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DROID: A Mission Concept to Accompany and Characterize Apophis through its 2029 Earth Closest Approach

Presentation #405.07 in the session Asteroids: Planetary Defense (Poster + Lightning Talk)

Published onOct 23, 2023
DROID: A Mission Concept to Accompany and Characterize Apophis through its 2029 Earth Closest Approach

The close approach of asteroid (99942) Apophis on April 13, 2029 presents a unique opportunity to achieve breakthrough science and support planetary defense goals. A mission concept to exploit this opportunity has been developed in a collaboration between NASA/JPL and CNES. The Distributed Radar Observations of Interior Distributions (DROID) mission would rendezvous with Apophis prior to Earth closest approach (ECA) and escort it through the encounter. DROID’s measurements can determine: the body’s shape and density; the size, distribution, and arrangement of blocks and voids in the interior; material movement on the surface or reshaping during the Earth flyby; as well as spin state changes. Its goals are to understand the interior structure of a (presumed) rubble pile asteroid and implications for its formation, evolution and response to deflection, and to understand how close planetary encounters affect asteroids. DROID provides unique high fidelity in situ data that complements and enhances Earth-based optical and radar observations of Apophis, as well as data collected by OSIRIS-APEX. DROID uses low-frequency (60 MHz) multi-static radar observations to probe Apophis’s interior, revealing the distribution of monolithic objects and voids within the body at 10’s of meter scale. The architecture employs a high delta-V ESPA Grande-class Mothership and two 12U CubeSats. The Mothership carries the CubeSats to Apophis, achieves the rendezvous cruise trajectory, performs high resolution imaging, and acts as a Direct-to-Earth (DTE) node for the constellation. After deployment, the CubeSats insert themselves into coordinated low orbits to perform monostatic and bistatic radar observations. A narrow-angle multi-band camera on-board the Mothership performs imaging for shape, morphology and geology. Wide-angle cameras on the two CubeSats support optical navigation. Internal structure is mapped using low frequency radar on the CubeSats. The radar is a version of JuRa flown on Hera/Juventas, modified to operate in a bistatic mode. Radar data products include 3D volumetric backscatter via monostatic/bistatic tomographic SAR, and average dielectric constant along interior bistatic ray paths with assessment of internal heterogeneity. Inter-Spacecraft Link S-band transponders on all spacecraft perform data transfer within the constellation, and synchronize the CubeSat clocks for accurate bistatic radar measurement.

>Acknowledgments: This work is being carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA (80NM0018 D0004), and at CNES.

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