Self-Healing Radiator Coolant Tubes for Spacecraft Thermal Control

Future space exploration missions require advanced thermal control systems (TCSs) to dissipate heat from spacecraft, rovers, or habitats to external environments. The typical layout for a thermal control system includes a large surface area radiator for heat rejection, embedded with fluid-filled heat pipes or coolant tubes with actively flowing liquid. Because radiators necessarily have a large footprint with exposure to space, they are particularly susceptible to strikes by micrometeorite and orbital debris (MMOD). Tubes breached by MMOD will invariably discharge their coolant, rendering the TCS inoperable. In this context, a particular need has emerged for self-healing coolant tubes for resilience to MMOD impact, as identified by NASA in SBIR Topic Z2.01. To meet this challenge, Creare proposes a unique coolant tube containment design, for which a multi layered tube wall contains a microporous metallic internal matrix filled with a liquid reactant. In Phase I, we collaborated with self-healing materials experts to select, develop, and evaluate a test matrix of polymer systems with the potential to provide passive self-healing with exposure to two typical radiator coolants, glycol-water and HFE-7200. Our work demonstrated seals up to 100 psid in two different prospective coolants using different custom polymer-based solutions. Further, we identified that more effective seals are possible by combining mechanical sealing methods with the developed chemical curing process. These hybrid systems use mechanical methods to slow the initial leak providing additional time for a more robust, hermetic chemical seal to take hold. Finally, we developed the overall thermal, fluid, structural, and mechanical design of an integrated radiator complete with advanced features for self-healing to compare mass and layout with traditional measures of MMOD protection, including structural shielding.