1、 Public Lessons Learned Entry: 6416 Lesson Info: Lesson Number: 6416 Lesson Date: 2012-2-3 Submitting Organization: GRC Submitted by: Ralph Zerick Subject: SpaceWire Cable Fabrication and Installation Abstract: This lessons learned addresses handling, fabrication, integration and test issues identif
2、ied during the use of Gore SpaceWire cable, part number GSC-05-82730-00, size AWG26. This wire was used in flight hardware intended for deployment on the International Space Station. Specific problems experienced with this wire as well as recommendations to avoid similar problems are discussed herei
3、n. Description of Driving Event: Preparation and execution of CoNNeCT Comm Performance and TVAC System Level Testing involved Gore SpaceWire cable, one cable stopped functioning after the flight enclosure was shipped to the vibration lab in preparation for system level vibration testing. Another cab
4、le stopped functioning after it was installed in the flight hardware, however, it had passed all tests performed during fabrication. Lesson(s) Learned: Cable EFA517-001, SpaceWire Cable #3 This cable stopped functioning after the flight enclosure was shipped to the vibration lab in preparation for s
5、ystem level vibration testing. Prior to final tie wrap installation to secure all the internal cable bundles and the movement to the vibe lab this cable was functioning properly. After extensive trouble shooting at GRC indicated a probable short or open, the cable was taken to the Naval Research Lab
6、oratory in Washington DC for further evaluation. Time Domain Reflectometry tests identified the conductor and location in the cable where an intermittent short existed. Destructive Physical Analysis confirmed the location of the short. Lack of detailed instructions in the process plan resulted in th
7、e omission of shrink tubing around the wires for protection when the backshell was installed. The technician who had been assembling the SpaceWire cables was away and his replacement was not aware the shrink tubing had to be installed as part of the assembly process. It was also very apparent the ex
8、panded Teflon insulation on the individual wires was very soft and susceptible to damage under even very light point compression. Cable EFA518 -002, SpaceWire Cable #4 This cable stopped functioning after it was installed in the flight hardware. It had passed all functional tests during assembly. Af
9、ter extensive troubleshooting it was determined alcohol used during the post solder cleaning process was absorbed by the expanded Teflon insulation, wicked its way up the cable, caused an insulation breakdown, and ultimate failure of the cable. Lack of drawing detail on the cable assembly drawing sh
10、owing the Micro-D connector face in relation to a right angle backshell resulted to the connector being incorrectly oriented during assembly. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Figure 1: Connector side by side with a dime Figure 2: Wires
11、 are insulated/protected from rubbing with the addition of kynar sleeving. Figure 3: Punctured insulation resulting in exposed conductor at pin 5. Figure 4: Wires compressed at exit of backshell. Recommendation(s): Provided by IHSNot for ResaleNo reproduction or networking permitted without license
12、from IHS-,-,-1. Ensure assembly drawings and process plans contain complete, clear, and detailed instructions. More than one technician should be capable of performing the required assembly processes. 2. Implement post assembly 60deg C, 8 hour bake-out step prior to use. Use ethyl alcohol for post s
13、older cleaning and do not wipe cable with alcohol after bake-out. 3. When handling and installing SpaceWire cable, never bend the cable with a bend radius smaller than 4”, 6” is preferred. This recommendation is from engineers at the Goddard Space Flight Center who have experience working with this
14、cable on several flight programs. Also note this bend radius is larger than what the manufacturer and SpaceWire Specification (ECSS-E-ST-50-12C) specify. 4. Wrap cable with two wrappings of 200A STRIP-N-STICK (Auburn Manufacturing Company) or similar foam material where tie wraps secure cable. Hand
15、install tie wraps, they should be snug but not tight against the foam material. 5. When installing cables in flight hardware, position and secured the SpaceWire cables in place one time and never unbend them. These cables should be installed as close to the final item as possible to minimize potenti
16、al damage. 6. Investigate alternative cables for SpaceWire use. Any 100 ohm characteristic impedance cable designed for a Low Voltage Differential Signals (LVDS) should work. Cable must also meet program material requirements. 7. Investigate possibility of obtaining Time Domain Reflectometry (TDR) e
17、quipment that can test cables less than 10 ft for use at GRC. If this is not possible, continue to utilize the Naval Research Laboratory to perform this test when required. 8. When working with a new cable/connector system with no previous experience, contact other NASA users for information on prob
18、lems they may have experienced. 9. Include a face view of the connector in the assembly drawing when orientation is important. Evidence of Recurrence Control Effectiveness: N/A Documents Related to Lesson: N/A Mission Directorate(s): Aeronautics Research Additional Key Phrase(s): Manufacturing and A
19、ssembly Safety and Mission Assurance.Product Assurance Additional Categories.Test Article Additional Categories.Communication Systems Additional Categories.Flight Equipment Additional Categories.Test & Verification Systems Engineering and Analysis.Engineering design and project processes and standar
20、ds Safety and Mission Assurance.Quality Additional Info: Project: CoNNeCT Comm Performance Approval Info: Approval Date: 2012-02-17 Approval Name: mbell Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Organization: HQ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
