The ALS community faces unique challenges for the interactive modeling of a closed life support system. A top-level model is being developed as part of the System Studies and Modeling team of NJ-NSCORT. This top-level model has been broken down into several groups one of which is the ‘Human Requirements’ or ‘Human Factor’apos in an ALSS.This model examines the physical needs of crew members with respect to the effects of varying mission lengths, habitats and specific human characteristics. The model can be investigated independent of and interactive with the top-level model to examine the human factor using an object oriented approach.Through the object oriented programming language, Java, this model is meant to be accessible to the ALS community to aid in system analysis. This paper will explain the structure and examine the utility of the model with known requirements of humans in space.