220 already been built and delivered with Braycote 600EF, and, since no appropriate seals existed in the MDDA  design, a cross -contamination question was raised regarding the potential impact of migration of one  lubricant into the region of the actuator where the other was located. Finally, there was extreme uncertainty  whether the part lubricated with Bray could be reliably relubricated with Pennzane due to differences in  wetting characteristics.  

Three tests were executed to provide confidence in: (a) the compatibility of the Pe nnzane with the HD  component materials, (b) the ability to maintain MDDA performance in the event of cross -contamination  due to lubricant migration, and (c) the ability of the MDDA to achieve 100% torque margin against a 5.1 Nm  (45 in- lb) requirement at th e MAIA coldest operational test temperature of -20°C. For (a), an accelerated  test would be completed, running the Drive Output Subassembly with the updated Pennzane lubricants,  after which inspection and chemical grease analysis would be completed. Regarding item (b), a Pin- OnDisc test was to be completed using a mixture of Rheolube 2000 and Braycote 600EF. Finally to address  (c), cold temperature testing would be completed to evaluate the trade between maximizing the Pennzane  grease and oil fill amounts and minimizing the cold temperature input drag.  

Rewetting & Initial Accelerated Test   The entire lot of HD units and Duplex bearings had been cleaned, inspected, and processed with Braycote  lubricants together, and thus, it had to be removed from all of them, including their phenolic retainers. The  units were all sent to the Laboratory for Applied Tribology at JPL, to be cleaned and re- processed. To  remove the Braycote, the parts were placed into a vapor degreaser, where they sat for several days,  followed by ultrasonic agitation, both using Vertrel XF. The Wave Generator subassemblies still  remained  intact, with bearings and spacers bonded onto the Wave Generators. Their disassembly was discussed,  but concerns that were presented regarding potential damage to the irreplaceable flexible bearings during  the disassembly and reassembly process prevailed. Some patches of corrosion were visible on the Wave  Generator bearing races, which were removed using Scotchbrite. The HD and the duplex bearings were  then grease plated using a 10% Rheolube 2000 and 90% Heptane by mass solution. An additional gre ase  fill of Rheolube 2000 with a mass of 0.1151 g was added to the Wave Generator bearings, resulting in  0.0027 g of Rheolube mass applied per each of the 42 bearing balls shared across the pair of bearings.  

In this configuration, the HD was reassembled into the Drive Output Subassembly along with a similarly  prepared Duplex bearing pair, and the accelerated test was conducted using the Endurance Test fixture.  The test article drove a 3.4 Nm ( 30 in- lb) load in the clockwise direction for 72 hours consecut ively at a rate  of 16 deg/s. No significant change resulted in input torque nor in speed across this test. The near -constant  input torque measured across the test gave confidence in the ability to re- wet the assembly with Pennzane  and to subsequently perform well under an aggressive set of initial conditions. After completion of the  72 hours, the test article was disassembled, revealing the Pennzane inside to have a normal consistency,  but to be grey in color. The grease sample was sent to the analytical chemistry lab to look for any signs of  a potential impending lubricant breakdown.  

The gray color of the lubricant was verified to be primarily iron and chromium, with a small amount of  titanium (the housing material), by XRF imaging. Fourier Transform Infr ared spectroscopy (FTIR) was  performed to determine that no significant changes had occurred in the bulk grease chemistry, and there  was no evidence of oxidation in the sample. The Direct Analysis in Real Time -  Mass Spectrometry (DART - MS) method showed no significant change in the molecular weight of the sample when compared to a  comparable new, un- tested sample as well. Overall, the accelerated test yielded a passing result, verifying  that the HD and the duplex bearing pair had been successfully rewetted,  and the Pennzane lubricants could  be trusted to be materially compatible with the HD.  

Pennzane Cold Testing   The components were cleaned using Heptane to remove the Pennzane, and re- coated with a fresh  Rheolube 2000/Vertrel XF 10/90 mass ratio grease plat e layer. This time a Nye Synthetic Oil 2001/  Rheolube 2000 slurry with a 50/50 mass ratio was also applied to the Wave Generator bearings and a  70/30 oil/grease ratio applied to the duplex bearings. The duplex bearings received 0.077 g of slurry to each