The Shenzhou XX mission crew members aboard China's Tiangong space station completed their first spacewalk on Thursday afternoon, the China Manned Space Agency said.

During the eight-hour operation, mission commander Senior Colonel Chen Dong and crew member Colonel Chen Zhongrui floated out of the Tianhe core module and installed debris-shielding devices, which had been put in place by the robotic arm before the spacewalk.

The pair also checked the condition of extravehicular instruments and fixed broken parts, according to the agency.

They returned to the space station at 4:49 pm. The mission's third astronaut, Colonel Wang Jie, stayed inside the space station and worked with ground controllers to provide assistance to the spacewalkers.

The spacewalk was the 21st that Chinese astronauts have ever carried out, and marked the fourth time Chen Dong floated outside the Chinese space station. He previously took part in three spacewalks during the Shenzhou XIV mission.

Thursday's spacewalk was the first for Chen Zhongrui.

Chen Dong and his teammates have been aboard the station since their arrival on April 25.

Before the spacewalk, they had conducted a host of assignments, including examining and performing maintenance on instruments, installing intravehicular devices, monitoring the space station environment and testing spacewalk suits.

The astronauts had also rehearsed medical emergency response efforts and engaged in scientific and technological tasks.

The Shenzhou XX crew is conducting China's 15th manned spaceflight and has become the ninth group of astronauts aboard Tiangong, which is currently the only operational space station independently run by a single nation.

Their predecessors in the Shenzhou XIX flight made three spacewalks during their six-month mission.

Orbiting Earth at a distance of about 400 kilometers, Tiangong has three permanent parts — a core module and two science capsules — and is regularly connected to several visiting crew and cargo spaceships.

zhaolei@chinadaily.com.cn