As to microgravity... I would amputate everyone's legs. Thus reducing redundant weight and calorie intake, making them more manoeuvrable, leaving only their arms needing resistance weight training, and also making them take up less space in fact! Also removes any need for complicated centrifuges and such.
Amputate their legs!? :blink:
How do you expect them to walk again if/when they decide to return home? :shifty:
The problems of microgravity, namely muscoskeletal and cardiovascular decay, actually have very little to do with legs, and I have a feeling metabolic requirements don't either. In microgravity, you waste away, legs or not. This is because you- not your legs, not your arms, your entire body, essentially, has to work less. No pesky gravity to deal with, so the body thinks "oh boy, I can slack off now!"
Unfortunately, laziness never did anyone much good... including biology. Which means that everything does decide to "slack off" and atrophy, but it does so that it gets to the point where it's unhealthy. After only a few months in space, those returning home are weak and need to become accustomed to Earth's gravitational pull again.
After years in space, you get to the point where bone becomes so porous that even a mundane force can be injurious- such as a pat on the back breaking a vertebra.
If anything, legs will lessen the impact of microgravity... as counterintuitive as it may seem. They actually provide slightly
more excersise for the rest of the body, because the arms have to pull around that extra mass.
The same goes for metabolic needs, as I'm pretty sure, that organs such as the brain and heart are the biggest energy users in the body, not the legs. And pumping blood through the legs- even in microgravity, is excersise for the heart, even if it's a little bit. I admit though that I know nothing about the cardiovascular systems of double amputees...
Legs are also not useless in microgravity, they are obviously not used for locomotion as they are on Earth, but they do allow for movement, and for aiding a person in positioning themself within a cabin, and even for shifting one's center of mass. In that regard I would consider double amputation to put astronauts at a disadvantage in terms of manuverability.
Centrifuges are not complex, they can actually be quite simple... my spinning fuel tank (or transhab, if you wish) idea is really simple as things go, even if it is untested (well, such an arrangement was tested on a Gemini mission, but not in such an elaborate manner and not with a spin fast enough to produce any appreciable acceleration, though astronauts did note objects slowly floating toward the direction of acceleration).
Granted, a despun section with a rotating seal would be pretty 'interesting', but it should not be impossible. If we can't build such a device for creating essential conditions for human survival, we cannot truely call ourselves a spacefaring race- or say that we have a chance of living for more than about a year in space.
And even if it is costly, it's worth it compared to the human rights uproar you'd get for amputating astronauts legs and sending them to their doom (by microgravity atrophication), even from your own citizens. Nevermind finding doctors willing to go against oath and cut off the perfectly healthy legs of several hundred people, and several hundred people willing to have their legs cut off and stay in a hostile environment till their bones could break from someone shaking their hand...
