Shenzhou 8, which will dock at the space station in 2011, will be unmanned, whereas Shenzhou 9 will carry crews to the station, Qi said.

Space docking is one of the most complicated aspects of the project because two crafts traveling at high speed will meet and connect together, said Su Shuangning, deputy general designer of China's manned space program.

"It is like pulling a thread through a needle's eye that is hundreds of kilometers away," said Su. As both the spacecraft and the space station are flying at speeds of more than 28,000 km per hour, any error in the docking process may lead to collision.

The ability to dock is critical to the program, as it allows for the delivery of supplies and personnel. After two modules connect, they will become a single unit so that astronauts can walk freely from one to the other, said Qi.

In the third stage, China will build a permanent space laboratory and a space engineering system. Astronauts and scientists will shuttle between Earth and the space station to conduct large-scale scientific experiments.

All the rockets and spacecraft use technology developed by scientists in China and the astronauts were also trained in the country, said Qi. The program's first stage costs less than 20 billion yuan ($2.93 billion), said Zhang Jianqi, deputy chief commander of China's manned space program.

The heavenly palaces

Tiangong I consists of a laboratory module and a service module. The laboratory module has controlled pressure, temperature, humidity and air so that astronauts can live and work in it. The service module supplies energy to power the spacecraft.

"Tiangong I is the first step in space station construction. We are going to build larger space stations in the future," said Zhang Luqian, a space science researcher in the Chinese Academy of Sciences. He said that astronauts work with sensitive equipment to observe incidents on Earth like earthquakes, tsunamis and volcano eruptions.

China is going to launch Tiangong II and Tiangong III around 2015, according to CNSA. Tiangong II will be primarily used for Earth observation and Earth science research. It will also be home to work in aerospace medicine and space science and technology. Tiangong III will focus on research in regenerative environmental control and life support systems, while it will also conduct experiments in space science and aerospace medicine.

In the third stage of the manned space program, a large space station attended by humans over the long term was scheduled to be launched in 2020, said Wang Zhaoyao at the conference held immediately after the return of Shenzhou 7 spacecraft.

Qi Faren, the chief designer of the Shenzhou family of spacecraft said that the large space station would comprise one core module, two experimental modules and one node module. The core module, which will be 20 tons in weight, will have multiple berthing mechanisms so that it can connect with a lifeboat or cargo spaceship.

The space station will be able to defend itself from space debries, Qi said. Space junk has caused concerns about the safety of spacecraft and space stations. Chinese scientists have attached great importance to research on space safety, said Qi. And research has already been done in this area- there is even a dedicated journal in China that covers space debris research.

"To make a spacecraft or space station safe from debris, there are three technical issues to be solved," Qi said. "Scientists must be able to observe and monitor the debris so that we can forecast its movement; then we should be able to dodge the debris. For instance, we can postpone the launch of the spacecraft or space station. In case dodging fails, a spacecraft or space station should be equipped with armor to fend off hits."