1、Lessons Learned Entry: 0348Lesson Info:a71 Lesson Number: 0348a71 Lesson Date: 1994-10-25a71 Submitting Organization: JPLa71 Submitted by: J.L. SavinoSubject: Magellan AACS RAM Upset During SRM Pyrotechnic Initiation Abstract: An NSI may have shorted to chassis ground a few seconds after the SRM sep
2、aration pyros were activated on Magellan, causing the loss of at least 2K of AACS memory RAM. Six recommendations are made for improving designs for electro-explosive-device initiation.Description of Driving Event: On August 12, 1990, 7.3 seconds after the SRM separation pyros were activated on Mage
3、llan, erroneous alert codes were received by CDS. These alerts were caused by the failure of the AACS Memory B of at least 2K of the TCC244 RAM.JPL was able to build a failure model which accurately matched the symptoms on the spacecraft. Through ground tests, it has been determined that by firing o
4、ne or more NASA Standard Initiator (NSI) a short to the chassis ground could take place. The short path could be due to the direct contact between the unburned portion of the squib bridgewire with the chassis, or more likely, due to the presence of conductive gases/materials (plasma generated by det
5、onation) between the squib bridgewire and chassis. When a short occurs, a large current can flow through the ground structure and thus a large differential voltage can be induced across the shorting path. Since the energy available during the short is very large (2.2 J), the intense source of electr
6、o magnetic interference can affect sensitive victim electronic circuits causing upsets or damages.The shorting hypotheses are not unique to Magellan. The impact of NSI shorts on space systems is strongly dependent on grounding and cabling configurations of each spacecraft, with potential mission ris
7、ks.Additional Keyword(s): ShieldingProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Reference(s):1. PFR 52235, ISA 88992. Magellan Anomaly Investigation, IOM 340-93-JLS 301, dated 12/9/933. Summarized Findings and Recommendations of the Mars Observer
8、Investigation Groups, IOM GEC: 250-94-009, dated 1/28/944. Mars Observer Loss on Signal: Special Review Board Final Report; JPL Pub. 93-28Lesson(s) Learned: Based on Magellan analysis and test plus work recently performed in support of Mars Observer, the design for electro-explosive-device initiatio
9、n may be inadequate.Recommendation(s): 1. Reconsider induced chassis current mechanisms along with coupled voltage transients for all spacecraft designs being developed.2. Consider eliminating the return path through the chassis back to the firing source (do not connect the firing source to the fram
10、e), thus isolating the firing source.3. Consider reducing the NSI activation current - NSI spec.: 1 amp, no fire; 3.5 amps, all fire.4. Consider locating the current limiting resistor in the “high-side“ line.5. Consider grounding the fire circuit shield at both ends.6. Consider opening the enable re
11、lay for the initiators just fired, before firing of the next pyro sequence devices (not between redundant pairs).Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Energetic Materials - Explosive/Propellant/Pyrote
12、chnicProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-a71 EnergyAdditional Info: Approval Info: a71 Approval Date: 1994-03-31a71 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-,-,-
