Selecting life support system for the crews of long duration space stations

The existing life support systems on the Russian Segment of the International Space Station (RS ISS) only provide a partial recycling of water and oxygen from human waste products, and therefore, in order to support the ISS operations, additional supplies of water, oxygen, food and life-support hardware with limited service life need to be delivered by cargo vehicles. This situation makes it necessary to develop life-support systems with closed-loop recycling. The paper provides a rationale for the method of selecting a life support system with an increased efficiency of water and oxygen recycling from waste products based on the variable mass of deliverable equipment for the next stage in the ISS development. It also provides block diagrams of the recycling life support systems operating onboard the ISS. The principal results of flight operation of these systems since the end of 2000 through mid-2014 when supporting a crew of three validated the method for selecting the life support system. Recommendation is made for the final configuration of the ISS RS modules to increase the efficiency of water and oxygen recycling from the crew waste products by extracting oxygen from the carbon dioxide using the Sabatier process and reclaiming water from urine and all elements containing moisture.