Future Spacecraft from the JPL will require increasingly sophisticated thermal control technology. A need exists for efficient, lightweight Vapor Compression Cycle (VCC) systems, for medium-to-low cooling loads (less than 2kW). While conventional VCC technology is relatively compact and efficient for multi-kW loads, it is difficult to find a system that strikes a balance between coefficient of performance, weight and size within the sub-kW range. The particular system proposed will be a highly efficient Mini-Heat Pump featuring custom compressor and heat-exchanger technology. The compressor is a highly efficient, high power density, orientation independent rotary compressor designed for 500W of heat removal, a temperature lift of 50K and with a Coefficient of Performance (COP) of 2. In the Phase II effort RINI proposes to continue development of the Mini-Heat Pump to increase compressor performance, study long term reliability, and design, build and test a deliverable prototype. Detailed compressor analysis will be performed, and the results will be applied to a compressor that will be integrated with a motor identified in Phase I for use with the heat exchangers from the Phase I. The Phase II effort will result in delivery of an efficient, lightweight, orientation independent, reliable and compact prototype heat pump for NASA missions.