Potentially  Influencing Parameter Modification  Observed Effect on noise  reduction Comment Lack of lubricant Extended nonoperation time  (storage time) Noise issue was more severe  after extended mechanism  storage time (some days)  Type of Lubricant Change from Z-25  to Nye oil and MAP  grease No improvement observed However: General  improvement of lubrication  performance over life could  be achieved by the changed  lubrication concept in  combination with steel balls.   Potential chemical  degradation of Z 25 in  combination with the steel  balls and steel races could be  avoided.  While the above measures 1) and 4) of Table 2 could be performed on Astrium site, the measures 2) and  3) directly related to the bearing configuration, had to be implemented by the bearing supplier but verified  on mechanism level. It was found that this process was extremel y time consuming and inefficient since it  was very difficult to intervene regularly into the supplier standard manufac turing process for implementing  any new parameter modification. Furthermore the bearing supplier himself was depending on lower tier  suppliers (e.g. for cage manufactu ring) so additional delays were re sulting as a consequence.  Therefore it was decided to perform all necessary further bearing investigations and modifications directly  at Astrium Satellites within the mechanism team. This approach allowed complete in-house control of the further investigation process without any un-necessary schedule delay. For this purpose all required  bearing dismantling and re-integration tools were manufactured and the bearing dismantling and mounting  process was defined in order to allow com plete handling and control of all necessary further bearing  modifications, independent from the bearing supplier. After dismantling the EQM bearings and cages on  Astrium site, all parts were inspected and no degradation or abnormal condition of parts or lubricant was  observed. After implementation and check of the above measures it was quite clear that the anomaly was generated  by the bearing cages as a consequence of occasionally occurring cage instability effects at the given  rotation speed. However the mechanism of action causing the instability effects with subsequent noise  production was not really understood.  Only three findings influencing the noise production remained:  The first important observation was that under low bearing pre-load the outer bearing races of a  bearing pair tended to slightly rotate w.r.t. each other. This led to the suspicion that during operation  unexpected forces produced by the cage are acting to the outer race.  The second observation was that at increase of cage stiffness (increase of cage cross section) the  noise effect got worse.  In addition it was observed, that after an extended storage time (e.g. weekend) the noise issue was  more severe than under continuous rotation. This was also in line with the fact that after delivery of the  EQM to the customer (long storage time resulting from tran sportation, unpacking, start-up activities)  the noise issue was observed again.  All three above observations lead to the conclusion that un-expected forces in the bearing were acting with  the result of subsequent noise production.  The observation made during the first EQM tests namely that after occurrence of a sudden hard noise in  the bearing the noise issue disappeared completely for all remaining test campaigns, could now be  126