The relationship between the duration and location of a manned space mission and significant life support resource costs is considered. These costs include mass, pressurized volume, energy, cooling and manpower. They are converted to common mass units (equivalent mass), and the probable range of values addressed. R&D and fabrication costs are hard to estimate and are not considered here, nor are any political constraints. With high equivalencies (e.g., cheap power), the relative effect of equipment mass is increased and in consequence the cost-effectiveness of bioregenerative life support rises dramatically.