An Efficient Freeze Tolerant Radiator for Single-Phase Active Thermal Control Systems

The next major step in human space exploration is to establish a sustainable presence on the Moon under the Artemis program. The NASA 2024 SBIR focus area Z13.05 Components for Extreme Environments, calls for heat rejection solutions that allow freeze and thaw cycles without experiencing any damage or performance degradation for human-rated spacecraft on the lunar surface. Specifically, NASA seeks novel freeze-tolerant coolant tubes in radiators or heat exchangers. Deep space habitats, such as Lunar Gateway, lunar landers, or surface habitats, require robust active thermal control systems (ATCS) to maintain cabin temperature despite wide fluctuations in heat loads (during crewed and un-crewed periods) and sink temperatures. NASA spacecraft to date have redundant dual loop single-phase ATCS architectures, because there are no known fluids that are both non-toxic (safe to use inside the habitat) and low-freeze point (reliable for use outside of the habitat). Thus, a low-freeze point fluid is utilized in an external loop and a non-toxic fluid (water) in an internal loop. Despite low-freeze temperature coolants, the external loop may still freeze, especially during lunar night. ISS and other heritage ATCSs permit higher pressures during freezing and thawing of coolant and prevent complete freezing during low heat loads. However, radiator tubes are still subject to structural failure under high pressure. The proposed innovation is a low-mass, corrosion-resistant, freeze-tolerant, deployable radiator for ATCS in a lunar surface habitat. The technology permits compression or expansion of the working fluid throughout the radiator system, enabling coolant freezing/thawing, while meeting other environmental and architecture requirements. The proposed innovation may even be used in a single loop architecture, removing the need of a dual loop and reducing system mass. In Phase I, Space Lab will investigate the feasibility of the Space Lab® FT-Radiator™ freeze-tolerant radiator.