SVD-accelerated T-matrix Method for Simulation of Scattering by Electrically Large Sphere Clusters and ISAR Imaging of Asteroid-like Bodies

China’s Tianwen-2 mission will carry a radar to detect the internal structure of the asteroid 469219 Kamoʻoalewa. The model of scattering from the asteroid is important for the mission. Grid-based methods like the finite-element method or the method of moments are impractical for asteroid-scale targets, due to prohibitive meshing and memory demands. Modeling asteroids as sphere clusters enables faster scattering simulations with significantly lower resource usage. The multiple-sphere T-matrix method is a full-wave simulation technique for computing electromagnetic scattering by clusters of spheres. For electrically large sphere clusters, iterative solvers require a new linear solve at each incident angle, which is time-consuming. This paper proposes an optimization based on singular value decomposition. It extracts information from solutions at the preceding incident angles to provide a superior initial guess for the solution at the current angle. This reduces the number of iterations required for convergence, yields a fivefold speedup in an 82-sphere test case, and enables completion of more complex scattering problems within the same wall-clock time. The proposed method is validated against the conventional approach. Inverse synthetic aperture radar imaging simulations are performed for four cluster models of asteroid-like bodies, including monolithic structure, nested monolithic structure, rubble-pile structure, and rubble-pile structure with cores. Their characteristic radar signatures are analyzed, especially the effects of structural configuration on trail length and morphology. The simulations use the parameters of the Tianwen-2 low-frequency radar and will aid future structural characterization of asteroid-like bodies in the solar system.