The Hera mission is set to deliver new insights into the formation and evolution of asteroids by studying the geophysical characteristics of the Didymos-Dimorphos binary system. Hera will investigate the moonlet Dimorphos up close to observe the effects of the impact of the U.S. DART mission. The mission also aims to study possible planetary defence techniques.

Hera is the first mission to rendezvous with a binary asteroid and with the smallest asteroid ever encountered, the first to probe an asteroid using radar tomography, and the first experiment to characterize an asteroid crater in situ. It is also carrying the first cubesats to orbit an asteroid up close.

Key figures

• 1,150 kg: mass of Hera
• 5 instruments on Hera spacecraft
• 12 kg: mass of each cubesat
• 5 instruments on cubesats
• 3 contributing French research labs
• 730 m: mean diameter of Didymos
• 150 m: mean diameter of Dimorphos

Key milestones

• September 2027: Scheduled end of mission
• June 2027: Juventas to attempt landing on Dimorphos
• January 2027: Separation of Juventas and Milani cubesats and start of proximity operations, exploring for 3 to 6 months, from a few tens of kilometres to a few kilometres
• December 2026: Rendezvous and start of manoeuvres to insert Hera on a trajectory close to the asteroid (30 km)
• March 2025: Flyby of Mars and Deimos
• 7 October 2024: Launch window opens for Hera
• August 2024: Hera satellite and Juventas and Milani cubesats depart ESTEC for launch site in the U.S.A (Kennedy Space Center)
• 26 September 2022: NASA’s DART impactor mission crashes into asteroid Dimorphos
• 24 November 2021: Launch of NASA’s DART impactor mission
• 2020: Start of satellite construction by consortium led by OHB
• 2019: Hera mission gets go-ahead from ESA
• 2017: ESA starts development of Hera mission
• 2013: AIDA project initiated by NASA and ESA
• 2007: ESA formulates asteroid deflection mission concept

Project in brief

Would we able to protect our planet against the threat of a near-Earth asteroid impact?

In July 1994, fragments from comet Shoemaker-Levy 9 smashed into Jupiter, generating a spectacular fireball show and raising the spectre of a threat that Earth had forgotten. While the risk of an Earth-crossing asteroid hitting our planet remains statistically low—less than one in every 500,000 years for a near-Earth asteroid (NEA) more than 1,000 metres across—the potentially catastrophic effects should encourage us to envision a strategy to counter the threat.

Through the international AIDA (Asteroid Impact and Deflection Assessment) initiative, for which one of the two coordinators is from France, space agencies are seeking to develop a planetary defence technique for a scenario in which an NEA might impact Earth. The method chosen as the least costly and most mature is the kinetic impact technique that consists in sending a spacecraft on a collision course with an asteroid to deflect it. To test out this concept, NASA crashed its DART (for Double Asteroid Redirection Test) impactor into Dimorphos, the moonlet in the Didymos binary asteroid system 11 million kilometres from Earth, on 26 September 2022. Hit by the impactor travelling at a speed of six kilometres per second, Dimorphos’s orbital period around its primary asteroid was shortened by 33 minutes (or 2.67 mm/s). The test thus provided experimental proof of the ability to deflect an asteroid’s course. Exactly how effectively it was deflected, which depends on the asteroid’s as yet undetermined mass, remains to be seen.

ESA’s Hera mission now aims to observe the effects of this impact in situ and study the binary asteroid’s geophysical characteristics. In particular, the amount of momentum imparted to Dimorphos is the key element here, as this reflects how effective the deflection was. Only part of DART’s energy was imparted to Dimorphos to change its path; the rest sent up a dust plume rising several tens of thousands of kilometres above the asteroid’s surface. Morphological deformations such as the excavation of a crater, cone edges, ejecta or even the asteroid’s shape also have a bearing on how much energy was transferred by the impact. Precisely identifying how DART’s energy was transferred to the asteroid will enable us to ascertain factors likely to improve planetary defence technology.

Hera is the first ever mission dedicated to observing a planned collision and the second rendezvous with a binary asteroid, which will occur just four years after the impact. Any structural changes and morphological deformations will thus still be very “fresh”, and some may indeed be ongoing. Measuring them precisely will deliver new insights into the collision processes behind the evolution of the solar system and its planets. Hera will also conduct the first ever radar survey of an asteroid’s interior with the JuRa instrument on the Juventas cubesat, for which the IPAG planetology and astrophysics institute in Grenoble is the French Principal Investigator. Data from this survey will be matched against the theoretical interpretations and models on which our current knowledge is founded.

Hera is set to accomplish several technological feats:

• Navigating autonomously around a low-gravity asteroid 
  This autonomy will be crucial when the spacecraft is far from Earth, as commands might take too long to arrive from the ground control centre and prevent it from achieving the mission’s goals.
• An inter-satellite link supporting communications between the spacecraft and its two cubesats is a first in interplanetary space.
• A cubesat has never landed on such a small body before. Proximity flight dynamics operations (as close as 2 kilometres) on a body approximately 150 metres involve determining trajectories in a very-low-gravity environment surrounded by uncertainties (thought to be a million times lower than on Earth). In this respect, Hera is also a technology demonstration mission.

The main Hera satellite will be controlled from the European Satellite Operations Centre (ESOC, in Darmstadt, Germany), and the Milani and Juventas cubesats from CNES in Toulouse, France, and the European Space Security and Education Centre (ESEC) in Redu, Belgium.

CNES’s role

France is supplying the receiver board for the JuRa low-frequency radar, for which the PI Alain Herique is from the IPAG research institute in Grenoble.

CNES is in charge of proximity operations for the Juventas and Milani cubesats, which will involve trajectory control and instrument tasking, from their separation from the Hera mothercraft to asteroid landings. These operations will be conducted with industry partners (SpaceBel, GomSpace and Tyvak) and instrument teams (IPAG, ROB, Helsinki University, INAF and UNIBO).

Contacts

Project Leader
Aurélie Moussi
E-mail: aurelie.moussi at cnes.fr

System Manager
Pâmini Annat
E-mail: pamini.annat at cnes.fr

Solar System Planets and Small Bodies subject matter expert
Francis Rocard
E-mail: francis.rocard at cnes.fr

Space Surveillance subject matter expert
Pascal Faucher
E-mail: pascal.faucher at cnes.fr