Miniature Turbine for Pulse-Tube/Reverse-Brayton Hybrid Cryocooler

Many future advances in NASAys ability to perform cutting edge space science will require improvements in cryogenic system technology, including the development of light-weight, low vibration, highly-efficient, long-life cryocoolers. One such cooler, currently under development, is the pulse-tube/reverse-Brayton (PT/RB) hybrid cooler. Of critical importance to success of the PT/RB is the development of the small-scale turbine required for the reverse-Brayton stage. We propose to build such a turbine for inclusion in a brassboard PT/RB soon to be constructed under a separate contract. The turbine will incorporate pressurized bearings that generate a supporting force by applying a high-pressure source of gas to a flow restriction that exhausts into the bearing clearance and onto the turbine shaft surface. Pressurized bearings provide support even in the absence of shaft rotation and therefore eliminate rubbing contact and increase the life and reliability of the bearing. Also, because pressurized bearings do not directly depend on viscous action for operation, relatively larger clearances can be used without significantly sacrificing rotordynamic performance at low temperatures, thus making them cost effective.