Multi-Objective Analysis of Ionic Liquid Properties for Spacecraft Thermal Control

In ECLSS, propylene glycol–water mixtures and, to a lesser extent, anhydrous ammonia have traditionally served as primary heat transfer fluids due to their favorable thermal properties, including low freezing points and efficient heat transfer. However, the potential application of ionic liquids (ILs) in this role remains underexplored. While primary properties such as heat capacity and viscosity are critical for thermal performance, secondary factors, such as toxicity, radiation stability, and material compatibility, are equally vital for ensuring crew safety during long-duration missions. This study presents a screening framework for evaluating IL candidates in spacecraft thermal applications. The methodology employs a custom software tool, IL-SCOPE, to manage the combinatorial complexity of IL design by evaluating fragment combinations, assembling feasible ILs, and calculating key thermophysical and safety properties. User-defined property targets and priority weightings refine the solution space, and multi-objective Pareto optimization identifies ILs aligned with mission-specific performance needs. IL-SCOPE operates in two phases: a reverse design stage that screens IL fragments (cations, anions, alkyl chains, and functional groups) against user-defined constraints, and a forward design stage that assembles feasible structures and calculates their properties using group contribution methods. Preliminary results demonstrate the potential of ILs to achieve tailored thermal properties while maintaining acceptable safety margins. Comparison with ILThermo data supports the internal consistency of the modeled outputs, and fragment-level analysis reveals chemical trends that can inform future formulation strategies. This work underscores the design flexibility of ILs and highlights their potential as mission-tunable thermal fluids in spacecraft environments.