REG NASA-LLIS-0371--1995 Lessons Learned - SEASAT Failure.pdf

1、Lessons Learned Entry: 0371Lesson Info:a71 Lesson Number: 0371a71 Lesson Date: 1995-01-24a71 Submitting Organization: JPLa71 Submitted by: R.F. CollinsSubject: SEASAT Failure Abstract: The SEASAT Spacecraft failed in orbit due to arcing between adjacent slip ring brush assemblies. It was discovered

2、that the Agena bus had been substantially modified, but were treated as a heritage design not requiring requalification. Plans should be made early in the project to fully evaluate the heritage of previously used equipment. When conducting a FMECA on electrical components, electrical short failure m

3、odes should be considered.Description of Driving Event: The SEASAT Spacecraft failed in orbit due to a massive and progressive short in the slip ring assembly connecting the rotating solar array to the power subsystem. The most probable cause of this short was the initiation of an arc between adjace

4、nt slip ring brush assemblies. The slip ring assembly was connected into the power system such that the adjacent brush assemblies were of opposite polarity, an arrangement particularly prone to shorting. The SEASAT prime contractor was aware of instances of slip ring failures due to shorting on othe

5、r projects, but did not communicate this information to the SEASAT project office. This lack of communication may have been the result of the classified nature of the other projects. The failure to give the slip ring assembly the attention it deserved was rooted in the contract structure and the SEA

6、SAT implementation policy. SEASAT was a dual contract; a fixed price for the Agena bus containing flight proven subsystems and a cost-plus award fee for the payload module which was integrated with the Agena bus. By contract, implementation plan, and resource constraints, JPL had no significant over

7、sight of the Agena bus. The failure review board established that the Agena power, attitude control, and data subsystems were substantially modified, but were treated as closely similar designs not requiring requalification. This consideration of the Agena bus as flight-proven standard equipment led

8、 to the failure to report significant component failures, waiving tests and weak compliance with specifications. In addition, the Failure Mode Effects and Criticality Analysis (FMECA) conducted on the power system did not Provided by IHSNot for ResaleNo reproduction or networking permitted without l

9、icense from IHS-,-,-consider shorts as a potential failure mode.Additional Keyword(s): Inherited Equipment, Slip RingsLesson(s) Learned: 1. “Heritage“ hardware designs, previously flown on prior missions, can still contain design errors.2. Consideration of electrical shorts as a potential failure mo

10、de during FMECA of the power system is of critical importance.Recommendation(s): 1. The uncritical acceptance of equipment that has been classified as “standard“ or “flight proven“ should be avoided, especially if modifications of any level have been made on this equipment. Plans should be made earl

11、y in the project to fully evaluate the heritage of previously used equipment. The degree of evaluation may have to be contractually defined on fixed-price contracts.2. When conducting a FMECA on the power system and other electrical components, electrical shorts should be considered as one of the po

12、tential failure modes.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 HardwareAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 1988-10-05a71 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-,-,-