1、Lessons Learned Entry: 0944Lesson Info:a71 Lesson Number: 0944a71 Lesson Date: 2001-01-01a71 Submitting Organization: WSTFa71 Submitted by: Regor SaulsberrySubject: Pyrovalve Anomaly Studies Description of Driving Event: Starting in 1995, WSTF tested approximately 50 pyrovalves in order to provide i
2、nsights into the Mars Observer and certain other spacecraft anomalies. The pyrotechnic blow-by past the ram was measured and characterized and overall valve speed and other physical properties were characterized. Pyrotechnic/propellant interaction testing also was accomplished; testing included simu
3、lation of the Telstar 402 and LandSat 6 failures, verification that the Mars 98 pyrovalve and actuation scenarios were safe, evaluation of the Interim Control Module actuations, and tests that characterized pyrotechnic induced propellant reaction rates. Some major safety implications are summarized
4、below.a71 Most of the valves with O-ring seals on Telsar 402, Landsat 6, and the Mars Observer produced significant hot pyrotechnic blow-by. (These were manufactured by one company.)a71 Telstar 402: Flight telemetry indicated that the propellant system was breached immediately following initiation o
5、f the second parallel pyrovalve. Actuation of the first valve introduced helium-saturated hydrazine into the evacuated downstream manifold. This created a very unfavorable scenario that greatly increased the chances of ignition. The second pyrovalve was liquid locked and some hydrazine foam may have
6、 been produced. Both WSTF and Lockheed Martin duplicated the scenario and both encountered explosions that were characteristic of the flight anomaly.a71 LandSat 6: This was very similar to the Telstar 402 anomaly. Significant differences included a small variation in the time between the actuation o
7、f the first and second parallel pyrovalve, and the materials from which that the pyrovalves were made. Telstar 402 used titanium valves and the LandSat 6 used stainless steel valves. Both types of valves caused similar explosions in WSTF testing.a71 Interim Control Module: This system used monometha
8、lhydrazine (MMH) and no explosions occurred in WSTF tesing, probably due to the fact that MMH is much less sensitive than hydrazine.a71 Mars 98: These tests were accomplished using separate hydrazine and nitrogen tetroxide Provided by IHSNot for ResaleNo reproduction or networking permitted without
9、license from IHS-,-,-systems and used very low blow-by valves (utilizing interference fit rams rather than O-ring seals). No system pressure increases were observed that were above water baseline test data. This indicated that blow-by was below the threshold for ignition of hydrazine, and that this
10、type of valve no reactivity with nitrogen tetroxide (as was observed with some titanium valves from OEA.)Engineers at Langley Research Center developed a test which measures the amount of energy required to actuate a valve by using a weight drop tower and then measures the energy output of the pyrot
11、echnic charge using a volume chamber. Comparing these energies determines if the valve is over or under-powered. It was determined that the Mars Observer and Telstar 402 valves were so over powered that they frequently broke chunks of titanium out of the ram stop at the end of the stroke.Lesson(s) L
12、earned: 1. Test pyrovalves the way you will use them on a mission. Regular lot acceptance tests and qualifications tests were accomplished. However, a propellant interaction test was not performed that could have identified this mission hazard. This was a major omission since the hot blow-by from th
13、ese valves was demonstrated to readily initiate the downstream hydrazine under the specific actuation scenarios tested.2. Test all corners of the operational box (with some margin of safety). In other words, test the valve/system under all the possible extremes. This may include maximum over and und
14、er pyrotechnic energy levels, min and max temperatures, and min and max system pressures. “Operational Margin“ testing is another consideration.Recommendation(s): 1. Test pyrovalves the way you will use them on a mission.2. Test all corners of the operational box (with some margin of safety).Evidenc
15、e of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): a71 ScienceProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Additional Key Phrase(s): a71 Configuration Managementa71 Energetic Materials - Explosive/Pro
16、pellant/Pyrotechnica71 Flight Operationsa71 Flight Equipmenta71 Hardwarea71 Parts Materials & Processesa71 Risk Management/Assessmenta71 Safety & Mission Assurancea71 Spacecrafta71 Test Articlea71 Test & VerificationAdditional Info: Approval Info: a71 Approval Date: 2001-07-10a71 Approval Name: Eric Raynora71 Approval Organization: QSa71 Approval Phone Number: 202-358-4738Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
