Among the advantages of the Stirling-cycle refrigerator are its compactness and the fact that it lends itself well to miniaturization. For instance, 0.5 W of refrigeration at 77°K has been obtained with a 25-W input and a total weight, including the drive motor and the heat exchanger, of 5 lb. These qualities are especially favorable in airborne applications, e.g., in infrared mapping. Since it seems likely that in the future, airborne applications will occur that need much lower temperatures, e.g., 10°K or below, it seemed worthwhile to investigate how low a temperature a miniature Stirling refrigerator might achieve.