Evaluation of integrated air interchange system performance is one of the important tasks in atmosphere revitalization system design to ensure a safe and habitable environment for all astronauts during the planned Orbiter and International Space Station (ISS) assembly missions. A multi-element fixed control volume integrated air interchange system performance computer model has been developed and upgraded for the evaluation of atmospheric characteristics inside all crew compartments of the Orbiter and ISS. The results from this computer model were utilized to assess and determine the Orbiter airflow supply capabilities, and to develop integrated air interchange system design limitations and requirements. Results from this performance model were also used to predict possible air interchange system operating constraints, such as occupancy limitations in each chamber, during the docked period of the missions. For validation of the computer model simulated results, flight data were obtained from ISS assembly missions #2A and #2A.1 and compared with the results from this model. Based on the comparison between model results and post flight data, it is concluded that this model can provide an acceptable and reasonable atmosphere prediction and evaluation for assessing all the habitable volumes inside the integrated Orbiter/ISS.