Hera

Artist's impression ofHera in orbit around the asteroid Didymos
Mission type	Didymos orbiter
Operator	European Space Agency
COSPAR ID	2024-180A
SATCATno.	61449
Website	heramission.space
Mission duration	1 year, 1 month, 17 days (elapsed) 2 years, 9 months (planned)[a]
Spacecraft properties
Manufacturer	OHB SE
Launch mass	1,128 kg (2,487 lb)
Dry mass	350 kg (770 lb)
Dimensions	1.6 × 1.6 × 1.7 m (5.2 × 5.2 × 5.6 ft)
Start of mission
Launch date	7 October 2024, 14:52:11 UTC[1][2] (10:52:11 am EDT)
Rocket	Falcon 9 Block 5B1061-23
Launch site	Cape Canaveral,SLC‑40
Contractor	SpaceX
Flyby ofDeimos
Closest approach	12 March 2025, 12:07 GMT
Distance	300 km (190 mi)
Flyby ofMars
Closest approach	12 March 2025, 12:51 GMT
Distance	5,000 km (3,100 mi)
65803 Didymos orbiter
Orbital insertion	November 2026[3]
Instruments AFC Asteroid Framing Camera TIRI Thermal Infra Red Imager PALT Planetary Altimeter RSE Radio Science Experiment HS HyperScout-H
Mission insignia Space Safety Programme Draco →

Hera is the firstplanetary defence spacecraft developed by theEuropean Space Agency (ESA).^[4] Its primary mission objective is to study theDidymos binary asteroid system that was impacted in 2022 byNASA'sDART spacecraft and contribute to validation of the kinetic impact method to deviate anear-Earth asteroid from a colliding trajectory with Earth.^[5]Hera has a mass of 1,128 kg (2,487 lb) and carries a payload of cameras, analtimeter, and aspectrometer. It is carrying two smallCubeSat spacecraft, calledMilani andJuventas. The spacecraft was launched on 7 October 2024 byFalcon 9.^[6]Hera is the first mission of ESA'sSpace Safety Programme.^[7]

Hera will measure the size and morphology of thecrater created as well as the momentum transferred by an artificial projectile impacting an asteroid, which will allow measuring the efficiency of the deflection produced by the impact. It will also analyze the expanding debris cloud caused by the impact.Hera is intended to fully characterize the composition and physical properties of the binary asteroid system including, for the first time, the sub-surface and internal structures. It will also perform technological demonstrations linked tooperations in the vicinity of asmall Solar System body and the deployment of and communication withCubeSats ininterplanetary space.^[5][8]

The main objective of theHera mission is to evaluate the kinetic impactor method for deflecting anear-Earth object. Thisplanetary defense method consists of modifying the trajectory of theasteroid by launching a spacecraft at a speed of a few kilometers per second. To fulfill this objective,Hera will determine:

• how much momentum transfer depends on the density, porosity and characteristics of the asteroid's surface and internal structure and
• what proportion of the kinetic energy is transferred in the fragmentation and restructuring of the asteroid or in the kinetic energy of the ejected materials.^[9]

Scientific objectives of the mission include exploring the properties of the two target asteroids: surface characteristics, internal porosity, and internal structure. The entire moonDimorphos will be mapped with a spatial resolution of a few meters and the vicinity of the impact with a resolution of 10 centimeters. The mass of the moon will be estimated with high accuracy, allowing a direct estimate of the momentum transfer efficiency from DART impact.^[10][11]

The mission's technological objectives include the production and testing of guidance software which, by using data from several sensors, will make it possible to reconstruct the surrounding space and thus to independently define a safe trajectory around the asteroid.^[12]

Hera also carries twoCubeSats which will be dropped once the asteroid is reached:^[13]

• Juventas will carry out subsurface and internal structure measurements, contribute to the determination of the gravity field, and provide information on the mechanical response of the surface when landing on Dimorphos
• Milani will collect spectral data from the surface of the two asteroids to study their surface composition and identify the presence of dust in the surrounding space

AIDA was the first operational program whose objective is to test a method of deflecting near-Earth asteroids. It was set up in 2013 jointly by scientists supported by NASA and ESA. Its objective was to test the use of an impactor-type device to deflect anasteroid that might strike the Earth. This program provided for the launch to thebinary asteroid65803 Didymos of two spacecraft: theDART impactor developed by NASA responsible for crashing at high speed on the smaller of the two asteroids and the AIM orbiter developed by ESA, which would measure the effects of the impact.^[14]

