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Predictions for the Dynamical State of the Didymos Binary System Before and After the DART Impact

Presentation #200.05 in the session Binary Asteroids and Radiation Forces.

Published onApr 25, 2022
Predictions for the Dynamical State of the Didymos Binary System Before and After the DART Impact

NASA’s Double Asteroid Redirection Test (DART) is the first full-scale demonstration of a kinetic impactor for planetary defense. The spacecraft is expected to impact Dimorphos, the secondary component of the Didymos binary asteroid system, in late September of 2022. The impact will cause a reduction in the binary semimajor axis and orbital period that will be measured with ground-based observations. By measuring the change in the binary mutual orbit period, the DART mission will provide an estimate of the momentum transfer enhancement factor, β, a critical parameter that describes the additional momentum transfer generated from escaping ejecta. Launching in 2024, ESA’s Hera spacecraft will rendezvous with Didymos to further characterize the system and the effects of the DART impact. Together, these spacecraft comprise the Asteroid Impact and Deflection Assessment (AIDA) cooperation between NASA and ESA. The Didymos system is a prototypical example of the Full Two-Body Problem (F2BP), where the translational and rotational dynamics are non-Keplerian and highly coupled owing to the irregular body shapes and their close separation.

Here we present a summary of current predictions for the dynamical state of the Didymos system before and after the DART impact. First, we focus our efforts on predicting the pre-impact spin state of the secondary, whose shape and spin are unknown. Then, we investigate the secondary’s post-impact attitude evolution and show that it is highly dependent on β and its own body shape which is assumed to be a triaxial ellipsoid. We show that Dimorphos’s spin state may evolve chaotically, depending on its shape, due to various resonances between the mean motion and Dimorphos’s libration and spin precession frequencies. Finally, we discuss the future prospects for measuring Dimorphos’s post-impact spin state as well as the implications of Dimorphos’s spin state for Hera’s arrival in 2026.

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