Direct osmosis (DO) is a two-step membrane concentration process that is being considered for longterm manned space missions. DO was selected because of its high water recovery, low energy use, no expendibles, and no phase changes.DO and factors affecting its performance are explained. The developed deliverable for recovering 97% of 120 I/day of wastewater consists of a two-stage DO system with urine fed to the second stage. The osmotic agent is reconcentrated using a three-pass, twostage reverse-osmosis system. Catalytic oxidation removes the trace organics that permeate the membranes. Estimated energy use is 130 kJ/kg (36 Wh/kg) of water recovered.