Long-life, high-capacity cryocoolers are a critical need for future space systems utilizing stored cryogens. The cooling requirements for planetary and extraterrestrial exploration missions, Crew Exploration Vehicles, extended-life orbital transfer vehicles, and space depots will range from 10 to 50 W at temperatures between 20 and 120 K. Turbo-Brayton cryocoolers are ideal for these systems because they are lightweight, compact and very efficient at high cooling loads, in addition to their inherent attributes of high reliability; negligible vibration; long, maintenance-free lifetimes; and flexibility in integrating with spacecraft systems and payloads. To date, space-borne turbo-Brayton technology has been developed for modest cooling loads. During the proposed program, Creare will develop an advanced, high efficiency turbine optimized for a high-capacity cryocooler. The advanced turbine will enable a landmark reduction in cryocooler input power and overall cooling system mass. In Phase I, we defined the cryocooler requirements for a particular mission class, developed the conceptual design of a multistage cryocooler to meet the requirements, developed the preliminary design of the advanced turbine and successfully performed proof-of-concept tests on the turbine. During Phase II, we will fabricate the turbine optimized to provide 5-20 W of net refrigeration at 20 K and demonstrate its performance at prototypical operating conditions.