SOLID ROCKET MOTORS

History

¶Issue

¶Was there sufficient time to correct the problems with the Solid Rocket Motor?

¶Findings

¶1. Problems with the joints which connect the Solid Rocket Motor casings were recognized for many years. While attempts were made to correct these problems, the measures taken were insufficient to provide a reliable joint.

¶2. The joint seal problem was recognized by engineers in both NASA and Morton Thiokol in sufficient time to have been corrected by redesigning and manufacturing new joints before the accident on January 28, 1986. Meeting flight schedules and cutting cost were given a higher priority than flight safety.

Summary of Casing Joint Design

¶Issue

¶Why did the aft field joint between the steel containers that hold the Solid Rocket Motor propellant fail to contain the burning gases of the propellant during lift-off and flight operations?

¶Findings

¶1. The design of the field joint was unsatisfactory and could not reliably contain the burning propellant gases under the range of operating conditions to be expected during the lift-off and flight phases.

¶2. The O-ring materials and putty used in the design of the joint were unsatisfactory as used on the Shuttle, particularly during the winter months. Furthermore, neither NASA nor its contractor, Morton Thiokol, can adequately control the quality or consistency of these kinds of materials, which are made from recipes known

¶(9) only by the manufacturer and which can be changed without certification and approval.

¶Recommendations

¶1. NASA should write and issue a new and more accurate performance specification which would cover the full range of thermal and structural requirements for the Solid Rocket Motors, with an adequate factor of safety for unusually low temperatures.

¶2. The Committee concurs with the Rogers Commission Report Recommendations on new joint design, but believes it is more appropriate to be more explicit in identifying the weaknesses in the joint design that need correction.

¶3. The field joints of the Solid Rocket Motors should be rede- signed to account for the following features while providing a significant factor of safety:

a. Movement in the joint, b. Proper spacing between tang and clevis, c. Seals made to withstand high and low temperatures under all dynamic thermal and structural loadings, d. Adequate sealing without the use of putty, e. Protection against insulation debonding and propellant cracking.

Testing and Certification

¶Discussion Only

Manufacturing Discussion Only

Stacking Operations

¶Issue

¶Was there any damage to the casing joints or contamination that occurred during the stacking operations when the Shuttle was assembled in the Vehicle Assembly Building (VAB) that could have contributed to the failure?

¶Finding

¶There was no evidence of joint contamination, fracture or other damage from foreign objects or due to casing ovality that contributed to the joint failure. Although certain problems occurred during stacking and the procedures were violated once, there was no evidence that these events contributed to the Flight 51-L accident.