"Ultimately what they are planning is a Chinese space station in about 2008 or so," said Brian Harvey, the Irish author of a book about China's space program. "To do that they will need to learn about how to survive on longer missions."

This is exactly what Shenzhou VI is all about, according to analysts of China's ambitious space program.

China's first man in space, Yang Liwei, spent his day in orbit two years ago strapped into his seat doing nothing much at all. Now the time has come for realistic experiments on how to survive in space for lengthy periods of time.

"This is obviously a very short mission compared to what the Americans and particularly the Russians are used to, but they need to build up their own experience in this area," said Harvey.

"So it's really doing the necessary groundwork for flying an orbiting space station."

Shenzhou VI also prepares for the space station by giving China experience in maintaining entire communities in space.

"You don't live in space alone, you live in space in groups and building towards, if you will, societies," said Joan Johnson-Freese, an expert on China's space program at the US Naval War College.

"So you want to show that you can actually have a working and living environment for more than one person," she said.

Once the Shenzhou VI crew is safely back on earth is when some analysts will start paying real attention.

One of them is Philippe Coue, the French author of a book on China's astronauts, who points out the space station will be based on existing Shenzhou technology.

China is most likely to launch two Shenzhou craft in 2007 so there will be two orbiting modules in space at a time, making a docking operation possible.

"If the operations proceed well, there will be a docking operation, and then in late 2008 or early 2009, a space station," said Coue.

That will still just be a small space station, smaller even than the original spartan space lab.

"They will very likely take one of their orbital modules, which they are able to leave in orbit, and then send up another Shenzhou and dock with it," said Johnson-Freese. "It's pretty spartan, but it's certainly a technology advancement."

But it could be that China has much more ambitious plans than that, not least because it is excluded from the 16-nation International Space Station (ISS).

In a speech in Hong Kong last year, the chief designer of China's space program Wang Yongzhi said China would launch a permanent manned space mission "within 15 years."

What he had in mind might just possibly be a much larger, full-fledged space station. A 20-tonne space station has already been designed, but the challenge is to get it into orbit.

"That's depending on getting the new launch vehicle. So what you need to look for will they develop the new heavy-lift launch vehicle," said Johnson-Freese.

"If they are going to do that it should be within the next five years that they will actually get it off the ground. If that happens, then the big space station can follow. But that's a prerequisite for the larger station."

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