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 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 redesigned 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.

Summary of Launch Operations

Issue 1

¶How was the decision to launch STS 51-L arrived at and why was it wrong?

Findings

¶1. The Flight Readiness Review for STS 51-L was conducted in accordance with established procedure.

¶2. The decision to launch STS 51-L was based on a faulty engineering analysis of the SRM field joint seal behavior.

¶3. Compounding this erroneous analysis were serious ongoing weaknesses in the Shuttle Safety, Reliability and Quality Assurance Program which had failed to exercise control over the problem tracking systems, had not critiqued the engineering analysis advanced as an explanation of the SRM seal problem, and did not provide the independent perspective required by senior NASA managers at Flight Readiness Reviews.

¶4. The initial response of Marshall managers to the attempts of Thiokol engineers to raise the issue of temperature effects on the SRM seals caused Thiokol management to discount proper technical concerns and engineering judgment in their recommendation to launch.

¶5. The Director of Marshall's Shuttle Projects Office may have violated NASA's Flight Readiness Review policy directive by failing to report the results of the January 27th teleconference to the Associate Administrator for Space Flight.

¶6. The decision of the STS Program Manager to launch despite the uncertainty represented by ice on the Fixed Service Structure was not a prudent effort to mitigate avoidable risks to the Shuttle.

¶7. The Launch Director failed to place safety paramount in evaluating the launch readiness of STS 51-L. 8. No launch should have been permitted until ice was cleared from the platform leading to the pad escape system.

¶9. Ice Team personnel and Rockwell contractors properly conveyed their inability to predict the post-ignition behavior of ice.

¶10. Post-flight analysis indicates that ice did not exhibit the behavior predicted by analysis, and that ice traversed a distance sufficient to strike the Shuttle during liftoff.

¶11. Failure to enforce a clear requirement for definite readiness statements contributed to failures in communication between NASA and its contractors during launch preparations.

Issue 2

¶Should firing room personnel be allowed to waive launch commit criteria or equipment redlines during a launch countdown without a well-developed technical reason for doing so?

Finding

¶NASA's management waived its own launch commit criteria on January 28, 1986, without a valid technical reason for doing so.

Retrieval, Transportation and Refurbishment

Issue

¶Were the motor casings used on STS 51-L damaged as a result of the retrieval, transportation and refurbishment operations following previous launches?

Finding

¶There was no evidence of damage to the casings or joint due to prior use or preparation for reuse.

EXTERNAL TANK

Issue

¶The External Tank was obviously involved in the accident. Was that involvement a cause or an effect?

Findings

¶1. The Committee adopts the "Finding" of the Rogers Commission that: "A review of the External Tank's construction records, acceptance testing, prelaunch and flight data and recovered hardware, does not support anything relating to the External Tank which caused or contributed to the cause of the accident."

¶2. The External Tank ruptured under the forces of a failed Solid Rocket Booster motor. These forces were far outside of any possible design considerations that could have been applied to the External Tank.

CREW SURVIVAL

Issue

¶Was the accident of STS 51-L on January 28, 1986, survivable? Finding

¶In the case of the tragic loss of the Space Shuttle Challenger and her crew on January 28, 1986, the Committee is convinced that the accident was not survivable.

SABOTAGE

Issue

¶Could the accident have been caused by sabotage, terrorism, or foreign covert action?

Finding

¶The Committee is convinced that there is no evidence to support sabotage, terrorism or foreign covert action in the loss of the Challenger.

ADDITIONAL AVENUES OF INVESTIGATION

Issue

¶Could the accident have been caused by some failure other than failure of the joint between the casings?

Finding

¶As of September 15, 1986, the Committee has not found any credible evidence to support any caiise of the Challenger accident, other than the failure of the aft casings joint in the right-hand Solid Rocket Booster. Nor has there been any substantial evidence of a secondary or parallel failure on Flight 51-L.

SOLID ROCKET MOTORS