Advanced space-borne instruments require cooling at temperatures of 10 K and below. These coolers will be used for as upper-stage cryocoolers for sub-Kelvin cryocoolers and instruments or the primary cooler for electro-optical instruments. Cooling loads for these detectors will range from 0.25 W to 1.0 W at the primary load site, with additional loads at higher temperatures for other subsystems. Due to jitter requirements, a cryocooler with very low vibration is required. In addition, a multistage cooler, capable of providing refrigeration at more than one temperature simultaneously, can provide the greatest system efficiency and lowest mass. Turbomachine-based Brayton cryocoolers are ideal candidates for these applications because they are highly efficient, lightweight, vibration-free, multistage compatible, and have long maintenance-free lifetimes. Creare has developed state-of-the-art components needed to create turbo-Brayton cryocoolers for these missions. During the current program, we propose to develop and demonstrate a two-stage cryocooler that provides refrigeration at 10 K, with additional cooling at 60 to 70 K. On the Phase I project, we will optimize the performance of an existing cryocooler for a particular NASA mission class and measure its performance. During the Phase II project, we plan to build an advanced cold-stage turboalternator, integrate it with the cryocooler and measure its performance at cold load temperatures as low as 10 K. We will use the test results to develop a design for a fully optimized, flight cryocooler.