REG NASA-LLIS-3759-2011 Lessons Learned - Space Shuttle High-Density Electrical Connector Retest.pdf

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1、Public Lessons Learned Entry: 3759 Lesson Info: Lesson Number: 3759 Lesson Date: 2010-08-25 Submitting Organization: KSC Submitted by: Annette Pitt Subject: Space Shuttle High-Density Electrical Connector Retest Abstract: Thousands of electrical connectors are used on the Space Shuttle Orbiter to al

2、low quick connection and disconnection of electrical circuits for maintenance, modification, inspection, or troubleshooting. NLS connectors (NLS is the prefix to the connector part number) are a frequently used type, are procured according to 40M38277 Marshall Space Flight Center (MSFC) specificatio

3、n, and are similar in construction to MIL-C-38999, Series II, connectors. NLS connectors are commonly referred to as high-density connectors because of their generally high number of small contacts per connector (up to 128 size 22D contacts in a single connector). From a design perspective, 128-pin

4、NLS connectors offer space and weight advantages but are challenging from a vehicle-processing perspective. Pictures of the front and back of an NLS connector are attached. The front view shows a bent pin. The back view shows the density of the wiring attached to the connector. Description of Drivin

5、g Event: Thousands of electrical connectors are used on the Space Shuttle Orbiter to allow quick connection and disconnection of electrical circuits for maintenance, modification, inspection, or troubleshooting. NLS connectors are procured according to MSFC specification 40M38277 and are similar in

6、construction to MIL-C-38999, Series II, connectors. NLS connectors are commonly referred to high-density connectors because of their generally high number of small contacts per connector (up to 128 size 22D contacts in a single connector). From a design perspective, 128-pin NLS connectors offer spac

7、e and weight advantages but are challenging from a vehicle processing perspective. First, the contacts of high-density connectors are more susceptible to bending during mating and demating than those of lower-density connectors. If the connector is damaged beyond repair, each connector contact must

8、be depinned and repinned a labor-intensive operation. Second, demating and reworking connectors have a significant effect on system-level retesting. According to the Orbiter Maintenance Requirements and Specifications Document (OMRSD), when a connector is demated, each pin must be functionally rever

9、ified after the connector is remated before the next mission. This requirement was imposed to detect bent or recessed contacts or other anomalies that could otherwise go undetected until the function was used during flight. In addition, the OMRSD requires that all replaced connectors be continuity-t

10、ested prior to power-up to verify that they were pinned appropriately. This requirement was imposed to ensure that flight hardware was not inadvertently electrically damaged because of a missed pin. Meeting these requirements for high-density connectors can be challenging, and the retesting alone ca

11、n take weeks. For example, the circuits of a 128-pin NLS connector can branch out to 15 or more other connectors. Continuity testing requires the demating of all those additional connectors, each of which carries its own retest requirements. This situation can quickly spiral into a retesting nightma

12、re, which can have significant effects on milestones. A worst-case example of this situation is retesting of the landing gear system. As one of the last steps of the Orbiter Processing Facility flow, the landing gear is functionally tested and then stowed. The Orbiter is then taken to the Vehicle As

13、sembly Building and mated to the External Tank and Solid Rocket Boosters. Once the Orbiter is vertical and mated, the landing gear cannot be functionally tested for the rest of the processing flow. Therefore, demating any connectors associated with those circuits must be avoided because retesting wo

14、uld require destacking and returning the Orbiter to the Orbiter Processing Facility. Lesson(s) Learned: Though high-density connectors offer many design benefits, they present significant challenges for vehicle processing and anomaly resolution. They are more susceptible to damage than low-density c

15、onnectors and carry significant retesting requirements if they are demated. High-density connectors should be used sparingly, and whenever possible, systems should not share a connector. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Back view: A hi

16、gh-density NLS connector with 128 wire segments is a challenge to vehicle processing. Front view: This high-density NLS connector has a bent pin (Number 115). Recommendation(s): Current technologies allow increased use of serial digital busses. When possible, these should be used to reduce the numbe

17、r of discrete circuits. Besides offering obvious design advantages, serial digital busses require less discrete system-level retesting. When possible, the ability to retest the circuits should be built into the vehicles electrical systems as opposed to requiring manual activation of hardware. Finall

18、y, high-density connectors should be used sparingly, and whenever possible, systems should not share a connector. Evidence of Recurrence Control Effectiveness: N/A Documents Related to Lesson: N/A Mission Directorate(s): Exploration Systems Additional Key Phrase(s): DDT/E Ground Operations Vehicle c

19、oncepts Level II/III requirements definition Long term sustainability and maintenance planning Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Lander Systems Launch Systems Logistics and maintenance Impact of human factors on systems requirements and

20、 designs Ground processing and manifesting Ground support systems Additional Info: Project: Space Shuttle Program Approval Info: Approval Date: 2011-03-01 Approval Name: mbell Approval Organization: HQ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-