Collected Reports of the Panel on Technical Evaluation of NASA's Redesign of the Space Shuttle Solid Rocket Booster (1988) / Chapter Skim
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Final Report, December 21, 1988
Final Report, December 21, 1988
Pages 59-71
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From page 59... ...
Fletcher Administrator National Aeronautics and Space Administration 400 Maryland Avenue, S.W., Room 7137 Washington, DC 20546 Dear Jim: I am pleased to submit herewith the final report of the National Research Counci1's Panel for the Technical Evaluation of NASA's Redesign of the Space Shuttle Solid Rocket Booster. Since our last report, two missions of the National Space Transportation System have been completed, STS-26 and STS-27, employing the redesigned solid propellant rockets.
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From page 60... ...
Their occurrence could have important consequences for program costs, since removing them could change the dimensions of the hardware enough to make it more difficult to find mating parts that provide the desired interference fit. Remaining Tasks in the Recovery Program While STS-26 was a successful mission, work remains to be accomplished before we would consider the redesign program to be complete.
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From page 61... ...
In addition to assessment of flight instrumentation data, these evaluations should include careful inspection of used hardware and a systemmatic assessment and documentation of the performance of seals, insulation, ablative materials, and metal components. The procedures should take account of the fact that in the case field joint and case-to-nozzle joint, upstream gas barriers will normally prevent combustion gases from reaching the primary seals, making it difficult to detect a degradation in the seals, materials, or surface finishes unless an upstream barrier fails.
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From page 62... ...
Often, only when major components fail does the focus shift to developing a firm understanding of how the components actually perform over the full range of operating environments. In response to the Challenger accident, the solid rocket booster recovery program initially focussed on determining how the originals y designed parts had failed, understanding their operation, and establishing the margins of safety of the redes igned components .
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From page 63... ...
Early in the testing program, three Joint Environment Simulator (JES) tests of the Challenger field joint configuration added greatly to the understanding of the probable contributing causes of the Challenger accident and, in fact, appeared to duplicate closely the operation of the joint under the conditions of the failure.
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From page 64... ...
Two other simulators, the Nozzle Joint Environment Simulator and the Transient Pressure Test Article, were developed during the course of the program which, along with the JES, proved extremely valuable for improving understanding of the operation of specific redesigned components. The Panel believes that these test devices were of critical importance in the design verification program and that some of these test setups should be retained in an operational condition.
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From page 65... ...
The Pane J is also a strong advocate of emphasizing testing that demonstrates the performance of design components at all levels under conditions more severe than would be encountered in flight. For the redesign joints, this testing included imposing purposely manufactured leak paths into test articles sufficient to guarantee that combustion gases would impinge on the respective barriers and seals for testing the performance of the new designs.
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From page 66... ...
We concluded that analyses, especially those whose objecfives are to predict structural failure, must be verified by carefully planned and properly simulated experiments that are well instrumented. We suggest that NASA could improve its modelling capability by shifting some attention from computer program development to development of good engineering insight through simple, meaningful validation experiments.
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From page 67... ...
In light of the important lessons learned in the course of the redesign program, both technical and administrative, about large and complex engineering programs, we suggest that NASA commission an independent, professional technical history of the booster rocket recovery program to benefit future NASA -- and possibly other national -- programs of similar scope. Risk Reduction through Product Improvement Although our formal task is completed with the successful return to flight, the Panel has been briefed on NASA's plans for program activities beyond STS-26.
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From page 68... ...
It is standard practice in the aeronautical industry to monitor flight performance (from components to systems to the vehicle) and to make modifications when the data base indicates that safety margins are below design requirements or potential failure modes are not adequately treated in the design.
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From page 69... ...
McDonald, of Morton Thiokol, Inc., who bore a primary responsibility for making the engineering j udgments required in the redes ign program and the burden 0 f cony inc ing us that they were r ight - - or accept ing our recommendations. We owe a special debt of gratitude to Russell Bardos, of NASA's Office of Space Flight, for assuring that we had the information we needed to ful f ill our charge, guiding us through the program' s organizational structure, and providing excel lent ~ iaison between the Panel and the respective leered s of NASA.
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