1、Lessons Learned Entry: 1486Lesson Info:a71 Lesson Number: 1486a71 Lesson Date: 2004-07-20a71 Submitting Organization: LARCa71 Submitted by: Charles E. HarrisSubject: Need for Increased Use of Formal Engineering Reports Abstract: Formal, archival documentation of the original investigation and the su
2、bsequent tests and analyses conducted to resolve the problem of the cracks found in the flowliners at the gimbal joint of the LH2 feedlines of the Orbiter fleet were substantially incomplete. The discipline of preparing and peer reviewing formal engineering reports leads to a high degree of accuracy
3、 and technical rigor.Description of Driving Event: The NESC performed independent tests and analyses to assess and resolve the flowliner cracking problem. Reliable and credible data must be collected from the Program in order to perform the assessment. In several cases the NESC found it difficult to
4、 collect those data in a reliable and credible format.Lesson(s) Learned: It has been two years since the cracks were originally discovered in the flowliners at the gimbal joint of the LH2 feedlines. In that time, numerous important observations, analyses, and tests have been accomplished. The ITA Te
5、am found extensive documentation archived on a web site (SSPWEB) maintained by the Program Office. However, the preponderance of documentation is in the form of briefing charts prepared for oral presentations. Also, the team found extensive technical information available from individual engineers w
6、orking on the problem resolution team. Unfortunately, much of this information was not properly documented in formal engineering reports. Also, there is no evidence that critical findings were formally peer reviewed. While numerous examples of incomplete documentation could be sited, two specific ex
7、amples are discussed below to illustrate the potential implications of the lack of technical rigor that might occur when formal documentation is not required and the results are not independently verified through peer review. Provided by IHSNot for ResaleNo reproduction or networking permitted witho
8、ut license from IHS-,-,-The location, orientation, and length of cracks originally found in the fleet in 2002 could not be determined from the original documentation given to the ITA Team. In fact, the numerous problem summary briefings given by engineers and senior team leaders, dating from August
9、2002 to January 2004, contained conflicting data on both the number of cracks found in each orbiter and the length of these cracks. To resolve these discrepancies, an extensive effort was required to re-analyze the original inspection data obtained in 2002. During this effort to establish accurate c
10、rack information, it was discovered that several cracks were kinked rather than extending in a self-similar crack growth direction as was implied by the sketches and analyses reported in the briefing charts. This is a significant finding because kinked cracks like those found in the orbiters, typica
11、lly exhibit bifurcation behavior and change crack growth direction due to complexities in the global stress field. This is critical information in determining the root causes of the cracks observed in the fleet. In fact, incorrect conclusions regarding the problem resolution could have resulted from
12、 this omission of critical evidence. As part of the investigation, two engine hot fire test series were conducted at Stennis Space Center. The purpose of these tests was to better understand the feedline flow physics and the associated forcing functions, which define the spectrum loadings on the flo
13、wliner. The first test series used a BTA with a fixed joint and without a flexible bellow. The second test series used a GTA with a gimbaled joint and flexible bellow. Not only did NASA invest considerable resources to conduct these tests, the interpretation of the test results has led to an escalat
14、ion in concern over the structural integrity of the flowliners and an additional expenditure of tens of millions of dollars in an attempt to develop a new flight rationale. Yet, there is no formal test report that documents the calibration of instrumentation, test procedures, sequence of test events
15、, test data acquisition, and post-test data reduction. Furthermore, there is no formal documentation of the engineering details regarding how the data was used to develop a loading spectrum and the associated prediction of the residual fatigue lives of the flowliners. Recommendation(s): Recommendati
16、on 1: Require formal reports to be generated for orbiter hardware inspections and for the results of testing. Recommendation 2: Institute a system whereby all documentation associated with the SSP be available in a single location. This information should include, but not be limited to, all plans an
17、d drawings, all qualification test plans and results, all flight data, and all subsequent testing plans and results. Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1. NASA
18、 Project and Program Plans, NPG 7120.5BMission Directorate(s): a71 Exploration Systemsa71 Sciencea71 Space Operationsa71 Aeronautics ResearchAdditional Key Phrase(s): a71 Program and Project ManagementAdditional Info: Approval Info: a71 Approval Date: 2004-09-22a71 Approval Name: Leslie Johnsona71 Approval Organization: LARCa71 Approval Phone Number: 757-864-9409Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
