REG NASA-LLIS-2838-2010 Lessons Learned Loads from Soft Goods Not Fully Considered During Design of Mechanical Systems.pdf

1、Public Lessons Learned Entry: 2838 Lesson Info: Lesson Number: 2838 Lesson Date: 2010-04-27 Submitting Organization: KSC Submitted by: Annette Pitt Subject: Loads from Soft Goods Not Fully Considered During Design of Mechanical Systems Abstract: The effects of soft goods (environmental seals, pressu

2、re seals, thermal barriers, etc.) were not fully considered during the design of several of the orbiter mechanical systems. During rerigging efforts at KSC, it was not possible to meet all the requirements in the drawings/specifications because much of the initial rigging was done without the instal

3、lation of these soft goods. Loads induced by the soft goods prevented the mechanisms from operating within the required ranges. This was most evident during the rerigging of OV-103s landing gear after the Columbia accident. The design process should ensure that the loads of soft goods are understood

4、 and considered. Also, field rigging specifications should be developed to allow for rework of the system postdelivery. Description of Driving Event: During the Columbia accident investigation and return-to-flight processing of OV-103 for STS-114, concerns were raised about whether the environmental

5、 seals for the landing gear were being compressed adequately. An investigation revealed that the compression was less than required by the certification. One reason for this was that the seals had been compressed over time and were no longer the correct height. Moreover, the landing gear doors were

6、not closing as far as intended in the original design. Review of the procedures from the original rigging at Palmdale and the KSC rerigging performed in the early 1990s revealed that there were problems complying with the spec. The mechanism could not be adjusted to allow the landing gear doors to b

7、e closed flush to the adjacent structure within the required 0.030 inch. This was caused by the loads applied to the doors by the environmental seals and thermal barriers around the perimeter of the doors. Lesson(s) Learned: There were no requirements to verify the seal compression. Proper compressi

8、on was assumed based on meeting the door-to-structure flushness requirement. There was also no requirement to verify the height of the seals. There was a postflight visual inspection only. Attempts to adjust the mechanism to obtain the proper seal compression and door position confirmed that the mec

9、hanism was not capable of overcoming the loads of the seals and other soft goods without exceeding other parameters of the rigging specification. Ultimately, some parts of the mechanism were instrumented to ensure that the loads in the critical components remained within acceptable limits. In additi

10、on, after the STS-114 rerigging effort was complete, small changes in seal or thermal-barrier stiffness (when components were replaced) resulted in unacceptable changes in the door positions. This often resulted in extensive testing and rework in subsequent flows. There were similar problems with ot

11、her orbiter mechanical systems, including the ingress/egress hatch and External Tank umbilical doors. Furthermore, when the system was reworked in the field, it was not always possible to comply with the mechanical rigging specifications. The specs were written from a manufacturing perspective, and

12、often the seals and other Thermal Protection System components were not installed. Following the spec in the field was not always practical because it required that the hardware be returned to the original build configuration. This resulted in partial compliance with the specs and the need for mater

13、ial reviews to document deviations from the spec or out-of-spec conditions. Recommendation(s): During the design process, it is important that all the loads be fully understood and considered. It appears that the loads created by compression of the soft goods were underestimated during the design of

14、 the landing gear door system. Specifications for the mechanical systems should address field rigging of the components postdelivery. These may be separate specs or sections within the original installation and rigging specifications. The specs should consider the configuration of the hardware in th

15、e field and attempt to minimize the effect on other systems and the processing schedule. Requirements should be established to verify that the hardware is being operated within the certified limits. This is especially important when changes in one system can affect the configuration of another syste

16、m. Communication between system teams is also critical so both teams understand when their hardware is affected. Evidence of Recurrence Control Effectiveness: N/A Documents Related to Lesson: Click here to download OV-103 LG rigging summary document Click here to download Landing Gear Rigging White

17、Paper Mission Directorate(s): Space Operations Exploration Systems Additional Key Phrase(s): 1.Spacecraft 1.Engineering design and project processes and standards Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,- 1.Long term sustainability and mainten

18、ance planning 1.Entry Systems 1.Orbiting Vehicles 1.Ground processing and manifesting 1.Ground Operations Additional Info: Project: Space Shuttle Program Approval Info: Approval Date: 2010-06-27 Approval Name: mbell Approval Organization: HQ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-