After an evaluation phase in the two space agencies, ESA decided at the end of 2016 to abandon the development of AIM due to lack of sufficient financial support from member states.^[15][16] NASA, for its part, decided to continue the development of DART. In this new context, terrestrial observatories were responsible for taking over partially the role of AIM.^{[citation needed]}

TheDART mission was launched on 24 November 2021 by aFalcon 9 rocket fromVandenberg Space Force Base and reached the binary asteroid65803 Didymos on 26 September 2022, colliding with its satelliteDimorphos at 23:16 UTC at a relative speed of about 6.6 km/s.^[17] The project incorporated the Italiannano-satelliteLICIACube, responsible for documenting and retransmitting the first 100 seconds of the impact.^[18]

In 2017, at the request of several member states of ESA, the agency resumed studies of a replacement for AIM, specifically a mission that was namedHera (after the Greek goddessHera).Hera is intended to fulfill all the objectives assigned to AIM that Earth-based observatories could not, using the components of AIM as much as possible.^[16]Hera was planned to be launched in October 2024 to catch a workable planetary/asteroid alignment and study the effects of the DART impact onDimorphos, the satellite of Didymos, 4 years after it occurred.^{[citation needed]}

TheHera mission was subsequently approved by the ESA Ministerial Council in November 2019.^[19] In September 2020, ESA awarded the construction of the spacecraft to a consortium of companies led byOHB, under a contract of 129.4 million euros.^[15] It also formalized the scientific team of the mission, made up of a principal investigator, scientific council, and four working groups^[20] covering all aspects of the mission and the scientific managers of the instruments.

Hera's Core Module and Propulsion Module have been connected atOHB Bremen in Germany in August 2023.^[21] In November 2023, the spacecraft has completed acoustic testing atESTEC in theNetherlands.^[22] TheMilani CubeSat, integrated inItaly, and theJuventas CubeSat, integrated inDenmark, were delivered to ESTEC for integration withHera in March 2024.^[23][24] The spacecraft moved to final testing in March 2024.^[25] In September 2024,Hera was transported to Florida byAntonov Airlines'sAN-124 cargo aircraft.^[26]

Hera launched on 7 October 2024 at 14:52 UTC by aFalcon 9 rocket lifting off fromSpace Launch Complex 40 (SLC-40) atCape Canaveral Space Force Station.^[28] Usually, Falcon 9 launches for beyondgeostationary transfer orbit are made from the nearbyLaunch Complex 39A (LC-39A) atKennedy Space Center due to SLC-40's focus onStarlink launches. However, LC-39A was in the midst of preparing for the launch of NASA'sEuropa Clipper on aFalcon Heavy later in the week, which lockedHera into using SLC-40. Additionally, the launch occurred while Falcon 9 was grounded due to a mishap with a second stage deorbit burn happening theSpaceX Crew-9 mission the previous month. AsHera was to be put into aheliocentric orbit however,FAA waived the grounding for its launch as an exception. The booster used for the launch was expended to help with the trajectory; it previously flew 22 times, including on missions likeSpaceX Crew-1 and theIXPE.^[29][30]

On 10 and 11 October 2024,Hera tested three of its science instruments (AFC, TIRI, and HyperScout H) by using them to take pictures of Earth and the Moon from a distance of more than one million km.^[31]

In October 2024, the two CubeSats aboardHera were briefly activated to confirm their nominal status and test their ability to communicate with Earth. This marked the first operation of CubeSats in deep space by ESA.^[32]

Following three successful test burns performed after launch, the spacecraft conducted its first deep-space maneuver on 27 October 2024, firing its three orbital control thrusters for 100 minutes and changing its velocity by ~146 m/s, and second on 6 November 2024, firing for 13 minutes and changing its velocity by ~20 m/s.^[33]

Hera performed agravity assist atMars on 12 March 2025, coming at a distance of 5,000 km (3,100 mi) from the surface. As part of the flyby, the spacecraft spent some time observing the Martian moonDeimos, imaging it from distance of 1,000 km (620 mi) and having its closest approach at 300 km (190 mi) away.^[34] During the flyby,Hera also autonomously locked onto impact craters and other surface features on Mars to track them over time, in a full-scale test of the autonomous navigation techniques it will use to navigate around its targets.^[35]

