REG NASA-LLIS-2856-2010 Lessons Learned Re-Certifying An Umbilical After A Modification.pdf

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1、Public Lessons Learned Entry: 2856 Lesson Info: Lesson Number: 2856 Lesson Date: 2010-06-20 Submitting Organization: KSC Submitted by: Annette Pitt Subject: Re-Certifying An Umbilical After A Modification Abstract: The flight element design agency modified the design of the External Tank Ground Umbi

2、lical Carrier Plate, which is used to vent hydrogen. The design changes were considered minor enough that modeling and simulation were deemed sufficient to certify the part for use. During STS-114 launch operations, a camera recorded a cryogenic liquid leaking from the shroud used for purging the um

3、bilical. Because oxygen liquefies before nitrogen, the evidence of liquid caused a concern that oxygen was liquefying from air and posing a risk to launch operation safety. Description of Driving Event: The Ground Umbilical Carrier Plates main quick disconnect (GUCP QD), originally a two-piece casti

4、ng, was modified into a one-piece casting. The difference in form/fit/function was thought to be minor enough that integrated testing of the QD with the overall assembly and connection with the ET hydrogen vent line would not be necessary. During STS-114 return to flight, there was significant inter

5、est in the formation of ice on umbilical interfaces. Camera views and inspection of the External Tank (ET) GH2 Vent Arm System/GUCP revealed that vapor was leaking from the GUCPs ice suppression shroud. Observations indicated that the vapor was cryogenic liquid flash-evaporating as it contacted the

6、air surrounding the shroud. Initially it was suspected that liquid air was forming around the umbilical, a potentially hazardous situation. After careful analysis, testing, and investigation, the cryogenic fluid was found to be liquid nitrogen, which was supplied from a heated nitrogen purge line th

7、at feeds an annular shell around the shroud. A gap at a telescoping interface on the shroud and low pressure inside the helium-purged inner section (which contacted the 420 F GUCP QD surface) allowed nitrogen to leak into the inner shroud and condense into liquid on the QD surface. This liquid then

8、pooled on the bottom of the shroud, leaked out, and flash-evaporated. After a rigorous test program and significant analysis, the ground shroud and GUCP QD were modified to prevent the nitrogen from liquefying through insulation and to prevent the nitrogen gas purge from reaching cryogenically chill

9、ed surfaces. These modifications controlled the helium and nitrogen purges so they could be properly contained and vented. Lesson(s) Learned: GUCP recertification was based on changes made to the GUCP only and did not include the interactions with the ground shroud. No functional testing was perform

10、ed with the new GUCP QD configuration with the ice suppression shroud. The GUCP QD modifications did not undergo a complete system-level test because the modifications were deemed passive and there was no change in form/fit/function, despite significant changes in the QD: going from a two-piece cast

11、ing to a one-piece casting with significantly more surface area. Analysis and thermal models of the component failed to predict the effect in operational conditions. Also, the purge shroud was not adequately investigated during initial conception and testing to determine when gases would begin to mi

12、x and nitrogen purge could begin to intrude upon cryogenically chilled surfaces. The inadequately tested modifications to the GUCP QD and the lack of close observation of vapor drips from the ice suppression shroud nearly caused the launch of STS-114 to be aborted. Recommendation(s): When modificati

13、ons are made on interfaces between elements, in-depth investigation of the operational conditions present at the interface should be performed. Before modifications to major interface components and recertification can be considered complete, interfaces should be tested as integrated systems, and wh

14、ere possible, the tests should replicate operational conditions. Evidence of Recurrence Control Effectiveness: Observations of the area have revealed controlled venting of the purges from the ice suppression shroud and no ice buildup, signifying that the purges are being managed correctly. Provided

15、by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Documents Related to Lesson: Click here to download ERB4-10-06 Presentation Click here to download ICD ERB 4-26-06 Presentation Click here to download Purge Shroud IFA closure Presentation Click here to download

16、 GH2 Vent Shroud Mod ERB May 2006 Presentation Mission Directorate(s): Space Operations Additional Key Phrase(s): 1.Launch support systems 1.Ground support systems 1.Launch Systems 1.Engineering design and project processes and standards 1.Cryogenic Systems Additional Info: Project: Space Shuttle Program Approval Info: Approval Date: 2010-07-07 Approval Name: mbell Approval Organization: HQ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-