Heck if one is keen on exploiting the moon-landing legacy NASA budget, push for more Biosphere 2 type projects nominally in preparation for space travel.

Programs of that sort are generally not self-sufficient and isolated enough to substantially reduce existential risk. For example, a gray goo scenario will hit those about as hard as it hits anywhere else. And such programs are rarely long-term enough to be able to remain isolated for long if normal infrastructure gives out.