The Chang’e-6 probe delivered the first samples of the far side of the Moon to Earth

For the first time, we have samples of the far side of the Moon on Earth. China’s space program has achieved a major milestone with the successful landing of the Chang’e 6 mission capsule with rocks and regolith from the hidden side of our satellite inside. The capsule landed as planned at 06:07 UTC on June 25, 2024 in the Banner Siziwang area of ​​the Inner Mongolia Autonomous Region (42°20’43″N, 111°25’05″E). Chang’e 6 is the second lunar sample return mission this century, following Chang’e 5, and the fifth successful automated sample return mission in history (in addition to the six manned Apollo missions that landed on the Moon). Weighing nearly a ton, Chang’e 6 is the fourth capsule to reenter the atmosphere from the Moon this century, following the Chang’e 5-T1, Chang’e 5 and Artemis I missions. The INTA station in Maspalomas (Gran Canaria) was responsible for accompanying the capsule on its final trajectory, thanks to an agreement between ESA and CNSA.

Previously, the capsule separated from the Chang’e-6 orbital segment at 05:22 UTC, approximately 5,000 kilometers from Earth. The orbiter performed a maneuver to avoid burning up in Earth’s atmosphere, and then at 05:41 UTC the capsule re-entered the atmosphere at 11.2 km/s – “second escape velocity” – over the South Atlantic. The capsule slowed down and exited the atmosphere again, then re-entered the atmosphere at a speed of about 8 km/s over the Indian Ocean. The device could continuously monitor the position of its center of gravity to adjust its trajectory during double reentry and thus maintain deceleration below a safety threshold. The parachute was deployed at an altitude of 10 kilometers. The capsule initially landed on its side, and rescue teams stood it upright before securing it and recovering it.

The Chang’e 6 capsule, like the Chang’e 5 T1 and Chang’e 5 mission capsules, has a similar shape to the Shenzhou manned capsules, although its dimensions are clearly much smaller. Unlike Shenzhou, the capsule hangs from the parachute not parallel to the ground, but at one point, so it contacts the ground in an inclined position. However, the Chang’e 6 capsule is not equipped with solid rockets like its manned version. In the coming days, we will know the exact number of samples that Chang’e-6 brought, although they are expected to be more than 2 kg (Chang’e-5 brought 1.7 kg, as it was unable to drill the drill to the maximum planned depth).

The Chang’e-6 mission was launched on May 3, 2024 at 09:27 UTC using the Long March CZ-5 Y8 vehicle. After trajectory correction, on May 8 at 02:12 UTC, it was launched into an initial retrograde orbit of 200 x 8600 kilometers with a residence period of 12 hours using the orbital segment engine. The small Pakistani cubesat ICUBE-Q launched the probe from this initial orbit on the same day at 08:14 UTC. In the following days, it was put into orbit with a period of 4 hours and, finally, into a circular orbit 200 kilometers long. On May 30, the descent segment separated from the orbital segment and reduced its periastron to 15 kilometers. On June 1 at 22:09 UTC, the descent stage engine ignited at periastron and final ignition began. Landing occurred on June 1, 2024 at 22:23 UTC in the outer rim of Apollo Crater, in the South Pole-Aitken impact basin (SPA). According to NASA’s LRO exploration team, the landing coordinates were 41.6385°S, 206.0148°E, with an altitude 5,256 meters below the average lunar radius.

After collecting samples from the far side using a drill and robotic arm and deploying a small mobile camera to photograph the probe on the lunar surface, the ascent phase of the mission’s ground segment took place on June 3, 2024 at 23:38 UTC. from the far side, leaving the descent step on the surface. During two days of activity, the Swedish solar wind sensor NILS (Negative ions on the lunar surface), delivered by ESA, operated for a total of three hours and confirmed for the first time the existence of negative ions on the lunar surface (in addition, NILS became the first official ESA instrument on the lunar surface). Six minutes later, the ascent stage was inserted into an initial orbit of 15 x 180 kilometers, and then raised the periastron to 50 x 180 kilometers. Once in a suitable position relative to the orbital segment, it performed another ignition to enter an orbit measuring 180 x 210 kilometers. As it approached the orbital module, it performed a final main ignition to make the orbit circular.

On June 6 at 06:48 UTC, the take-off stage was docked with the orbital segment using a system of clamps and rods, designed to level out the large difference in the masses of the two vehicles and, in addition, allowing for relatively important errors in tolerances. acceptable in terms of position and speed compared to other connection methods. The docking took place near the eastern border between the visible and hidden sides. Three clamps located in the orbital module were connected to three rods of the upper stage. For 1 second, the clamps were partially closed, and in the remaining 10 seconds, the system adjusted the closure sequence to align the vessels. During the last 10 seconds of docking, the relative position was fixed. The sample container was then transferred from the ascent stage to the orbital module’s return capsule using a mechanical rack transfer mechanism. The ascent stage then separated and will deorbit around June 8, colliding with the lunar surface.

For its part, the orbital segment ejected the docking system (before docking, it ejected the connecting cone with the landing segment) and waited in lunar orbit for the Earth and Moon to align so it could return to Earth. On June 20 at 15:38 UTC, the orbiter successfully completed its return to Earth cycle and was launched into a wide orbit with an inclination of 41.9 degrees relative to our planet. The study of samples from the hidden side of the Moon is a priority of the international scientific community due to the difference between this hemisphere and the visible one (the crust of the hidden side has a smaller surface area covered with basalts Maria due to greater thickness). Additionally, the South Pole-Aitken Basin (SPA) is the oldest and largest on the Moon. Studying it will allow us to better date the history of our satellite and understand its evolution. NASA has proposed several New Frontiers-type missions to return samples from the far side of the Moon, as is the case with the MoonRise proposal, but none have come to fruition. Be that as it may, today, 55 years after Apollo 11 brought back the first lunar samples, there are already rocks and regolith on the far side of the Moon on Earth.

Video of the landing of the Chang’e-6 capsule (remember that the capsule is similar in shape to the capsule of the Shenzhou ships, but smaller). pic.twitter.com/o3JmvjwyqW

— Daniel Marin (@Eurekablog) June 25, 2024