Already mired in financial problems, the ISS ran into a colossal technical hitch in February with the loss of the US shuttle Columbia.

That left only three shuttles, causing a chain delay all along the ISS assembly programme and casting a shadow over whether the platform would ever be used for serious scientific research.

The disaster has postponed construction by at least a year, reduced the outpost to a skeleton crew and inflicted a crippling blow to the US capacity to haul spars, modules and heavy equipment to assemble mankind's only home in space.

That means only the Russians, the cash-strapped junior partner to the Americans in the 16-nation US-led programme, now have the capacity to service the ISS, using Soviet-era hardware to provide a lifeboat, rotate the crew and bring up fresh supplies.

But, if China so wanted -- and the United States swallowed its pride -- Chinese spaceships could also join the programme, experts say.

"The Chinese government wants to show the populace that it can carry out top-notch achievements in space, and demonstrate to people abroad that it has joined the big boys," said a specialist with the French agency CNES.

"Beijing especially wants to get the message across that it has the credentials for joining the ISS."

Apollo moonwalker Buzz Aldrin, in an interview with the specialist news website space.com, said NASA should extend "a hand of welcome" to China's taikonauts at the ISS.

It should hire China to provide a Shenzhou lifeboat for the space station in 2006, when the present generation of Russian Soyuzes -- the model from which Shenzhou's capsule is inspired -- have to be replaced there, he said.

"I don't think we need to have a knee-jerk reaction," Aldrin said. "I think we calmly welcome them into the orbital flight regime. We should offer to work out some mutually attractive means of advancing both of our interests."

It will take time for Washington to digest the Shenzhou flight and decide whether to invite the Chinese aboard its prestigious but cash-burning project, said Doug Millard, curator of space science at the Science Museum in London.

"This is a big, geopolitical question, a lovely symbol of how the world is changing as China emerges," he said in an interview.

"The problems are political more than technical. The (Shenzhou) mission could be used (by China) as some sort of bargaining counter, although it will also reinforce concern in some American quarters about what the future holds as far as China is concerned."

If the United States rejects the idea of a Chinese role in the ISS, Beijing would still have the option of assembling its own space station, using Shenzhou's orbital module -- left aloft after the capsule, containing its human cargo, separates and heads for home -- as the first building block.

"It would be like Mir," Millard said. "Mir worked and despite all the problems, it delivered. China may well go for this utilitarian solution."

SPACE.WIRE