Development Testing and Subseque nt Failure Investigation of a Spring Strut Mechanism  Jared Dervan*, Brandan Robertson**, Lucas Staab+, Michael Culberson++and Joseph Pellicciotti+++ Abstract The NASA Engineering and Safety Center (NESC) and Lockheed Martin (LM) performed random  vibration testing on a single spring strut development unit to assess its ability to withstand qualification-level random vibration environments. Failure of the strut while exposed to random vibration resulted in a follow-on failure investigation, design changes, and additional development tests. This paper focuses on  the results of the failure investigations referenced in detail in the NESC final report [1] including identified  lessons learned to aid in future design iterations of the spring strut and to help other mechanism developers avoid similar pitfalls.  Introduction Commodities are transferred between the Multi-Purpose Crew Vehicle (MPCV) crew module (CM) and  service module (SM) via an external umbilical that is driven apart with spring-loaded struts after the  structural connection is severed, as shown in Figure 1. The spring struts must operate correctly for the modules to separate safely. The MPCV program plan did not include development vibration testing of this  strut for the Exploration Flight Test 1 (EFT-1) mission, thus any design problems discovered as a result of  vibration testing would not have been found until the component verification testing, potentially causing  large program schedule delays. The MPCV Program Chief Engineer submitted a request to the NESC to  perform random vibration testing on a single spring strut development unit to mitigate this risk.    The objective of the NESC assessment was to perform development vibration testing on a flight-like  umbilical spring strut and evaluate the strut’s behavior during and after the test. Roles and responsibilities were distributed between NESC personnel and the MPCV Program prime contractor, LM. As part of the test program, low-level vibration and performance tests (consisting of force-displacement  curve generation) were to be performed prior to and following a qualification-level random vibration  testing to characterize the baseline system response and performance and help detect changes as a  result of the random vibration testing. The random vibration portion of the test was to begin at low levels, ramping in increments through maximum predicted environment (MPE) levels to qualification levels (MPE  +6 dB for the MPCV Program) and held at qualification levels for 3 minutes in each axis while in a stowed configuration. Pre- and post-test inspections and collection of digital imagery were planned. Following the  testing and performance evaluations, the strut was to be disassembled and inspected for damage/wear  with a report detailing the findings. During random vibration testing of the last test configuration, the spring strut encountered a failure of the  forward locking elements resulting in a rotation of the strut and subsequent fatigue failure. A follow-on root cause investigation was performed that identified supporting rationale for a failure scenario that  included aspects of design, analysis, test, and workmanship. Lessons learned pertaining to areas of joint  *NASA Marshall Space Flight Center, Huntsville, AL **NASA Johnson Space Center, Houston, TX +NASA Glenn Research Center, Cleveland, OH ++Lockheed Martin Space Systems Company, Littleton, CO +++NASA Goddard Space Flight Center, Greenbelt, MD /g51/g85/g82/g70/g72/g72/g71/g76/g81/g74/g86/g3/g82/g73/g3/g87/g75/g72/g3/g23/g21/g81/g71/g3/g36/g72/g85/g82/g86/g83/g68/g70/g72/g3/g48/g72/g70/g75/g68/g81/g76/g86/g80/g86/g3/g54/g92/g80/g83/g82/g86/g76/g88/g80/g15/g3/g49/g36/g54/g36/g3/g42/g82/g71/g71/g68/g85 /g71/g3/g54/g83/g68/g70/g72/g3/g41/g79/g76/g74/g75/g87/g3/g38/g72/g81/g87/g72/g85/g15/g3/g48/g68/g92/g3/g20/g23/g16/g20/g25/g15/g3/g21/g19/g20/g23/g3 391