1、Lessons Learned Entry: 0351Lesson Info:a71 Lesson Number: 0351a71 Lesson Date: 1994-11-14a71 Submitting Organization: JPLa71 Submitted by: C.S. Guernsey / B.J. WagonerSubject: Galileo Messerschmitt-Bolkow-Blohm (MBB) Ten Newton Hot Start Phenomena Abstract: During confidence testing of the MBB Galil
2、eo Ten Newton (N) Engine at MBB in November 1988, rapid increases in combustion chamber temperature (“hot starts”) were sometimes observed immediately after ignition of the engine. Examination of test data from the previous flight engine acceptance tests showed evidence of hot starts, but JPL had no
3、t witnessed these earlier tests.The lesson recommends several measures to assure that rocket engine development and qualification test instrumentation and test documentation are sufficient to detect and diagnose combustion instabilities. Description of Driving Event: During confidence testing of the
4、 MBB Galileo Ten Newton (N) Engine at MBB in November 1988, rapid increases in combustion chamber temperature were sometimes observed immediately after ignition of the engine. These “hot starts“ required manual intervention to stop the test before overheating could produce engine damage. Subsequent
5、examination of test data from the previous flight engine acceptance tests revealed that the “hot start“ phenomena had also been present in those tests. JPL did not witness, or request detailed data from, these earlier tests.The “hot start“ phenomena was eliminated by moving the engine trim orifices
6、downstream of the engine valve and changing the flight operating mode of the thrusters. The design change was based on empirical testing of several configurations, since the instrumentation available did not allow the nature or cause of the phenomena to be precisely determined. Over 20,000 firings w
7、ere conducted after the orifice change without further occurrences of “hot starts“. Other combustion instabilities (NCR 892) and unacceptable thermal performance (NCRs 884, 889, AND 894) were, however, noted in some pulse mode and continuous firings. The Galileo mission was redesigned to avoid Provi
8、ded by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-continuous firings of the 10 N thrusters and to restrict pulse mode duty cycles so that the impacts of “hot starts“ or other thermal instabilities, should they occur in flight, would be minimized.The “hot st
9、art“ phenomena is now known, based on subsequent data collected for other spacecraft projects, to be a 30 KHz acoustic instability of the MBB 10 N combustion chamber and injector. It is likely that the instability was triggered by severe ignition transients which were alleviated by the new orifice c
10、onfiguration. Bubbles saturated in the propellant, produced by the original orifice configuration, also appear to be a contributing factor to triggering the instability.Additional Keyword(s): Supplier TestingReference(s): NCR #883Lesson(s) Learned: 1. Lack of appropriate rocket engine development an
11、d qualification test instrumentation and test documentation can result in failure to detect and diagnose combustion instabilities.2. Bubbles saturated in the propellant can be a contributing factor to triggering rocket engine combustion instability.Recommendation(s): 1. Critical rocket engine compon
12、ent subsystem test procedures and actual performance should be carefully monitored by appropriate technical and quality assurance personnel.2. Test data from all qualification and flight acceptance testing of critical rocket engine component subsystems should be obtained, reviewed, and archived by J
13、PL.3. The stability of new rocket engine designs should be intensively studied early in the development and/or qualification cycle.4. Rocket engines should be tested with propellants which have been verified to be saturated with pressurant gas.Evidence of Recurrence Control Effectiveness: N/ADocumen
14、ts Related to Lesson: N/AMission Directorate(s): Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-N/AAdditional Key Phrase(s): a71 Energetic Materials - Explosive/Propellant/Pyrotechnica71 Research & Developmenta71 Test & VerificationAdditional Info: Approval Info: a71 Approval Date: 1992-10-01a71 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-,-,-
