REG NASA-LLIS-1217-1998 Lessons Learned Sharp edge hazard from break-off assemblies.pdf

1、Lessons Learned Entry: 1217Lesson Info:a71 Lesson Number: 1217a71 Lesson Date: 1998-10-21a71 Submitting Organization: JSCa71 Submitted by: Steven Jeffers/ Ronald A. MontagueSubject: Sharp edge hazard from break-off assemblies Description of Driving Event: “Hi-Lite“ (similar to Hi-Lok) pin and collar

2、 fasteners are widely used on ISS Power Module structural assemblies. As part of an internal sharp-object-damage (SOD) identification and mitigation activity, it has been noted that small burrs are present on most installed collars. When accessible to an astronauts EMU external surfaces, these burrs

3、 pose a sharp object hazard with risk of damage to the EMU outer fabric.Root cause: As part of “Hi-Lite“ fastener installation, a wrench is applied to a drive nut integral with the fastener collar. At a given torque, the drive nut shears from the collar body; the drive nut is then scrapped. This she

4、aring action typically leaves burrs on the collar surface.Lesson(s) Learned: Any installation that results in deliberate shearing or break-off during assembly requires specific assessment for sharp object hazards to astronauts wearing pressurized space suits.Recommendation(s): 1. This condition was

5、first noted on a qualification test article. When the qualification article was assembled, most Hi-Lite fasteners were installed with the collars facing “outward“ to ease the mechanics access to the nut element. On subsequent flight units, a concerted effort was made to install fasteners with the co

6、llars facing “in“, greatly reducing potential EMU access to the burr hazard.2. 3. On collars that cannot be reversed, plans are in place to encapsulate all exposed collars with a sealant compound.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-4. Thi

7、s same issue can be attributed to other fastener types (e.g., lockbolt and many types of blind bolts and rivets) as well. Any fastener whose installation involves shearing or breaking off of any element has high potential for leaving a sharp edge or burr.Evidence of Recurrence Control Effectiveness:

8、 N/ADocuments Related to Lesson: N/AMission Directorate(s): a71 Exploration Systemsa71 Space Operationsa71 Aeronautics ResearchAdditional Key Phrase(s): a71 Extra-Vehicular Activitya71 Flight Equipmenta71 Ground Equipmenta71 Hardwarea71 Parts Materials & Processesa71 Risk Management/Assessmenta71 Sa

9、fety & Mission Assurancea71 Test & VerificationAdditional Info: Approval Info: a71 Approval Date: 2002-06-17a71 Approval Name: Ronald A. Montaguea71 Approval Organization: JSCa71 Approval Phone Number: 281-483-8576Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-