By Jonathan Amos Science correspondent, BBC News
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 Gansu Province is likely to occur between 21:16 and 21:31 local time (13:16-13:31 GMT).
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 300-400km-high orbit and will be untended 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.