It should be noted that the use of the silicon nitride balls and its material dissimilarity to its friction couple,  steel, has shown remarkable lubrication life extensions in other applications and has for years allowed the  luxury of using just oil in critical applications that require extreme torque quietness over extended periods  of time. The oil is not damaged as fast as with all-steel bearings and therefore extra grease or grease dams  for life extension are not needed. The lubricant life tests, discussed in a later section, should bear this  conclusion out and provide more real data for the aerospace mechanism community.  Cartridge Runout Verification  To measure and document the axial and radial runout requirements given in Table 1, the bearing vendor  developed new test hardware to verify cartridge performance. A non-contacting, capacitive picometer  sensor was mounted in adaptable setups to determine synchronous and asynchronous TIR at the four  specified interfaces and at both 360 and 180 RPM. Initial setups indicated that external electrical and  mechanical noise, structural modes, and sensor surface squareness, generally in that order of effect, were  all contributors to significant measurement error. By diligent effort, all error sources were eliminated.  Electrical noise was addressed by establishing a thorough grounding scheme, as well as by establishing  an electrically “quiet” facility location and controlling local equipment usage. Structural noise was addressed  by redesigning to a very stiff sensor mounting block and a stiff structural loop between the sensor and  cartridge mounts. The motor drive signature was isolated using a pulley with an O-ring driving a jack shaft  supported by Rulon bearings then coupled to the cartridge with Tygon tubing. By attention to sensor  positioning, it was noted that the surface squareness of the sensor relative to the cartridge could be altered  by indexing (i.e., rotating on axis) the transducer body by 90° to 270°. The sensor output was sent to a dualtrace spectrum analyzer to display the displacement in time and frequency components. After corrective  actions, by taking a time trace reading with no shaft motion, static sensor readings in all four locations  indicated approximately 0.0127-µm (0.5-µin) noise. During high-speed shaft rotations, sensor displacement  vs. time gave us a total runout (synchronous and asynchronous) and the frequency trace served to  distinguish between synchronous and asynchronous runout. The result was that virtually all runout was  synchronous (that is, on the orders of rotations).  Cartridge Performance Predictions and Verifications  Performance predictions  During the superduplex cartridge fabrication, an effort was begun to predict starting and running torque at  360 RPM for inclusion in the drive electronics design capability. To that end, analysis and tests were used  to predict performance. Generally, bearing torque consists of a load torque caused by sliding and rolling  friction between components in the bearing, and a viscous torque, due to the plowing and squeezing of the  lubricant. The load torque is largely dependent on loading, and weakly dependent on speed, while the  viscous torque is largely dependent on speed, and weakly dependent on load. Both BRSG10 and ORBIS  bearing analysis codes provide similar estimations of load torque at zero speed, as show in Table 5, given  the same assumption of coefficient of friction.  Table 5. Load and Speed Torque Predictions  BRGS10 ORBIS units  Load Torque Est. mu = 0.08, P = 60 [lb] 6.9 (0.974) 6.8 (0.96) mN-m (in-oz)  Viscous Torque Est. 350 cSt, LQF = 0.3 39.5 (5.6) 25.4 (3.6) mN-m (in-oz)  Viscous Torque Est. 240 cSt, LQF = 0.3 30.1 (4.35) 19.9 (2.82) mN-m (in-oz)  The viscous torque is affected by the lubricant viscosity and quantity of lubricant in the bearing. The lubricant  viscosity is affected by temperature while the quantity of lubricant and its effect on torque is dependent on  the size of the bearing, type of lubricant, and other miscellaneous factors. This leads to an empirical factor,  called lubricant quantity factor (LQF) used in viscous torque estimation and the need for testing to anchor  NASA/CP—2018-219887 106