<div class="htmlview paragraph">This paper describes the approaches to Environmental Control and Life Support (ECLS) loop closure that have been studied for a permanently manned Space Station, by the NASA Concept Development Group (CDG) and industry. The paper explains the rational behind the level of loop closure chosen for ECLS expendables and why this level was chosen. The paper also explains potential synergistic interactions, between ECLS subsystems and other vehicle systems, which can lessen vehicle expendable penalties and help simplify required ECLS hardware, interfaces and control. Of particular significance are the potential interfacing of the ECLS subsystem which concentrates the metabolic CO₂ removed from the atmosphere, with propulsion system resistojets and the use of cryogenic boiloff to satisfy crew metabolic needs. The paper shows the trade-offs that must be performed in order to make a selection from available options.</div>