2) The slip ring wires used Tefzel wire insulation per MIL-W-22749/44 and M27500-28SR2S23.  There were numerous instances wherein the wire insulation cracked at bend radiuses (Figure 9).  This required a lot of tedious repair work and inspection. Similar problems were also seen on the  Tefzel motor hookup wires. While the definitive cause of this was not determined, no cracking  was seen in the second, flight spare slip rings where the wire used was procured from Raychem  as Raychem wire had been used on the rest of Windsat with no cracking. When digging into other  experience with this problem it was found that the Tefzel cracking seemed to occur most often in  the presence of elevated temperature epoxy/potting cure operations. However, no definitive  causeleff ect relationship was determined.  i  Figure 9. Cracked Tefzel Wire  3) As mentioned previously, the slip rings were cleaned and lubricated by Ball Aerospace. During  cleaning an analysis of the solvent rinse was conducted, which revealed silicone contamination.  The slip ring specification prohibited any silicone materials, lotions, etc from being used on or  near the slip rings as silicone contamination can cause lubricant dewetting and form compounds,  which result in slip ring noise. The source of the contamination was eventually traced to Kapton  tape that was mislabeled by the tape vendor and contained silicone adhesive, even though it was  labeled as acrylic adhesive. A lengthy cleaning process was undertaken to remove the silicone  from the slip rings. If not for the extraordinarily thorough cleaning and lubrication process  procedures at Ball, the slip rings would likely have had silicone contamination problems, which  would have resulted in disastrous consequences. It is recommended that solvent rinse analvsis  be conducted durina slip rina Drocessina of slip rina assemblies.  4) The Windsat slip ring had 137 rings and 274 brushes in a 305-mm (12-inch) length. Slip ring-to-  brush alignment was very challenging and key to proper functionality. Alignment features and  tight tolerances were necessary to properly control alignment. Additionally, a detailed thermal  model/analysis was performed to analyze the effect of thermal gradientdtemperature on slip ring  to brush alignment. Finally, displacement during vibration was analyzed to ensure that brushes  would not “jump rings” during vibration testing/launch. None of these conditions presented a trivial  problem. Furthermore, as the slip rings wear, they create wear debris which tends to get pushed  to the sidelout of the contact path with continued rotation. During normal operations the slip rings  are maintained within a narrow 25-30°C temperature band. However, occasionally the spacecraft  goes into a radiation upset induced safe hold which turns everything off and the slip rings cool to  approximately 0°C. Starting up from this temperature results in displacement of the brushes due  to differential thermal expansion and presents an opportunity for “running in the debris on the side  of the road. In fact, the sliD rina/brush disDlacement at cold temDerature may have Dlaved a Dart  in the on-orbit anomalv that will be discussed in detail later as both on-orbit BAPTA anomalies  occurred within weeks of a safe hold event.  5) The Windsat slip rings were lubricated with a thin film of oil supplied by Ball Aerospace. During  cold temperature acceptance TVAC testing (-20 to 5°C) slip ring noise was found. This noise was  due to hydrodynamic effects of the thickened oil at these temperatures. It was determined that  21 6