Deflecting asteroid Itokawa by subsurface explosion: Effect of explosion position on asteroid angular velocity change

Explosion deflection has recently become an important topic in hazardous asteroid deflection. Changes in asteroid velocity and angular velocity, as well as the degree of structural damage, should be fully considered in the explosion deflection scheme. This study investigates the effect of explosion position on the deflection of the asteroid 25143 Itokawa. First, we propose a mathematical model to quickly determine the changes in the angular velocity of Itokawa with explosions at different positions, and verified its reliability through numerical simulations. Mathematical model indicated a maximum 349-fold difference in Itokawa's angular velocity change under explosions at different positions, and revealed that the decisive factor is the force arm (maximum 850-fold difference), not the moment of inertia (maximum 4.01-fold difference). Then, to demonstrate the effect of porosity on shock wave propagation, we established a mesoscopic model based on the porosities of Itokawa's head and body. We used the single-material arbitrary Lagrangian-Eulerian (ALE) and finite element-smoothed particle hydrodynamics (FE-SPH) adaptive methods to simulate the deflection of the asteroid with a 300-kt TNT-equivalent explosion at different positions 10 m underground. The simulated changes in asteroid velocity and angular velocity were consistent with the predictions of the mathematical model. Finally, we investigated the effects of the asteroid geometry and material composition on the shock wave propagation and asteroid damage evolution (material response and structural response).