Conclusion  This paper has shown that lubrication or motion affects bearing thermal conductance in both magnitude  and sensitivity to operational conditions, such as temperature and axial load. In practice, engineers  typically use heritage information from applications using similar bearings within a comparable system to  obtain an estimate of bearing thermal conductance. But in some cases heritage information is altogether  lacking due to a new or a one-of-a-kind system. Engineers have often used analyses for a first-order  approximation of bearing thermal conductance, but the basic analytical equations apply to a non-  lubricated, static bearing. Information available on other bearing types is sometimes used as well.  However, drastic difference in both thermal conductance magnitude and sensitivity to variables such as  axial load and temperature is dependent on bearing lubrication and state of motion. As a consequence,  engineers need to evaluate where bearing conductance data came from, what conditions it represents,  and whether those conditions reflect the application at hand before using the data to predict temperatures  of a rotational device in space.  Acknowledgements  This work was funded by The Aerospace Corporation Independent Research and Development (RAD)  program. The authors will also like to extend our deepest gratitude to our management, in particular, Dr.  Michael R. Hilton. It was his outstanding support that made this research possible.  References  1.  2.  3.  4.  5.  6.  7.  8.  9. Yovanovich, M. M., “Analytical and Experimental Investigation on the Thermal Resistance of Angular  Contact Instrument Bearings,” Instrumentation Laboratory, E-221 5 (1 967), Massachusetts Institute of  Technology, Cambridge, Massachusetts, 85p.  Yovanovich, M. M., “Thermal Constriction Resistance Between Contacting Metallic Paraboloids:  Application to Instrument Bearings,” Proceedings of Heat Transfer and Spacecraft Thermal Control,  (1971), M.I.T, Cambridge, MA, pp. 337-358.  K. T. Stevens, M. J. Todd, “Thermal Conductance Across Ball Bearings in Vacuum,” Report Number:  ESA-ESTL-25, (1 977), National Centre of Tribology, Risley (England), 51 p.  A. A. M. Delil, J. F. Heemskerk, and J. P. B. Vreeburg, “Design Report on the ESRO Test Rig to  Measure the Thermal Conductance and Friction Torque of Rotating Bearings in Vacuum,” Report  Number: NLR-TR-74069-U, (1 974), 9Op.  J. F. Heemskerk, A. A. M. Delil, J. P. B. Vreeburg, “A Test Rig to Measure the Thermal Conductance  and Friction Torque of Bearings in Vacuum,” European Space Tribology Symposium, (1 975), Frascati,  Italy, 18p.  Rowntree, R. A., Todd, M. J., “Thermal Conductance and Torque of Thin Section Four-Point Contact  Ball Bearings in Vacuum,” Report Number: ESA-ESTL-54, National Centre of Tribology, Risley,  England, (1 983), 57p.  Rowntree, R. A., “Stiffness, Torque, and Thermal Conductance of Thin-Section Four-Point Contact  Ball Bearings for Use in Spacecraft Mechanisms,” Proceedings of the Ist European Space  Mechanisms & Tribology Symposium, (1 983), Noordwijk, Netherland, pp. 91 -100.  Anderson, M. J., Roberts, E. W., and Rowntree, R. A., “The Thermal Conductance of Solid-Lubricated  Bearings at Cryogenic Temperatures in Vacuum,” Proceedings of the 30th Aerospace Mechanisms  Symposium, (1996), European Space Tribology Lab., Cheshire, England, pp. 31 -45.  Nakajima, K., “Thermal Contact Resistance Between Balls and Rings of a Bearing Under Axial,  Radial, and Combined Loads,” Journal of Thermophysics and Heat Transfer, 9, (1 995), pp. 88-95.  10. P. D. Fleischauer and M. R. Hilton, “Assessment of the Tribological Requirements of Advanced  Spacecraft Mechanisms,” Materials Research Sociefy Symposium Proceedings, (1 989), pp. 9-20.  11. Y. R. Takeuchi, J. T. Dickey, S. M. Demsky, K. K. Lue, J. J. Kirsch, P. P. Frantz, “A Methodology in  Measuring Thermal Properties of Bearings in Motion,” Proceedings of the 75th Annual Thermal and  Fluids Analysis Workshop, (2004), JPL, Pasadena, CA, 25p.  12. A. Leveille, BRGSI OC, (a bearing analysis code), The Aerospace Corporation, El Segundo, CA.  302