''Hera'' is a spacecraft developed by the

European Space Agency The European Space Agency (ESA) is a 23-member International organization, international organization devoted to space exploration. With its headquarters in Paris and a staff of around 2,547 people globally as of 2023, ESA was founded in 1975 ...

for its space safety program. Its primary mission objective is to study the Didymos binary asteroid system that was impacted four years earlier by the

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

Double Asteroid Redirection Test The Double Asteroid Redirection Test (DART) was a NASA space mission aimed at testing a method of planetary defense against near-Earth objects (NEOs). It was designed to assess how much a spacecraft impact deflects an asteroid through its trans ...

(DART) spacecraft and contribute to validation of the kinetic impact method to deviate a

near-Earth asteroid A near-Earth object (NEO) is any small Solar System body orbiting the Sun whose closest approach to the Sun (perihelion) is less than 1.3 times the Earth–Sun distance (astronomical unit, AU). This definition applies to the object's orbit aro ...

from a colliding trajectory with Earth. It will measure the size and morphology of the crater 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 to operations in the vicinity of a

small Solar System body A small Solar System body (SSSB) is an object in the Solar System that is neither a planet, a dwarf planet, nor a natural satellite. The term was first defined in 2006 by the International Astronomical Union (IAU) as follows: "All other objects ...

and the deployment of and communication with CubeSats in interplanetary space. ''Hera'' has a mass of and carries a payload of cameras, an

altimeter An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth under water. Ty ...

, and a

spectrometer A spectrometer () is a scientific instrument used to separate and measure Spectrum, spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomeno ...

. It is carrying two small

CubeSat A CubeSat is a class of small satellite with a form factor of cubes. CubeSats have a mass of no more than per unit,, url=https://static1.squarespace.com/static/5418c831e4b0fa4ecac1bacd/t/5f24997b6deea10cc52bb016/1596234122437/CDS+REV14+2020-07-3 ...

spacecraft, called ''Milani'' and ''Juventas''. The spacecraft was launched on 7 October 2024 aboard a

SpaceX Space Exploration Technologies Corp., commonly referred to as SpaceX, is an America, American space technology company headquartered at the SpaceX Starbase, Starbase development site in Starbase, Texas. Since its founding in 2002, the compa ...

Falcon 9 Falcon 9 is a Reusable launch system#Partial reusable launch systems, partially reusable, two-stage-to-orbit, medium-lift launch vehicle designed and manufactured in the United States by SpaceX. The first Falcon 9 launch was on June 4, 2010, an ...

launch vehicle and will study the results of the DART impactor, four years after impact. DART impacted the asteroid

Dimorphos Dimorphos (formal designation (65803) Didymos I; provisional designation S/2003 (65803) 1) is a natural satellite or minor-planet moon, moon of the near-Earth object, near-Earth asteroid 65803 Didymos, with which it forms a Binary asteroid, bina ...

, the smaller of two objects forming the binary asteroid 65803 Didymos, on 27 September 2022. The launch vehicle, B1061, previously used for the Crew-1 mission, was expended on this flight.

Goals

The main objective of the ''Hera'' mission is to evaluate the kinetic impactor method for deflecting a

near-Earth object A near-Earth object (NEO) is any small Solar System body orbiting the Sun whose closest approach to the Sun ( perihelion) is less than 1.3 times the Earth–Sun distance (astronomical unit, AU). This definition applies to the object's orbit a ...

that threatens to crash into Earth. This deflection method consists of modifying the trajectory of the asteroid by launching a spacecraft at a speed of a few kilometers per second. Of all the methods, this is the most mature because it relies on the use of available and inexpensive spacecraft technologies. To fulfill this objective, ''Hera'' must 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. ''Hera'' also has high scientific objectives. It must collect the characteristics of the two asteroids: surface characteristics, internal porosity and internal structure. In particular, ''Hera'' will be the first mission to measure the subsurface and internal structures of an asteroid. For this, it will use the JuRA low-frequency radar on board the

Juventas (see below). The entire moon, Dimorphos, 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 of Didymos will be estimated with high accuracy, allowing a direct estimate of the momentum transfer efficiency from DART impact. The mission also includes several technological objectives. The most important thing is the production of a 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. ''Hera'' also carries two CubeSats which will be dropped once the asteroid is reached: * Juventas, which must 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 and * Milani, with the mission of collecting spectral data from the surface of the two asteroids (surface composition) and identifying the presence of dust in the surrounding space.

