THE DOUBLE ASTEROID REDIRECTION TEST (DART): EXPECTED CHANGES TO THE HELIOCENTRIC ORBIT OF (65803) DIDYMOS

Launched on November 23, 2021, NASA's Double Asteroid Redirection Test (DART) is set to impact the moonlet of the (65803) Didymos binary asteroid system in Fall of 2022. The aim of NASA's first dedicated planetary defense technology demonstration, DART, is to uncover how much momentum is imparted onto an asteroid during a kinetic impact at hyper velocity (6km/s) by altering the mutual orbit of the binary system. Predictions for the momentum transfer during a kinetic impact range substantially, due to the fact that ejecta are coming off the target in addition to the momentum imparted by the DART spacecraft. Ejecta that are escaping the gravitational pull of the asteroid cause a momentum enhancement characterized by the momentum enhancement factor, beta. Momentum carried away by the ejecta not only affects the mutual orbit of the Didymos pair, but also the heliocentric orbit of the entire Didymos system. Since the Didymos system has close approaches with the Earth over the next century, we investigate how possible changes in the heliocentric orbit of the Didymos system affect close approach distances between the binary asteroid and the Earth. Our predictions are based on the exact launch date and likely arrival conditions for the DART spacecraft and show that future encounters with the Didymos system do not pose a significant hazard. We also show that instantaneous momentum transfer models that neglect the "low thrust" caused by slower ejecta can influence the accuracy of post deflection impact risk assessments.