The descent of the spacecraft on the dark side of the moon is revealed

Earlier this year, on January 3rd, the Chinese Chang'e-4 (CE-4) probe made a historic first landing safely on the other side of the Moon.

All previous landings, whether inhabited or robotic, were nearby, including the Chang-e-3 from China, safely arrived in 2013. Landing on the underside is harder because, with the bulk of the moon annoying, the mission The controllers on Earth have no direct way to communicate with the lander.

To solve this problem, the Chinese space agency began by launching a communications satellite called Queqiao in a fixed orbit about a million kilometers above the moon. This allowed him to relay signals between Earth and Chang'e.

Thanks to this, the Chinese team was able to conduct investigations on the moon, including piloting and collecting data on the mobile of Chang & # 39; e-4, Yutu-2, which has so far traveled 285 meters of the lunar surface and among other things. , discovered rocks that seem to have been ejected from the mantle of the moon by an old and deep impact.

But one thing was elusive: Change'e-4 was not visible from Earth and no one was really sure of its exact location. Of course, they knew that the crater Von Kármán, a 180-kilometer depression in the southern hemisphere of the Moon, was almost facing the Earth. But in the absence of radio tracking or telemetry on Earth, the exact location was not known precisely.

To find it, Jianjun Liu, of the Chinese Academy of Sciences in Beijing, and his colleagues used images of the spacecraft's landing camera, retransmitted to Earth by the Quequiao satellite after landing, to replenish the trajectory of the spacecraft during its descent. They also used pictures of the Chang'e landing site returned by the Yutu-2 rover at the beginning of his explorations.

Based on this information and maps of the lunar dark side provided by NASA's Lunar Reconnaissance Orbiter, Chinese scientists were able to not only locate the landing site of the spacecraft within a radius of two meters, but also deduce its descent trajectory, the autopilot looking for a safe. Landing site.

According to Liu's team, "we have reconstructed the trajectory of the descent, illustrating barely perceptible maneuvers of the space shuttle during the approaching landing," said the Liu team: "We have reconstructed the trajectory of the descent.

The result, says a non-Chinese scientist, who asked not to be identified to be considered an "interested observer" rather than an expert on landings on the moon, seems to be primarily a technical study of "how they performed the landing and the lander understood the terrain to stay near the target and not landing on a big rock. "

The scientist adds, "I can imagine that NASA engineers will find this very interesting when planning the next landing mission, somewhere.

Liu's team said this discovery was also important for the Moon's orbital maps undergoing ground verification. "As a permanent artificial marker on the far side of the moon, the location of the LG CE-4 (…) can serve as a potential checkpoint," they write. "The result will provide a valuable geodetic data point for … the subsequent lunar exploration."

The results are published in the journal Nature Communications.