The French DORN instrument successfully completes its lunar mission aboard the Chang’E 6 lunar probe

Launched on May 3 aboard a Long March 5 rocket from the Wenchang site, China’s Chang’E 6 probe completed a successful mission to the far side of the Moon, and has now brought back to Earth the first samples from this region of the Moon, at the end of a 53-day round trip. The probe carried several international payloads, including the DORN instrument, the first active French instrument to be deployed on the lunar surface.

The French DORN instrument was designed and built at IRAP, the Institut de recherche en astrophysique et planétologie (CNES/CNRS/Université Toulouse III – Paul Sabatier), under CNES contract management, in collaboration with CNRS and the Institute of Geology and Geophysics of the Chinese Academy of Sciences (IGG-CAS), who was responsible for the instrument after its delivery to China, and who participated with the French team and a team from the China University of Geosciences Beiijng (CUGB) in DORN operations in Beijing during the mission. DORN aims to study the origin and dynamics of the Moon’s very thin atmosphere, as well as the thermal and physical properties of the lunar soil, surface dust mixing, and to improve satellite measurements of uranium, by making the first measurements of radon and polonium, two radioactive tracers, on the lunar surface.

The instrument was switched on for the first time on May 6 during the cruise to the Moon, at a distance of 327,000 km from the Earth, for a duration of 10 hours. The aim of this first measurement was to measure the background noise of the space environment and any natural terrestrial contamination (the detectors having been exposed to terrestrial atmospheric radioactivity for several months).

On May 8, as the new Moon approached, Chang’E 6 successfully inserted itself into lunar orbit, on an elliptical trajectory with a 12-hour period, from which the Pakistani Cubesat iCube-Qamar successfully ejected, taking its first photos of the Moon.

This insertion was followed by a second braking maneuver on May 9 to move into an elliptical orbit with a period of 4 hours. It was in this orbit that DORN began its orbital measurements on May 17, a few days after the passage of the historical solar storm of May 10-11. These measurements were extended on May 18 and 19, for a total duration of 32 hours, during which several commands were sent to the instrument to control the volume of data produced. The few data sent back to Earth on this occasion enabled us to establish that the instrument’s 16 detectors were operating nominally. DORN was thus able to acquire data on the fluxes of charged particles in the solar wind and track their decay over time. The Moon’s shielding effect on these particle fluxes was also observed.

On May 22, Chang’E 6 passed into circular orbit around the Moon at an altitude of 200 km, with a period of around 2 hours. On the night of May 23, DORN was switched back on for a period of almost 5 days (111 hours), in order to carry out orbital measurements of radon and polonium distribution on the Moon.

As the sun rose over the landing site, Chinese engineers began the final orbital maneuvers on May 28, culminating in the perfectly successful landing of Chang’E 6 on June 2 in the Apollo crater, in the South Pole Aitken basin. A few hours after this critical step, and shortly after the first samples were collected, DORN was able to begin its measurements on the lunar surface. These were completed before the preparatory phases for lift-off of the sample return module, which took place on schedule on June 6. DORN, on the other hand, has ceased its mission and will not be returning to Earth. It is now an “eternal” resident of the far side of the Moon.

For the duration of the mission, a team of French scientists and engineers was able to take part in DORN operations in Beijing, from the National Astronomical Observatory Center (NAOC), in collaboration with the Chinese part of the DORN team, made up of researchers, engineers and students from the Institute of Geology and Geophysics of the Chinese Academy of Sciences (IGG-CAS), the China University of Geosciences Beijing (CUGB) and the China Academy of Aerospace Science and Innovation (CASI). This strong integration of the two parts of the team made the experiment a success.

About DORN

Started at the end of 2019, the DORN project is the first cooperation between France and China in the field of solar system exploration, and the result of a close and fruitful collaboration between the Institut de Recherche en Astrophysique et Planétologie (IRAP, CNRS/Université Toulouse III/CNES) and IGG-CAS, with the support of CNES, LESEC (Lunar Exploration and Space Engineering Center) of CNSA, the China Academy of Space Technology (CAST) and NAOC. Designed, developed, assembled and tested by IRAP (PI Pierre-Yves Meslin, project managers King Wah Wong and Aurélie Moussi from CNES), it was delivered to China in August 2023, where its responsibility passed into the hands of IGG-CAS (Co-PI Prof. He Huaiyu, project manager Li Jiannan), who supervised its integration on the lander and carried out interface tests.

The project was also carried out in collaboration with CEA (LNE-Laboratoire National Henri Becquerel), Observatoire Midi-Pyrénées (OMP), SUBATECH, GIP d’Arronax and Albedo Technologies, with scientific partners from Christian-Albrechts University in Kiel, Institut de Physique du Globe in Paris, and Centre de Recherches Pétrographiques et Géochimiques (CRPG, CNRS-Université de Lorraine).

Further Resources

• Press Release of the Université de Toulouse III
• Press Release of the CNES
• CNES Video : Succès de la mission Chang’e 6/DORN sur la face cachée de la Lune

IRAP Contact

• Pierre-Yves Meslin, Pierre-Yves.Meslin@irap.omp.eu