Quoted By:
>The last major discussion of erosion was at the Level I Flight Readiness Review for STS 51-F (July 2, 1985).153 An analysis of the failure of the nozzle primary O-ring to seal due to erosion on flight STS 51-B (April 29, 1985) was presented. This serious erosion was attributed to leak check procedures. An increase in the nozzle leak check to 200 psi was proposed to be a cure. There was no mention of the fact that .171 inches of erosion on the primary O-ring far exceeded a more recent analysis model prediction of .070 inches maximum possible erosion. This was a revision of the former prediction of .090 inches. The launch constraint activated after STS 51-B was not specifically listed in the Level I Flight Readiness Review for 51-F. The Commission has also not found any mention of the duly 1985 constraint, or its waiver for subsequent Shuttle flights, in any Flight Readiness Review briefing documents.
>The Commission's review of the Marshall and Thiokol documentary presentations at the various Flight Readiness Reviews revealed several significant trends. First, O-ring erosion was not considered early in the program when it first occurred. Second, when the problem grew worse after STS 41-B, the initial analysis of the problem did not produce much research; instead, there was an early acceptance of the phenomenon. Third, because of a belief that in-flight O-ring erosion was "within the data base" of prior experience, later Flight Readiness Reviews gave a cursory review and often dismissed the recurring erosion as within "acceptable" or "allowable" limits. Fourth, both Thiokol and Marshall continued to rely on the redundancy of the secondary O-ring long after NASA had officially declared that the seal was a non-redundant single point failure. Finally, in 1985 when temperature became a major concern after STS 51-C and when the launch constraint was applied after 51-B, NASA Levels l and II were not informed of these developments in the Flight Readiness Review process.
