7)  9) this noise could be “burned through” with the 2 Amps of current used on the power rings but not  with the 100 mA of current used on the signal rings. Additionally, the rings that exhibited oil  exhibited a bead of excess oil that clung to the brush at the ring contact (Figure 10). Rings  without this oil bead did not seem to show cold temperature noise. This problem was solved by 2  methods: 1) re-oiling the slip rings with a slightly lower quantity of oil which did not result in the oil  beads at the ring contacts, and 2) adding a heater to the slip rings to try to keep the rings above  5°C. After retesting with the lower oil quantity there was no noise found all the way down to -2OC.  Figure 10. Original Oil Quantity (Left) Final Reduced Oil Quantity (Right)  Since the Windsat slip rings had a high life cycle requirement and slip ring noise & wear are a  function of brush force, the brush force was measured on all 274 of the slip ring brushes. This  brush force inspection was a difficult. Dainstakina process. but it Daid off in that it revealed that  desDite the best of efforts and tolerancina. manv of the brush forces were sianificantlv out of  -.  It is typically believed that the environment (air vs. vacuum) does not affect gold on gold slip rings  but does affect silver/MoSp slip rings. On Windsat, we found that after running at 30 rpm for  approximately one week in air we would get high-frequency slip ring noise. This noise would  clean up / go away after several days of running at 30 rpm in nitrogen or vacuum. While there  were no timelfunds to investigate the mechanism for this, it is postulated that an extreme  pressure additive in the oil may be oxidizing in air to form insulating compounds. In N2 or vacuum  this material may be wordpushed away and cannot form in the absence of oxygen. This didn’t  seem to have any adverse impact on the performance of the life test units. Additionally it had no  impact on Windsat as air drag limited the speed of the full up Windsat payload in air to a few rpm  and there was never enough revolutions in air to run into this problem.  The Windsat slip rings are constructed from a stack of slip ring modules. Prior to the module  “stacking” the individual modules were thermal cycled to screen for “bad bond” or rings going  open circuit. These screening tests resulted in rejecting a module with multiple opens and finding  a module with one bad circuit that was relegated to a spare, prior to wiring and any “pain”.  The slip ring brush design was an exact copy of the DSCSll design. However, since DSCS had  fewer and smaller diameter rings, the brush placement differed. Unfortunately, the placement  used left the tips of the brushes dangerously close to the brushlring contact point. In fact a few of  the brushes created large piles of run-in debris, which was traced to contact at the brush tip and  “digging in”. Fortunately, this only affected a few brushes and enough spare rings were available  to reassign these circuits.  SliD rinas are verv process-sensitive devices. It has taken decades to learn all of the Drocesses that need  to be controlled/Daid attention to in order to Droduce reliable sliD rinas. Manv of the DeoDle who “learned  these lessons” have left and the Droaram should make sure that those details have been carried forward  into the current Droduction or the “heritaae” cited mav not be valid. This issue was encountered when  building the Windsat slip rings, which traced their heritage back to the DSCSll program, last built in the  1970’s. There were actually still several people at the slip ring vendor and Ball who worked on the DSCSll  slip rings. However, undoubtedly there was a lot that was forgotten, especially when it came to “why it  was done that way”. The Windsat slip ring design was very similar to DSCSll but not the same. One  “heritage” mistake we made on Windsat was to copy the DSCSll signal and power brush design, exactly  217