1、Lessons Learned Entry: 0435Lesson Info:a71 Lesson Number: 0435a71 Lesson Date: 1996-07-17a71 Submitting Organization: JPLa71 Submitted by: J.A. RobertsSubject: Ground Support Equipment Failure Caused Damage to SEASAT-A (1978) Abstract: A SEASAT-A subassembly was damaged during thermal-vacuum test du
2、e to the configuration of GSE test equipment. A reed relay in a commercial data scanner was connected to circuits requiring +5 volts; its failure permitted the SEASAT-A circuits to be exposed to scans as high as 31 volts.It is important to assess the design of commercial support equipment and consid
3、er what a failure of an internal part might do to the flight hardware. Description of Driving Event: (Relevant Historical Lesson(s) Learned)A commercial data scanner using a bank of reed relays failed during thermal-vacuum testing of the SEASAT-A Synthetic Aperture Radar (SAR) Transmitter subassembl
4、y. Transmitter circuits requiring +5 volts were exposed to as high as 31 volts during each scan, resulting in catastrophic failure in the +5 volt circuits of the Transmitter. This problem caused about a two-week slip in the overall schedule, including the loss of 3 days of a one-week thermal-vacuum
5、test and three days to repair the Transmitter.The nature of this problem could have caused the failure to occur anytime the sensor was operated with the ground support equipment as it was configured. The Transmitter GSE was configured with 15 separate regulated power supplies of various voltages. To
6、 allow automatic data acquisition of power supply voltage and current readings during the test, a data scanner driven by a computing calculator was implemented. This scanner consists of a bank of reed relays sequentially addressed by the calculator to acquire each power supply terminal voltage. Each
7、 power supply terminal was connected to a scanner reed relay switch terminal. The other side of the switches were then tied Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-together to the bus, similar to a multiplexer arrangement. In the thermal-vacu
8、um test, one of the reed relays failed to open. As a result, each succeeding power supply terminal that was scanned became electrically tied to the one connected to the relay that failed to open. The failed relay was connected to +5 volt supply. The other supply voltages ranged up to +31 volts. The
9、JPL calibration Lab uses this type of data scanner at the present time.Additional Keyword(s): GSE Interface FMECAReference(s): SEASAT SAR P/FR 4891Lesson(s) Learned: The problem was caused by using a commercial piece of equipment without looking into its internal nature and considering what a failur
10、e in an internal part might do to the flight equipment. Previously, the SAR Transmitter had been tested at the contractors facility, using the same set-up, with no problem.Recommendation(s): This failure could have been avoided by providing an isolation resistor between each power supply terminal an
11、d the scanner. The voltmeter used to make the measurement has an input impedance of several megohms, so an isolation resistor of up to 100K ohms would have provided ample protection without affecting significantly the measurement accuracy.The difference between flight configuration and GSE configura
12、tion must be kept in mind. The normal inputs, connected to the spacecraft power converter, are isolated by at least 10K ohms. There is a need to be continuously conscious of the differences between flight and test configuration. The catastrophic potential of a reed relay failing to open was overlook
13、ed in this case. Support equipment failures must be prevented from propagating to the flight hardware.Evidence of 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
14、IHS-,-,-Additional Key Phrase(s): a71 Configuration Managementa71 Energya71 Flight Equipmenta71 Ground Equipmenta71 HardwareAdditional Info: Approval Info: a71 Approval Date: 1995-10-16a71 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-,-,-
