reaches around 60°C. Recent reexamination of the BF actuator operation time line by the NESC showed  that the actual average mission actuator operating time was 16 minutes (1280 cycles) rather than the 24  minutes. Based on these facts, the shortest lived startktop test of 12.8 hours (61.4 cycles) was used to  life the BFA shaft bearings. This calculation yielded a bearing life of 12 missions including a safety factor  of 4.  Conclusions  1.  2.  3.  4.  5.  6.  1.  2. Initial test results of full scale bearing testing at 60°C indicated that previously flown and re-lubricated  Body Flap Actuator shaft bearings were acceptable for 22 Shuttle Missions with a safety factor of 4.  Subsequent bearing testing at 23°C show the lubricant life is reduced at lower operating  temperatures.  Results of full scale bearing stop\start testing at 23°C showed that new bearings were acceptable for  12 Shuttle Flights with a factor safety of 4.  Efforts to duplicate the blackened balls observed on one of the Shuttle Body Actuator shaft bearings  were unsuccessful. The blackened balls were produced in testing, but only after lubricant failure and  severe wear are initiated. SEM analysis showed that the test blackened balls are not very similar to  the flight ball. The test blackened balls were in much worse condition and had a more textured  surface with smalls cracks observed. The flight bearing with blackened balls did not suffer a lubricant  failure. The flight blackened bearing was in relatively good condition with smooth wear surface.  The Raman Spectroscopy, XPS and EDS analysis of the flight black ball detected the presence of  carbon-rich layer on an iron oxide-rich layer and both with fluorine. The detection of amorphous  carbon, fluorine and FeF3 in both the carbon-rich surface layer and the iron oxide under layer were  significant since local degradation of the PFPE lubricant appeared to be in part responsible for the  black coating observed on the balls and raceways of P/N 5902050, S/N V6L009, bearing removed  from S/N 402 BF actuator. The origin of the thicker, black iron oxide-rich layer under the carbon-rich  layer is not well understood. Because it occurred only on the wear surfaces, the tribological chemical  reactions in the ballhace wear interface did cause the black coating. Most investigators felt that high  temperatures below 200°C contributed to the black coating formation. Local lubricant starvation within  the ball path of the bearing may have generated local heating with temperatures high enough to  cause the remaining lubricant film to degrade and react with the 52100 steel surface, effecting  formation of a complex oxide layer that resulted in the black coating on the wear surfaces. While the  system may have recovered locally after the blackened coating event, the oxide layer formed was  apparently effective in separating the working surfaces of the bearing, preventing its failure, and  serving as a surrogate solid film lubricant.  The strength, geometry, metallurgical structure and wear of the black coated bearing were found to  be essentially identical to other BF shaft bearings after Shuttle flights. No evidence of severe wear  was observed. Therefore, shaft bearings with black tribological coatings like S/N V6L009 are  expected to perform successfully for at least 12 more Shuttle missions.  The severe wear mode caused failure of the shaft bearing and determined the bearing life. The onset  of severe wear is thought to be caused by ball/race metal adhesion after all the Braycote 601EF  grease is depleted from the interface.  Lessons Learned  When space mechanisms are qualified by accelerated life testing, bearings should be qualified by  real-time life testing. Bearings enduring the highest stresses, longest operating lives or highest  temperatures in the mechanism application should be life tested as part of the qualification process.  Bearing life and lubricant life was found to be shorter at lower temperature even though the lubricant  tribological decomposes or degrades more rapidly at higher temperature.  267