I've been toying around the concept of how to make humans more reliable for space missions, and once idea i had was to use the same material used to power rovers as "food" for humans. pic related is the general idea, a biomineralised core of an alpha emitting isotope with high power output ( Gd148/ Pu238) encapsulated by a porous biomineralised platinum casing which both acts as a alpha particle shield preventing damage in the rest of the cell, and to catalyse the radiolytic splitting of water into various water decay species which can be utilised to recycle ATP from ADP with atpsynthase taken from hydrogen oxidising bacteria which is spread of a secondary membrane which prevents free radicals leaking into the organelle and its respective DNA (it would have its own DNA like mitochondria) based on back of the napkin calculations the whole organelle would be around 7-10 microns wide which is on par with chloroplasts. a human engineered to express these organelles would not need to eat or breathe, for 150 years, would be extremely cold tolerant ( although vitamins would be needed) seems an ideal candidate for martian explorer?