REG NASA-LLIS-0306--1993 Lessons Learned Galileo Ulysses Helicoil Bolt Problems on RTGS.pdf

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1、Lessons Learned Entry: 0306Lesson Info:a71 Lesson Number: 0306a71 Lesson Date: 1993-09-15a71 Submitting Organization: JPLa71 Submitted by: D. D. LordSubject: Galileo/Ulysses Helicoil/Bolt Problems on RTGS Abstract: During installation of the Pressure Release Devices (PRD) to the Galileos RTGs, the f

2、our screws anchoring each PRD failed to pull snug to the RTGs. A year later, a screw attaching a PRD to the Ulysses RTG seized and sheared. The problem was attributed to inexperience with the helicoil locking feature. Avoid use of helicoils, and provide detailed assembly procedures for locking devic

3、es.Description of Driving Event: On October 7, 1989, during installation of the Pressure Release Devices (PRD) to Galileos RTGS, the four screws anchoring each PRD failed to pull snug to the RTGS when the assembly crew applied what was considered to be acceptable torque. Further insertion of the scr

4、ews was halted and washers were added to allow a snug fit. Analysis and a vibration test indicated that the thread engagement was sufficient to proceed with the launch.On October 2, 1990, during installation of the PRD to the Ulysses RTG, the fourth and last attachment screw seized and subsequently

5、sheared. Extensive analysis and consultation with General Electric indicated that a sufficient safety margin existed to proceed with the launch even with the PRD anchored by only three screws.Neither of these incidents in any way compromised the safety or functionality of the PRD/RTG.On October 16,

6、1990, a PRD anomaly review board was established to investigate the cause of these anomalies and make recommendations. The board has found that the Galileo anomaly resulted from inexperience with the helicoil locking feature. The Ulysses screw seizure most likely resulted from prior use of an unlubr

7、icated cover screw and/or some earlier degradation of the helicoil.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Additional Keyword(s): FastenerReference(s): JPL D-9625, Galileo/Ulysses Pressure Release Device (PRD) Anomaly Review Board Report; PFR

8、 #54340 AND #54365.Lesson(s) Learned: 1. Helicoil locking devices can cause problems in applications requiring repeated engagements of the locking feature.2. Potential problems, associated with temporary screw insertions into helicoils, can be minimized if shorter lubricated screws are used to assur

9、e minimal penetration of the locking mechanism.Recommendation(s): 1. The use of helicoils should be avoided.2. The use of locking devices should require the generation and use of detailed assembly procedures, clearly identifying potential problem areas and torquing limits for both temporary and fina

10、l installations.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Hardwarea71 Parts Materials & ProcessesAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 1993-02-04a71 Approval Name: Carol Dumaina71 Approval Organization: 125-204a71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-