v4p318

Report of the PRESIDENTIAL COMMISSION on the Space Shuttle Challenger Accident

Volume 4 Index

Hearings of the Presidential Commission on the Space Shuttle Challenger Accident: February 6, 1986 to February 25, 1986

FEBRUARY 10, 1986 SESSION

[318] [Ref. 2/10-18] General Conclusions.

All O-ring erosion has occurred where gas paths in the vacuum putty are formed
Gas paths in the vacuum putty can occur during assembly, leak check, or during motor pressurization
Improved filler materials or layup configurations which still allow a valid leak check of the primary O-rings may reduce frequency of O-ring erosion but will probably not eliminate it or reduce the severity of erosion
Elimination of vacuum putty in a tighter joint area will eliminate O-ring erosion if circumferential flow is not present - if it is present, some baffle arrangement may be required
Erosion in the nozzle joint is more severe due to eccentricity; however, the secondary seal in the nozzle will seal and will not erode through
The primary O-ring in the field joint should not erode through but if it leaks due to erosion or lack of sealing the secondary seal may not seal the motor

[Ref. 2/10-19] Recommendations.

The lack of a good secondary seal in the field joint is most critical and ways to reduce joint rotation should be incorporated as soon as possible to reduce criticality
The flow conditions in the joint areas during ignition and motor operation need to be established through cold flow modeling to eliminate O-ring erosion
QM-5 static test should be used to qualify a second source of the only flight certified joint filler material (asbestos-filled vacuum putty) to protect the flight program schedule
VLS-1 should use the only flight certified joint filler material (Randolph asbestos-filled vacuum putty) in all joints
Additional hot and cold subscale tests need to be conducted to improve analytical modeling of O-ring erosion problem and for establishing margins safety for eroded O-rings
Analysis of existing data indicates that it is safe to continue flying existing design as long as all joints are leak checked with a 200 psig stabilization pressure, are free of contamination in the seal areas and meet O-ring squeeze requirements
Efforts needs to continue at an accelerated pace to eliminate SRM seal erosion