In order to pursue space colonization, long duration spaceflight, and human missions to Mars, we will need closed ecological life support systems which provide sustainable use of limited resources. While such systems are in various stages of development, we lack knowledge regarding the functional stability of closed ecological life support systems (CES) for long-duration space missions. Our global Earth Biosphere CES functioning is based upon statistical regulations, which are provided by planetary buffers. All current deviations caused by human activity are currently absorbed by these 'planetary buffers'. Man-made Closed Ecosystems function at the limits of their natural stability due to insufficient buffer capacities and thus needs to be replaced or supplemented by other more appropriate control approaches. Previous research has indicated that purposeful control from human can increase stability levels if specific algorithms compatible to natural mechanisms are applied. Theoretical analysis is being done on data obtained in different Closed Ecosystems and has been shown that certain limits of functional stability exist for each specific system in terms of average material cycle rate and range of fluctuations. These limits are determined by: the system's buffer capacities, the slowest (basic) material cycle in the system, natural structure of the circulating chemical elements cycles and Human Factors material load. Numerical estimates are provided for carbon cycles and it has been shown that stability of cycles in man-made ecosystems are more than a thousand times less than for global planetary cycles. Human Control could increase this low level of stability tremendously, but requires a certain level of understanding for closed material cycles development inside each specific system. This presentation will primarily discuss interactions between smallscale human crews and the available limited resources required for a CES functioning. Since there are limited resources in a CES, instead of continuously increasing consumption as would be possible in an unlimited environment, self-sustainable behaviors/activities must be practiced. This paper will address the limitations for human adaptation in a space environment and how to optimize human and environment interaction in a CES. Applications to manned space exploration will be considered in the context of understanding human motivation.