1、Lessons Learned Entry: 0184Lesson Info:a71 Lesson Number: 0184a71 Lesson Date: 1992-10-28a71 Submitting Organization: KSCa71 Submitted by: Lisa L. MusgraveSubject: LO2/LH2 Vent and Relief Position Indicator Switch Description of Driving Event: The LO2 and LH2 vent and relief valve position indicator
2、 switch tolerance allows the valve to indicate “closed“ when it may be open up to 0.30 inch. This condition could allow undetected ullage gas leakage prior to launch. Hot GO2 may auto-ignite the ET thermal protection system (TPS) after SSME ignition. GH2 in flight can cause fire and loss of TPS whic
3、h could result in a catastrophic situation. The vent/relief valve uses a position indicator switch that is highly accurate. However, no matter how accurate, no position indicator can accurately assure closure because leakage rates for qualification and acceptance are roughly 5E-6 lb/sec. Therefore,
4、a redesign to eliminate the hazard has proven to be virtually impossible.Lesson(s) Learned: Inaccuracies in vent/relief valve position indicator switch may cause gas leakage, resulting in fire and loss of flight hardware and/or orbiter.Recommendation(s): Perform outdoor wind tunnel testing of vent/r
5、elief valve to provide data, quantifying leak rates below which the hazard is eliminated.Evidence of Recurrence Control Effectiveness: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-N/ADocuments Related to Lesson: N/AMission Directorate(s): a71 Spac
6、e Operationsa71 Exploration SystemsAdditional Key Phrase(s): a71 Flight Equipmenta71 Ground Operationsa71 Hazardous/Toxic Waste/MaterialsAdditional Info: Approval Info: a71 Approval Date: 1994-06-06a71 Approval Name: James G. Klinea71 Approval Organization: KSC/HEIa71 Approval Phone Number: 407-867-7614Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
