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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7 Interim Report #7: September 9, 1988
7 Interim Report #7: September 9, 1988
Pages 47-58
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From page 47... ...
Our conclusions are based on engineering judgment and the results of tests, the number of which has been necessarily small. Since our last report, the Panel has conducted four formal meetings and members of the Panel have attended a number of test readiness reviews; the QM-6, QM-7, and PVM-1 static tests; technical interchange meetings on the outer boot ring, aft skirt, and insulation debond problem; the design certification review' and an inspection of the stacked boosters to be used in the next flight (STS-26~.
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From page 48... ...
With few exceptions, no alternative design of a major component was carried to full-scale, full-duration testing. The principal exception, an alternative design for the nozzle outer boot ring, turned out to be needed and, because it was available, many months of delay were avoided when the original baseline design failed in the DM-9 static test.
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From page 49... ...
(5) The O-ring seals could be exposed to jets of combustion gases through blowholes in the putty of the original design; this exposure has been reduced or eliminated by replacing the putty with a thermal barrier of bonded insulation (the so-ca1 leaf J-sea1~.
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From page 50... ...
The results of a nozzle technology development program initiated before the accident led to improved control of the materials used to make the parts as well as to changes in the cloth layup patterns. A limited number of ground tests suggest that the thermal performance of these parts has been substantially improved.
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From page 51... ...
In practice, several changes in the first flight set were made after the two boosters were constructed when certification activities identified deficiencies. For example, the alternative outer boot ring design replaced the original redesign; new igniter bolts were installed to restrict the gap opening; and insulation debonds were repaired.
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From page 52... ...
(1) The motor will have been test f ired while conditioned to the highest and lowest operating temperature specified in the design requirements, with the low temperature test (QM-8 ~ coming after the resumption of flight but before a cold temperature launch.
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From page 53... ...
The analysis of the outer boot ring, for example, did not account for torsion, used incorrect loads, and had an inappropriate failure criterion, yet the results of analysis were originally used to select the baseline design. A similar caution is warranted for the application of current models to plastic deformation of metal parts and to complex structures, such as the aft skirt.
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From page 54... ...
As indicated earl ier, the low temperature certification static motor test is schedu~ ed to be conducted be fore the f irst cold temperature launch. After mission STS-2 6, a full°scale case j oint is to be subj ected to multiple cycles of pressure ~ oading and then burst to identify effects of multiple uses and validate structural analyses.
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From page 55... ...
The case field joint design requires relatively precise control of the dimensions of the capture feature and the mating clevis leg: a few thousandths of an inch on a cylinder approximately 12 feet in diameter may be critical not only for its intended operation but also for reuse. Making accurate, precise measurements in this context has not proven to be easy.
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From page 56... ...
Included in this category are: O-rings in the safe and arm device that have less than the specified squeeze on the rotor shaft; fully threaded bolts in nozzle internal joint #5; case-liner edge bonds built without the benefit of the most recent process controls; nozzles that have been subjected to removal and replacement of the outer boot ring; and the so-called custom-fitted vent port plugs. In addition, putty in the igniter joints of the STS-26 boosters -- and one of the STS-27 boosters -- has been mechanically tamped to reduce the potential for blowholes although this process will not be followed in the future.
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From page 57... ...
More can still be accomplished to improve safety and reliability after flights resume, however, as a number of important issues in the design and verification program have been deferred or are sti11 unresolved. Among these are: the adequacy of new procedures for making the case-insulation bonds for future flight articles; the adequacy of repairs to case-insulation bonds; the structural performance of nozzle parts and bonds; the occurrence and effects of blowholes in the adhesive in the case-to-nozzle joint; effects of long term storage on installed elastomeric seals and bonds; the accuracy and reliability of measuring and matching case segments; the adequacy of the aft skirt design; the potential need to prevent the establishment of differential pressure across the nozzle flexible boot; the verification of structural analysis by a burst test of a full-scale case; the potential for achieving the required number of reuses of case segments; and the removal of materials that contain asbestos.
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From page 58... ...
NASA and its contractors have worked diligently on the redesign and testing program and deserve to be recognized for their efforts. The redesigned solid rocket boosters have incorporated a large number of improvements that 8 _ ~ _ ~ _ _ a snouts resume In cons~aeran~v ennancea sarerv and reliabiliLv.
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