Comparison of Bioregenerative and Physical/Chemical Life Support Systems

Popular depictions of space exploration as well as government life support research programs have long assumed that future planetary bases would rely on small scale, closed ecological systems with crop plants producing food, water, and oxygen and with bioreactors recycling waste. In actuality, even the most advanced anticipated human life support systems will use physical/ chemical systems to recycle water and oxygen and will depend on food from Earth. This paper compares bioregenerative and physical/chemical life support systems using Equivalent System Mass (ESM), which gauges the relative cost of hardware based on its mass, volume, power, and cooling requirements. Bioregenerative systems are more feasible for longer missions, since they avoid the cost of continually supplying food. However, computations of the required ESM show that the much higher initial cost of biological/ecological human life support makes it much more expensive than physical/chemical life support even for multi-year missions. The least expensive life support for brief human missions uses direct provision of all food, water and oxygen from Earth without any recycling. The familiar breakeven and ESM ratio analysis repeated here confirms these well-known and widely accepted results. The inescapable conclusion makes the substantial past efforts to develop bioregenerative life support appear surprisingly impractical.