The basic launch module technology is identical between Shenzhou V and VI, but experts have been able to count about 100 novelties.

And astronauts Fei Junlong and Nie Haisheng will be a great deal busier than Yang Liwei, China's first man in space who attained world fame after sitting in the same position for 21 hours while orbiting the earth 14 times.

"You will see a much bigger experimental package," said Brian Harvey, the Irish author of a book on China's space program.

"And obviously on a five-day mission, they will have much more time to carry out these experiments."

Technicians and scientists on the ground have been put to the test too, for this time life-support systems must be extended to last for five days rather than one, and be able to keep two astronauts alive at the same time.

"In Shenzhou V he was strapped to his chair, basically wore a diaper for bathroom uses," said Joan Johnson-Freese, an expert on China's space program at the US Naval War College.

"In this one, there'll be space bathroom facilities, they will have meals on board that they will be able to heat up, they will be able to work in a shirt-sleeve environment so it's moving forward in life-support capabilities."

Not all the new developments will be only in orbit. The Shenzhou spacecraft is merely the highly visible tip of the iceberg.

During the Shenzhou VI flight a "thorough, comprehensive test" of China's tracking system on the ground will take place, according to Harvey.

"They will also be testing out their tracking network, which has ground stations in China, but also they have four tracking ships that are deployed around the world, the Southern Ocean, in the South Atlantic, and they will have one in the Indian Ocean, and probably a fourth one in the north Pacific.

"They also have ground tracking stations, in Namibia, this is an important one because it is used for controlling the re-entry back into the earth's atmosphere."

David Baker, a London-based space policy analyst with Jane's Defence Weekly, said there are real challenges to five days in orbit rather than just one.

A certain level of confidence is needed, as the earth will spin underneath the spacecraft, meaning that at certain points it will inevitably be outside of any Chinese-controlled landing sites.

"It's really like crossing a mountain, and taking the amount of food and water you think you'll need, but knowing that you could very well run into problems, and you'd be far too far from home simply to dash back quickly," he said.

As the Shenzhou VI starts preparations for landing on the Inner Mongolian steppe in five days' time, the first crucial chapter in China's manned space program is nearing its conclusion.

"The first flight of the Shenzhou launch vehicle was really just to make sure that everything worked and that's not just in space but on the ground as well, the tracking, the communications, the data, the telemetry, all of those things," said Baker.

"The first one, you would always expect this to be very low-capability, but the vehicle, the spacecraft, the people involved are capable of much more, and that is now what is being extended, but these are test flights."

For all the novelty, China is not risking the lives of its astronauts, said Harvey.

"The last Shenzhou unmanned missions stayed up for up to five days, so they're not trying to do anything that their unmanned versions of Shenzhou have not done already," he said. "So I don't consider it to be a particularly risky mission."

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