It has been proposed by NASA JSC studies, that the most mass efficient (non-nuclear) method of Lunar habitat cooling is via photovoltaic (PV) direct vapor compression refrigeration. This system uses a thermal radiator, a solar PV array, and a vapor compression refrigeration device. Such a system significantly reduces total system mass as compared to an all radiator cooling architecture. Since the start of initial prototype testing in the mid 1990s, several refrigeration systems have been proposed, studied, built, and tested. The basic goal of each system has been to achieve the highest possible efficiency at the optimal system lift. Most notably, a two-stage refrigeration system and an expander turbine for a single-stage system were developed. Both sought to eliminate or recover the energy loss associated with irreversible expansion at the throttling valve, but both fell short of efficiency targets. Then, Paragon proposed a novel refrigeration architecture that was successfully demonstrated during the Phase I period. This system can achieve, in theory, near Carnot efficiency limits and does so in a practical and achievable way. Not only can this technology provide significantly improved performance (reduced weight) for NASA's Lunar habitat cooling application, but it has excellent potential as a commercial product.