Re: One Way Trip
There are various ways to provide spin which can drastically reduce the effects of micro-G (also, any time under thrust) and as for radiation damage, as you noted you can use water as a very effective shield (as a bonus it's got an acceptable mass and has other uses) and even if you need something more substantial, you only need to shield the crew compartment, not the entire frame + payload + fuel tanks.
I don't think an (optimal) 80 days under those conditions would be unbearable, especially if you selected colonists with appropriate psychological profiles (and given the nature of the mission waiting at the end of the trip you'd be fucking mental not to).
Biting the hand that feeds IT
