During a NASA Phase I SBIR program, ACT addressed the need for light-weight, non-venting PCM heat storage devices by successfully demonstrating proof-of-concept of a vapor chamber with a PCM-based wick structure. The principal objective of the Phase II program is to design, fabricate, and test a full-scale PCM vapor chamber. Goals of the Phase II program include establishing thermal and structural design requirements. ACT will also develop a thermal storage model for integration into the heat transport model developed in Phase I. A custom microPCM will be developed and screened with the assistance of subcontractor SwRI to obtain optimum properties for thermal performance. ACT will also design, fabricate and test a sub-scale PCM vapor chamber with relevant form factor and a fraction of the full-scale heat load. Upon successful demonstration of the sub-scale unit, two full-scale PCM vapor chambers will be fabricated and tested. Both full-scale units will undergo extensive thermal performance testing. At the end of the Phase II project, one of the full-scale PCM vapor chambers will be delivered to NASA for further testing, and the other will remain at ACT for extended life testing.