The European Space Agency’s Hera mission is the European contribution to the joint ESA-NASA Asteroid Impact Deflection Assessment (AIDA) collaboration for planetary defence. Launched on the 7th of October 2024 by a Falcon 9 from Cape Canaveral, Hera is enroute to the Didymos binary asteroid system, where it will investigate the aftermath of NASA’s DART impact on Dimorphos, providing crucial post-impact characterization to validate kinetic impactor models. Furthermore, Hera carries onboard two 6U-type cubesats, Milani and Juventas, which will be released during proximity operations and provide additional close-range measurements of the Didymos system.
The main spacecraft is operated by the Hera Mission Operations Centre (HMOC) at ESOC, which includes ESA’s Flight Dynamics team for deep-space missions, while the cubesats are operated by a separate Cubesats Mission Operations Centre (CMOC) in Redu.
To ensure the success of the Hera mission, which involves operating the mothercraft as well as two cubesats in the challenging environment of the Didymos-Dimorphos binary asteroid system, FD operations are key. Some of the most critical challenges faced by the FD team include a) designing trajectories in the Didymos system, maximizing the scientific return while ensuring spacecraft safety and respecting numerous spacecraft constraints; b) achieving simultaneous orbit determination of two bodies and three spacecraft with multiple observable types, including optical centroiding and landmarks, which require sophisticated image-processing techniques; c) initializing, tuning, and monitoring an extremely complex onboard autonomous navigation system; and d) coordinating and planning navigation, pointing, and payload operations, both within HMOC and externally with CMOC and instrument teams, to meet highly ambitious scientific objectives.
The goal of this paper is to provide an overview of the Hera mission from the FD perspective, covering briefly few relevant aspects of cruise operations and more in depth the extensive planning and testing underway at ESOC to ensure the highest level of readiness for proximity operations.
First, key highlights from commissioning and cruise operations are presented. Although not as unique as the upcoming asteroid phase, these have presented several opportunities for the FD team to better prepare for a successful mission at the Didymos system. These include the early commissioning of autonomous navigation functions, a Mars swingby with a challenging Deimos flyby for scientific and autonomous functions rehearsal purposes, and the design of a fast-arrival scenario with a compressed braking sequence. These will allow Hera to begin proximity operations with good confidence on the spacecraft capabilities and already at the end of October 2026 - one month earlier than originally planned - gaining valuable time in proximity of the binary asteroid system and improving data return due to lower Earth distances.
A high-level description is then provided of proximity operations, covering Hera trajectory design, the planned operational timelines and FD ground cycles, and the full set of FD activities, from spacecraft monitoring and telemetry processing to generating commands for attitude control, orbit control, and navigation cameras. This includes the complex image processing and OD setup required to estimate spacecraft and asteroid dynamics from radiometric, optical, and inter-satellite measurements, as well as a novel timeline-planning approach derived from Rosetta, where operations are streamlined by exploiting synergies between navigation and science objectives.
Finally, particular focus is given to the split of responsibilities between ground-based and onboard navigation functions, showing how the two must operate cooperatively. Ground navigation will initially allow to operate from 20-30 km distances, to characterize and later refine the knowledge of the Didymos system dynamics as the spacecraft flies closer, to perform orbit determination for the cubesats and to initialize different onboard autonomy modes. These will be progressively phased in, starting with centroid-based pointing, followed by optical–laser altimeter data fusion, and ultimately fully autonomous trajectory-control manoeuvres. The successful engagement, ground monitoring and tuning of these functionalities is key to achieve the ambitious goal of flying as low as 1 km from the DART impact crater on Dimorphos.
Together, the activities summarized in this paper describe the FD effort supporting the mission from launch throughout cruise and asteroid operations, aiming to ensure that Hera can achieve all its scientific and planetary-defence goals.