Centroiding method for small celestial bodies with unknown shape and small size

Focused on small celestial body deflection missions using a kinetic impactor spacecraft, we propose a method for estimating the center of small objects with unknown shape and small size, which relaxes the requirement for prior information of the object shape model and lowers the risk of missing the target. The impact center is inferred using the visible part of the object in a single image. In the first step, the illuminated part of the object’s true contour is segmented from the whole contour extracted from the image based on the prior information of the illumination direction. In the second step, the concave–convex characteristic of the illuminated contour is identified. In the third step, one of two modes, moment estimation or skeleton center estimation, is chosen based on the concave–convex characteristic to calculate the impact center. The proposed algorithm was verified by a simulation study under various conditions. Due to the problems of the unknown model shapes of small objects and complex illumination conditions in kinetic impact missions, the proposed centroiding algorithm will play an important role.