PASSIVE ASTEROID RADIO TOMOGRAPHY WITH THE JUPITER-IO CMI T. Marshall Eubanks, Asteroid Initiatives

Introduction: An important goal in the in situ exploration of asteroids by spacecraft is the determination of not just the surface characteristics of a target asteroid, but also its interior structure, such as density, porosity and compositional changes at depth. Information about the complex dielectric constant along a raypath, which is related to these quantities, can be determined by monitoring the transmission and reflection of High Frequency (HF) radio waves in the band 1 40 MegaHertz (MHz), as has been demonstrated by numerous terrestrial Ground Penetrating Radars (GPRs) and in space by the MARSIS (1.3 5 MHz) and SHARAD (15 25 MHz) radar systems currently in orbit around Mars. While these radars have a demonstrated ability to image 100s of meters beneath the Martian surface, they are optimized for Martian orbit conditions, which are largely not applicable to missions to small Near Earth Asteroids (NEA). MARSIS and SHARAD operate∼300 km from the Martian surface, andx are fairly large and powerintensive (SHARAD uses a 10 W transmitter and MARSIS requires 60 watts total DC power). For a solar sail powered mission to a 50-meter diameter NEA the spacecraft will not be able to stop with respect to the target, so that any reconnaissance will be done as a series of close flybys. A smaller “cubesat” type spacecraft with solar sail propulsion, such as the the Near Earth Asteroid (NEA) Solar Scout [1], will not be able to afford the power budget of a typical GPR, or the mass and complexity required for a two spacecraft bistatic radar system such as the CONSERT system operating between Rosetta and Philae. This paper will explore another possible solution for internal imaging of small bodies, Passive Asteroid Radio Tomography (PART) using a coherent natural radio source, the Jovian Io-DAM, which has also been proposed as the source for passive reflectometry of subsurface oceans on Europa and the other Galilean satellites[2].