Low-Cost Compressor Motor for High Efficiency Cryocoolers

There are currently no low-cost, long-life, space-quality cryocoolers capable of being produced for $500,000 each at a production rate of 50/year. Long-life space cryocoolers typically cost several million dollars each or more, due in part to requirements and interfaces that can vary from program to program. Tactical military (avionics) cryocoolers cost much less and are produced in large quantity, but cryocooler operating lifetime suffers significantly, with 6,000-12,000 MTTF typical for tactical Stirling cryocoolers. In contrast, space pulse tube cryocoolers built by Lockheed Martin Space (LMS) have a predicted reliability of 0.984 at 10 years, corresponding to a MTTF of 6,000,000 hours. Electron Energy Corporation (EEC) and team partner LMS propose to improve the efficiency and input power capability of LMS’s Midi compressor, for use on a 5 W at 77 K cryocooler. The current motor is a moving magnet design with a ring magnet, an external stator coil, and pole pieces. This configuration has a relatively low motor actuator constant and relatively high motor side forces. EEC will develop a state-of-the-art motor configuration with all axially-magnetized magnets and one coil winding. This design provides more powerful, lower-loss performance and will significantly reduce the cost because of the innovation and manufacturing process improvement. The system reliability is expected to be improved by reducing the input power requirements while increasing the magnetic field performance. Furthermore, we expect to reduce motor side load forces, which will result in a decrease in exported vibration from the compressor. In Phase I, EEC will design a new compressor motor for the Midi cryocooler compressor. Based on detailed investigation of the existing Midi compressor motor, a new configuration will be optimized, and then thermodynamic analysis of the cryocooler will be conducted. Finally, a magnet prototype will be produced to verify the magnetic properties and conduct a thermal cycling test over the expected range of operating temperatures. In Phase II, we will finalize the design of the compressor motor, and build two prototypes based on the Phase I results. All prototypes will be manufactured and integrated at EEC’s facilities. EEC’s vertically integrated manufacturing capability and 50 years of magnet production and magnet system development experience will enable us to implement a “fast prototyping” process. In Phase III, we will focus on the commercialization of the cryocooler compressor motor and development of mass production capabilities. Approved for Public Release | 20-MDA-10643 (3 Dec 20)