Project history

AIDA the joint project with NASA

AIDA ''Aida'' (or ''Aïda'', ) is a tragic opera in four acts by Giuseppe Verdi to an Italian libretto by Antonio Ghislanzoni. Set in the Old Kingdom of Egypt, it was commissioned by Cairo's Khedivial Opera House and had its première there on 24 De ...

is 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 is to test the use of an impactor-type device to deflect an

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

that might strike the Earth. This program provides for the launch to the

binary asteroid A binary asteroid is a system of two asteroids orbiting their common barycenter. The binary nature of 243 Ida was discovered when the Galileo spacecraft flew by the asteroid in 1993. Since then numerous binary asteroids and several triple a ...

65803 Didymos of two spacecraft: the DART 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 must measure the effects of the impact. After an evaluation phase in the two space agencies, the European Space Agency decided at the end of 2016 to abandon the development of AIM due to lack of sufficient financial support from member states. 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. The DART project would evolve thereafter by incorporating the LICIACube nano-satellite, released before the impact and responsible for taking and retransmitting the first 100 seconds of it.

Renaissance of the European project

In 2017, at the request of several member states of the European Space Agency, the ESA resumed studies of a replacement for AIM, specifically, a mission that was named ''Hera'' (named after the Greek goddess of marriage

Hera In ancient Greek religion, Hera (; ; in Ionic Greek, Ionic and Homeric Greek) is the goddess of marriage, women, and family, and the protector of women during childbirth. In Greek mythology, she is queen of the twelve Olympians and Mount Oly ...

). ''Hera'' must fulfill all the objectives assigned to AIM that Earth-based observatories could not, using the components of AIM as much as possible. ''Hera'' was planned to be launched in October 2024 to catch a workable planetary/asteroid alignment and study the effects of the DART impact on

, the satellite of Didymos, 4 years after it occurred. The ''Hera'' mission was subsequently approved by the ESA Ministerial Council in November 2019. In September 2020 the European Space Agency awarded the construction of the spacecraft to a consortium of companies led by OHB, under a contract of 129.4 million euros. It also formalized the scientific team of the mission, made up of a principal investigator, scientific council, and four working groups covering all aspects of the mission and the scientific managers of the instruments. The mission moved to final testing in March 2024.

DART

The DART mission, launched on 24 November 2021 at 06:21 UTC by a

rocket from

Vandenberg Space Force Base Vandenberg Space Force Base , previously Vandenberg Air Force Base, is a United States Space Force Base in Santa Barbara County, California. Established in 1941, Vandenberg Space Force Base is a space launch base, launching spacecraft from the ...

reached the binary asteroid 65803 Didymos on 26 September 2022, colliding with its satellite

at 23:16 UTC at a relative speed of about 6.6 km/s.

Mission timeline

Launch

''Hera'' launched on 7 October 2024 at 14:52 UTC by a

rocket lifting off from Space Launch Complex 40 (SLC-40) at

Cape Canaveral Space Force Station Cape Canaveral Space Force Station (CCSFS) is an installation of the United States Space Force's Space Launch Delta 45, located on Cape Canaveral in Brevard County, Florida. Headquartered at the nearby Patrick Space Force Base, the sta ...

