The Radio Science Experiment on Hera, Juventas and Milani

Hera, the European Space Agency’s pioneering planetary defense mission, was successfully launched on October 7, 2024, from Cape Canaveral aboard a SpaceX Falcon 9 rocket. This milestone marks a critical step in the Asteroid Impact and Deflection Assessment (AIDA) collaboration, which Hera undertakes in synergy with NASA’s DART mission. The mission's primary objective is to perform an in-depth post-impact analysis of the Didymos binary asteroid system, focusing on Dimorphos, the smaller moon that served as DART’s impact target.

Hera’s investigations aim to evaluate the effectiveness of the kinetic impactor technique as a method for asteroid deflection, while also providing critical insights into the physical and compositional characteristics of Dimorphos. These findings will not only refine our understanding of asteroid behavior under kinetic impact but also contribute to developing strategies for planetary defense against potential future asteroid threats.

Central to Hera’s scientific approach is its advanced radio science experiment. This includes an X-band radio link, which supports high-precision Earth-based two-way range and range-rate measurements, alongside Delta-Differential One-Way Ranging (Delta-DOR) observations. Additionally, the mission leverages inter-satellite ranging between Hera’s main spacecraft and its two CubeSats, Juventas and Milani, complemented by optical navigation imaging and altimetry data. Together, these techniques will significantly enhance the accuracy of Hera's data and allow for a more comprehensive reconstruction of the impact event and its aftermath.

This work provides a summary of the Hera radio science experiment investigation, the experimental framework and operational plans during its cruise phase and its close-proximity operations at the Didymos system. Furthermore, it discusses the expected scientific outcomes of Hera’s radio science experiment, emphasizing its pivotal role in advancing planetary defense capabilities and contributing to the broader goals of asteroid science.