Reliability Requires Using Direct Supply, Not Recycling, for Space Life Support

Space life support provides atmosphere, water, temperature and humidity control, waste management, and fire suppression for the spacecraft crew. Failures of these functions can harm the astronauts and serious accidents have occurred. NASA has worked to develop recycling life support systems since the 1960’s and has used them on the International Space Station (ISS) for nearly two decades, but all other US space missions have used the direct supply of life support materials. Recycling systems have been justified as saving launch mass and reducing cost for long missions, where the total mass of resupply materials is very large. But now a greatly reduced launch cost makes direct supply much less expensive than recycling for all projected future human missions. Direct supply uses flight proven tanks and cannisters that are much simpler, cheaper, and more reliable than recycling systems. The ISS life support system has had frequent failures that create high risk and require excessive crew time to repair. Space life support should be designed to have very high reliability and minimum risk. Achieving high reliability requires using direct supply life support and precludes using complex undependable recycling systems.