. Usually, Falcon 9 launches for beyond

geostationary transfer orbit In space mission design, a geostationary transfer orbit (GTO) or geosynchronous transfer orbit is a highly elliptical type of geocentric orbit, usually with a perigee as low as low Earth orbit (LEO) and an apogee as high as geostationary orbit ...

are made from the nearby Launch Complex 39A (LC-39A) at

Kennedy Space Center The John F. Kennedy Space Center (KSC, originally known as the NASA Launch Operations Center), located on Merritt Island, Florida, is one of the NASA, National Aeronautics and Space Administration's (NASA) ten NASA facilities#List of field c ...

due to SLC-40's focus on

Starlink Starlink is a satellite internet constellation operated by Starlink Services, LLC, an international telecommunications provider that is a wholly owned subsidiary of American aerospace company SpaceX, providing coverage to around 130 countries ...

launches. However, LC-39A was in the midst of preparing for the launch of NASA's

Europa Clipper Europa Clipper (previously known as Europa Multiple Flyby Mission) is a space probe developed by NASA to study Europa (moon), Europa, a Galilean moon of Jupiter. It was launched on October 14, 2024. The spacecraft used a gravity assist from Mar ...

on a

Falcon Heavy Falcon Heavy is a super heavy-lift launch vehicle with partial reusability that can carry cargo into Earth orbit and beyond. It is designed, manufactured and launched by American aerospace company SpaceX. The rocket consists of a center core ...

later in the week, which locked ''Hera'' into using SLC-40. Additionally, the launch occurred while Falcon 9 was grounded due to a mishap with a second stage deorbit burn happening the

SpaceX Crew-9 SpaceX Crew-9 was the ninth operational NASA Commercial Crew Program flight and the 15th crewed orbital flight of a Crew Dragon spacecraft. Originally scheduled to carry a crew of four to the International Space Station (ISS) in mid-August 2024 ...

mission the previous month. As ''Hera'' was to be put into a

heliocentric orbit A heliocentric orbit (also called circumsolar orbit) is an orbit around the barycenter of the Solar System, which is usually located within or very near the surface of the Sun. All planets, comets, and asteroids in the Solar System, and the Sun ...

however, the

Federal Aviation Administration The Federal Aviation Administration (FAA) is a Federal government of the United States, U.S. federal government agency within the United States Department of Transportation, U.S. Department of Transportation that regulates civil aviation in t ...

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 like

SpaceX Crew-1 SpaceX Crew-1 (was also known as USCV-1 or simply Crew-1) was the first operational crewed flight of a SpaceX Dragon 2, Crew Dragon spacecraft and the maiden flight of the Crew Dragon Resilience, Crew Dragon ''Resilience'' spacecraft. It was ...

and the

IXPE Imaging X-ray Polarimetry Explorer, commonly known as IXPE or SMEX-14, is a space observatory with three identical telescopes designed to measure the polarization of cosmic X-rays of black holes, neutron stars, and pulsars. The observatory, ...

. Following the launch, the spacecraft conducted a deep-space maneuver in November.

Mars flyby

''Hera'' performed a gravitational assist at

Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

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 moon Deimos, imaging it from distance of 1,000 km (620 mi) and having its closest approach from 300 km (190 mi) away. 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.

Arrival at Didymos

The spacecraft will reach the

65803 Didymos on 28 December 2026, four years after DART, 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:

Spacecraft

The main

bus A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a motor vehicle that carries significantly more passengers than an average car or van, but fewer than the average rail transport. It is most commonly used ...

of Hera 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. The

solar panel A solar panel is a device that converts sunlight into electricity by using photovoltaic (PV) cells. PV cells are made of materials that produce excited electrons when exposed to light. These electrons flow through a circuit and produce direct ...

s 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 two

s named ''Juventas'' and ''Milani'', with a range of 60 km. Spacecraft orientation is maintained by 4

reaction wheel A reaction wheel (RW) is an electric motor attached to a flywheel, which, when its rotation speed is changed, causes a counter-rotation proportionately through conservation of angular momentum. A reaction wheel can rotate only around its center ...

gyroscope A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining Orientation (geometry), orientation and angular velocity. It is a spinning wheel or disc in ...

s, using

star tracker A star tracker is an optical device that measures the positions of stars using photocells or a camera. As the positions of many stars have been measured by astronomers to a high degree of accuracy, a star tracker on a satellite or spacecraft may ...

s and solar sensors, as well two ''Asteroid Framing Cameras'' (AFC). Attitude guidance is through the ''Planetary Altimeter'' (PALT). https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=HERA

Scientific instruments

Asteroid framing cameras (AFC)

The main instruments of ''Hera'' 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.

