The Shenzhou-9 spacecraft and its carrier rocket, the Long March-2F, are transferred to the launch pad at the Jiuquan Satellite Launch Center in Gansu Province on Saturday. The manned spacecraft is expected to be launched later this month to dock with orbiting Tiangong-1 space lab module. Photo: CFP

Three astronauts will be sent to space in mid-June to perform China's first manned space docking mission, marking a breakthrough in grasping essential technology and moving a step closer to building a space station around 2020.

It will also be the first time China sends female astronauts into space, though the list of names has yet to be revealed.

The Shenzhou-9 manned spacecraft and its carrier rocket, the Long March-2F, were vertically transferred to the launch pad at the Jiuquan Satellite Launch Center in Gansu Province on Saturday, and will dock with the orbiting Tiangong-1 space lab module later this month, a spokesperson with China's manned space program told media.

June 16 afternoon has been selected as the first launch opportunity, Chinese media quoted an anonymous insider as saying.

The Shenzhou-9 is expected to stay in space for 15 to 20 days, and the astronauts will conduct experiments inside the Tiangong-1 lab module.

This will be the first manned space docking carried out by China. The unmanned Shenzhou-8 spacecraft has twice successfully docked with the Tiangong-1 by remote control since November.

"It means China's spacecraft will become a genuine manned shuttle tool between space and Earth. It can send human beings to space stations or space labs," said Zhou Jianping, chief designer of the manned space program.

Tiangong-1, which blasted off in September 2011, was lowered to docking orbit in early June and is orbiting normally, said Zhou.

Tests will be conducted on the spacecraft and the rocket as well as the astronauts in the next few days.

Manned space docking is a technique that is essential to master, as it has a higher success rate than automated, unmanned space docking, experts said.

"The advantage of manned space docking is that astronauts can take immediate action should anything go wrong during the process," said Pang Zhihao, managing editor of Space International magazine hosted by the China Academy of Space Technology.

Pang said China still lags behind the US in terms of space exploration technology, but China is the third country in the world to independently master the three basic techniques of human spaceflight, space walking and space docking.

"This paves the way to independently building a space station in the future," said Pang.

China has spent billions of dollars to boost space exploration in recent years. In 2003, China successfully launched its first human spaceflight and in 2008 Chinese astronauts made the first space walk.

China plans to launch its own manned space station around 2020, by which time international space stations are expected to retire, possibly leaving China as the only country with a space station.

Last year, the government announced a five-year plan for space exploration, which revealed that China plans to launch two space labs and explore manned moon-landing by 2016.

The docking will also put under the spotlight the first Chinese female astronaut to go into space.

The two female astronauts were chosen according to the same criteria as men in 2009 and have been undergoing training. The two candidates, Liu Yang from Henan Province and Wang Yaping from Shandong Province are both 34 years old, and married with children.

"Female astronauts are more sensitive and better at communication, which will be beneficial in long, arduous spaceflights," said Pang.

Xinhua contributed to this story