In 1989, NASA began the modeling of life support systems using ASPEN, adetailed chemical process simulation software package. In the past year, several atmospheric revitalization subsystems (ARS) were modeled at a relatively low level of detail (called ‘system level’) using ASPEN. These models included partial reduction of Martian CO2 and a bioregenerative life support subsystem (BRLSS).The individual component and subsystem models were integrated into three different system-level ARS models: a baseline physico-chemical case, a case with a BRLSS, and a case using partial reduction of Martian CO2. These ASPEN models included the FORTRAN interfaces necessary for integration with another program, G189A, to perform “quasitransient” modeling (periodic pseudo-steady-state model passes with transient updating in between).Finally, detailed models were prepared for several ARS subsystems. Detailed reactor models were prepared for the two CO2 reduction reactors (Bosch and Advanced Carbon Formation), and for the low-temperature trace contaminant oxidation reactor. A detailed model will be prepared for the Sabatier reactor. In addition, the detailed EDC model of Lin & Winnick was modified and integrated with ASPEN.