China's Chang'e-6 lands on moon's far side to collect samples

BEIJING, June 2 (Xinhua) -- China's Chang'e-6 touched down on the far side of the moon on Sunday morning, and will collect samples from this rarely explored terrain for the first time in human history, the China National Space Administration (CNSA) announced.

Supported by the Queqiao-2 relay satellite, the lander-ascender combination of the Chang'e-6 probe successfully landed at the designated landing area in the South Pole-Aitken (SPA) Basin.

Chang'e-6 consists of an orbiter, a returner, a lander and an ascender. Since its launch on May 3 this year, it has gone through various stages such as Earth-moon transfer, near-moon braking, lunar orbiting and landing descent. The lander-ascender combination separated from the orbiter-returner combination on May 30, said the CNSA.

The landing site is at an impact crater known as the Apollo Basin, located within the SPA Basin. The choice was made for the Apollo Basin's potential value of scientific exploration, as well as the conditions of the landing area, including communication and telemetry conditions and the flatness of the terrain, said Huang Hao, a space expert from the China Aerospace Science and Technology Corporation (CASC).

Huang added that the terrain on the far side of the moon is more rugged than the near side, with fewer continuous flat areas. However, the Apollo Basin is relatively flatter than other areas on the far side, which is conducive to landing.

After the landing, the probe is scheduled to complete sampling within two days. It has adopted two methods of moon sampling, which include using a drill to collect subsurface samples and grabbing samples on the surface with a robotic arm.

According to Jin Shengyi, another space expert from the CASC, the Chang'e-6 probe development team has built a simulation lab in advance to ensure a smooth sampling process.

The team members will set up a full-scale replica of the sampling area based on Chang'e-6 exploration results on the environment, rock distribution, and lunar soil conditions around the landing site. Using this simulation, they will develop and verify sampling strategies and equipment control procedures to ensure the accuracy of instructions.

Due to the moon's obstruction, the Earth-moon communication window period on the far side of the moon, even with the help of the Queqiao-2 relay satellite service, is still shorter than that on the near side. Therefore, the sampling time of Chang'e-6 will be reduced to about 14 hours, compared with the 22 hours used by its predecessor Chang'e-5.

To save time and improve efficiency, the development team has made the sampling process more intelligent, allowing Chang'e-6 to execute instructions and make judgments autonomously to reduce the Earth-moon interactions, Jin said.

For example, after the ground control sends an instruction, the probe will execute the corresponding program in multiple actions and then use the real-time data collected by the sensors to evaluate if the instruction is well executed, thus autonomously working in a closed loop without the ground control sending command on each action.

About 1,000 instructions were sent during the entire sampling process of Chang'e-5. For Chang'e-6, the number is expected to be reduced to about 400.