Closed Ecological Systems

Long term life support requires the use of a closed ecological system. The attainable degree of closure is determined by the extent of conversion achieved in the waste recovery system. Organisms used in such systems must be reliable, useful, and integrable. Strictly speaking, a completely closed ecological system implies a photosynthetic component, because oxygen is produced biologically only through photosynthesis. However, the same result can be attained by substituting electrolysis of water for photosynthesis in the production of oxygen. Photosynthetic systems generally have algae as the green plants, whereas nonphotosynthetic systems use bacteria of the genus Hydrogenomanas as the key organism. An integrated life support system consisting of a mammal (mouse or mice), algae, and bacteria, and named Microterella by the writers, was developed and used by the writers to demonstrate that closed ecological systems (in the strict sense) are suitable for life support in space. The development of the Algatron, a growth unit of which a mechanically rotated algal-bacterial culture is an essential feature, considerably enhances the practical feasibility of the Microterella system.