Advanced Developments for Low Temperature Turbo-Brayton Cryocoolers

Abstract

Turbo-Brayton cryocooler technology that has been space qualified and demonstrated on the Near Infrared Camera/Multi-Object Spectrometer (NICMOS) cryocooler is being adapted for applications with lower cooling loads at lower temperatures. The applications include sensor cooling for space platforms and telescopes at temperatures between 4 K and 35 K, where long life and reliable, vibration-free operation are important. This paper presents recent advances in the miniaturization of components that are critical to these systems. Key issues addressed in adapting the NICMOS cryocooler (NCC) technology to lower temperatures involve reducing parasitic losses when scaling to smaller size machines. Recent advances include improvements in the efficiency of a small, permanent magnet driven compressor that operates at up to 10,000 rev/sec in self-acting gas bearings and the successful demonstration of a 2 mm diameter shaft operating in pressurized gas bearings.

The compressor is important for cryocoolers with input powers between 50 W and 100 W. The miniature shaft and bearing system has applications in compressors and turbines at temperatures from 300 K to 6 K. These two technology milestones are fundamental to achieving exceptional thermodynamic performance in low temperature turbo-Brayton systems. This paper discusses the development of these components and test results, and presents the implications of their performance on cryocooler systems.