Thermal energy storage systems with 300 -- 1000 kJ/kg energy density through either phase changes or chemical heat absorption are sought by NASA. This proposed effort will design, fabricate and demonstrate an energy storage system utilizing a composite of silicone polymers (organosiloxanes) and sorption materials. The proposed technology would provide cooling from a source at 100o
C or higher. In proof-of-concept experiments, related composites have already been produced, and energy densities exceeding 400 kJ/kg have been demonstrated. The innovative encapsulation technology can provide a barrier that prohibits poisoning of the sorption material by planetary atmospheric gases, and ensuring long-duration storage and safe handling before and during mission. The composites can be produced in a form that facilitates conformal coverage of intricate parts and hard to reach surfaces.