The asteroid surface clutter simulation and separation based on the Asteroid Core Scan Radar of the Tianwen-2 mission

In 2026, China's Tianwen-2 mission is scheduled to arrive at the near-Earth asteroid 469219 Kamoʻoalewa (also known as 2016 HO3) to conduct close-range detection and sample return operations. The Tianwen-2 spacecraft carries the Asteroid Core Scan Radar (ACSR), a dual-frequency radar capable of both penetration and imaging. During the hovering phase, the ACSR will utilize Inverse Synthetic Aperture Radar observations to characterize the dielectric properties and internal structure of the asteroid.

In contrast to other planetary orbiting radars, such as the MARSIS on Mars, the operational environment of the ACSR differs. Firstly, Kamoʻoalewa features a small radius (~40-100 m) and a short rotation period (~0.467 h) compared to Mars. Thus, unlike an orbital observation of a large-scale target such as Mars, the ACSR continuously illuminates a rotating asteroid, resulting in more complex, time-varying scattering conditions. Secondly, due to the ACSR's close-range observation altitude (~600 m), the spherical nature of the antenna's radiated field cannot be ignored. Finally, given the small size of the target, the strong surface clutter may overlap the weaker subsurface echoes from the asteroid’s subsurface. Therefore, an effective and precise surface clutter suppression is essential for revealing the internal structure of Kamo'oalewa.

In this study, we will present the simulation, separation, and analysis based on the working circumstances of the ACSR. To address the complex surface conditions, the proposed surface clutter simulation is based on a physical optics method and considers the curvature of the spherical wavefront. Besides, a joint cross-correlation and moment-matching procedure is deployed to calibrate the potential orbital fluctuations. Our result shows that this approach works well in separating internal signals from radar observations. It will provide essential support for the radar data processing and scientific interpretation of the upcoming Tianwen-2 mission.