Subject: Re: Richard Feynman explains why Mars a one way trip
Well...we can shield if we start digging. Hard to take a cave into space, though. Albaby mentioned a moonbase. It would have to be sub-lunar. Not sure how many meters, but I would guess at least 10 meters. Otherwise the inhabitants would get their DNA shredded. The few realistic designs I have seen for such an installation usually had the water tanks above the habitation to increase shielding.

That's right - which is why it's devilishly hard to solve for a long-term habitation on Mars with existing tech. We have a very difficult choice. We can shield from cosmic radiation and high energy particles by going underground - but we don't yet have a way to create artificial gravity underground. We can create artificial gravity in orbit around Mars (using rotating spacecraft) - but we don't yet have a way to protect against cosmic radiation and high energy particles in space.

Those two things together create a very difficult obstacle to having space children. Because you might need both (radiation protection and gravity) to raise humans to physical maturity. While adults can protect against the health problems of low gravity, you can't put a baby on a treadmill. (Well, you can - but it won't have the effect you're looking for).

Our species evolved in gravity, and all our physical development and growth processes operate using gravity. Babies in particular experience much of their muscular development by acting against gravity - lifting their head, lifting their limbs and bodies, etc. It's entirely possible that this won't be a problem, but there's far more reason to be concerned about it than with biological functions like swallowing (which you can do standing on your head) that were initially concerning to scientists.