Limiting Future Collision Risk to Spacecraft An Assessment of NASA's Meteoroid and Orbital Debris Programs (2011) / Chapter Skim
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5 Risk Assessment and Uncertainty
5 Risk Assessment and Uncertainty
Pages 40-46
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From page 40... ...
. In essence, a PRA attempts to determine the overall risk associated with a particular program or a mission stage by factoring in all known risks, and their corresponding uncertainties, if known.
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From page 41... ...
The higher figures come from the working engineers, and the very low figures from management."5 After the Columbia shuttle accident, the accident investigation board again urged NASA to enhance its risk analyses.6 This lack of attention to probabilistic risk assessment by NASA management had resulted in the MMOD programs finding it difficult to become part of any overall risk assessment associated with mission design and operations, since there was no agreed upon procedure for doing so. This is less true today: NASA management has become increasingly aware of the necessity for risk management, as reflected in NRC studies concerning MMOD with regard to the space shuttle 7 and the International Space Station (ISS)
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From page 42... ...
Recommendation: Although NASA should continue to allocate priority attention and resources to col lision risks and conjunction analysis, it should also work toward a broad integrative risk analysis to obtain a probabilistic risk assessment of the overall risks present in the MMOD domain in which all sources of risk can be put in context. UNCERTAINTY Communication of Information About Uncertainty NASA's work on reducing the threat to spacecraft posed by orbital debris and meteoroids faces increasingly challenging problems stemming from the complexity of physical changes in space, changing spacecraft designs, increased international use of space and contributions to debris, and private and public sector initiatives in space.
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From page 43... ...
This briefing led to the current Haystack observation program. In July 1993, a briefing to the Shuttle Program Office about the uncertainty of possible damage to the space shuttle during a predicted Perseid meteor storm led to a delay in the STS-51 launch and the beginning of the current meteoroid program at Marshall Space Flight Center.
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From page 44... ...
22 When this type of analysis is performed to relate characteristic size to RCS, it is heavily weighted toward the more numerous smaller objects. Consequently, if such an analysis were applied to relate impact damage to some characteristic size, it might easily be weighted toward smaller, but higher density iron or aluminum oxide debris objects.
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From page 45... ...
Caampued, Debris Size Estimation from Radar Cross Section Data Using Quadratic and Non-Parametric Classifiers, XonTech, Inc. Report No.
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From page 46... ...
While the calculation and communication of uncertainty information to decision makers, including those who plan space missions, has improved at NASA, it is also apparent that a fully integrated cataloging and assessment of MMOD-related uncertainties does not routinely occur in mission-planning and decision-making activities¾as noted above, this type of information is typically conveyed to management when the uncertainties are either small enough to be ignored, or large enough to be obvious so that either more data or some sort of corrective action is required. Since many of these decisions appear to be made at the program level, effective communication of uncertainty information both to the public and to the proper management levels is an issue of considerable importance that needs constant reevaluation and oversight.
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