Abstract: A thermal management system adapted to vent a two-phase working fluid into an environment having a higher pressure than a vapor pressure of a working fluid corresponding to a set point of the system including a secondary vessel containing a secondary species. The system includes a primary vessel containing the working fluid and the secondary species, and at least one valve to selectively control venting of a mixture of the working fluid and the secondary species from the primary vessel to the environment. The system includes at least one valve connected between the primary vessel and the secondary vessel to selectively control charging of the secondary species into the primary vessel.