Table 1. Motor Failure Timeline of Events  August 2015 Failure 1 – Motor Acceptance Test Thermal Cycling  November 2015 Initial investigation of Failure 1 completed  December 2015 Start of Capture Latch Acceptance Test  February 2016 Failure 2 – Capture Latch Acceptance Test Thermal Cycling  March 2016 Failure 3 & 4 – Capture Latch Acceptance Test Thermal Vacuum  July 2016 Failure Investigation and Redesign complete  October 2016 Restart Capture Latch Acceptance Test  Failure Investigation Summary  After the occurrence of Failure 1, the supplier performed a failure analysis. The supplier confirmed the B  string of the motor functioned properly even though the A string had failed, indicating the failure was not  related to mechanical binding inside the motor assembly. Further, they were able to validate the failure was  isolated to the motor, not the test equipment or the motor controller. Fault isolation testing showed that on  the A string of the motor, one of three HEDs on each string was non-operational. Pre-teardown imaging of  the motor was determined to be possible but impractical due to the difficulty of imaging through the metal  casing of the motor. Additionally, the motor could not be disassembled without damage due to the  permanent manner in which the casing was assembled. Therefore, it was determined that the only practical  troubleshooting step remaining was a destructive teardown of the motor, to be followed by X-Ray imaging  and physical inspection of the affected HED subassembly. These steps were performed, but no clear cause  of the failure was identified.   Out-of-place solder was observed adjacent to the failed HED; however, it could not be determined whether  this solder was the cause of the failure or if it had flowed there during the teardown, which involved heating  up the motor to loosen epoxy on the casing. A review of the soldering processes for the HED was performed  and a defect in the process was identified. A full fault tree was developed for the issue, but no additional  likely causes were identified at the time. The soldering process issue was determined to be the most likely  cause of the failure.   Failure 2 occurred approximately four months after Failure 1. After the failure occurred, an investigation  along with troubleshooting testing began. The test setup was exonerated as the cause of the failure  following a thorough inspection and checkout of the equipment. A full timeline outlining the history of the  failed unit was developed, starting with assembly and test of the motor/controller at the supplier and  continuing up through the failure. The timeline showed that unit had performed nominally through all  assembly and test activities, until TVAC testing. Erratic behavior in the CLA began to emerge during the  TVAC test. During operation of the Capture Latch Motor, there are three parameters monitored, current and  voltage applied to the active string and voltage on the inactive string. Voltage on the active string is  controlled by the test equipment and remains relatively constant. Current provides an indication of motor  performance, although the current measurement is taken between the test equipment and motor controller  and not between the motor and motor controller.   Because the controller affects the current demand through its own usage and current limiting, it does not  provide direct insight into the motor performance. But large variations in current are indicative of motor  behavior. The third parameter measured during Capture Latch Motor operation is voltage on the inactive  string, which provides an indication of the speed of the motor. Since the motor has dual windings, the  inactive string generates current during operation. Like the current reading, this is also filtered through the  controller, so the reading at the test equipment is not a direct measurement. However, large variations are  indicative of changes in motor speed. In Failure 2, the motor current exhibited significant current dropouts  on the B string during the hot test.   NASA/CP—2018-219887 490