Mars Transit Life Support, Open, Closed, or Mixed?

Brief human space missions such as Apollo and shuttle used material storage to provide life support but long missions such as a trip to Mars and back are expected to use a recycling life support system similar to the one on the International Space Station (ISS). Mars transit life support design is investigated considering requirements, performance, reliability, cost, and risk. The launch cost, crew size, and reliability are variable parameters that affect the life support design choice. Greater launch cost and larger crew size tend to make recycling more cost-effective than resupply. A higher reliability requirement tends to favor resupply over recycling. A mixed system combining direct supply of minimal survival materials for very high reliability with additional materials provided by recycling systems seems the best choice.