In response to NASA SBIR solicitation H3.01 "Thermal Control for Future Human Exploration", Advanced Cooling Technologies, Inc. (ACT) is proposing a novel Phase Change Material (PCM) vapor chamber to ameliorate the temperature fluctuations encountered during planetary (or lunar) orbit. The PCM vapor chamber will consist of a packed bed of micro-encapsulated PCM beads surrounded by a two-phase working fluid. The PCM beads will act as both a highly efficient thermal storage medium, as well as a wick structure for capillary pumping of the two-phase working fluid. The two-phase heat transfer by the working fluid increases the effective thermal conductivity of the PCM by a factor of 1000 or more. This approach eliminates the need for embedding thermally conductive metal fins or carbon foam, which typically consume at least 50% of the system mass in traditional PCM heat exchangers. The PCM vapor chamber not only has the potential to exceed a 2/3 PCM mass ratio using paraffin wax, but also provides several advantages over the state-of-the-art, water-based PCM heat exchangers. The concept proposed by ACT will eliminate the need for metal fins and foams, and significantly reduce the mass of non-PCM materials. In addition, the PCM vapor chamber can serve as either a stand-alone thermal capacitor or a dual thermal capacitor/heat exchanger.