An assessment of the state of cryocooler technology for space applications

Abstract

A survey is made which identifies more than 30 long life coolers for space applications covering a wide variety of thermodynamic cycles and confignration types. These coolers range in capacities from a few milliwatts to over 10 W at temperatures from 10 K to over 120 K and include single and multi-stage designs. The primary objectives of this study were to provide a hardware summary and performance comparison for potential space cryocooler users and to serve as an aid to the Air Force in determining future cryocooler development. Funding for these coolers are being provided by the Depamnent of Defense, NASA, and various other government agencies in the US. and abroad as well as by internal research and development monies from a number of companies throughout the world. The study identifies several existing fight qualified coolers and at least 12 programs which are l i l y to provide flight qualified units for cooling in the range of 10 to 150 K before the turn of the century. The survey presents an overview and status of the maturity of the various cryocoolers and uerfonnance comparisons are made at 35 K, 60 K, and 100 k.

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“…Considerable extrapolation was required from current space-qualified, long life, mechanical cryocooler technology. 86 These refrigeration systems are typically used for very small (~0.1 to ~10. W) heat loads, primarily IR sensors, low temperature optics, and other instrumentation.…”

“…Published mass and power scalings were used despite the considerable extrapolations required, rather than applying large ground based systems that rely on utilizing the ambient terrestrial environment. A gaseous helium Stirling cycle system (an extrapolation from an MMS 4K model) 86 with a 3°K low temperature sink (T L ) was used to refrigerate the solid/liquid D 3 He fuel pellets. A gaseous helium Stirling cycle system (an extrapolation from the Ball Hybrid J-T/Stirling system) 86 with a T L of 10°K was used to refrigerate the slush hydrogen propellant.…”

“…A gaseous helium Stirling cycle system (an extrapolation from an MMS 4K model) 86 with a 3°K low temperature sink (T L ) was used to refrigerate the solid/liquid D 3 He fuel pellets. A gaseous helium Stirling cycle system (an extrapolation from the Ball Hybrid J-T/Stirling system) 86 with a T L of 10°K was used to refrigerate the slush hydrogen propellant. A liquid nitrogen, multistage Joule-Thomson (J-T) system (somewhat similar to a Ball liquid nitrogen-based COOLLAR 65/120 J-T system) 86 with a T L of 64.3°K was used to refrigerate the 65°K, 25 TF/PF/divertor/magnetic nozzle superconducting coils and the central conductor.…”

“…Multi-stage reverse Brayton systems appeared to have the lowest specific masses compared to Stirling systems, particularly at higher cooling capacities. 86 An ambient heating temperature of 172°K was used (corresponding to average Mars orbit heat flux) to approximate an effective mission average, outer solar system thermal environment. With the tankage insulation and shielding described earlier, approximately 0.0725 W/m 2 was the average thermal power per (multilayer insulated) area to be removed (Q) from the propellant and fuel tanks using Equation 34 (where C 1 = 8.95E-08 and C 2 = 5.39E-10).…”