Methods of transfer of cryogenically stored reserves from the ISRU plant will need to be defined prior to the astronauts' departure. While the bioregenerative life support experiment will provide valuable experience in bioregenerative life support system technology, it will not be depended upon as a life support backup. Further development of closed loop bioregenerative technology such as that used in the Biosphere experiments is needed before we can place any level of dependence upon the bioregenerative life support system. This hybridization would provide the benefits of in-situ foodstuff production and, by maintaining dependence upon the robust primary life support systems, it would allow for the flexibility needed in bioregenerative systems. In a Mars-based greenhouse, it must remain possible for the astronauts to use existing life support systems to compensate for the dynamic nature of biological systems.
Humans are the most valuable component of Mars exploration, but perhaps also the most fragile.
Unprecedented demands will be placed both on humans and their support technologies for the 600 days they may spend on the Martian surface. Resources will be precious, entailing a precarious balance between cost and comfort, performance and risk. The crews will need their own skills and training and specialized support systems to meet the new challenges of the missions. The nominal crew size for this mission is six. Considerable effort will be required to determine absolute requirements for crew size and composition.