Crew Water Requirements for Life Support on a Near-Term Human Mission to Mars

This paper reviews requirements for water supply rate for life support of human crews on deep space missions such as Mars, and methods to provide that water supply. The literature on required water supply flow rate to support human crews on deep space missions is inadequate, typically with a few terse estimates lacking analysis or explication. These estimates were generated in an era where saving mass was critical and the allocations were skimpy. Here, we provide new, updated estimates of suggested water supply flow rate (at three levels of comfort) to support human crews on deep space missions in an era where mass in deep space is far more affordable. The total mass of water required for the mission is significant, but appropriate in the era of huge launch vehicles like the Starship. It was widely believed that water recycling systems are necessary to reduce mission mass in the era of high launch costs. However, the reliability of recycling technology is poor, as evidenced by experience on the International Space Station. Use of spares to replace subsystems that fail was proposed to greatly improve reliability, and that works good on paper as shown by probabilistic analysis, but the logistics of implementation are problematic. Bringing water from Earth is the best way to supply crew requirements for limited missions likely to be the first human landings on Mars. For futuristic missions of great extent, either recycling or use of indigenous water from Mars would be needed. In any mission, if possible, bringing a survival level of water from Earth is strongly recommended.