BEIJING • Over about 12 dramatic minutes, China's Chang'e-4 probe descended and softly touched down on a crater on the far side of the Moon yesterday in a space first.
The probe, comprising a lander and a rover, landed at a pre-selected landing area at longitude 177.6 deg east and latitude 45.5 deg south on the far side of the Moon at 10.26am, the China National Space Administration announced.
Chinese space experts chose the Von Karman Crater in the South Pole-Aitken Basin as the landing site for Chang'e-4, amid rugged, high mountains and lofty hills.
Measuring 180km in diameter, Von Karman is relatively flat in its bottom, which made it the best choice for landing. The landing site was surrounded by mountains as high as 10,000m.
One of the designers of the lander, Mr Li Fei, said that when the process began, an engine was ignited to lower the craft's relative velocity from 1.7km per second to close to zero, and the probe's attitude was adjusted to face the Moon and descend vertically.
When it descended to an altitude of about 2,000m, its cameras took pictures of the lunar surface so the probe could identify large obstacles such as rocks or craters, said Mr Wu Xueying, deputy chief designer of the Chang'e-4 probe.
At 100m above the surface, it hovered to identify smaller obstacles and measure the slopes on the lunar surface, Mr Wu said. After calculations, the probe found the safest site, and continued its descent.
When it was 2m above the surface, the engine stopped, and the spacecraft landed, with four legs cushioning against the shock.
Chang'e-4 made an almost vertical landing, said Mr Wu Weiren, chief designer of China's lunar exploration programme.
Mr Zhang He, executive director of the Chang'e-4 probe project, from the China Academy of Space Technology, said: "We chose a vertical descent strategy to avoid the influence of the mountains on the flight track."
The whole process was automated, with no intervention from ground control, but relay satellite Queqiao (Magpie Bridge) transmitted images of the landing process back to Earth, he said.
The relay satellite was launched in May and is now running on a halo orbit about 65,000km from the Moon, where it can see both Earth and the Moon's far side.
The Von Karman Crater is named after a Hungarian-American mathematician, aerospace engineer and physicist and is located within the Aitken Basin, the largest, deepest and oldest crater in the solar system. The Aitken Basin is about 2,500km in diameter and 13km in depth.
The basin may contain information about the Moon that has so far eluded scientists, such as whether it once had water. Exploration in this area will also provide first-hand data and clues on the evolution of the Moon, Earth and solar system.
An alternative site had been identified in case the landing was not successful. This was the Chretien Crater, situated about longitude 13 deg away from Von Karman. The plan was that if Chang'e-4 failed to touch the surface of Von Karman on the first day, it could land in the alternative area on the second day.
Chang'e-4 began its life as a backup for China's Chang'e-3 probe, which was launched in 2013 and was the first Chinese spacecraft to soft-land on and explore an extraterrestrial object.
Many of the components and parts for the probes were designed and manufactured together. However, Chang'e-3 landed on the Sinus Iridum, or the Bay of Rainbows, on the moon's near side.
XINHUA
