Hibernation and torpor, prospects for human spaceflight?

Despite substantial technical progress in the last decades, long-distance human space travel beyond the Earth-Moon system still represents a challenge. Resources for sustaining humans in good physical and mental health on such journeys are important drivers of complexity and cost. Every kilogram of mass and every cubic meter of volume reduction will reduce the total cost and increase the feasibility and thus the chances of success of such missions. Torpor and hibernation are solutions developed by animals to cope with severe resource restrictions and hostile environments. Reducing the demands on life support systems by putting humans into a state of hibernation might appear like a story straight out of science fiction. This chapter attempts to demonstrate that this concept is no longer in the realm of science fiction by providing an overview of the current scientific understanding of the processes of hibernation and torpor.