This study aims at advancing mathematical and computational techniques for reconstructing the interior structure of a small Solar System body via Computed Radar Tomography (CRT). We introduce a far-field model for full-wave CRT and validate it numerically for an orbiting distance of 5 km using a synthetic 3D target asteroid and sparse limited-angle data. As a potential future application of the proposed method, we consider the Deep Interior Scanning CUbeSat (DISCUS) concept in which the goal is to localize macroporosities inside a rubble pile near-Earth asteroid with two small spacecraft carrying a bistatic radar.

We have performed an initial stage conceptual design study for the Deep Interior Scanning CubeSat (DIS-CUS), a tandem 6U CubeSat carrying a bistatic radar as the main payload. DISCUS will be operated either as an independent mission or accompanying a larger one. It is designed to determine the internal macroporosity of a 260-600 m diameter Near Earth Asteroid (NEA) from a few kilometers distance. The main goal will be to achieve a global penetration with a low-frequency signal as well as to analyze the scattering strength for various different penetration depths and measurement positions. Moreover, the measurements will be inverted through a computed radar tomography (CRT) approach. The scientific data provided by DISCUS would bring more knowledge of the internal configuration of rubble pile asteroids and their collisional evolution in the Solar System. It would also advance the design of future asteroid deflection concepts. We aim at a single-unit (1U) radar design equipped with a half-wavelength dipole antenna. The radar will utilize a stepped-frequency modulation technique the baseline of which was developed for ESA's technology projects GINGER and PIRA. The radar measurements will be used for CRT and shape reconstruction. The CubeSat will also be equipped with an optical camera system and laser altimeter to support navigation and shape reconstruction. We provide the details of the measurement methods to be applied along with the requirements derived of the known characteristics of rubble pile asteroids. Additionally, an initial design study of the platform and targets accessible within 20 lunar distances is presented.

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