REG NASA-LLIS-0399--1995 Lessons Learned - Galileo Arc Welding Anomaly.pdf

1、Lessons Learned Entry: 0399Lesson Info:a71 Lesson Number: 0399a71 Lesson Date: 1995-06-07a71 Submitting Organization: JPLa71 Submitted by: H.R. MineSubject: Galileo Arc Welding Anomaly Abstract: During arc welding of a Galileo propulsion fuel line, an arc to the spacecraft caused an uncontrolled tra

2、nsient pulse of current that flowed through portions of the spacecraft structure and electronics. The potential for anomalies to introduce transient currents prompted recommendations involving interface design, planning of welding operations, and evaluation of electrical and insulation characteristi

3、cs.Description of Driving Event: During final reassembly and welding of the 400-N Rocket Engine Assembly fuel line (part of the Galileo Retro Propulsion Module - RPM), an arc was seen to jump between the welding head and the RPM oxidizer line (a distance less than 0.1“). The result of this arc was a

4、 pit in the oxidizer line (determined non-critical) and an uncontrolled transient pulse of current which flowed through portions of the spacecraft structure and electronics.It was recognized that this welding procedure was potentially hazardous. This welding procedure had been used when the RPM had

5、been previously assembled on the flight spacecraft and two separate reviews were conducted prior to performing the final weld.Review of the anomaly identified several subsystems (Spin Bearing Assembly ball bearings, oxidizer tubing, encoder electronics, slip rings, RPM rocket engine pressure transdu

6、cers, and RPM heaters) which were along the potential current paths of the arc from the arc contact point on the oxidizer line. Analysis of these subsystems determined that the subsystems had not been compromised. Tests simulating the worst case conditions on identical ball bearings demonstrated tha

7、t there was no change to the surface after the current pulse which would degrade the bearing performance.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-A review of the welding anomaly concluded that the spacecraft was not damaged or overstressed. Th

8、ere was, however, the impact of the additional work and analysis required to respond to the anomaly.Reference(s): PFR #54818 and #54282Lesson(s) Learned: 1. The complicated thermal and mechanical interface design of the RPM forced welding assembly and disassembly operations into a confined area, lea

9、ding directly to a hazardous operation.2. Unforeseen anomalies can introduce uncontrolled transient pulses of current into mechanisms which are not designed to conduct electricity.Recommendation(s): 1. Spacecraft design should emphasize simplicity in interface design. Attempts should be made to allo

10、w for the design, development, assembly and test of subsystems as independent units.2. In planning welding operations, a simulation of the physical configuration of the components in the area of the welding operation should be included, in addition to the existing tests for weld integrity.3. Contact

11、 start welders should be considered where welding operations present the possibility of arcing problems such as were encountered during the assembly and welding of the Galileo Propulsion subsystem fuel line.4. The electrical and insulation characteristics of mechanisms such as the ball bearings in t

12、he Spin Bearing Assembly, which are not designed to conduct electricity, should be evaluated during the design process and consideration be given to electrical isolation of such mechanisms.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/APro

13、vided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Additional Key Phrase(s): a71 Parts Materials & Processesa71 Policy & PlanningAdditional Info: Approval Info: a71 Approval Date: 1991-03-28a71 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-,-,-