"Adapting Ionomer-Membrane Humidity Control Technologies for Spacecraft Evaporative Cooling"

Heat rejection using the latent heat of water has been a method of spacecraft thermal control since the Apollo era in applications where heat rejection via radiation is impractical or insufficient to accomplish mission goals. Key examples of this are spacesuit portable life support systems (PLSS) where there is insufficient surface area for radiators, or crew capsule thermal control systems where cooling is required for mission periods without a suitable view to space. Over the last decade, membrane-based evaporative cooling has become the state-of-the-art via the Spacesuit Water Membrane Evaporator (SWME). This technology uses hollow-fiber membranes to allow the controlled evaporation and venting of water for cooling the Exploration Extravehicular Mobility Unit (xEMU) spacesuit. However, this is not the only membrane capable of evaporative cooling. Ionomer membranes are strong candidates for evaporative coolers due to their robustness, high water transport, and nearly-100%-efficient evaporative cooling potential. Paragon Space Development Corporation is investigating the use of its Ionomer-membrane Water Processing (IWP) humidity control hardware, used on the CST-100 Starliner and Lunar Gateway, as an evaporative cooler to demonstrate the efficacy and versatility of the technology. This paper presents testing results for a benchtop version Spacecraft Water Advanced Membrane Pervaporative Exchanger (SWAMPE); an evaporative cooler comprised of one or more IWP bundles, and compares this technology to the NASA SWME. In performance testing, a single IWP bundle demonstrated heat rejection of 700 to 1500W over an inlet temperature range of 15 to 50°C, respectively, at a rough vacuum of 5 to 8 Torr (0.7-1.1 kPa) and with >95% water utilization. Therefore, a SWAMPE bundle rejects ~3x more heat per unit volume than SWME with potential for 5x via optimization. This performance, coupled with the robustness of the IWP bundle, makes it an extremely promising candidate for Exploration and commercial space thermal control systems.