The asteroid explorer Hayabusa2 touched down on the asteroid Ryugu twice. During the touchdown of Hayabusa2, some objects on the surface of the asteroid were scattered toward the vehicle. The following image shows the area around the touchdown point taken by Hayabusa2 immediately after touchdown.
The possible causes of this phenomenon are that Hayabusa2 shot the projectile into the surface of the asteroid when it was sampling, and that Hayabusa2 fired the thruster when it left the surface. Although the scattering of celestial objects due to projectile injection is a unique problem for Hayabusa2, the scattering of celestial objects due to thruster injection is likely to increase in all future missions which includes landings. If the scattering celestial surface objects hit the spacecraft, the spacecraft may be destroyed. In addition, if it adheres to the rangefinder and the observation equipment, it may interfere with the mission execution.
Therefore, it is very important to understand the dispersal mechanism and behavior of objects on the surface of a celestial body by thrusters. This is because the impact of surface objects lifted by thrusters on a spacecraft will greatly degrade the engineering and physical results required of the spacecraft, and thus the success or failure of the exploration mission itself will be greatly affected.
There are three possible reasons for the thrusters to be rolled up on the surface of an object. The first is that the thrusters are digging craters in the ground, and the second is the effect of the original terrain. The third is that the thruster plumes from multiple thrusters collide with each other, creating an upward force.
We conduct 1G and micro gravity experiments of gas injection into simulated soil under vacuum in order to investigate the interaction between thruster plume and asteroidal regolith. We also aim to reproduce the sand lift during touchdown for various astronomical and spacecraft combinations by performing DEM-CFD simulations for similar conditions.
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