Hyperspectral imager – HyperScout-H

HyperScout-H is a hyperspectral imager that must provide images in a spectral range between 665 and 975 nm (visible and near infrared). The instrument makes its observations in 25 distinct spectral bands. It is developed by ''cosine Remote Sensing''. This is a specific version developed for ''Hera'', different from the standard HyperScout.

Planetary altimeter (PALT)

PALT is a micro-

Lidar Lidar (, also LIDAR, an acronym of "light detection and ranging" or "laser imaging, detection, and ranging") is a method for determining ranging, ranges by targeting an object or a surface with a laser and measuring the time for the reflected li ...

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 (1

milliradian A milliradian (International System of Units, SI-symbol mrad, sometimes also abbreviated mil) is an SI derived unit for angular measurement which is defined as a thousandth of a radian (0.001 radian). Milliradians are used in adjustment of ...

). The altitude measurement accuracy is 0.5 meters. Its frequency is 10

Hertz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or Cycle per second, cycle) per second. The hertz is an SI derived unit whose formal expression in ter ...

Thermal Infrared Imager (TIRI)

TIRI is a thermal infrared imager provided by the

JAXA The is the Japanese national air and space agency. Through the merger of three previously independent organizations, JAXA was formed on 1 October 2003. JAXA is responsible for research, technology development and launch of satellites into o ...

, 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.

X-Band Radio Science (X-DST)

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 the

Doppler effect The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The ''Doppler effect'' is named after the physicist Christian Doppler, who described ...

. The measurements relate to the radio exchanges between ''Hera'' and Earth stations but also between ''Hera'' 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.

CubeSats

Two

type nanosatellites, named Milani and Juventas, are transported by ''Hera'' 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. The

affected radio link is used to measure the characteristics of the gravitational field of the binary system. They have a visible light camera and

s which are used to determine the dynamic variations of Didymos. Finally, the two CubeSats are equipped with

accelerometer An accelerometer is a device that measures the proper acceleration of an object. Proper acceleration is the acceleration (the rate of change (mathematics), rate of change of velocity) of the object relative to an observer who is in free fall (tha ...

s 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 is developed by GomSpace while Milani is made by Tyvak International.

CubeSat Juventas

Juventas aims to determine the geophysical characteristics of Dimorphos. The probe must map its

gravity field In physics, a gravitational field or gravitational acceleration field is a vector field used to explain the influences that a body extends into the space around itself. A gravitational field is used to explain gravitational phenomena, such as ...

and determine its internal structure as well as the characteristics of its surface. To fulfill these objectives, it carries the following instruments: * The JuRa

radar Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...

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 GRASS

gravimeter Gravimetry is the measurement of the strength of a gravitational field. Gravimetry may be used when either the magnitude of a gravitational field or the properties of matter responsible for its creation are of interest. The study of gravity c ...

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 the

CubeSat Milani

The CubeSat Milani (named after Andrea Milani) aims to take images and measure the characteristics of the possibly present dust. It must map the two asteroids forming the

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 ASPECT hyperspectral 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 VISTA thermogravimeter is responsible for detecting dust (5 to 10 microns), volatiles (such as water) and light organic materials.

Notes

References

Bibliography

* *

External links

Hera mission
by Côte d'Azur Observatory
Hera mission
by

Hera and Planetary Defense

COSPAR The Committee on Space Research (COSPAR) was established on October 3, 1958 by the International Council for Science, International Council for Scientific Unions (ICSU) and its first chair was Hildegard Korf Kallmann-Bijl. Among COSPAR's objec ...

2021, P. Michel, 4 February 2021.
Science return of Hera

2021, P. Michel, 2 February 2021.
Youtube channel
of the NEO-MAPP project.
The Planetary Science Journal, volume 3, number 7, 2022, July, 15th
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