To better understand the effects of perturbing the organism over the course of long-term space missions, there is a need to provide NASA with a practical and validated tool for modeling human performance in space under normal and stressed conditions. We will build this tool around the technology of Task Network Modeling. Task network modeling has been developed and applied in other similar domains for the past twelve years. By being able to predict human performance under stress with task network models, NASA will be better able to 1) design a user interface to support the human during high-demand periods, 2) allocate functions between the human and machine, including dynamic allocation of functions, 3) develop methods whereby intelligent agents may be used to assist humans in high stress periods, and 4) develop methods for maximizing situational awareness during high stress periods. Fundamentally, this project will produce a human engineering methodology for NASA that builds upon existing software tools and modeling technology.