REG NASA-LLIS-0373-1995 Lessons Learned In-Flight TWTA Anomaly.pdf

1、Lessons Learned Entry: 0373Lesson Info:a71 Lesson Number: 0373a71 Lesson Date: 1995-01-25a71 Submitting Organization: JPLa71 Submitted by: Jim TaylorSubject: In-Flight TWTA Anomaly Abstract: A bad weld in the cathode support structure of a Traveling Wave Tube Amplifier was postulated as the failure

2、mode for degradation of the Mariner 71 downlink signal level.Adequately monitor the parts screening methods as well as contractor-specified manufacturing processes and test procedures, and improve contingency planning for the mission operations phase. Description of Driving Event: The anomaly happen

3、ed during Earth occultation on Mariner 71s forty-eighth orbit of Mars. When the DSN reestablished telemetry reception after occultation, several temperature and spacecraft power channels associated with Traveling Wave Tube Amplifier (TWTA) 2 were in alarm. The station confirmed a loss of 0.5 dB in d

4、ownlink signal level that was indicated in the telemetry. The project elected to switch to the redundant TWTA-1 by ground command about two hours after the first observation.JPL and the subcontractors were never able to pinpoint the cause of the anomaly, even as to location in the tube itself or in

5、the amplifier. Recommendations from the investigators included contingency plans in the event of yet more severe TWTA-1 problems, as they deemed TWTA-2 still operable in the low-power mode. (These TWTA-1 problems never occurred.)During the anomaly investigation, contractor quality assurance programs

6、 were reviewed and the process procedures used to assure high quality welds were found to be inadequate. One possible failure model postulated a weld failure in the cathode support structure.Lesson(s) Learned: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from

7、IHS-,-,-1. Contractor quality assurance programs and process controls may not be adequate for providing flight components capable of meeting mission requirements.2. Potential partial failure modes during the mission operations phase require contingency planning.Recommendation(s): 1. The projects sho

8、uld allocate enough resources so that JPL personnel can adequately monitor the parts screening methods as well as contractor-specified manufacturing processes and test procedures.2. Contingency planning for the mission operations phase should take into consideration potential partial failure modes,

9、particularly where functionally redundant units are involved.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Flight Operationsa71 Safety & Mission AssuranceAdditional Info: Approval Info: a71 Approval Date: 1985-12-19a71 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-,-,-