1、Lessons Learned Entry: 0624Lesson Info:a71 Lesson Number: 0624a71 Lesson Date: 1999-06-03a71 Submitting Organization: JPLa71 Submitted by: J. Forgrave/C. Farguson/D. OberhettingerSubject: Design, Test, and Inspection of Semi-Rigid RF Cables (1997) Abstract: The Sea Winds test program demonstrated th
2、at semi-rigid coaxial RF cable failures are difficult to avoid. Semi-rigid RF cable failures often cannot be detected by visual examination. During inspections following vibration test of the Sea Winds SES, hairline cracks were missed several times. Testing of protoflight models (PFMs) may permit on
3、ly in-situ visual examination of components, while structural mass model (STM) tests typically allow cables to be removed from the unit for close examination. After a cable assembly passes environmental test, a second “identical” cable may fail due to minor differences in manufacture and installatio
4、n. Consider using flexible cable. Where semi-rigid cabling is preferred, the lesson recommends standardization of cable receiving inspection, assembly, and installation. It also suggests several cable installation and test measures.Description of Driving Event: The Scatterometer Electronics Subsyste
5、m (SES) for the Sea Winds spacecraft featured six semi-rigid coaxial radio frequency (RF) cables spanning two independent structures within the SES. After two cables failed during the initial SES vibration test, four additional cycles of redesign and test were required before the cables were judged
6、acceptable. Two of the five tests were performed on SES protoflight models (PFM) and three on structural mass models (STM). Each of the six cables required varying degrees of redesign, including changes to cable material, strain relief, mounting configuration, and bonding, that impacted the Sea Wind
7、s schedule.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-refer to D descriptionD The process of cable redesign and retest is complicated by lack of repeatability. Minor uncontrolled variations in cable manufacture, routing, and mounting; JPL “impro
8、vements“ in the cable configuration; and differences between the PFM and STM units, alter the dynamic characteristics of the test article. Furthermore, cracks in semi-rigid cables are very difficult to detect while they are installed. Cable failures may not be visually detected until the cables are
9、removed from a test model, but they cannot easily be removed for inspection without damaging the cables and invalidating the vibration test results. If a cable failure was not detected and the SES was launched with a cracked cable, thermal transients could widen that crack, and the resulting signal
10、attenuation could cause loss of science data.Additional Keyword(s): developmental model, coaxial cable, coax cable, waveguideReference(s):1. JPL Problem/Failure Report No. SWD0752. J. Forgrave and C. Farguson, “Concerns Regarding Q-SCAT/Sea Winds SES Semi-Rigid Cable Qualification Status,“ JPL IOM 5
11、052-98-045 of 3/1/98.3. C. Kuo, “Fatigue Analysis if SESs Coax Cables,“ JPL IOM 352G: 98:025/CPK of 5/11/98.Lesson(s) Learned: 1. The Sea Winds test program demonstrated that semi-rigid coaxial RF cable failures are difficult to avoid. 2. Consider using flexible cable. If the design decision is to u
12、se semi-rigid cabling, provide ample strain relief loops, structurally join the two cable mounting points so that the load path does not go through the cable, and ensure that the natural frequency of the cable does not match the resonant frequency of the support structure. Stress and fatigue analysi
13、s should be performed on the cables to establish margin. 3. Semi-rigid RF cable failures often cannot be detected by visual examination. During inspections following vibration test of the Sea Winds SES, hairline cracks were missed Provided by IHSNot for ResaleNo reproduction or networking permitted
14、without license from IHS-,-,-several times. 4. When inspecting semi-rigid cables after vibration testing, use a magnifying glass with very good lighting, and look very carefully for cracks. 5. During thermal vacuum testing of semi-rigid cables, carefully monitor RF output signals for signs of signal
15、 drift that may indicate a cracked cable. Consider conducting several thermal cycles to increase the likelihood of crack detection. 6. Testing of PFMs may permit only in-situ visual examination of components, while STM tests typically allow cables to be removed from the unit for close examination. 7
16、. Where funding and schedule permits, structures joined by semi-rigid cables should be tested in a developmental model, such as an STM, that facilitates cable removal and inspection. 8. After a cable assembly passes environmental test, a second “identical“ cable may fail due to minor differences in
17、manufacture and installation. 9. To the extent feasible, cable receiving inspection, assembly, and installation should be standardized so that test results on one cable are valid on subsequent articles. Recommendation(s): See lesson(s) learned.Evidence of Recurrence Control Effectiveness: N/ADocumen
18、ts Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Parts Materials & Processesa71 Test & VerificationAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 1999-06-04a71 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-,-,-
