(Photograph) - Paul Murdin (pictured) is director of science and microgravity at the British National Space Centre, the organisation that oversees research funds for British space studies. He has seen at least two attempts by the US to persuade the British to participate in the International Space Station.

"There have been lots of opportunities for us to join," he says, "and people who are in the project are motivated to keep asking us because the fact that one major nation takes this independent 'we don't want to join you' stance is damaging to its credibility."

The latest attempt to get Britain to join, a debate initiated by the prime minister's office, was two years ago. Murdin managed the process that looked at the arguments for British scientists participating in the space station. There were several options offered by Nasa.

"The largest scenario was: did we want to spend Pounds 100 million on sending a module? The smallest was: did we want to send an astronaut to Houston for training that wouldn't cost us anything? In fact," Murdin adds, "it would have cost us something - it would have cost us that person, an enthusiastic gung-ho chap, or lady, by taking them out of the job they were in and we'd have to pay."

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The criterion used by the group assessing the request was: what could we (the British) get out of it? Murdin revealed how this applied to one intriguing suggestion - that Britain supply ion engines to the space station to provide a continuous boost that would maintain it in orbit. At the moment, the station has chemical propulsion rockets that are made to fire after the station has drifted into a lower orbit. The thrust then raises it higher and switches off, until the station has drifted down again.

"That was particularly interesting," says Murdin, "because we have a certain kind of expertise not available in the US, at Marconi and at Dera (the Defence Evaluation Research Agency). The question is: what would we get back? In the case of the engine, we managed to find industry willing to supply it, but they didn't think it would be beneficial. In some ways they thought it would be a hindrance, by giving away secrets to the US.

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"The argument that carries weight with me is that the space station is an essential next step towards the exploration of the Moon and planets. There is a body of knowledge to be gained by simply being in space for long periods. But is this the time to do it? Maybe later is better, when it's not as difficult," he says.

Many of the American space scientists admit that in the end the enterprise is principally a romantic one. "If it were romantic and cheaper I'd have no difficulty with that," says Murdin.