Low Temperature, Low Capacity Cryocooler Technology

Future astrophysics missions require efficient, low temperature cryocoolers to cool advanced instruments or to serve as the upper-stage cooler for sub-Kelvin refrigerators. Potential astrophysics missions include Lynx, Origins Space Telescope, and the Superconducting Gravity Gradiometer. Cooling loads for these missions are 50 to 300nbsp;mW at temperatures of 4 to 10nbsp;K, with additional loads at higher temperatures for cooling shields and other subsystems. Due to low jitter requirements, a cryocooler with very low vibration is needed for many missions. Turbo-Brayton cryocoolers have space heritage and are ideal for these missions due to negligible vibration emittance and high efficiency at low temperatures. Technologies have been demonstrated or are under development for refrigeration loads in the range of 200nbsp;mW to 500nbsp;mW at 4 to 10nbsp;K, respectively. Many future missions have lower refrigeration requirements and require commensurably lower input power. Further miniaturization is needed for the cold turbine to provide high cryocooler efficiency and low input power when loads are reduced to 50 to 150nbsp;mW. On the proposed program, Creare plans to advance recent developments in gas bearings and miniature permanent magnet alternators to a smaller turbine capacity than attempted to date. On the Phasenbsp;I project, we will perform analyses and fabrication trials to demonstrate feasibility of a turbine optimized for 50 to 150nbsp;mW at 4 to 10nbsp;K. On the Phasenbsp;II project, we will build and demonstrate the turbine in a cryocooler.