BEIJING (AP) — Two Chinese astronauts went on a spacewalk Saturday from a new space station that is due to be completed later this year.

Cai Xuzhe and Chen Dong's installed pumps, a handle to open the hatch door from outside in an emergency, and a foot-stop to fix an astronaut's feet to a robotic arm, state media said.

China is building its own space station after being excluded by the U.S. from the International Space Station because its military runs the country's space program. American officials see a host of strategic challenges from China’s space ambitions, in an echo of the U.S.-Soviet rivalry that prompted the race to the moon in the 1960s.

The latest spacewalk was the second during a six-month mission that will oversee the completion of the space station. The first of two laboratories, a 23-ton module, was added to the station in July and the other is to be sent up later this year.

The third member of the crew, Liu Yang, supported the other two from inside during the spacewalk. Liu and Chen conducted the first spacewalk about two weeks ago.

They will be joined by three more astronauts near the end of their mission in what will be the first time the station has six people on board.

China became the third nation to send a person into space in 2003, following the former Soviet Union and the United States. It has sent rovers to the moon and Mars and brought lunar samples back to Earth.