1、Lessons Learned Entry: 0427Lesson Info:a71 Lesson Number: 0427a71 Lesson Date: 1996-12a71 Submitting Organization: JPLa71 Submitted by: J.A. Robertsa71 POC Name: Joseph Okoneka71 POC Email: Joseph.J.Okonekjpl.nasa.gova71 POC Phone: 818 354-9300Subject: SEASAT-A Synthetic Aperture Radar (SAR) Data Li
2、nk Power Amplifier (1977) - (Revised) Abstract: A crack in an RF circuit ceramic substrate was revealed by a potentially mission catastrophic loss of output power during thermal-vacuum test of a sensor module. This crack was due to substrate weakening caused by use of a dental drill used for circuit
3、 tuning (by removing conductor material) during the final amplifier assembly process. Microwave RF circuit design that involves the practice of flight unit tuning by removal of conductive material, such as by use of abrasive or cutting tools, should be compatible with the substrate and circuit mater
4、ial, the packaging design, and other relevant factors. The Lesson Learned and Recommendations section in this 1977 lesson learned were revised in 2006 to reflect current practice in the use of abrasive and cutting tools to tune RF circuits.Description of Driving Event: (Relevant Historical Lesson(s)
5、 Learned)The SEASAT-A Synthetic Aperture Radar (SAR) Data Link suffered a 25-dB loss in output power during the Sensor Module Thermal Vacuum Test. This failure would have been catastrophic in flight, causing loss of all SAR data.The cause of the failure was a crack in an RF circuit ceramic substrate
6、. The crack opened the DC bias supply to an RF amplifier. Structural analysis of the substrates showed weakening caused by use of a dental drill used for circuit tuning (by removing conductor material) during the final amplifier assembly process. This process inevitably removed some substrate materi
7、al, by gouging or cracking Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-the substrate. Without this initial damage, the substrate material would have survived the expected thermal environment.Tuning of the flight RF circuit was done without benefi
8、t of new artwork. Because of cost and schedule pressures, design changes were made on the brassboard model and implemented on the flight model without benefit of a prototype.(A similar failure had occurred 8 months before during SAR System Thermal Vacuum Test. The earlier failure was originally attr
9、ibuted to an open solder joint in a bias circuit. In hindsight, the actual cause was probably a cracked substrate. At the time of the earlier failure, Voyager launch priorities precluded the assembly of the team, which made the diagnosis of the later failure.)Additional Keyword(s): Fabrication Techn
10、ique, Environmental Test, Spacecraft RadarReference(s):SEASAT P/FRs 1275, 3388Lesson(s) Learned: The tuning of RF circuits using abrasive or cutting tools to remove conductive material from the boards may cause mission critical damage that is not easily detectable. Recommendation(s): Microwave RF ci
11、rcuit design that involves the practice of flight unit tuning by removal of conductive material, such as by use of abrasive or cutting tools, should be compatible with the substrate and circuit material, the packaging design, and other relevant factors. Post-tuning inspection is mandatory.Evidence o
12、f Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Additional Key Phrase(s): a71 Hardwarea71 Parts Materials & ProcessesAdditional Info: Approval Info: a71 Approval Date: 1996-02-29a71 Approval Name: Carol Dumaina71 Approval Organization: JPLa71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
