European Hera probe launched to study double asteroids Didymos and Dimorpho

The European Hera probe is already on its way to the double asteroid Didymos and Dimorpho. On October 7, 2024, at 14:52 UTC, Falcon 9 BLock 5 launched from SLC-40 at Cape Canaveral Space Force Station along with the European Space Agency’s (ESA) Hera probe, carrying the interplanetary spacecraft Milani and Juventas. cubesats. After two firings of the second stage, Falcon 9 placed the payload on an escape trajectory relative to the Earth at a hyperbolic speed of 5.6 km/s. This trajectory represents an orbit around the Sun with a size of approximately 1.01 x 2.27 astronomical units and an inclination of 2.3 degrees. If all goes well, Hera will arrive at Didymus on December 14, 2026, after three maneuvers and a Mars flyby in March 2025. The launch marked the first Falcon 9 launch since the Crew-9 took off on September 28. , when the second stage failed during the deorbit launch.

The FAA has since suspended launches of the Falcon 9 fleet, but it decided to issue a special clearance for the Hera launch, given that the second stage was not going to be taken out of orbit, but rather placed on an escape path (this and the fact that the Release Window Didymus is only open until October 27th, and if it doesn’t come out, Hera will have to wait two years). To make full use of the Falcon 9’s energy, the B1061 stage, on its 23rd mission, was retired. It was SpaceX’s 95th orbital mission this year, the company’s 10th interplanetary mission, and the 208th Falcon 9 liftoff from SLC-40.

Hera is a 1,081 kg probe built by OHB System for ESA. The ship’s hull has a cubic design with a 1.6 meter rib and a wingspan of 11.5 meters with deployed solar panels 5 meters long and 14 square meters each. The position control system (PCS) consists of 16 hydrazine motors of 10 Newton thrust, arranged in pairs at the corners of the cubic structure, to which must be added six motors of similar thrust, located in a ring on the underside of the probe. designed to perform motor maneuvers to correct the trajectory. The X-band High Gain Antenna (HGA) has a diameter of 1.13 meters.

Hera is carrying 11 scientific instruments to study the effects of NASA’s DART probe colliding with the asteroid Dimorphos, a moon of Didymos (Dimorphos and Didymos in English). Recall that DART collided with Dimorpho on September 26, 2022 at a speed of 6.1 km/s, creating a huge amount of debris over ten thousand kilometers long, including 37 large rocks. As a result of the impact, Dimorpho’s orbit around Didim was shortened by 33 minutes, the current period being 11 hours 55 minutes. Hera must analyze the Dimorph’s current state to compare it to its pre-collision appearance and thus be able to measure the effectiveness of the collision in changing its orbit. Did the DART accident leave a 25-meter crater? Or one of 50 meters? Or perhaps it changed the shape of the entire asteroid? In addition, Hera must determine the mass of the Dimorph, which is currently not precisely known and is a fundamental parameter for measuring the effectiveness of the DART collision as a planetary defense tool. Another goal is to figure out Dimorpho’s internal structure, key information for planning missions of this type. Dimorpho has a diameter of about 151 meters, and Didymus reaches 780 meters.

The main tools are: AFC camera (Asteroid framing camera), two panchromatic cameras (black and white) made in Germany by Jenoptik, which will take images in the visible region thanks to two sensors with a resolution of 1020 x 1020 pixels; infrared camera TIRI (Thermal infrared thermal imager), a contribution from the Japanese space agency JAXA, which will observe two asteroids in the mid-infrared to elucidate the structure and composition of their surfaces (it is based on a similar instrument flown on the Hayabusa2 mission to the asteroid Ryugu); SMC camera (Spaceship surveillance camera), manufactured in Italy for ESA by TSD-Space with a 4 megapixel CMOS sensor and intended for production selfie ship to review its status, focusing on the deployment of two CubeSats; the Dutch spectrometer HyperScout H, which will observe the dual system at 25 frequencies, from ultraviolet to near-infrared; and finally a German LIDAR from Jena-Optronik with a 1550 nanometer laser capable of lifting Dimorpho’s terrain map with an accuracy of 1 meter.

In reality, due to the very low gravity, Hera will not orbit Didymus or Dimorpho, but will move around their common barycenter at a relative speed of 12 cm/s, so she will devote herself to flying over both asteroids, often drawing arcs. trajectory adjustments. This technique is inherited from the one used in the Rosetta mission. Once on Didymus, Hera will deploy two 6UXL cubesatellites, Milani and Juventas, which will orbit the binary system and attempt to land on Dimorpho. Milani, developed by the Italian company Tyvak, will observe two asteroids using the Finnish ASPECT camera (Asteroid Spectral Scanner), which will take Dimorfo images in the visible and near-infrared wavelengths with a resolution of up to 1 meter. It also features a VISTA dust detector (Field Thermogravimetric Volatile Analyzer), camera and lidar. The cubesat is named after Andrea Milani, a mathematics professor at the University of Pisa who has collaborated with ESA on several asteroid missions. The original name of the cubesat was APEX (Asteroid Exploration Explorer). Milani will observe Dimorpho from about 10 kilometers, and then from 2 kilometers.

On the other hand, Juventas’ goal is to analyze Dimorpho’s internal structure using JuRa radar (Juventas Radar), with two retractable antennas of 1.5 meters each (the YRa design is a simplified version of CONSERT from Rosetta). JuRa is a collaboration between France, Germany and Luxembourg. In addition, Juventas has a camera, LIDAR and GRASS instrument (Gravimeter for studying small bodies of the Solar system), the contribution of Belgium and the Spanish company EMXYS to the measurement of the gravitational field of two bodies. It will initially be placed in orbit around Didyma, perpendicular to Dimorpho’s. Then, at the end of the mission, it will use its simple nitrogen propulsion system to orient itself and attempt to land on the asteroid. For her part, at the end of her mission, Hera could try to land on Didymus.

In November 2024 and February 2026, Hera will perform two deep space maneuvers to adjust its trajectory. Hera will pass by Mars on March 12, 2025, at a distance of 6,000 kilometers and approximately 1,000 kilometers from Deimos. In October 2026, it will make its final maneuver to rendezvous with the binary system. When Hera arrives at Didim in December 2026, it will be 195 million kilometers from Earth.

It makes sense that Hera would be launched in order to be able to observe the effects of DART live. And indeed, that was the original plan. In 2015, ESA introduced the AIM probe (Asteroid impact mission), the European part of the AIDA mission (Asteroid impact and deflection assessment), which the US facilitated with DART (Double Asteroid Redirection Test). AIM was intended to include more specialized landers such as MASCOT 2. But in 2018, AIM was canceled for budget reasons and a simplified version called AIM-Lite or AIM-D2 was initially proposed instead (Asteroid Impact Mission – Deflection Demonstration), and then Hera. To save budget, Hera would be released four years after DART (it would end up being only two years later because DART was delayed too). In turn, AIDA was a version, implemented in cooperation with the United States, of other entirely European proposals such as the Spanish Don Quixote mission. Looking to the future, ESA wants to launch the Hera-based RAMSES probe in 2029 to study the asteroid Apophis. But first, at the end of 2026, Hera will show us the state of Dimorph.