scope:

Description of Driving Event:

During a hardware performance evaluation, Solid Rocket Motor (SRM) clevis and tang sealing surface diameters were assumed to be stable and were not remeasured during refurbishment. Subsequent testing revealed growth in the diameters after hydroproof (and possibly flight) which introduced an unrecognized variable into o-ring squeeze calculations. The static o-ring compression after mating is influenced by these actual hardware dimensions and the degree of segment concentricity, and are critical to hardware performance. During the STS 51-L Investigation, measurements were made on refurbished and reused segments, and the data indicated that segment circumferences at the sealing surfaces change with repeated use.