Human Hypometabolism for Long Duration Spaceflight: Possibilities and System-level Consequences
- Paper number
IAC-05-D1.1.07
- Author
Dr. Mark Ayre, European Space Agency (ESA)/ESTEC, The Netherlands
- Year
2005
- Abstract
The enabling technologies to send unmanned missions to the outer planets obviously already exist. For human missions to such destinations minimisation of transit time will be a key driver, and further advances in propulsive efficiency will work to reduce journey times. However, upper limits to this efficiency (assuming reaction propulsion and ignoring the prospect of exotic propulsion concepts such as ftl) in the near-term are likely to place lower limits on journey times, which could easily take years if not more. This is especially true when considering the mass penalty associated with human missions: life support system (LSS) costs, both physical and psychological, will constitute a significant part of the mission mass, and life-support will be strong drivers of the propulsive requirements for the mission. Given these likely problems associated with life support and the associated mass penalty, an alternative approach is to somehow reduce LSS load to a minimum, whilst still maintaining crew health and effectiveness to acceptable levels. For future manned missions, complete automation during transit periods is not an unreasonable goal. If this were the case, the mission requirement for crew activity during these periods would collapse to zero, introducing the possibility of some form of hypometabolic stasis (HS), by which both the physical and psychological requirements of the crew could be minimised. Induction of a state similar to hibernation observed in certain animals, with a concomitant reduction in resource and psychological requirements, would reduce drastically the requirements imposed on the LSS in virtually every area. This paper first assesses whether human hypometabolism is worth investigating by considering the likely trip-times for manned missions to the outer planets using inertially confined fusion (the ne plus ultra of reaction propulsion concepts) using a field-free approximation. It is shown that even with very high performance propulsion, trip-times to the outer planets are still of the order of years in duration. The physical and psychological requirements of astronauts during such voyages are discussed, and the fundamental problem of their impact at a mission-level is outlined. The beneficial effects of including HS within a typical deep space mission architecture are then considered. These effects include: a significant reduction in the amount of consumables required and/or a relaxation of LSS closure requirements and hence reduction of LSS fragility; large avoidance of the psychological problems associated with long duration spaceflight away from Earth orbit (for which we have no precedent); the extension of mission abort options due to the ability to prolong crew survival in various abort situations; and the possible use of HS as a medical facility in the event of serious illness. A case-study involving the Human Mars Mission architecture is then presented to give an indication of the wet-mass reduction made possible using an HS. In summary, the mass, volume and operational benefits associated with placing the crew into torpor during transit periods are likely to be very considerable: These could in turn allow new classes of missions to be possible, or would allow relaxation of propulsion subsystem requirements and/or trip-time reductions for extant mission classes. Given this, the paper concludes that HS for long duration spaceflight is a very useful (even potentially enabling) technology, and is therefore a worthy topic for consideration.
- Abstract document