  We have performed an initial stage conceptual design study for the Deep
Interior Scanning CubeSat (DISCUS), a tandem 6U CubeSat carrying a bistatic
radar as 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 sup- port 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.
