模拟Chelyabinsk小行星进入的烧蚀实验

烧蚀是小行星极高速进入地球大气层后最重要的现象之一,在很大程度上决定了小行星的质量/尺寸变化、飞行轨迹、甚至光辐射特性. 为观测小行星材料在超高速高温流场中的烧蚀现象,在电弧加热器上开展了模拟Chelyabinsk小行星事件典型弹道状态(速度约5.6 km/s,高度17 km,流星体直径1 m)的烧蚀实验. 试件为钝头外形,头部半径20 mm,半锥角18$^\circ$. 作为对比,试件分别采用玄武岩和碳钢材料. 成功记录了清晰的烧蚀动态过程,观察到两种材料试件表面的熔融损失流动、以及玄武岩试件的蒸发喷射和崩裂剥落等现象,全程测得烧蚀气体发射光谱、试件实时外形变化、表面热图变化等数据. 分析结果显示了两种材料明显不同的烧蚀现象和质量损失机制:碳钢在高温气流冲击作用下溅射成大量微小液滴,跟随气流高速流失;玄武岩质量损失以熔融物剪切流动为主,并伴随少量块状剥落及蒸发喷射. 烧蚀时间为4 s,玄武岩和碳钢的质量损失及驻点后退量分别为37.9 g,72.7 g以及7.3 mm,13.1 mm,估算玄武岩材料的有效烧蚀焓约为2.6 MJ/kg,两种材料的烧蚀光谱测量组分与电镜能谱扫描结果吻合. 

ARCJET ABLATION EXPERIMENT TO SIMULATE THE CHELYABINSK ASTEROID ENTRY

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.