OBJECTIVE: The objective is to devise and demonstrate a small and light cryocooler capable of hosting electronics requiring a 4 Kelvin (K) operating temperature in a Size, Weight and Power (SWaP) constrained tactical environment such as Unmanned Aerial Vehicle (UAV). DESCRIPTION: A central impediment to the tactical fielding of Nb superconducting electronics is the total lack of an extremely compact, low power, 4K cooler with the ~100 mW of lift required for an operationally exciting system for man-portable and UAV platforms, where fleet interest in new hardware is strongest. While numerous ideas of how to reduce the 4K heat load are being explored, the power and volume of 4K coolers is dominated by the lift required at higher temperatures, usually 77K where liquid N2 boils. There are no logistics issues with liquid nitrogen supplies as it is 80% of air, safe to handle, and air liquefiers already exist on larger platforms to supply breathing oxygen to pilots, etc. Thus this topic explores the possibility of small (4L is small enough for Electronic Warfare (EW) pods) closed cycle, low power He coolers running within a vented bath of liquid N2 or in contact with some other thermal battery. Trades will be required between hold time and volume/weight, adjustment of compressor design for higher density and viscosity of gas, and design of venting to handle roll and pitch of a tactical platform. The Commercial Off-The-Shelf (COTS) cryocoolers currently used for functionality demonstrations are fully closed cycle. The cold parts are about 10L in size, but the COTS room temperature compressor is over 90 lb., a cubic foot in size, and requires 1.5kW from the wall. Fully closed cycle, potentially tactical, coolers being worked reveals that>60% of the power and vast majority of weight arises from the ~77K stage. Thus attention should be paid to the possibility of going to a modular design which uses passive cooling for achieving the 77K start. The essential innovation is the off-loading of the power cost of charging the thermal battery to the platform that represents the sensor's home base. PHASE I: Design a first prototype based on the design concept defined in the Phase I proposal. Estimate the hold time/heat lift/weight trades of proposed design. In option period further reduce technical risk and prepare to execute design. PHASE II: After consultation with the Navy Technical Point of Contact (TPOC), finalize design of the first demonstration unit and construct at least the highest risk components. Potentially complete the first demonstration prototype and test the conformance of its behavior with the projected trade space. Then demonstrate its potential to cool to operating temperature with a simple government furnished superconducting chip. PHASE III: Collaborate with a system integrator and a superconducting system vendor to demonstrate a combined superconducting receiver packaged on your cooler. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The prime commercial application area is the instrumentation industry. Low temperatures are well known to reduce thermal noise, making small signals easier to see. Thus, the most sensitive infrared (IR) and radio frequency (RF) sensors operate at well below room temperature, as do very low power magnets, as in Magnetic Resonance Imaging and chemical analysis tools. A cooler of the desired sorts could be used to cool infrequently used magnetometers since the thermal cycling time between room temperature and 4K will be much shorter in this sort of system than in fully closed cycle machines. Whether mobile, small volume, or both magnetic field requiring sensors or x-ray machines are candidates should be considered. Space exploration is another area that has historically utilized thermal batteries. REFERENCES: 1. Smith, Joseph L."High Efficiency Modular Cryocooler With Floating Piston Expander."2001. United States Patent 6205791, filed July 6, 1999, publication March 27, 2001. 2. University of Wisconsin - Proceedings of the 14th International Cryocooler Conference."Modeling, Development and Testing of a Small-Scale Collins Type Cryocooler", http://conferences.library.wisc.edu/index.php/icc14/article/view/63. 3. Sicovic, Aleksandar, Momcilo Milinovic and Olivera Jeremic. 2010."Experimental Equipment Research for Cryogenic Joule-Thompson Cryocoolers Comparison in IR Technology Sensors", DOI: 10.5545/sv-jme.2010.259. http://en.sv-jme.eu/data/upload/2011/12/09_2010_259_Sicovic_04.pdf 4. Ishimoto, S., S. Suzuki, M. Yoshida, M.A. Green, Y. Kuno, and W. Lau."Liquid Hydrogen Absorber for Mice."http://www.osti.gov/bridge/servlets/purl/988169-EYTwiG/988169.pdf.