change in preload over temperature due to a difference in material thermal expansion coefficients was  determined by analysis to be an acceptable detriment, given the other benefits of silicon nitride.   The sleeve material of 440C stainless steel was used in order to minimize thermal expansion coefficient  differences between bearing rings and the sleeve (Table 4). The sleeved cartridge fits into an aluminum  housing, which provides the structural connection to the instrument optical bench. With precision fits, the  separation and support provided by the stainless steel sleeve minimizes the effect of the thermal expansion  coefficient differences between the steel bearing and aluminum housing.  Table 4. Structural Component Material Properties Al 6061-T6 440C Ti-6Al-4V  Modulus 69 GPa 205 GPa 114 GPa  Poisson's Ratio 0.33 0.283 0.33  Density/Specific  Gravity 2.7 g/cc  (0.098 lbm/in3) 7.8 g/cc  (0.282 lbm/in3) 4.43 g/cc  (0.16 lbm/in3)  Thermal Expansion  Coefficient 23.6e-6 1/C 10.2e-6 1/C 8.6e-6 1/C  Type Aluminum Stainless Steel Titanium  The ball retainer material is machined phenolic, MIL-I-24768, Type FBE, often used in many space  applications due to its light weight and ability to be properly impregnated with the lubricating oil, acts as an  oil reserve. To provide additional lubrication reservoirs, Nysorb® rings, also impregnated with oil, were  designed to fit into outer race inner grooves.  Analysis Approach  A bearing analysis was conducted to ensure that the assembled and integrated bearing cartridge would  meet design and performance requirements. This analysis was performed concurrently with detailed design  of the cartridge to aid final design decisions, such as material selection and fits. The analysis ensured that  two primary requirements were met: the maximum mean contact stress in the bearing must be within  allowable limits during launch and the final preload range during operation was suitable for the rotating  telescope. The goal was to have an appropriate preload range over the expected operating temperatures  and the given manufacturing tolerances of the piece parts. A higher preload means a shorter fatigue life  and higher drag torque, while a lower preload might compromise the stiffness of the system. An example  preload goal range might be between 44.5 N (10 lbf) and 445 N (100 lbf) preload. The analysis also ensured  no truncation of the contact ellipse on the land, as well as provided estimates for running torque and  stiffness.  Key parameters that affect the analysis results include:  •Material properties (Young’s modulus, Poisson’s ratio, coefficient of thermal expansion) •Bearing geometry (bearing size, raceway curvature, contact angle, straddle) •Mounting (clamping force, interference fits, initial preload) •Operating parameters (temperatures, speed, launch loads, preload) With the materials, geometry, and operating parameters fixed, the final design decisions were related to  the mounting of the bearing into the sleeve and housing. Therefore, this bearing concept described above  leads to a number of issues that must be accounted for in the detailed design and mounting analysis:   •Clamping effect on preload •C-spacer effect on raceway parallelism •Sleeve fitting effect on preload •Sleeve/housing fit NASA/CP—2018-219887 101