Future Spacecraft and instruments for NASA's Science Mission Directorate will require increasingly sophisticated thermal control technology. A need exists for efficient, lightweight Vapor Compression Cycle (VCC) systems, for medium-to-low cooling loads (i.e. less than 2 kW). 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-VCC featuring custom compressor and heat-exchanger technology. The compressor is a highly efficient, high power density rotary compressor designed for 500 W of heat removal with a Coefficient of Performance (COP) of 3. In the Phase I effort Rini Technologies Inc. (RTI) proposes to develop a compressor capable of handling variable heat loads up to 500 W, with variable temperature lift capability to suit NASA's specific needs. Detailed component testing will be performed, and the results coupled with NASA's specific needs will result in a complete system recommendation for a Phase II effort. The following Phase II effort will result in delivery of an efficient, lightweight, reliable and compact prototype VCC for NASA missions.