1、Lessons Learned Entry: 0436Lesson Info:a71 Lesson Number: 0436a71 Lesson Date: 1996-07-17a71 Submitting Organization: JPLa71 Submitted by: J.A. RobertsSubject: Receiver 1 Power Converter Failure on Voyager 2 (1978) Abstract: A Voyager telemetry failure was attributed to over-length screws that cause
2、d conductive end-caps to contact areas not sufficiently coated by conformal coating. The lesson provides recommendations for design of captivated inserts, QA monitoring of assembly, application of conformal coatings, and planning of ground activities.Description of Driving Event: (Relevant Historica
3、l Lesson(s) Learned)Voyager 2 Receiver 1 operated normally from launch until an inadvertent activation of the on-board command loss routine switched it out and put Receiver 2 into use. Receiver 2 would not lock to the uplink to receive a command to stop the loss routine, and it later was found to ha
4、ve a shorted loop capacitor. Twelve hours later, the routine again selected Receiver 1. The Voyager flight team, knowing the spacecraft was already on the High-Gain Antenna (HGA), transmitted a series of HGA select commands to stop the routine without having any other effect on the spacecraft. The f
5、irst command of the series was received and stopped the routine. Several receiver telemetry channels began changing unexpectedly between two subsequent HGA select commands, and within 11 seconds the receiver power converter had failed; this was one-half hour after Receiver 1 had been turned back on.
6、 Anomalous telemetry data occurred in other subsystems during the receiver failure, with several indications in the photopolarimeter and an in crease in radio frequency noise in one channel of the harmonic radiation experiment of the planetary radio astronomy instrument.The Voyager document, “Voyage
7、r 2 Command Receiver 1 Failure Analysis,“ details the telemetered failure indications and measurements from the other subsystems sent at the same time. It also hypothesizes a failure model fitting all the observations and based on confirming laboratory testing Provided by IHSNot for ResaleNo reprodu
8、ction or networking permitted without license from IHS-,-,-of Voyager assemblies, subsystems, and instruments.Additional Keyword(s): Surveillance, Captive Inserts, Conformal Coatings, Mission OperationsReference(s):1. Project Document 618-817, “Voyager 2 Command Receiver 1 Failure Analysis,“ Arthur
9、G. Gussner, Oct. 19792. Voyager Incident Surprise Anomaly (ISA) 1783, and Voyager P/FR 41029Receiver Failure Model:The hypothesized failure model asserts that a resistive short from the 30-volt return line to chassis existed somewhere in the spacecraft at the time of the receiver failure. This first
10、 short had no effect on operation by itself and could not be detected by telemetry. Then a short to chassis occurred in the receiver, intermittent during the first three seconds and then continuous. This second short completed the short circuit and caused the receiver fuses to open. The location of
11、the short outside the receiver is unknown. The short in the receiver, by itself, would not have caused the failure.The receiver short is believed to have been caused by a metal particle from a captivated insert contacting areas not sufficiently coated by the solithane conformal coating.The inserts a
12、re steel, constructed with a disk captivated in the end of the insert to prevent metal shavings from the screw or the insert from entering the electronic housing. The receiver short is believed to have been caused by the conductive end-caps that were pushed out of the inserts by over-length screws w
13、hen the transponders, containing the receivers, were assembled to the spacecraft bay outer shear plates. As shown in the diagram, if the screw installed in the insert is too long, the captivated metal disk is pushed loose and a “donut“ of the insert is pushed loose with it. (The screws may have been
14、 too long through tolerance buildup in design, or wrong-length screws could have been inserted during assembly by error.)An examination of Voyager residual hardware revealed that the brush-on solithane conformal coating did not cover all areas, especially areas such as the edges of component leads w
15、here they were lap-soldered to circuit traces, bends in leads, the tops of horizontal leads, the edges of etched circuit traces, and the perimeters of transistor cans.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-refer to D descriptionD Lesson(s) L
16、earned: Effects of both plus and minus component tolerances must be examined in design.Telemetry measurements can be used to detect imbalances between the chassis-supply and chassis-return voltages, such as would be caused by the original Voyager short.Recommendation(s): Tolerancing of screw length
17、normally is examined to ensure adequate penetration. For captivated inserts, buildup of tolerances in the other direction becomes important. Captivated inserts should be designed so that conductive pieces of the insert are retained and will not fall into the electronics.Assembly of spacecraft bays s
18、hould be closely monitored by the Quality Assurance organizations to verify that only screws of the proper length are used.The application method for conformal coating relied on to prevent electrical shorts must not leave uncoated conductors.Procedures governing required or planned ground activities
19、 and their interaction with stored on-board “automatics“ must be carefully established and used.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Mission Directorate(s): a
20、71 N/AAdditional Key Phrase(s): a71 Hardwarea71 Parts Materials & ProcessesAdditional Info: Approval Info: a71 Approval Date: 1995-11-03a71 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-,-,-
