The binary near-Earth asteroid (65803) Didymos is the target for the Asteroid Impact and Deflection Assessment (AIDA) concept with two primary spacecraft: NASA’s DART (Double Asteroid Redirection Test) impactor and ESA’s Hera orbiter (Cheng et al. 2018; Michel et al. 2018). DART is NASA’s first planetary defense mission and will be the first demonstration of asteroid deflection by a kinetic impactor. The DART spacecraft will impact Dimorphos, the secondary in the Didymos system, and modify its orbit through momentum transfer. DART will launch in late 2021 and is scheduled to impact in September/October 2022. The DART spacecraft will carry ASI’s LICIACube (Light Italian Cubesat for Imaging of Asteroids, Dotto et al. 2021) to observe the DART impact event and the resulting impact ejecta.
A key scientific goal of the DART and Hera missions is to measure and characterize the deflection caused by the DART impact. The impact will change the satellite orbit period, which will be measured by ground-based facilities in the post-impact period. Hera, scheduled for launch in 2024 and rendezvous in 2026, will provide in-situ observations of the physical properties of the Didymos system and its post-impact dynamical state. We need to understand the baseline, unperturbed dynamics of the system to understand the effects of impact. The DART/Hera Observations Working Group was tasked with characterizing the Didymos-Dimorphos system properties with sufficient accuracy to measure the change in the binary orbital period to within 7.3 seconds. This measurement is a small, but observable fraction of the current orbital period of the satellite (Porb=11.92 hours). The observed period change is a critical input to the calculation of the momentum transfer enhancement parameter (“Beta”). We obtained lightcurve observations during the most recent apparition (December 2020 to March 2021) to further characterize the system. We combined these observations with past data (2003-2019) to establish the state of the system before impact to a high level of precision. We will discuss our state of knowledge from previous observations (through 2019), results from our 2020-2021 observations, and our preliminary plans for pre and post-impact observations in 2022.