Load Alignment with Respect to Bearing Pad Both the front and the rear journal bearings used in this pump utilize axial grooves machined into the  carbon sleeves. These grooves serve to disrupt the half frequency whirl flow pattern and delay the transition to turbulence in the fluid film. A detriment to bearing performance caused by this feature is to  weaken the load capacity of the bearing when the load is oriented on or near one of these grooves. This  orientation can reduce bearing load capacity by 55% compared with an orientation where the load is wellcentered on the pad. During the assembly procedures of the pumps, no control measures were put in place to dictate the orientation of these grooves. Therefore this is a truly random variable, which may or  may not become significant depending also on the orientation of the additional imposed loads. Physical inspections of the failed hardware revealed that the rear bearing wear was concentrated at one of these axial grooves. In fact, the wear was so severe that the 1.5-mm-deep groove was no longer a visible  feature and the wear had gone deeper than the bottom of the groove. The evidence strongly implies that  the orientation of the load on a groove is a major contributing factor to the failure of the ammonia pump.However, the load orientation only serves to diminish the load capacity, a force acting in this specific  direction must be present to overload the bearing and cause the damage. Lubricant Jet Force on Rear Bearing A unique feature of the secondary flowpath on the failed ISS ammonia pump was the single lubricant feed  supply hole to the rear bearing. In addition to having just one supply hole to the rear bearing the lubricant was directed radially toward the shaft extension aft of the bearing. This is in contrast to the notional pump  shown in Figure 3. Examination of the right side of this figure shows that the lubricant to the rear bearing is canted toward the rear endplate of the motor, not toward the shaft, and that there are symmetric supply  holes to the rear bearing. This design practice ensures that no net force is imposed on the rear bearing due to the lubricant supply and secondary flowpath of the motor. However, the design that was implemented on the failed ammonia pump permitted a radial load to be imposed on the rear bearing due  to the jet force of the lubricant feed. An analysis was conducted on the magnitude of this force as a function of pump rotational speed. The results of this analysis are cross-plotted on Figure 6 and show that  this force can overload the 7.5 micrometer load capacity limit of the bearing at 12500 rpm. Furthermore, the finding of the physical inspections revealed that the wear on the rear bearing was in the direct  opposite direction from the lubricant feed hole. There are two strong indications that the lubricant jet force  on the rear bearing was the root cause of the bearing failure and initiated the damage to the rear bearing  carbon. First, the load margin analysis showed that the jet force alone could overload the rear bearing at 12500 rpm without considering the additional effects of the previous four factors providing additional bearing loads or reduced capacity. Second, the wear pattern was consistent with a uni-directional load  causing a static angular misalignment, which is the expected manifestation of the single jet force aft of the rear bearing.  Recovery and Modified Operations The tactical recovery for the ISS from the 2010 ammonia pump failure was the replacement of the pump  ORU with a functional on-orbit spare. Three EVAs were used to accomplish this task. Full function and operation of the ISS was restored by this activity. The strategic recovery focused on restoring the full 15year operational life of the pump module and ensuring that the ISS had a full complement of spares available to complete its projected life. In order to accomplish the strategic objective, additional questions needed to be answered and the root cause of the failure needed to be verified. Of primary importance was the determination that the failed pump was an ‘in family’ pump and no extenuating factors impacted the reduced life of the pump. A comprehensive review was conducted on all of the build records and qualification tests. No information was uncovered that would suggest that the failed pump had a unique history that would predispose it to premature failure. This finding placed an emphasis on the verification of the root cause and potential modifications to the operating procedures to restore pump life for future  modules. The lack of a ground asset that could be instrumented to validate a root cause scenario limited  the ability of the team to conduct comprehensive validation testing. A recommendation for future system  development is to maintain ground assets such that in-space anomalies can readily be investigated. 459