China will start the second round of astronauts selection to replenish a more demanding mission that will complete orbiter docking, said Deng Yibing, chief engineer of the astronaut training center yesterday.

The selection will start after the Shenzhou-7 mission ends, which accomplished China's first spacewalk yesterday afternoon. Excellent candidates from the fresh team may be involved in the Shenzhou-10 mission, which will seek a breakthrough in the orbiter docking technology, a more demanding job, Deng told reporters in the news center of the Shenzhou-7 manned space program.

China picked the first batch of 14 astronauts in 1998 in preparation for the country's manned space flights. The country sent its first man into space in 2003 in the Shenzhou-5 spacecraft. Two years later, two men orbited the earth in Shenzhou-6. The current Shenzhou-7 mission carried three astronauts.

Some of the first 14 astronauts are still capable of fulfilling the Shenzhou-10 mission as their ages and skills will not be a problem," said Deng.

But some of them will have to retire because of age, said Huang Weifen, deputy designer of Shenzhou-7's astronaut system, on Saturday. The retired astronauts will join the training programs or the management team, according to Deng.

To master the orbiter docking technology, China's second step before the ultimate goal of building a permanent space station, is a very complicated job, and has higher demands on astronauts, Deng said.

As the docking has to be partly assisted by manual operation of astronauts, Deng said, they should be selected "very cautiously" and they have to go through "rigorous" training to qualify the mission.

The docking technology will first be tested on the unmanned Shenzhou-8 and Shenzhou-9 spacecraft. The manned mission will be launched if everything goes well, said Li Yuqing, a consultant of the spacecraft system of the Shenzhou-7 mission.

Aerospace expert may also have the chance to fly aboard Shenzhou-10, and the physical requirement for them will be less tougher than that for astronauts, said Huang Weifen.