A parametric analysis of the life support systems was completed, from which scaling laws were developed and adapted to computer solutions. This new tool permits the evaluation of a great variety of life support system types and combinations. The interdependencies and interrelations within the life support system itself can be evaluated, as well as the interactions between the life support system, spacecraft, and other systems. Representative data are presented for several partially closed life support system configurations usable for manned Earth orbital missions. The life support systems are principally affected by alternative degree of closure, the functional methods selected for the various subsystems, and mission requirements. Variations in the method or equipment used to provide a given recovery process, such as for carbon dioxide reduction, are shown in terms of the weight, volume, electrical power required, and spare parts for the particular subsystem involved, as well as for the other subsystems and the whole system. Results are given to show the influence of input variables such as mission duration, crew size, logistic supply intervals, and emergency requirements such as meteoroid puncture or solar flare activity.