China’s Shenzhou-21 crewed spacecraft undocked from the country’s space station at 11:14 a.m. Friday (Beijing time) and has begun its mission to bring the Shenzhou-20 astronauts back to Earth, according to the China Manned Space Agency.

Shenzhou-21 will later re-enter the atmosphere and return via ground control, with astronauts Chen Dong, Chen Zhongrui and Wang Jie on board.

The Shenzhou-20 spacecraft does not meet the requirements for the astronauts' return and will remain in orbit to continue relevant experiments, said the CMSA.

Tiny cracks have been found in a viewport window of Shenzhou-20’s return capsule, most probably caused by the external impact from space debris, according to the CMSA.