On 11 May 2025, the mission has captured images of the asteroid(1126) Otero from a distance of approximately 3 million km and on 19 July 2025 of the asteroid (18805) Kellyday from a distance of approximately 6 million km in order to perform instrument tests and to demonstrate agile spacecraft operations useful forplanetary defence.^[36] In October 2025, ESA announced thatHera was on track to arrive atDidymos in November 2026—a month earlier than originally planned.^[37] Between 25 October and 1 November 2025,Hera was passing through thecometary tail of the third knowninterstellar object, the comet3I/ATLAS. The spacecraft flew 8.2 million km from the tail's central axis.^[38][39]

The spacecraft will reach thebinary asteroid (65803) Didymos in November 2026, four years after DART,^[37] to begin six months of investigation.Hera will be the first to make a rendezvous with a binary asteroid. Once close to the double asteroid, five stages will follow:

The mainbus ofHera has a box-shape based on a central tube and adapter cone of 1.6 × 1.6 × 1.7 meters. Two solar panel wings extend from opposite sides, and a high-gain dish antenna is mounted on one face. Total launch mass of the spacecraft is approximately 1214 kg, the dry mass is 696 kg. Spacecraft deployed dimensions are 2.2 x 11.4 x 2.2 meters. Thesolar panels have an area of about 13 square meters. The spacecraft will use 712 W at the nominal 2.4 AU distance. Bi-propellant chemical propulsion is used for 16 orbit control thrusters and 6 reaction control thrusters, all 10-N motors. Total available delta-V is about 1300 m/s. Communications with the ground are X-band (~8.4 GHz), with two low gain antennas in addition to the high-gain dish. S-band communications (~2.2 GHz), using patch antennas, will be used to communicate with the twoCubeSats namedJuventas andMilani, with a range of 60 km. Spacecraft orientation is maintained by 4reaction wheels,gyroscopes, usingstar trackers and solar sensors, as well two Asteroid Framing Cameras (AFC). Attitude guidance is through the Planetary Altimeter (PALT).^[41][42][43]

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The main instruments ofHera are the two AFC cameras (Asteroid Framing Cameras), developed by the company JenaOptronik. Identical and redundant, they each have a FaintStar panchromatic sensor of 1020 x 1020 pixels with a telephoto lens. The field of view is 5.5 x 5.5 degrees, and the spatial resolution reaches one meter at a distance of 10 kilometers. These cameras are to provide physical characteristics of the surface of the asteroid Didymos and Dimorphos as well as the crater created by DART and the Juventas landing zone.^{[10][44][45][46]}

HyperScout-H is a hyperspectral imager that must provide images in a spectral range between 650 and 950 nm (visible and near infrared). The instrument makes its observations in 25 distinct spectral bands. It is developed bycosine Remote Sensing. This is a specific version developed forHera, different from the standard HyperScout.^[47][48][49]

PALT is a micro-Lidar planetary altimeter using a laser emitting an infrared light beam at 1.5 microns. Its track on the ground is 1 meter at an altitude of 1 kilometer (1milliradian). The altitude measurement accuracy is 0.5 meters. Its frequency is 10Hertz.^{[citation needed]}

TIRI is a thermal infrared imager provided by theJAXA, the Japanese space agency. The spectral range observed is between 7 and 14 microns and it has 6 filters. Its visual range is 13.3 x 10.6°. The spatial resolution is 2.3 meters at a distance of 10 kilometers.^{[citation needed]}

The mass of the two asteroids making up the binary system, the characteristics of their gravity field, their rotational speed, and their orbits will be measured using radio wave disturbances caused by theDoppler effect. The measurements relate to the radio exchanges betweenHera and Earth stations but also betweenHera and the CubeSats. Due to the low orbit in which the CubeSats will circulate, these last measurements are crucial to determine the gravity of Didymos.^{[citation needed]}

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TwoCubeSat type nanosatellites, namedMilani andJuventas, are transported byHera and released before arrival in the asteroidal system(65803) Didymos. They are responsible for carrying out investigations that complement those of their carrier ship. Both CubeSats are built around a similar platform. These are 6U-XL CubeSats with a mass (including propellant) of approximately 12 kilograms. They are 3-axis stabilized and have a cold gas propulsion system. They communicate with the mothership in S-band. TheDoppler effect affected radio link is used to measure the characteristics of the gravitational field of the binary system. They have a visible light camera andstar trackers which are used to determine the dynamic variations of Didymos. Finally, the two CubeSats are equipped withaccelerometers which will be used to determine the properties of the surface of Dimorphos if the CubeSats land on its surface as planned at the end of their mission.Juventas was developed byGomSpace andMilani byTyvak International.^{[citation needed]}

The CubeSatJuventas aims to determine the geophysical characteristics of Dimorphos. The probe will map itsgravity field and determine its internal structure as well as the characteristics of its surface.

