Reverse Turbo-Brayton cryocooler (RTBC) is a possible solution for NASA long term Zero-Boil-off (ZBO) hydrogen storage system for future space missions. RTBC cryocooler can have similar thermal efficiency as the current state-of-the-art LH2 cryocoolers with much less weight and size. The miniature helium compressor is the key component for this system, because it contributes the major portion in weight reduction. The present paper concentrates on the performance evaluation of an aerodynamically scaled miniature single-stage air compressor design, which is the first stage in the prototype of the future two-stage inter-cooled helium compressor. The single stage centrifugal compressor, designed by the authors, features a radial impeller, an axial diffuser driven by an integrated high speed permanent magnet synchronous motor run on ceramic ball bearings. In this paper, issues addressing performance of a miniature machine such as the present integrated single-stage centrifugal compressor and issues including thermal management, rotordynamics, effect of blade tip clearance, testing techniques are discussed. According to the test results, the design of the single stage was successful and established a solid base for the future two-stage helium compressor design.

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