Space Shuttle Body Flap Actuator Bearing Testing for NASA Return to Flight  Timothy R Jett', Roamer E. Predmore'*, Michael J. Dube" and William R. Jones, Jr+)  Abstract  The Space Shuttle body flap (BF) is located beneath the main engine nozzles and is required for proper  aerodynamic control during orbital descent. The body flap is controlled by four actuators connected by a  common shaft and driven by the hydraulic power drive unit. Inspection of the actuators during  refurbishment revealed three shaft bearings with unexpected damage. One was coated with black oxide  on the balls and race wear surfaces, a second contained a relatively deep wear scar, and the third with  scratches and an aluminum particle in the wear track. A shaft bearing life test program was initiated to  measure the wear life and explain the 5.08-micrometer wear scar. A tribological analysis was conducted  to demonstrate that the black oxide coated wear surfaces did not damage the bearing, interfere with the  lubrication, or cause severe bearing wear. Pre-damaged (equivalent of 30 missions), commercial  equivalent bearings and previously flown shaft bearings were tested at axial loads, speeds, and  temperatures seen during flight operations. These bearing were successfully life tested at 60°C for 24  hours or 90 flights. With a safety factor of 4X, the bearings were qualified for 22 flights when only a  maximum of 12 flights are expected. Additional testing at 23°C was performed to determine the lubricant  life and to further understand the mechanism that caused the blackened balls. Test results indicating  bearing life was shortened at a lower temperature surprised the investigators. Start\Stop bearing testing  that closely simulates mission profile was conducted at 23°C. Results of this testing showed lubricant life  of 12 flights including a safety factor of four. Additional testing with bearings that have the equivalent of 30  missions of damage is being tested at 23°C. These tests are being performed over the Shuttle load profile  to demonstrate the residual bearing life in the actuators exceeds 12 missions. Testing showed that the  end of the shaft bearing life was characterized by bearing temperature rise, preload drop, and the onset  of a severe wear bearing failure mechanism. The severe wear failure mechanism is characterized by  rough wear scars, extensive bearing wear and steel transfer between the balls and the races.  Introduction  The BF is part of the Space Shuttle Orbiter control system that operates primarily during the critical  descent maneuvers. The Shuttle body flap is supported and controlled by four body flap actuators (BFA)  sharing a common, segmented drive shaft. The common shaft is driven by the hydraulic power  distribution unit. During inspection of these actuators, one of the input shaft bearings was discovered to  have blackened balls and a blackened wear track in the race after the actuator had completed  approximately 20 missions [I, 21. It was deemed unacceptable for service, replaced and the used grease  was discarded. Visual examinations of most of the BF actuators in the fleet revealed no evidence of  blacken balls or race wear tracks in the shaft bearings. The used shaft bearings were cleaned, inspected,  re-lubricated and reinstalled in the actuators or scrapped. Subsequent microscopic inspection and  metrology of these shaft bearings revealed significant wear and possible plastic deformation in a second  shaft bearing [3]. A third shaft bearing was found to have scratches and an aluminum particle in the wear  track. To determine if actuators with used bearings were acceptable to re-fly for twelve missions, a  bearing test program was initiated at the Marshall Space Flight Center.  Lf NASA Marshall Space Flight Center, Huntsville, AL + NASA Goddard Space Flight Center, Greenbelt, MD ++ SWALES\Glenn Research Center, Cleveland, OH SWALES/Goddard Space Flight Center, Greenbelt, MD  Proceedings of the 38 Aerospace Mechanisms Symposium, Langley Research Center, May 17- 19,2006  253