Heat Transfer Across Ball Bearings in Vacuum

Accurate spacecraft bearing temperature predictions often require both system and bearing level heat source and thermal conductance information. Bearing thermal conductance data is usually the most significant unknown in the development of the thermal model and little has been published in open literature on the subject. Consequently experiments have been conducted at The Aerospace Corporation to address this topic, with special attention given to applications such as high-speed momentum and flywheels. An experiment was designed to measure thermal conductance across a single bearing under both static and dynamic states. This paper will describe the test results for an angular-contact ball bearing under controlled inner race rotational speed, axial load, and thermal conditions. Tests were conducted on both dry and Nye Pennzane SHF2001 synthetic oil lubricated bearings. Test data showed that thermal conductance is sensitive to a complex interdependent set of variables including maximum run-in speed, axial load and temperature. A basic physical understanding of the heat transfer mechanism across a bearing was developed based on experimental results.