REG NASA-LLIS-0486-1996 Lessons Learned - Conduct Post Test Examination of Lot Acceptance Hardware for Incipient Failures (1993).pdf

1、Lessons Learned Entry: 0486Lesson Info:a71 Lesson Number: 0486a71 Lesson Date: 1996-12-19a71 Submitting Organization: JPLa71 Submitted by: C. GuernseySubject: Conduct Post Test Examination of Lot Acceptance Hardware for Incipient Failures (1993) Abstract: During lot acceptance test of ten Mars Obser

2、ver pyro valves, none failed. Yet, post-test examination showed that each of these valves had sustained erosion (burning) of about 50 percent of their threads. A study showed that some firings result in the pyro being ejected from the valve body at speeds of approximately 200 m/s, which could damage

3、 critical hardware.Users of NSIs should be alerted to this possibility. Acceptance or qualification testing should include post-test examination of inferred margin or incipient failure modes. The use of titanium in pyrotechnic applications should be avoided. Description of Driving Event: As part of

4、the Mars Observer mission failure investigation, the acceptance test lot of the Mars Observer pyro valves were examined for thread erosion. The pyros were suspect because of tests that had been made on European Space Agency (ESA) pyro valves and initiators, which showed that some firings result in t

5、he pyrotechnic initiator being ejected from the valve body at speeds of approximately 200 m/s. The pyro valves and NASA standard initiators (NSIs) used aboard Mars Observer were designed to the same specifications, though they were not identical to the ESA hardware.During lot acceptance test, none o

6、f the ten pyro valves tested had failed- all fired, and none ejected their initiators. Following the Mars Observer failure, examination showed that each of these valves had sustained erosion (burning) of about 50 percent of their threads. The erosion was caused by combustion of the titanium thread m

7、aterial with the combustion products of the initiator. This examination was not required in the original lot acceptance test of the parts.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Were the thread loss to cause ejection of an initiator, severe d

8、amage to the spacecraft wiring, propellant tanks, and other critical hardware could result. For example, one of the Mars Observer initiators was located such that it would impact the monomethylhydrazine (MMH) propellant tank if it were ejected. The JPL Mars Observer Special Review Board considered a

9、 failed pyro valve charge initiator to be a potential cause of the loss of the Mars Observer mission.Reference(s): “Report of the Mars Observer Mission Failure Investigation Board,“ (Coffey report), December 31, 1993.Lesson(s) Learned: 1. Successful lot functional acceptance tests may not detect inc

10、ipient failure modes without post-test examination.2. Explosive initiators produce hot, reactive products which may create ejecta ranging from tiny debris particles to portions of the valve body, especially in the presence of titanium which is a highly reactive metal.Recommendation(s): 1. Alert user

11、s of NSIs to the possibility of damage from ejected initiators.2. Parts and materials lot acceptance or qualification functional testing should include post-test examination to look for signs of inferred margin or incipient failure modes and should include destructive testing if necessary.3. The use

12、 of titanium in pyrotechnic applications should be carefully reviewed or avoided due to its highly reactive nature.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Energetic Materials - Explosive/Propellant/Pyro

13、technicProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-a71 Flight Equipmenta71 Hardwarea71 Spacecrafta71 Test & VerificationAdditional Info: Approval Info: a71 Approval Date: 1997-01-24a71 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-,-,-