Conceptual Assessment of a Lipid-Based Liquid Water Storage System for Lunar Life Support and Exploration

Abstract

Human lunar and planetary exploration can be simplified by the exploitation of in situ resources. High priorities are placed on propellant and life support consumables, such as oxygen and water. The latter can be considered a biproduct of propellant production, and is essential for sustained human presence. Its existence was detected on the Moon and on Mars. However, its endemic occurrence as ice can make storage and transportation difficult, so a conversion to its liquid state often is preferable. The disadvantage of this is that energy-intensive active heating systems are required to prevent freezing. Recently, a method was presented that potentially can eliminate this disadvantage by maintaining the liquid state down to −120°C, even at pressures as low as 0.1 mbar. This is achieved by mixing the water with a commercially available lipid, thereby forming a lipidic mesophase. Transportation of the mesophase in cryogenic hydraulic networks is achieved easily by pumping, and this can be exploited to design a centralized closed-loop liquid water storage system for a lunar base. The distinguishing feature is that the tanks can be placed outside the human habitats. Key system components are potentially manufacturable in situ. In this work, an architecture for the life support part of such a system is proposed, and the key chemical processes are demonstrated experimentally. The first of these is the scale-up of the water–lipid enrichment process by a factor of 5 from typical laboratory scales. The second is the extraction of water from the mesophase by distillation. It is shown that 79% by weight of the water is extractable for reuse, and the remainder presumably forms an azeotrope with the lipid. The power required to circulate the mixture between human habitats and external tanks is estimated to be <41 kW for a crew of 10. Water can be mixed with a commercially available lipid using a simple thermal process. A surprising attribute of this mixture is that it remains liquid, i.e., it does not freeze, at temperatures as low as −120°C. As a result, pumps can be used to transport the liquid through hydraulic networks. This can be exploited to construct water supply and storage networks in cold environments without the need for an active heating system. Potential applications of this technology are in extraterrestrial and terrestrial environments. The former includes the development of lunar and planetary installations for life support and exploration as part of the ongoing effort to extend human presence beyond Earth. The latter include water storage and supply systems for cold terrestrial environments in which access to clean liquid water is required but such water scarce. Examples are regions above the Arctic circle, Antarctica, high-altitude environments, or, generally, regions with extended freezing periods.