Design and validation of asteroid core scan radar (ACSR) of Tianwen-2

<p indent="0mm">China will carry out Tianwen-2 mission to conduct exploration, sampling, and return operations for the near-Earth asteroid 2016HO₃, followed by a detailed investigation of the main-belt comet 311P. The asteroid core scan radar (ACSR) aboard the probe aims to acquire radar echoes from the surface and subsurface of small celestial bodies, thereby facilitating the study of their internal structures. To achieve both deep penetration and high resolution, the ACSR incorporates two frequency channels: a low-frequency channel ranging from 130 to <sc>170 MHz</sc> and a high-frequency channel spanning from 300 to <sc>1500 MHz.</sc> The low-frequency channel can penetrate up to 50 m into an asteroid with a thickness resolution better than 5 m, while the high-frequency channel can penetrate over 8 m with a thickness resolution superior to 0.25 m. The low-frequency channel employs compact polarization to obtain more comprehensive target information. This study introduces the instrument requirements, system composition, working principles and modes, ground calibration and verification tests and results of the ACSR, serving as a reference for scientific data processing and application.