China postpones Chang'e 7 robotic lunar mission

China's Chang'e 7 robotic lunar mission has been postponed, the China Manned Space Agency announced on Sunday.

In a brief statement, the agency said that after comprehensive assessments, the Chang'e 7 mission headquarters had reached a conclusion that the lunar expedition cannot be carried out within this year's scheduled launch window as it had failed to meet launch criteria.

The decision was made in accordance with the principles of prudence, reliability and absolute safety, the statement explained without providing more details.

A launch window is a specific period of time during which a rocket must lift off in order to reach its intended orbital destination.

According to experts, choosing a launch window for a space mission is not a matter of convenience, but a mixture of multiple factors that require careful calculations.

Because Earth rotates on its axis and the target, such as the moon or another planet, is also moving, the geometry between the launch site and the final destination changes constantly. A rocket can only reach its preset position when all the orbital, communication and other conditions align simultaneously. If the liftoff point misses that window, the mission must wait until the next opportunity, which could be days, weeks or even months later.

While the Earth-moon transfer windows open roughly once a month, Chang'e 7's destination — the lunar south pole — imposes far stricter constraints, restricting usable launch opportunities to just one or two per year.

The Chang'e 7 is set to become China's seventh robotic mission to the moon, tasked mainly with searching for traces of water on the silver celestial body.

A Long March 5 carrier rocket, with the Chang'e 7 probe on top of it, was moved to its launch service tower at the Wenchang Space Launch Center in Hainan province on Wednesday, when the space agency announced that launch would take place "in due course in the coming days".

The Chang'e 7 was transported by air to the coastal spaceport in April, while the Long March 5 rocket arrived in July by ship.

They were assembled and tested at the spaceport.

To date, China has conducted six robotic missions to explore the moon. The most recent, a 53-day Chang'e 6 mission, took place in the summer of 2024, representing the world's first attempt to bring back samples from the far side of the moon.

The historic mission successfully retrieved a total of 1,935.3 grams of samples from the far side.

zhaolei@chinadaily.com.cn