Closed ecological life support systems : cycling of carbon, nitrogen and water

Abstract: Materially closed life support systems containing biological components that provide atmosphere, food and water for a human crew has been investigated for use in space travel since the 1960s. The internal cycling of organic material is the essence of these systems and their design and function is the question at issue for this thesis, which has been conducted as a literature study. Different approaches for closed life support systems, almost purely biological as well as involving physicochemical control and buffer systems are presented. The experiments include Bios-3, Biosphere 2, CEEF and MELiSSA. These systems have different approaches with advantages and disadvantages and encounter different problems. They are built around the production of organic matter by photosynthetic organisms, mainly higher plants, which produce food and drive the water cycle through their transpiration and respiration. Energy in the form of light is assumed to be available. To close the carbon cycle, organic waste must be oxidised to carbon dioxide, making carbon available for re-fixation by the plants. Nutrients must also be recovered in a form available for plant uptake, nitrogen in particular has been considered. Complete closure has not been achieved. Leakage of atmosphere from the systems prove to constitute a significant problem, removing substantial amount of nitrogen and oxygen from the system. In addition to facilitating future long-range space missions these concepts and techniques might also prove particularly useful in establishing a more sustainable society.