Report of the PRESIDENTIAL COMMISSION
on the Space Shuttle Challenger Accident
Volume 5 Index
Hearings of the Presidential
Commission on the Space Shuttle Challenger Accident: February 26,
1986 to May 2, 1986.
MARCH 7, 1986 SESSION (part 2 of
2)
[1202] [Ref. 3/7-74 1 of
2] Failure Scenario 4B.
FAILURE SCENARIO 4B
FAILURE MECHANISM
- PRIMARY O-RING BLOW-BY AND ICE IN JOINT
EFFECTING SECONDARY O-RING OR JOINT CLEVIS DIMENSION
ASSESSMENT METHOD
- TESTS TO EVALUATE JOINT DIMENSION CHANGES
WITH WATER FREEZING IN JOINT
- TESTS TO EVALUATE SEALING CHARACTERISTICS
WITH COLD GREASE DOWNSTREAM OF SECONDARY O- RING
- ANALYSIS TO EVALUATE POTENTIAL FOR WATER
FREEZING IN JOINT TO UNSEAT SECONDARY 0 RING
FINDINGS TO DATE
- STS-51L EXPOSED TO APPROXIMATELY 7 INCHES
OF RAIN DURING PAD STAY
- POST INCIDENT INVESTIGATION REVEALED THAT
WATER WAS PRESENT IN JOINTS OF STS-9 WHEN DESTACKED TO REPLACE AFT
SEGMENT NOZZLE
- TESTS SHOW EFFECTS OF ICE ON CLEVIS
DIMENSION CHANGE ARE NEGLIGIBLE
- ANALYSIS SHOWS THAT:
- FREEZING OF WATER BENEATH COLUMN I AIR
BETWEEN TOP OF PIN AND SECONDARY 0 RING WILL NOT RESULT IN
UNSEATING 0 RING (MAX. DELTA P APPROXIMATELY 2 PSIG)
- WATER FREEZING BENEATH A COLUMN OF GREASE
REQUIRED TO EFFECT SECONDARY 0 RING
- SCENARIO OPEN PENDING FURTHER TEST
RESULTS
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