<div class="htmlview paragraph">A second-generation system model has been developed to account for the movement of carbon, hydrogen, and oxygen through the various life support system components. It accounts for edible and inedible biomass and the water content of plant materials, and models various crops based on growth and transpiration rate tables, including multiple overlapping crops of the same or different species. It also calculates mass, volume, energy use, heat rejection, and manpower required for each component, including varying power use, heat rejection, and manpower as a function of the crop, and equivalent mass (EM) for each cost factor and for the system. Results are displayed graphically. The model was developed using G2, a commercially available modeling package. Enhancements are under consideration to improve the modeling of waste management and to account for minerals and variations in crew metabolism. The ability to use data directly from the NASA KSC ABF to drive this model is currently being implemented, with the intent to investigate model-based control.</div>