This paper studies the vapor biowaste electric propulsion systems and the impact of the evolving advance life support oxygen recovery cycles and subsystem trade-offs on the biowaste expendable composition and mass balances. The results of a computer analysis of the potential performance of three representative compositions used as propellants in electrothermal thrusters are presented, including propellant specific impulse, chamber heating requirements, and electric power input needed for the attitude control of a typical 12-manned earth-orbiting space station. Reaction product compositions at various locations from chamber to plume are also presented.