Given the small number of crew needed for an initial programme of missions, it ought to be possible to select from the population of the Earth a number of superbly able and healthy people who simply accept the risk.

I sometimes suspect that the proposers of sending older people to Mars are getting on a bit themselves and wish for a spot they otherwise would be denied. (Nothing personal Mr Bright, I'm sure you'd be an admirable astronaut and I'd happily launch with you if we were given the chance). You don't need to select crew from a subset for whom the calculus of risk of death versus ongoing life on Earth is different in some way. You just need crew who are willing to take the risks, whatever their reasons.

NASA selects superbly fit people because they can. I don't see the crises one is likely to encounter in space are ones that superb fitness is going to help much.

There's no way I'm going in a tin can to Mars :-) so that's not my motivation.

I'm sure there are many young people who would be willing to go on a one way ride to Mars and certain death. I suspect that would be politically impossible, though.

I'm sure there are many people who want to launch me on a one way trip to Mars!

Most if the machinery could be tried on the moon first. If we adopt a Mars Direct approach, a return vessel with in-situ refuelling capability would arrive and recommissioning itself before the crew even left Earth, and we might even trial the return vehicle in an automated there-and-back mission first. With all these factors, I think the chances of success could probably be improved to perhaps 90% arrival and 70% return. Pure guesses though, of course.

I agree that establishing a self-sustaining moon base would be far more achievable and useful, and would make a Mars mission a lot more practical.