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Hera is a European Space Agency (ESA) mission to visit the asteroid Didymos and its moon Dimorphos as part of the NASA/ESA Asteroid Impact and Deflection Assessment (AIDA) collaboration. The initial misson of the collaboration, the NASA Double Asteroid Redirection Test (DART) will have visited the asteroids earlier and impacted Dimorphos with sufficient momentum to effect a measurable change in its orbit. Hera will revisit the system roughly 5 years later for a follow-up assessment, primarily pertaining to planetary defense and evaluation of the kinetic impact deflection. The planetary defense objectives of the Hera mission are to: measure the mass of Dimorphos to determine precisely the momentum transfer efficiency; investigate the crater in detail to improve our understanding of the cratering process in the low-gravity regime and the mechanisms by which the crater formation is related to the momentum transfer efficiency; observe subtle dynamic effects (e.g. libration imposed by the impact, orbital and spin excitation of Dimorphos) that are impossible to detect by groundbased observations; and characterize the surface and interior of Dimorphos to allow scaling of the momentum transfer efficiency to different asteroids. The science objectives include characterizing the binary system, surface structures, regolith mobility and surface geophysics.

Spacecraft and Subsystems

The main bus of Hera has a box-shape based on a central tube and adapter cone. Two solar panel wings extend from opposite sides, and a high-gain dish antenna is mounted on one face. Total mass of the spacecraft is approximately 1280 kg. The solar panels have an area of about 13 square meters. Bi-propellant chemical propulsion is used for 16 orbit control thrusters and 6 reaction control thrusters. Total available delta-V is about 1300 m/s. Communications with the ground are X-band, with two low gain antennas in addition to the high-gain dish. S-band communications will be used to communicate with two CubeSats, with a range of 60 km.

Mounted on the top deck, Hera will carry two Asteroid Framing Cameras (AFCs), the Hyperscout-H spectral imager, a Thermal InfraRed Imager (TIRI), and the two CubeSats, Juvenitas and Milani. A microLIDAR instrument, the Planetary ALTimeter (PALT), is mounted near the lower deck. Hera also has an X-DST X-band transponder for radio science.

Mission Profile

Launch is scheduled for October, 2024, in a launch window extending from 8 to 25 October. Launch will nominally be on an Ariane 6.4, with the possibility of launch on a Falcon 9 as a backup. A deep space maneuver (DSM) is scheduled for two weeks after launch, followed by a Mars swingby within 5000 - 8000 km and a Deimos flyby in March 2025. A DSM in January, 2026 puts Hera towards Didymos/Dimorphos. The orbital capture sequence begins on 14 December 2026 and ends with orbit insertion in late January or early February 2027. Backup launch opportunities exist in 2025 with arrival in late 2030, and in 2026, with arrival in early 2031.

After orbit insertion, Hera will have five observation phases. The first phase, the Early Characterization Phase, will begin at orbital insertion and last about 6 weeks. It consists of hyperbolic arcs bringing the spacecraft within 20-30 km of the asteroid, alternating in 3-day and 4-day arcs. The objective of this phase is to determine the global shape, mass, density and thermal and dynamical properties of both asteroids. Target areas for later close flybys will also be determined. The next phase the Payload Deployment Phase, will last about 2 weeks and will involve release and early support of the cubesats. It will involve the same trajectory as the Early Characterization Phase. Following this, the hyperbolic arcs are brought to 8-20 km distance from the asteroids for the Detailed Characterization Phase. This phase will result in meter-scale mapping of the asteroids and determination of thermal, spectral, and interior properties. This phase lasts about 4 weeks.

The close approach distance is reduced to 4 km for about 6 weeks for the Close Observation Phase. Full autonomous attitude guidance, including feature tracking and use of the Planetary Altimeter laser, will be necessary for this phase, which will result in 12 flybys and high-resolution investigations, including of the DART impact crater. A final, 6 week long, Experimental Phase will have the flybys lowered to 1 km or less. Observations of the surface will reach the decimeter level for morphological, spectral, and thermal properties, including observations of the DART impact crater. This phase will end with Hera landing on the surface of Didymos.

For more information on the initial AIDA mission to Didymos, DART, see:

Alternate Names

  • Asteroid Impact and Deflection Assessment (AIDA)

Facts in Brief

Launch Date: 
Launch Vehicle: 
Launch Site: ,

Funding Agency

  • European Space Agency (International)


  • Planetary Science

Additional Information

Questions and comments about this spacecraft can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail
Dr. Patrick MichelMission Principal
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