1、Lessons Learned Entry: 0485Lesson Info:a71 Lesson Number: 0485a71 Lesson Date: 1996-12-12a71 Submitting Organization: JPLa71 Submitted by: C. GuernseySubject: Isolate the Propulsion Pressurization System from the Propellant Tanks (1993) Abstract: The “most probable cause” of the Mars Observer missio
2、n failure was identified as migration of substantial amounts of nitrogen tetroxide oxidizer upstream through the check valves where it condensed on the cold tubing. When the pressurization sequence was executed upon Mars encounter, the liquid oxidizer may have mixed rapidly with fuel in the lines an
3、d detonated. The recommendations included (1) preventing hazardous propellant vapor migration and (2) performing thermal analysis of pressurization systems to identify incipient conditions for propellant condensation.Description of Driving Event: The Mars Observer propulsion system design was inheri
4、ted from an Earth-orbital application and incorporated a pressurization system employing helium to maintain the propellant tanks at a constant pressure. Regulation of propellant tank pressure prevents the tanks from rupturing, which would likely cause loss of the spacecraft. As gases are exchanged,
5、pressure regulators and check valves prevent propellant and oxidizer from entering the pressurization system and causing a hypergolic reaction.Although nominal leakage through regulator check valves is anticipated, the pressurization system is fully isolated from the oxidizer tank early in an Earth-
6、orbital mission following achievement of final orbit. For a Mars mission, however, high propellant usage is not required until months after launch, and substantial amounts of nitrogen tetroxide (NTO) oxidizer may migrate upstream through the check valves. Since the Mars Observer pressurization plumb
7、ing was cold for much of the cruise, liquid or gaseous NTO migrating through the check valves could have condensed on the cold tubing. When the pressurization sequence was executed upon Mars encounter, liquid NTO could have mixed rapidly with monomethylhydrazine (MMO) fuel in the pressurization line
8、s. The resulting combustion Provided by IHSNot for Resale-,-,-could have ruptured the tubing, venting the helium pressure tank, damaging Mars Observer or inducing an unrecoverable spin. The Mars Observer Special Review Board identified this scenario as the “most probable cause“ of the mission failur
9、e.Additional Keyword(s): Bipropellant Propulsion System, Propellant Vapor DiffusionReference(s):1. “Adoption of an Earth-Orbital Propulsion System Design for a Planetary Mission,“ Lesson Learned No. 1-110.2. “Report of the Mars Observer Mission Failure Investigation Board,“ December 31, 1993.Lesson(
10、s) Learned: 1. Interplanetary missions should provide a means to positively isolate the pressurization system from the propellant tanks when high flow rates are not required, or ensure that the effect of propellant vapor migration into the pressurization system is benign.2. When check valves leak pr
11、opellant vapors, lower temperatures upstream may cause propellant vapor condensation in the pressurization system. Perform thermal analysis of pressurization systems to identify incipient conditions for propellant condensation.Recommendation(s): NoneEvidence of Recurrence Control Effectiveness: N/AD
12、ocuments Related to Lesson: N/AMission Directorate(s): a71 ScienceAdditional Key Phrase(s): a71 Energetic Materials - Explosive/Propellant/Pyrotechnica71 SpacecraftProvided by IHSNot for Resale-,-,-Additional 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
