The objectives set forth by NASA's Space Exploration Initiative (SEI) include the construction of a lunar base and the manned exploration of Mars early in the 21st century. However, current life support system technology is not capable of supporting such missions and remains one of the most fundamental limitations of space exploration. To date, life support systems have consisted of exhaustible supplies that limit missions to relatively short durations. This method has sufficed so far; however, if humans are to truly break away from Earth, it will be necessary to reproduce the characteristics of the terrestrial biosphere in extraterrestrial locations.Bioregenerative technology incorporates plants and animals as processors in a regenerative life support system. Controlled Ecological Life Support Systems (CELSS) use bioregenerative technology to recycle system consumables, therefore increasing system self-sufficiency and breaking the limitations imposed by traditional life support system designs. The study of this technology is of great basic value not only for its applications in space but also for its benefits to life on Earth. The need for the reclamation and purification of water and the control of airborne contaminants grows more evident as Earth's natural resources are either exhausted or soured. The creation of waste-free industrial production is vital to the continuing development of our society.Although bioregenerative technology is not a new concept, relatively little hardware exists for space applications. As a result, little is understood concerning total system performance or the possible effects bioregenerative technology may have on other life support subsystems. Through the use of computer simulation, we have been able to address these issues. This paper discusses the results of computer simulations that have been used to model a functioning CELSS and examines what effects bioregenerative technology may have on an initial lunar outpost.Computer simulation technology can be used to provide a mathematical test-bed for life support system design concepts that could increase system closure for extended duration missions. We have used a general understanding of human and plant physiology to develop mathematical relationships that describe the performance of these bioprocessors. We then used these subroutines in the construction of computer models that represent advanced environmental control and life support system (ECLSS) configurations. Simulations were conducted to test system resupply characteristics and evaluate system performance. We are also working to validate the algorithms used in our simulations so that we may apply them with some degree of confidence. This is an important step because the information gained from any system simulation is only as good as the algorithms that represent the system components.Although computer simulation is a useful tool and a necessary first step, it cannot replace laboratory experimentation. In most of the governing equations used in our simulations, assumptions have been made to simplify system behavior. At this early stage of CELSS development, it would be inappropriate as well as impossible to capture all of the details necessary to model every aspect of system performance. This leaves any simulation incomplete. However, with each study iteration, more detail is incorporated into the computer models. Our intent is to use computer simulation as a compass that points us in the right direction and prepares us for the prototype phase of the system development. Once the direction is clear, laboratory experimentation will dictate the final configuration.