As part of the current mission, the Shenzhou XI-Tiangong II combination will test rendezvous and docking technologies, verify the life-support capability of the spacecraft-space lab combination, conduct research and test engineering experiments, according to Wu Ping, deputy director of the China Manned Space Agency.

The journey's most important task is to examine China's technologies and equipment to support long-term stays in space and to observe the physical and psychological effects on astronauts, explained Shi Yong, a senior designer of manned spacecraft at the China Academy of Space Technology.

He said Jing and Chen will use a treadmill, exercise bike and other equipment in Tiangong II to keep fit, and they will also wear a special uniform to avoid muscle atrophy.

Zhang Bonan, chief designer of Shenzhou XI at China Academy of Space Technology, said the reason the spacecraft is carrying two astronauts instead of three like its predecessor, the Shenzhou X, is that the spacecraft and space lab have a limited accommodation capacity. Also, the astronauts' duration in space is longer.

The Tiangong II's life-support system does not use recycling technologies, which limits the number of astronauts, he said, although future additions to the space station will include such technologies.

Experts said the Shenzhou XI-Tiangong II mission, together with the previous missions, would pave the way for the nation's aspiration to have a permanent manned station, which planners say will consist of three parts — a core module that will be attached to two labs, each weighing about 20 metric tons.

China plans to launch the core module of the space station in about 2018 and complete the construction of the whole station around 2022.