was fixed on the ground allowing us to fully utilize our torque margin with full closed loop servo  performance. It is common to demonstrate margin by analysis only or via friction torque measurements  but less common to verify closed-loop servo torque margin performance. Onlv the closed-loop servo  toraue marain test performed would have cauaht our resolver noise problem. Additionally, the large  margins built into all aspects of the design helped in the decision to fly “as-is” with numerous  problems/defects that will be described hereafter.  Desian/Test For Indefinite Stall At Hot TVAC  The NRL standard test program for the Windsat BAPTA required testing the BAPTA under stalled  conditions at worst case hot thermal vacuum until the BAPTA reached thermal equilibrium. Designing the  BAPTA to survive these conditions and performing this test gave us the confidence that it was extremely  difficult to damage the BAPTA by mistakes or anomalies on the ground or on-orbit. As point of fact, during  the Windsat on-orbit anomaly the BAPTA drive motor was hammered back and forth with full stall current  at 13 Hz for 15 minutes with no damage.  Don’t Put Precision Feedback Device (Resolver) In A Load Path  The Windsat BAPTA resolver was mounted at the end of the BAPTA, which supported the cantilever,  mounted slip ring assembly. As such all cantilevered slip ring launch loads were transmitted through the  resolver mounting structure. While this structure was capable of handling these loads, the resolvers are  precision bonded to this structure and some slight settling of the resolver position was seen after the first  BAPTA vibration and thermal vacuum testing. After this initial “set” the position did not drift noticeably and  was thus more of a “headache” than a real problem. The layout of the Windsat BAPTA does not leave  many optional locations for locating the resolver (Le., out of a load path). However, for future designs  consideration should be given to placement of precision feedback devices relative to load paths.  Blind Holes, Filtered Vents & Labvrinth Seals Prevent Contamination Problems - Both Goina In And  Cominq Out - Especially On Slip Rinas  The Windsat BAPTA and slip rings had a design requirement for blind holes whenever possible and  filtered vents and/or labyrinth seals to prevent contamination problems. Many drives have suffered  anomalies due to contamination in bearings or air gaps. This is especially critical on designs with slip  rings. Slip rings with the life requirements of Windsat create significant amounts of wear debris. Managing  this debris and keeping it out of bearings, air gaps, (and shorting rings) it a crucial part of the design. In  the Windsat design the slip ring assembly had labyrinth seals that kept the slip ring debris contained  within the slip ring and away from bearings, motors, and resolvers. Slip ring barriers were made with  heights large enough to prevent debris buildup ring shorts. Additionally, all power + rings were grouped  together and all returns were grouped together to minimize potential shorting paths. On the signal side we  had alternating “odd & even” side brush blocks for consecutive signal wiring and ring assignments of  shield, +, -, shield (4 rings per twisted shielded pair, Figure 5) to prevent adjacent circuit shorting and  minimize noise and crosstalk. A final lesson was learned from inspecting the old DSCSll slip ring life test  unit, which was full of wear debris. It was found that the oil impregnated reservoirs used to help replenish  the relatively high vapor pressure oil used in the 1970’s had a side benefit of acting as a “fly trap” to  collect a thick layer of wear debris away from the critical brushlring interface. Thus while the new low  vapor pressure oil used on the Windsat slip rings did not need oil reservoirs, they were maintained for  their “wear debris management” function.  Figure 5 - Signal Rings - Twisted Shielded Pairs  21 2