Future NASA planetary science missions will incorporate detectors, sensors, shields, and telescopes that must be cooled to cryogenic temperatures. These missions have very limited access to solar power and therefore reducing the cryocooling system power is more critical than for earth-orbiting satellites. On this program, Creare proposes to develop and demonstrate an innovative Stirling cryocooler that efficiently produces refrigeration at 30 K and rejects heat at about 150 K. A key component of the proposed cryocooler, its regenerator, will be optimized on this program to obtain high efficiency over this operating temperature range. The innovation is a regenerator fabricated by a unique process to enhance its heat capacity near its target cooling temperature and therefore increase the overall thermal efficiency of the cryocooler. The proposed cryocooler is built on technologies developed for commercial Stirling cryocoolers that are extremely compact and efficient while rejecting heat at 300 K. In Phase I, we will develop the regenerator fabrication process, measure the performance of a subscale regenerator under prototypical conditions, and optimize the cooler design for optimum performance. In Phase II, we will fabricate full-size regenerators, characterize their performance, integrate a regenerator into a Stirling cooler, and optimize the cryocooler operating parameters to maximize its performance. At the end of Phase II, we will deliver a cryocooler to NASA for further performance characterization.