectively. The estimated effective enthalpy of ablation was 2.6 MJ/kg, the component measured by emission spectroscopy conforms to the electron microscopy (EDS) scanning.

Key words: asteroid, entry, ablation, arc-heater, experiment