China is taking a stepped approach to the development of its human spaceflight programme
China is due to launch its first space laboratory, Tiangong-1.
The 10.5m-long, cylindrical module will be unmanned for the time being, but the country's astronauts, or yuhangyuans, are expected to visit it next year.
Tiangong-1 will demonstrate the critical technologies needed by China to build a fully fledged space station - something it has promised to do at the end of the decade.
The space lab is set to ride to orbit atop a Long March 2F rocket.
State media say the lift-off from the Jiuquan Satellite Launch Centre in the Gobi Desert is likely to occur between 21:16 and 21:31 local time (13:16-13:31 GMT). Meteorologists report that weather conditions should be good.
The Long March will put Tiangong in a near-circular path around the Earth, just a few hundred km above the surface.
It will operate in an autonomous mode, monitored from the ground. Then, in a few weeks' time, China will launch another unmanned spacecraft, Shenzhou 8, and try to link the pair together.
This rendezvous and docking capability is a prerequisite if larger structures are ever to be assembled in orbit.
Commentators say Russian technology, or a close copy of it, will be used to bring the two craft into line.
Assuming the venture goes well, two manned missions (Shenzhou 9 and 10) should follow in 2012. The yuhangyuans - two or three at a time - are expected to live aboard the conjoined vehicles for up to two weeks.
- Tiangong-1 will launch on the latest version of a Long March 2F rocket
- The lab will go into a 350km-high orbit and will be unattended initially
- An unmanned Shenzhou vehicle will later try to dock with Tiangong
- The orbiting lab will test key technologies such as life-support systems
- China's stated aim is to build a 60-tonne space station by about 2020
Tiangong means "heavenly palace" in Chinese. The programme is the second step in what Beijing authorities describe as a three-step strategy.
The first step was the development of the Shenzhou capsule system which has so far permitted six nationals to go into orbit since 2003; then the technologies needed for spacewalking and docking, now in progress; and finally construction of the space station.
At about 60 tonnes in mass, this future station would be considerably smaller than the 400-tonne international platform operated by the US, Russia, Europe, Canada and Japan, but its mere presence in the sky would nonetheless represent a remarkable achievement.
Concept drawings describe a core module weighing some 20-22 tonnes, flanked by two slightly smaller laboratory vessels.
Officials say it would be supplied by freighters in exactly the same way that robotic cargo ships keep the International Space Station (ISS) today stocked with fuel, food, water, air, and spare parts.
There has been much talk about China becoming involved in the ISS project itself, and the fact that it has adopted many Russian engineering standards would certainly make it technically possible for Shenzhou vehicles to visit the orbiting complex.
Europe, too, has argued that additional partners could help spread the cost of running what is an extremely expensive endeavour. But political differences between China and the US would appear to make such involvement unlikely in the near-term.
"These are decisions that have to be taken by the whole ISS partnership; everyone has to agree," says Karl Bergquist from the European Space Agency's (Esa) international relations department.
"You also have to see whether it is something which would interest a country like China, given their ambitions in space. They have advanced so far in their plans that they will probably go ahead and develop their own station," he told BBC News.
Thomas Reiter, the director of human spaceflight at Esa, was asked to comment on the status of China's space programme during a seminar this month at the London School of Economics.
"I think the Chinese want to prove to themselves and others that they are on a level," he said. "At that point, it becomes a moment for discussion on greater co-operation. We are certainly drifting towards each other."
The director said he could envisage the day when yuhangyuans made visits to European astronaut training facilities.
Currently, most of Europe's engagement with China falls in the area of space science.
Esa participated in the Double Star mission, a pair of satellites sent into orbit to study the Sun's interaction with the Earth's magnetic field.
There is also co-operative work in Earth observation, assisting the Chinese with the development of applications to interpret satellite data.
In the UK, manufacturer Surrey Satellite Technology Limited announced recently that it would be making three high-resolution imaging spacecraft for the purpose of mapping China.
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