To fulfill these objectives, it carries the following instruments:

• The JuRaradar operating in the 50–70 MHz frequency with a spatial resolution of 10 to 15 meters. It is the first instrument to probe the inner layers of an asteroid. It uses two dipole antennas with each branch measuring 1.5 meters. Each measurement session can last up to 45 minutes. It occupies a volume of less than 1U and its mass is less than 1300 grams.
• The GRASSgravimeter whose dynamic range is 5 x 10⁻⁴ and sensitivity is 5 x 10⁻⁷. Its mass is less than 380 grams.
• A camera.
• The radio link with the mother ship (measurement of theDoppler effect).^{[citation needed]}

The CubeSatMilani (named afterAndrea Milani) aims to take images and measure the characteristics of the possibly present dust. It will map the two asteroids forming thebinary asteroid 65803 Didymos, characterize their surface, evaluate the effects of the DART impact, contribute to the measurements of the gravitational field of the asteroids, and determine the characteristics of the dust clouds possibly located around the asteroids.

To fulfill these objectives, it carries two instruments:

• The ASPECThyperspectral imaging spectrometer is the main instrument. It works in visible and near infrared light (0.5 to 2.5 microns). Its spatial resolution is 2 meters at 10 kilometers and its spectral resolution is less than 40 nanometers (20 nanometers in the visible). It has a total of 72 channels.
• The VISTAthermogravimeter is responsible for detecting dust (5 to 10 microns), volatiles (such as water) and light organic materials.^{[citation needed]}

• Near-Earth Object Coordination Centre (ESA's NEOCC)
• Planetary Defense Coordination Office (NASA's PDCO)
• Double Asteroid Redirection Test (DART mission)
• List of European Space Agency programmes and missions

• Michel, Patrick; Cheng, A.; Küppers, M.; Pravec, P.; Blum, J.; Delbo, M.; Green, S.F.; Rosenblatt, P.; Tsiganis, K.; Vincent, J.B.; Biele, J.; Ciarletti, V.; Hérique, A.; Ulamec, S.; Carnelli, I.; Galvez, A.; Benner, L.; Naidu, S.P.; Barnouin, O.S.; Richardson, D.C.; Rivkin, A.; Scheirich, P.; Moskovitz, N.; Thirouin, A.; Schwartz, S.R.; Campo Bagatin, A.; Yu, Y. (June 2016)."Science case for the Asteroid Impact Mission (AIM): A component of the Asteroid Impact & Deflection Assessment (AIDA) mission"(PDF).Advances in Space Research.57 (12):2529–2547.Bibcode:2016AdSpR..57.2529M.doi:10.1016/j.asr.2016.03.031.S2CID 42465954.
• Michel, Patrick; Kueppers, Michael; Sierks, Holger; Carnelli, Ian; Cheng, Andy F.; Mellab, Karim; Granvik, Mikael; Kestilä, Antti; Kohout, Tomas; Muinonen, Karri; Näsilä, Antti; Penttila, Antti; Tikka, Tuomas; Tortora, Paolo; Ciarletti, Valérie; Hérique, Alain; Murdoch, Naomi; Asphaug, Erik; Rivkin, Andy; Barnouin, Olivier; Bagatin, Adriano Campo; Pravec, Petr; Richardson, Derek C.; Schwartz, Stephen R.; Tsiganis, Kleomenis; Ulamec, Stephan; Karatekin, Ozgür (October 2018)."European component of the AIDA mission to a binary asteroid: Characterization and interpretation of the impact of the DART mission"(PDF).Advances in Space Research.62 (8):2261–2272.Bibcode:2018AdSpR..62.2261M.doi:10.1016/j.asr.2017.12.020.S2CID 55274187.

• Hera mission byCôte d'Azur Observatory
• Hera mission byEuropean Space Agency
• Hera and Planetary Defense,COSPAR 2021, P. Michel, 4 February 2021.
• Science return of Hera,COSPAR 2021, P. Michel, 2 February 2021.
• Youtube channel of theNEO-MAPP project.
• The Planetary Science Journal, volume 3, number 7, 2022, July, 15th.

• Space probes launched in 2024
• 2024 in Florida
• October 2024 in the United States
• Missions to minor planets
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• European Space Agency space probes
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