1、Public Lessons Learned Entry: 3177Lesson Info:a71 Lesson Number: 3177 a71 Lesson Date: 2010-04-20 a71 Submitting Organization: KSC a71 Submitted by: Annette Pitt Subject: Development and Evolution of the Main Propulsion Helium Signature Test Abstract: This lesson learned addresses the development an
2、d evolution of a test technique for revalidating the Space Shuttle Orbiter Main Propulsion System (MPS) during ground turnaround operations between flights. This test technique, the Helium Signature Test, is an end-to-end leak check of the entire MPS and serves as a final validation of flightworthin
3、ess. A test such as the Helium Signature Test can be used for any enclosed hazardous system with a control volume to ensure overall system integrity before the hazardous medium is introduced. Description of Driving Event: The Main Propulsion System (MPS) for the Space Shuttle consists of the three S
4、pace Shuttle Main Engines (SSMEs) and the fluid lines and components that connect the SSMEs to the External Tank and the ground systems. During the Flight Readiness Firing (FRF) of the orbiter Challenger, OV-099, at KSC before its first flight, the Hazardous Gas Detection System (HGDS) detected a ma
5、ssive hydrogen concentration spike while the SSMEs were running. This leak was large enough to exceed the flammability limits established for the orbiters aft compartment during flight. STS-6, Challengers first flight, was put on hold until the source of the leak was found and the leak corrected. Th
6、e Helium Signature Test, initially developed to find the source of this leak, works by pressurizing the MPS propellant systems with helium and sampling the aft fuselage atmosphere using the HGDS. Any helium leaking from the MPS would mix with the air in the aft fuselage and be detected as an increas
7、e in the helium concentration in the aft fuselage. By measuring this change in helium concentration and knowing the air purge flow rate for the aft fuselage, a total system leak rate can be calculated in standard cubic inches per minute (scim). The Helium Signature Test was later refined to be an im
8、portant preflight leak test. Lesson(s) Learned: While point leak checks of individual threaded, flange, brazed, and welded joints are important validations of joint integrity for new and not-yet-validated joints, as well as good interval checks of the health of these components, they do not cover al
9、l possible sources of propellant leakage. Fatigue or wear during a previous flight or damage during ground processing could result in leakage from a component that was not leak-checked, or that was leak-checked before the damage occurred. An overall system leak check performed as close as possible t
10、o aft fuselage closeout for flight gives the best confidence that the system is ready to support safe flight. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Recommendation(s): At the end of the Space Shuttle program, a modified version of the origin
11、al test was used to leak-check the SSMEs before they were installed in the orbiter. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-A test such as the Helium Signature Test can be used for any enclosed hazardous system with a control volume to ensure
12、 overall system integrity before the hazardous medium is introduced. Evidence of Recurrence Control Effectiveness: The Helium Signature Test was used to detect several leaks before flight. Issues with LH2/LO2 repressurization flex hoses and GH2 flow control valve O-rings were first detected by using
13、 this test. Documents Related to Lesson: AIAA- 87-0293 Development of the Helium Signature Test for Orbiter Main Propulsion System Revalidation Between Flights Click here to download AIAA Helium Signature Test Paper Click here to download Helium Signature Test Paper White Paper Mission Directorate(s
14、): a71 Space Operations Additional Key Phrase(s): a71 1.Ground processing and manifesting Additional Info: a71 Project: Space Shuttle Program Approval Info: a71 Approval Date: 2010-09-08 a71 Approval Name: mbell a71 Approval Organization: HQ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
