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How do you weigh the need for vicarious heroes against the stunning drain on finances if you fly people to Mars? With huge difficulty, it seems. But according to Martin Turner, the effort and cost will be worth it. As preparation for the arguments back and forth about the choice between flying just the mind, or flying its wetware too, Expedition Mars (Springer Verlag, £24.50) is a good launch pad for a survey of the technology we have and what we will need to make that expedition a reality. He tackles it all – from Wernher von Braun and the…