Study on Hypersonic Aero- and Aerothermo-Dynamic Characteristics of Natural Atmospheric Entry Object

抄録

In this paper, the aerodynamic characteristics of natural, atmospheric entry objects at hypersonic speeds are numerically studied. As a typical example of such objects, asteroid 101955 Bennu is selected. Orbit simulation is conducted by solving the three-body problem to obtain the initial velocity and angle of atmospheric entry. Based on the constructed shape model, the surface pressure distribution is calculated by the Newtonian method, as well as the force and moment coefficients by pressure integration over the surface. To validate the results of Newtonian analysis, wind tunnel experiment using real asteroid model is conducted. Good agreement is obtained between numerical and experimental results. Then, the atmospheric entry trajectory is predicted. Assuming the initial velocity as 12.36 km/s with an angle of 28.34° to the horizon, the landing time from 120 km is estimated to be 9.86 s. During the landing process of an object with a large ballistic coefficient like Bennu (BC = 6.9 × 10⁵ kg/m²) , the aerodynamic drag force is proved to be small. For such large asteroids, the atmosphere of the Earth is not dense enough to cause significant mass loss and velocity decrease. But for smaller and much more common meteoroids with a small ballistic coefficient, the existence of atmosphere will significantly alter their trajectories and final masses. For such small meteoroids, the landing time required with a large entry velocity v₀ may be longer than that with a small v₀. Given an entry velocity beyond a certain value, the meteoroid will even burn up before it reaches the ground.