ESA's XMM-Newton space observatory, the flagship of European X-ray astronomy, is after its launch in 1999 the most powerful X-ray telescope ever placed in orbit. The mission originally had a design goal of a 10 years lifetime is planned to be operated long into its third decade since spacecraft and instruments are operating admirably without major problems. The most significant degradation was noticed since summer 2008 when one of the reaction wheels started to show an intermittent anomalous behaviour; sometimes during stable pointing RW1 had a jump, with increased value of drawn current. After some investigation it was recognized to be the well-known problem of cage instability in the bearings. Later on RW2 showed the same symptoms. A cure -or mitigation -for this problem consists in a re-lubrication of the ball bearings of the reaction wheel. Re-lubricating the bearing in flight is possible thanks to the design of an oil reservoir placed in the proximity of the ball bearing. In December 2011 it was decided to switch RW1 off to avoid further degradation of the bearing, reconfiguring the AOCS with RW 2-3-4, and on 12 November 2012 the bearing was re-lubricated for the first time with a special procedure. Since the cage instability appeared again after few days a longer relubrication was attempted on 27 November 2012. This second re-lubrication was not conclusive, since another event of cage instability occurred during the following month. On 18 December 2012 it was decided to switch off again the RW1, to be on the safe side. At the same time a re-lubrication of RW2 was performed. This paper describes the challenges to re-lubricate two RWs and the outcome of such operations.
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