BEIJING (AP) — A group of Chinese astronauts faces a delayed return to Earth after their spacecraft was believed to be struck by a small piece of debris.

Their return, originally scheduled for Wednesday, will be pushed back to an unspecified date, according to state broadcaster CCTV, which offered no further details.

The three astronauts from the Shenzhou-20 mission flew to the Tiangong space station in April and were finishing their six-month rotation. The group consists of team leader Chen Dong, fighter pilot Chen Zhongrui and engineer Wang Jie.

Their replacements on the Shenzhou-21 mission had successfully docked onto the space station on Saturday.

China has made steady progress with its space program since 2003. It has built its own space station and has a goal of landing a person on the moon by 2030.