Molecular manufacturing (MM) will provide for the direct fabrication of diverse structures. It has been suggested that this will allow the direct manufacture of air, food and water, the consumables for life support. This paper examines the concept of a Closed Environment Life Support System (CELSS) provided by MM. The examination includes deriving the functions necessary for MM based CELSS, reviewing the feasibility of meeting those requirements, and the development of an initial system architecture, including more in-depth design of representative key elements.
One conceptually simple requirement is to support the oxygen cycle, producing ~0.9 kg per person per day of O2. This requires chemical transformations, which MM should accomplish mechanosynthetically. Thus, examination of the oxygen cycle includes illustration of key mechanosynthetic steps. Furthermore, this process should occur in a continuous, repetitive fashion, calling for a molecular mill architecture. Thus, the examination also shows translation of mechanosynthetic steps into a molecular mill design.
Similarly, examination of the water cycle includes the illustration of key mechanosynthetic steps, and the translation of such steps into elements of a molecular mill design. While CELSS must provide at least ~1.8 kg per person per day of water for consumption, water is also used for many other purposes. This results in a significant portion of the water cycle being purification, chemical separation rather than transformation.
In comparison with the previous two cycles, the inputs and outputs to support the food cycle are much more diverse. Accordingly, the system requirements to support the food cycle are much more extensive. While the system need only provide ~0.6 kg per person per day of food, that material is vastly more complex than breathable air or potable water. The examination of the food cycle addresses the general requirements that must be supported, and classes of specific requirements, without specifying in full depth how each particular food item would be handled. Nonetheless, this provides a sufficient anchor to develop a system design to support the food cycle.
The CELSS is responsible for maintaining a habitable environment. Beyond ensuring that there is enough of the materials needed to support life in the environment, this also requires ensuring that that is not too much of other threatening materials that endanger life. This requires identifying and removing impurities that build up in the environment.
An overall process control is described for such a CELSS, based on surging capacity to remove materials from the environment as their concentrations rise. Concerns with this process control are discussed, and its adequacy is defended.
The system also must be maintained. A key strategy is the use of MM to manufacture replacement components for those that wear-out or threaten to fail.
Finally, this paper presents a top-level system design, integrating the various components. This baseline for MM CELSS will provide a basis both for refining the system concept, and for designing more extensive molecular nanotechnology systems, such as spacecraft, that include CELSS as one of their subsystems. One interesting preliminary result is that the cross-over mission duration, where it becomes more advantageous to recycle all life-support consumables, rather than store some, shortens from years, with currently planned technologies, to the order of a day when using performance estimates from (Drexler, 1992).