Scattering Tendency of Surface Objects during Thrusting in Vicinity of Celestial Body

Abstract

When a spacecraft fires its thrusters near the surface of a celestial body, objects on the surface of the body are scattered in the vertical direction and adhere to the cameras and ranging instruments mounted on the spacecraft, degrading their performance. In order to establish a future spacecraft design theory that is less sensitive to the scattering of surface objects, we first investigate the scattering factors and scattering tendencies of surface objects. We predict that celestial surface objects are scattered according to the wall angle of the crater created by the thruster plume. The relationship between the crater shape and the object dispersal angle is not fully understood. Mechanisms of crater formation include viscous erosion, which creates craters with a small wall angle, and bearing capacity failure, which creates craters with a large wall angle. Here, we experimentally clarify the transition point between the two crater formation mechanisms when the thruster plume penetrates soil with various shear strength values. We find that the objects disperse along the crater wall for both mechanisms. Based on the results, we examine measures for preventing the spacecraft from being hit by scattered surface objects.