Other studies [8, 91 of lubricant life extension under a nitrogen cover gas have emphasized the role of an  oxygen impurity component in the cover gas interacting with both an additive in the lubricant and with  clean iron exposed by tribological action. The results presented here on oils without additives indicate that  neither oxygen nor clean iron is a necessary aspect of life extension under an impure cover gas. Neither  is the presence of an additive an essential aspect of the life extension process. Rather, the passivation of  active sites on the surface of the bearing steel by water vapor is the governing mechanism that reduces  the attack on the lubricant molecule itself.  Amlication to Testinq  The first implication of these results for testing of space mechanisms is that life-testing devices such as  bearings in a nitrogen environment to simulate vacuum is permissible with sufficient -absence of water  vapor. However, the severe restrictions required on the water vapor levels may eliminate any cost savings  versus vacuum testing. The second implication is that the device housing may contribute water molecules  to the device’s environment, since water always desorbs from an unbaked surface. This water flux  captured in a housing with limited access to vacuum can provide a degree of protection to the lubricant  that is not available in a more open geometry such as in the present test arrangement. In this sense the  present test arrangement provides a very severe test.  Conclusions  Both the PFPE and the MAC lubricants are tribochemically degraded in vacuum as evidenced by the  finite lifetimes they both exhibit in these tests. Tests in controlled environments indicate the lifetime of  both lubricants is extended if water vapor is present in the environment. The effect of water vapor is  evident at quite low levels (4 ppm) in the present tests. These results imply that sites must exist on the  bearing steel’s surface that can attack the lubricant molecules. These sites are chemically passivated by  water vapor, thus reducing the attack rate and allowing a longer lubricant life. An independent  understanding and chemical characterization of these sites is not available at present. These results  imply that testing of those mechanisms whose life is limited by lubricant consumption in an environment  with water vapor, even at very low concentrations in a nitrogen atmosphere, can lead to mechanism  lifetimes that are much longer than will be realized in vacuum service. Thus in terms of a “lessons  learned, it is advisable to provide water and oxygen sensors for the mechanism test environment.  Acknowledgments  I thank Dr. Kenneth W. Street for requesting tests whose results motivated this study.  References  1.  2.  3.  4.  5.  6.  7. Carre, D.J. “Perfluoropolyalkylether Oil Degradation: Inference of FeF3 Formation on Steel  Surfaces under Boundary Conditions”, ASLE Transactions, 29 (1 986), 121 -125.  Carre, D.J., “The Performance of Perfluoropolyether Oils under Boundary Lubrication Conditions”,  Tribology Transactions 31 (1 988), 437-441.  Novotny, V.J., Karis, T.E. and Johhnson, N.W., “Lubricant Removal, Degradation, and Recovery  on Particulate Magnetic Recording Media”, Journal of Tribology, 1 14 (1 992), 61 -67.  Pepper, S.V. and Kingsbury, E.P., “Spiral Orbit Tribometry - Part 11: Evaluation of Three Liquid  Lubricants in Vacuum”, Tribology Transactions, 46 (2003) , 65-69.  Bazinet, D.G., Espinosa, M.A., Loewenthal, S.H., Gschwender, L., Jones, W.R., Jr., Predmore  R.E., “Life of Scanner Bearings with Four Space Liquid Lubricants”, Proceedings of the 3fh  Aerospace Mechanisms Symposium, Johnson Space Center, May 19-21,2004.  Carre, D.J., “The Use of Solid Ceramic and Ceramic Hard-coated Components to Prolong the  Performance of Perfluoropolyalkylether Lubricants”, Surface and Coatings Techno/ogy, 43/44  Jones, W.R., Jr., Jansen, M.J., Chen, G-S., Lam, J., Baker, M., Lo, J., Anderson, M. and  Schepis, J.P., “The Effect of 17-4PH Stainless Steel on the Lifetime of a Pennzane@ Lubricatyf  Microwave Limb Sounder Antenna Actuator Assembly Ball Screw for the Aura Spacecraft”. 7 1 (1990), 609-617.  289