1、Lessons Learned Entry: 0408Lesson Info:a71 Lesson Number: 0408a71 Lesson Date: 1996-06-24a71 Submitting Organization: JPLa71 Submitted by: J.A. RobertsSubject: Mariner71 Fuse Incident (1970) Abstract: Mariner71 testing was delayed when replacement of one blown fuse required the removal of a module c
2、ontaining other fuses necessary to the safe testing of the spacecraft, thereby postponing further testing on all the affected components. Located fuses in the fused devices instead of concentrating them in the power subsystem does leave the cabling unprotected by the fuses, but the reliability of th
3、e cabling is so high that this lack of protection is usually well justified.Description of Driving Event: (Relevant Historical Lesson(s) Learned)Mariner71 testing was delayed when replacement of one blown fuse required the removal of a module containing other fuses necessary to the safe testing of t
4、he spacecraft, thereby postponing further testing on all the affected components.Fuses for the Data Storage Subsystem (DSS) tape recorder and several other subsystems were located within the power subsystem. During test, several devices, including the tape recorder, were removed from the spacecraft
5、while other tests continued. This would have reduced the electrical load below the level required for stable operation of the power conditioning unit. To ensure stability, a dummy load was connected in place of the DSS that had been removed. However, the load applied had too low an impedance. Whenev
6、er spacecraft power was reapplied, the tape recorder fuse blew at its 1 amp design value and successfully protected the power subsystem.The blown tape recorder fuse, along with other fuses were tightly packaged and conformally coated within the power distribution module. To replace the fuse, the ent
7、ire unit had to be returned to the vendor for 7-10 days. This prevented further testing on all devices whose fuses were also contained Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-within the unit, delaying the test program.Additional Keyword(s): P
8、ackagingLesson(s) Learned: Fuses should be located within the device being fused, rather than concentrating them within the power subsystem.Recommendation(s): Fuses are normally coated in place. The unit in which they are installed must be removed from the spacecraft to replace the fuse. Removing a
9、fused device is preferable to removing elements of the power subsystem because it causes less disturbance to the test. Moving the fuse to the device does leave the cabling unprotected by the fuse but the reliability of the cabling is so high that this lack of protection is usually well justified.Mar
10、iner69 and Mariner71 had fuses in various locations. Some were concentrated in the power subsystem; others were within the individual devices. Since that time, fuses have usually been located within each individual device being fuse.Evidence of Recurrence Control Effectiveness: N/ADocuments Related
11、to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Flight Equipmenta71 Parts Materials & Processesa71 SpacecraftAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 1995-09-21a71 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-,-,-
