© 2016 Sierra Nevada Corporation   125 Life Test Method  

In order to simulate on- orbit conditions as closely as possi ble while balancing total test duration, cost, and  setup simplicity ; a life test was performed using the following parts, methods, parameters , and criteria.  

Test Articles   Program requirement s dictated that the life test bearings be manufactured with the same bearing  geometry, ball and raceway material, ball separator material, raceway finishing process, and internal  bearing preload as the flight bearings . It was also important to test a large enough sample to be  statistic ally significant . In order to accomplish this most accurately, six  duplex bearing sets were taken  from the flight procurement manufacturing lot  and allocated to the life test . Additionally, all bearings in this  lot (flight and life test) were lubricated wi th the same lubricant lot, quantity, and application method.  

Life Test Mounting   The test bearings are mounted in the same back -to-back duplex arrangement as the flight bearings . The  bearing clamping arrangement utilizes comparable stiffness clamps with t he same number of fasteners  and fastener torque to create the same nominal clamp forces as flight . The tolerances of the fixture  mounting diameters and shoulders are held the same as the flight part drawings and the same adhesive shimming procedure is util ized to minimize inner to outer race misalignment and wobble.  

Life Test Parameters:   • Primary  Life Test  Goal:  64.2 million shaft revolutions (1X Operating Life) within 20 months   • Secondary Life Test Goal:   128.4  million shaft revolutions  (2X Operating Life)   • Revised Life Test Goal:  Test to failure as defined by termination criteria listed below   • Load:  No external load, internal bearing preload of  133.4 N ( 30 lb) nominal   • Speed:  74 RPM , selected to balance maintaining equivalent  film thickness  and lubrication regime  while reducing test duration  as previously described   • Direction:  Unidirectional continuous operation   • Pressure:  Vacuum  of 6.67E -4 Pa ( 5X10-6 Torr) or better    • Temperature: No active thermal control , vacuum chamber located in an ambient lab environment,  natural self-heating of bearing housings allowed up to the maximum predicted on-orbit operating  temperature of 36°C  

Life Test Data Monitoring   The following key parameters were monitored throughout the life test to ensure required conditions were  met:  • Torque: Friction torque periodically monitored and recorded using an data l ogger with a sample rate  of once per millisecond for a duration of one minute, collected every  hour  • Temperature: Bearing  housing temperat ures were recorded once an hour   • Revolution Count:  P roximity switch counting once per revolution  

Life Test Termination Criteria   Friction torque is the most direct measurement of bearing health available and as such is used as the primary factor in determining when a “test to failure” is completed as follows:   • Friction torque exceeding 1 25% of the initial setup running torque    Conditions that would warrant pausing the life test in order to determine credibility and impact of the data  would be out of family torque conditions such as:   • A sudden increase in bearing friction torque and/or steady state temperature   • An excessively erratic friction torque trace when compared to prior test data or to other bearings  under test