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Expedition tasked with number of firsts for China
Last Updated: 2020-11-25 08:55 | China Daily
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A Long March-5 rocket, carrying the Chang'e-5 spacecraft, blasts off from the Wenchang Spacecraft Launch Site on the coast of southern island province of Hainan, on Nov 24, 2020. [Photo/Xinhua]

The Chang'e 5 lunar mission will need to overcome a succession of challenges and difficulties before it can be declared a complete success, project insiders said.

Mission spokesman Pei Zhaoyu said Chang'e 5 will be the first Chinese spacecraft to carry out sample collection and launch operations on an extraterrestrial body, and these maneuvers will be extremely demanding and sophisticated in terms of technology and engineering complexity.

After the samples are collected and packed into the ascender, it will need to be lifted into lunar orbit to rendezvous and dock with the combined orbiter and re-entry capsule in an exceptionally accurate, delicate manner. Otherwise, it will be damaged and fail to deliver the samples, he added.

Even at the very beginning of the mission, Chang'e 5 had to go through some new operations, said Pei, who is deputy director of the China National Space Administration's Lunar Exploration and Space Program Center. He explained that it was the first Chinese lunar mission to use the Long March 5 heavy-lift carrier rocket and the Wenchang Space Launch Center in Hainan province. All the previous Chang'e programs were carried on Long March 3 rockets launched from the Xichang Satellite Launch Center in Sichuan province.

Yu Dengyun, deputy chief designer of China's lunar exploration program, said: "First of all, Chang'e 5's most important task will be collecting lunar samples. The environment on the lunar surface, such as the gravity there, is very different from that on Earth. So we must ensure that our technologies are functional and reliable during the collection and packing processes.

"The next challenge will be lifting the sample-carrying ascender from the moon. All of our launches so far were made from Earth, but the coming launch will take place on lunar soil and use the Chang'e 5's lander as the launchpad. Consequently, the challenge will be whether our equipment can handle the complicated operation as it was designed to do."

Previous rendezvous and docking by Chinese spacecraft occurred in low-Earth orbit-hundreds of kilometers above the planet-but this time it will take place in lunar orbit nearly 380,000 km away, Yu said.

The last challenge, he said, will emerge during the re-entry process as the re-entry capsule will descend through Earth's atmosphere at a speed of 11.2 kilometers per second, much faster than almost all previous Chinese spacecraft.

"The ultrafast speed will verify the aerodynamic design, heat-resistant materials and flight control system on the re-entry module," Yu said.

Reasons for predawn launch time explained

Many people have asked why the China National Space Administration chose to launch the Chang'e 5 in the early morning, which forced those wanting to witness the spectacular event to get up well before sunrise.

The robotic lunar probe was sent from the Wenchang Space Launch Center in the island province of Hainan, South China, at 4:30 am.

The launch time was decided by mission planners and rocket designers based on several considerations, said Qian Hang from the China Academy of Launch Vehicle Technology, which built the Long March 5 carrier rocket used to lift the probe.

"The first element we considered when choosing the launch time was the preferred trajectories and the relative position between Earth and the moon," said Qian, from the academy's general design department. "The selected time must fit with several requirements - from the trajectories of the rocket, the orbiter as well as the re-entry capsule."

The second factor taken into account was the sun.

"Launching the rocket before sunrise helped to avoid the impact of solar radiation on the rocket, especially a possible burst of solar wind," he said.

The third reason behind the early morning launch was the amount of cloud cover. At night, the cover is thinner, creating favorable conditions for signals communications between ground control and the Chang'e 5.

The last consideration was monitoring and tracking Chang'e 5 from the ground, Qian said. If the mission started in the daytime, the strong sunlight could "dazzle" the telescopes. Instead, the night sky allowed ground-based monitors to better track and observe the trajectory of the lunar probe after it separated from the rocket, he said.

(Editor:Wang Su)

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Expedition tasked with number of firsts for China
Source:China Daily | 2020-11-25 08:55
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