Design Rules for Space Life Support Systems

This paper describes engineering rules of thumb for life support system design. One general design rule is that the longer the mission, the more the life support system should use regenerable technologies and recycling. A more specific rule is that, if plants supply more than about half the food, the plants will provide all the oxygen needed by the crew. There are many such design rules that can help in planning the analysis of life support systems or in assessing design concepts. These rules typically describe the results of steady state, “back of the envelope,” trade-off calculations. They are useful in suggesting plausible candidate life support system designs or approaches. Life support system engineers should consider the basic design rules and make quick steady state calculations as a guide before doing detailed design.