The Hera Radio Science Experiment at Didymos

With a targeted launch in October 2024, the European Space Agency’s Hera mission is set to rendezvous with the Didymos binary asteroid system in early 2027 and aims to conduct a detailed post-impact survey of the system following NASA’s DART impact on the smaller asteroid Dimorphos. This work describes the Hera Radio Science Experiment (RSE), which aims to precisely estimate the values of some key physical parameters of Didymos and Dimorphos, including their mass, extended gravity field, rotational state, and absolute and relative orbits. The expected accuracies in the parameters of interest are evaluated through a multi-arc covariance analysis performed using Caltech-JPL’s MONTE code. The analysis will show the information content provided by various observation types collected during the mission, including Earth-based radiometric measurements, optical images, altimetry measurements, and satellite-to-satellite tracking of the Juventas and Milani CubeSats. Furthermore, the influence of the dynamical model implemented within the orbit determination filter will be addressed regarding achievable accuracies of the estimated parameters and operational considerations.