Post-Challenger Evaluation of Space Shuttle Risk Assessment and Management (1988) / Chapter Skim
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Appendix E: An Improved Critical Item Risk Assessment Procedure for the National Space Transportation System
Appendix E: An Improved Critical Item Risk Assessment Procedure for the National Space Transportation System
Pages 125-138
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From page 125... ...
SUCCESS PATHS and STATUS CODE FOR REDUNDANCY/BACKUP are really descriptions of system or subsystem architectures. They affect risk by affecting the probabilities in the last Failure Mode 1 2 Severity Definition (A)
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From page 126... ...
3. PROPOSED IMPROVEMENTS As an improvement to Reference f3I, the Committee proposes the procedure described in Tahie E-1 below: All failure modes with the same Worst Damage State Given Lack of Redundancy or Reclunclancy Failure wouic]
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From page 127... ...
, Section 3.4, are very relevant to assessing the Probability of Primary Failure During Mission in Table E-1. Other factors include: Product design certification test results Manufacturing process qualification test results · Engineering analytical models · Related industry data · Etc.
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From page 128... ...
In the language of Table E-1 we have: TABLE E-3 Application of Table E-1 to the SAM Field Joint Language of Table E-1 Primary failure during mission Redundancy failure given primary failure Worst damage state Application to Field Joint Erosion and blowhy of the primary O-ring Failure of the secondary O-ring given erosion and blowhy of the primary O-ring Loss of life and vehicle The reason for considering this scenario is that ciata are readily available. Also in Reference FI]
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From page 129... ...
The results of a maximum likelihood analysis of these ciata under the above mociel yields the values in Table E-4. TABLE E-4 Maximum Likelihood Analysis of the SRM Field Joint Primary O-Rino Erosion Data Parameter cY Maximum Likelihood Estimate 78 -.17 0024 _— 90% Confidence Interval [ -.1, 15 7]
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From page 130... ...
The predicted probability per joint of primary O-ring erosion at 31° ~ joint temperature and 200 psi leak check pressure is p(31,200~=.95 [probability of - Primary Erosion The 90 percent confidence interval for the "probability of primary O-ring erosion" is shown in Attachment S and is t.S, 1.04. This shows that the extrapolation to 3-~° E; introduces considerable uncertainty in the estimate.
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From page 131... ...
(7) A statistical analysis of secondary erosion given primary erosion and blowby shows no statistically significant effects of joint type joint temperature or leak check pressure.
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From page 132... ...
This suggests a value approaching ~ for the probability of Toss of life and vehicle given total seal failure. Thus the closest probability value of ~ from Table E-2 column Probability of Worst Damage State, is selectee!
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From page 133... ...
Finally, the state of knowledge curve for A was clerive(l by propagating the state of knowledge 6 struct~ons tor Preparation ot critical item Mask Assessment (CIRA)
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From page 134... ...
ATTACHMENT 1 NASA's Proposed CIRA Technique.
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From page 135... ...
(Leh) Nozzle/Prlmary Forward Fleld/ Prlmary Nozzle/Prlma~y Att FleldfPrlmary IgnNorfPrlmary FonNard Fleld/Prlmary NozziolPrlmary l~nNerfPrlma~y Inncr GaskcV Prlmary Center Fleldt Prlmary Ccntcr Fleldt Secondaly Nozzle/Prlmary Forward Fleld/ Prlmary Nozzis/Prlmary Dash (-)
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From page 136... ...
(3) On STS 41-C, btt aft flold had a hot gas path detected In thc putty wIth an Indlcatlon ot heat on thc primary O-rlng.
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From page 137... ...
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From page 138... ...
·. a' ,~ 60 65 70 75 80 85 TEMPERATURE ATTACHMENT 6 90 Percent Confidence Interval for the "Probability of Mission Field Joint Failure," as a Function of A4.
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