1、Public Lessons Learned Entry: 6144 Lesson Info: Lesson Number: 6144 Lesson Date: 2010-11-1 Submitting Organization: MSFC Submitted by: Kristen Kinder Subject: Shuttle External Tank Engine Cut Off Feed Through Connector Failure Abstract: After much investigation (and launch scrubs), a problem was iso
2、lated to the feed through connector in the bottom of a hydrogen tank. Electrical connector integrity can be significantly impacted at cryogenic temperatures. Description of Driving Event: STS-114 external tank and subs were plagued with the loss of the wet/dry indication of the low level cut off sen
3、sors. This caused many launches to be scrubbed. Thinking the problem was with the sensors themselves, great effort was spent on improving them (e.g. swage connections, x-rays, etc.), but the problem kept recurring. Finally, after much investigation (and launch scrubs), the problem was isolated to th
4、e feed through connector in the bottom of the hydrogen tank. A design change to the connector changed the orientation and surface area involved between the mating sides. When the tank was filled, moist atmospheric air was drawn into the connector. The water in the air would freeze and as the connect
5、or chilled down and contracted, the electrical connection on one or more of the pins would be lost. After the tank was drained and it heated back up, the connection would be reestablished. After the problem was isolated to the feed thru connector, the Centaur Program told of how they had the same pr
6、oblem with their connector and how they fixed it by soldering the external connection, rather than relying on the mechanical connection alone. Lesson(s) Learned: Electrical connector integrity can be significantly impacted at cryogenic temperatures. The mechanical design of electrical connectors can
7、 be affected by environmental conditions at cryogenic operating temperatures that may not be obvious to electrical or electronic design disciplines. Recommendation(s): Changes to electrical systems should be reviewed for failure modes other than strictly “electrical” causes; mechanical response of s
8、ensors to extreme environments is a broadly applicable area of concern in system design at NASA. Operating environments and their potential effects on materials and mechanisms should be identified and mitigated as early in the design process or the design change process so that the problem is not fi
9、rst detected when the vehicle is sitting on the launch pad. Operational check-out procedures could be reviewed to determine if changes to check-out sequences could identify potential problems prior to a launch attempt. The information learned from the Centaur Program should have been communicated to
10、 the vendor or to some industry wide bulletin board. The vendor then should have taken responsibility to notify other users of the product of the potential problem that may exist in their application if used in similar conditions, and of any corrections or fixes to the problem. The process could be
11、similar to a Government-Industry Data Exchange Program (GIDEP) alert or an information bulletin from an automobile manufacturer about a potential defect. Keep the vendors involved. Evidence of Recurrence Control Effectiveness: N/A Provided by IHSNot for ResaleNo reproduction or networking permitted
12、without license from IHS-,-,-Documents Related to Lesson: Lessons Learned Entry: 1844 STS-122 ECO Sensor Anomaly Mission Directorate(s): Exploration Systems Space Operations Additional Key Phrase(s): 1.Spacecraft 1.Flight Operations 1.Vehicle concepts 1.Level II/III requirements definition 1.Launch Systems 1.Propulsion 1.Cryogenic Systems 1.Launch Vehicle Additional Info: Project: Shuttle / New Launch Vehicle Approval Info: Approval Date: 2012-03-19 Approval Name: mbell Approval Organization: HQ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
