Both test units survived an applied torque of 7.34 N-m (64.9 in-lb). At this point, the aluminum test shafts  suffered material failures where the lock washers dug into the aluminum. After this occurred, the tests were halted and the application of higher torques was not attempted. It is important to note that the neither the epoxy nor the tolerance ring were tested to the point of failure. Post-test analysis showed that  the applied torque was an order of magnitude less than the rated torque capacity of 76.3 N-m (675 in-lb) for a ring of that size. For the epoxy shaft, a simple analysis (shown in Equations 1 and 2) converted the  applied torque to shear stress at the interface between the shaft and the epoxy layer. Results showed  that the applied torque caused a shear stress of 303 kPa (44 psi) in the epoxy layer, which is nearly two  orders of magnitude lower than the epoxy’s rated shear strength of 26 MPa (3800 psi).  /g2162=/g2254 /g2200=374 N (84 lbf) (1)  /g2252/g2201/g2190/g2187/g2183/g2200 =/g2162 /g2157=/g2162 /g2250/g2186/g2190=303 kPa (44 psi) (2) The aforementioned testing indicated that both the epoxy and the tolerance ring were well-suited to  handle the torques exerted by the scanner assembly. Due to schedule constraints, it was not possible to conduct additional tests in order to fully characterize both the epoxy and the tolerance ring. Despite the  disadvantages mentioned in Table 4, epoxy was selected as the mating mechanism because of institutional knowledge of working with epoxies and its known flight heritage. For future applications, we would like to reopen the trade and continue characterization of the two  methods, particularly the behavior of a tolerance ring assembly subjected to random vibration. The  benefits that the tolerance ring provides over epoxy, such as a simplified installation process and ease of  disassembly, make the tolerance ring a desirable option. During assembly, the process had to be halted for 24 hours in order to let the epoxy cure. Had a tolerance ring been used to mate the rotor and the shaft, this portion of the assembly process would have only taken minutes. However, installation of the  tolerance ring requires the use of an arbor press, which is typically not found in a clean assembly room.  Another possible issue is the interaction between a steel arbor press and the high-strength permanent magnets in the rotor; a special assembly jig would likely be needed to protect the rotor from damage during installation.  Bearing Lifetime Analysis The critical component inside the scanner assembly is the bearing, which mechanically supports the  motor shaft and facilitates rotation with a low-friction lubricant. Failure of the bearing would cause the  motor to seize, and lead to a science mission failure. Design requirements state that the scanner assembly motor must survive for a minimum of 6 months of continuous operation, with 12 months being  the objective. Assuming continuous rotation at 60 rpm, the bearing must survive for 15.8 million  revolutions to meet the 6-month nominal mission lifetime, and 31.5 million revolutions to meet the  12-months objective mission lifetime. A lifetime analysis of the bearing was performed, using equations provided by the vendor. 13The equation used to estimate bearing lifetime is presented in Equation 3. /g1838=/g1853 /g2869/g1853/g2870/g4672/g3004 /g3017/g3293/g4673/g2871 (3)  /g47is the number of revolutions (in millions), /g38is the dynamic load rating of the bearing, /g51/g85is the  equivalent radial load acting on the bearing, /g68/g20is an adjustment factor for reliability percentage, and /g68/g21is  an adjustment factor for ball material. The equivalent radial load is defined as the purely radial load that, if  applied to the bearing, would result in the same lifetime as a bearing under radial and/or axial loading. Mathematically, it is defined by Equation 4. /g1842/g3045=/g1850 /g1848 /g1832 /g3045+/g1851 /g1832 /g3028 (4)  532