Future manned mission venturing into deep space will require sophisticated thermal control systems to protect against extreme environments ranging from direct illumination by solar radiation to complete darkness. To manage these extremes, heat exchangers composed of phase change materials that can expand and contract without causing structural damage, will be essential. This project will further-engineer ionic liquid-based phase change materials (PCMs) to: (1) tune the melting point for ORION platform heat exchanger applications, (2) further-elevate thermal conductivity for both solid and liquid, and (3) evenly-regulate heat transfer among components. In Phase I, InnoSense LLC (ISL) developed effective PCM formulations and tested their thermal properties. These materials exhibited high heat of fusion (254-272 kJ/kg) with low volume expansion (4-6%) compared with the current standard, pentadecane (~6-7%). We demonstrated IonoTherm to have higher thermal conductivity, heat storage, thermal diffusivity and thermal inertia over pentadecane. Further, tests indicated that IonoTherm did not corrode metallic substrates, phase-separate or degrade. In Phase II, ISL will fine-tune the PCM formulation and evaluate it in a flight level prototype heat exchanger. A NASA prime contractor has teamed with ISL to transition ISL's IonoTherm, and perform independent testing during Phase II and beyond under simulated field conditions.