Toxicity Mitigating Single-Fluid Cooling System for Manned Spacecraft

The thermal control systems (TCS) for manned spacecraft are typically two-loop designs where a low freezing point single-phase liquid is used exterior to the manned vessel to reject heat through the radiator array, and a single-phase thermal loop inside the manned vessel that uses a non-toxic liquid is used for payload cooling and space conditioning. As an example, the Orion TCS uses HFE-7200 liquid (-138°C pour point) in the radiators, and PGW in the manned cabin. These loops interface through a shared heat exchanger that is external to the manned vessel to ensure that the working fluid for the external loop cannot leak into the manned cabin. This architecture is necessary for crew safety (most very low freezing point fluids are somewhat toxic or untested) but comes with a mass penalty due to the duplicity of prime movers (pumps), mass of the intermediate heat exchanger, and extra radiator surface area to account for the additional temperature delta required for the intermediate heat exchange process.The two-loop mass penalty is a driving force toward reducing the TCS to a single working fluid. However, the toxicity risk must be mitigated for this architecture to be realized. Mainstream proposes to replace the two loop TCS architecture with a single loop TCS architecture that has toxicity mitigating technology.