1、Lessons Learned Entry: 0420Lesson Info:a71 Lesson Number: 0420a71 Lesson Date: 1996-07-08a71 Submitting Organization: JPLa71 Submitted by: J.A. RobertsSubject: VO75 Pressure Regulator Leakage and Work-Around Procedures (1976) Abstract: The pressure regulator in the Viking Orbiter Propulsion Subsyste
2、m started leaking following a pyro firing that occurred prior to the near-Mars TCM. Likely causes were corrosion or residue from propellant migration or pyro valve blowby, or particulate contamination. Recommendations included using separate regulators for the fuel and oxidizer sides, incorporating
3、a bellows in the pyro valve to eliminate blowby, and adding a isolation valve between the regulator and propellant tank.Description of Driving Event: (Relevant Historical Lesson(s) Learned)The pressure regulator in the Viking Orbiter-1 (VO-1) Propulsion Subsystem, after having performed without inci
4、dent through the completion of the near-Earth midcourse Trajectory Correction Maneuver (TCM), leaked when 265 days later it was brought back on-line by the opening of an explosive valve which had isolated the regulator and propellant tanks from the pressurant tanks through the coast period prior to
5、the near-Mars Trajectory Correction Maneuver. The regulator leakage was detected by virtue of a continual rise in the fuel and oxidizer tank pressures. Propellant tank pressure data show that the regulator had been leak-tight up to the end of the near-Earth Trajectory Correction Maneuver, when the p
6、ressurant isolation pyro valve was actuated closed.The near-Mars TCM burn duration was lengthened considerably and an additional unscheduled TCM made. This relieved pressure and increased ullage. After Mars Orbit Insertion (MOI) the regulator was valved off from the pressurant supply. It was elected
7、 not to isolate the regulator immediately, then re-open for MOI.The VO-2 approach sequence was also revised, but differently. The pressurant supply was left Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-isolated until MOI, the TCM being made in “bl
8、ow down“ mode.An analysis of telemetry data ruled out: a scratch in the regulator poppet or seat, and housing weld failure. Remaining possibilities are: 1) corrosion and/or residue formation in the regulator circuit - due to propellant migration and/or pyro valve blowby, and 2) particulate contamina
9、tion.Additional Keyword(s): Material Compatibility, Propellant Feed SystemReference(s): IOM 344S-76-258, September 14, 1976, “Pressure Regulator Failure Analysis, VO75 Propulsion Subsystem, PFR 35408,“ G. Yankura to F. C. VoteLesson(s) Learned: The micro-scale effects of long-term propellant exposur
10、e should be investigated in order to better critique regulator design.Recommendation(s): Design corrective measures of propulsion pressurization subsystems which should be considered are:1. using separate regulators for the fuel and oxidizer sides2. incorporating a bellows in the pyro valve to elimi
11、nate blowby3. adding a isolation valve between the regulator and propellant tank to minimize propellant migration into the regulatorEvidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Energetic Materials - Explosiv
12、e/Propellant/Pyrotechnica71 Pressure VesselsProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Additional Info: Approval Info: a71 Approval Date: 1996-04-04a71 Approval Name: Carol Dumaina71 Approval Organization: JPLa71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
