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 21, 1986 SESSION. (part 2 of
2)
[1325] [Ref. 3/21-34 1 of
2] External Tank.
EXTERNAL TANK
W. LITTLES
MARCH 21, 1986
W-4
[Ref. 3/21-34 2 of 2]
External Tank: Investigation Approach.
EXTERNAL TANK
INVESTIGATION APPROACH
- REVIEWED ALL STS 51-L DATA
- REVIEWED CHALLENGER EXTERNAL TANK
HISTORY
- ALL BUILD PAPER
- ALL X-RAYS
- EVALUATED POTENTIAL ANOMOLIES ON FAULT
TREE
W-5
[1326] [Ref. 3/21-35]
Fault Tree Evaluation.
FAULT TREE EVALUATION
STRUCTURAL FLAW
FAILURE MECHANISM
- FAILURE OF EXTERNAL TANK DUE TO STRUCTURAL
FLAW OF CRITICAL SIZE
ASSESSMENT
- BUILD PAPER AND X-RAYS RE-REVIEWED--NO
INAPPROPRIATE DISPOSITIONS FOUND
- X-RAY RE-REVIEW DID IDENTIFY A 0.4'
INTERNAL FLAW IN A WELD LOCATED ON THE -Z AXIS IN A 2058 RING
FRAME WELD
- ANALYSIS SHOWS FLAW DOES NOT DEGRADE
STRUCTURE BELOW REQUIRED SAFETY FACTORS
- RECOVERED HARDWARE INCLUDES THIS FLAW,
NO EVIDENCE OF FLAW PROPAGATION
- NO INDICATION OF LEAKAGE DURING PRE-PRESS
AND ASCENT PHASES UNTIL AFTER 66 SECONDS
FINDING
- IMPROBABLE THAT STRUCTURAL FLAW INITIATED
THE FAILURE OF THE EXTERNAL TANK
W-6
[1327] [Ref. 3/21-36]
Fault Tree Evaluation.
FAULT TREE EVALUATION
STRUCTURAL OVERLOAD
FAILURE MECHANISM
- STRUCTURAL OVERLOAD INITIATES
FAILURE
ASSESSMENT
- LIFTOFF AND FLIGHT LOADS WERE WITHIN
DESIGN LIMITS (80 PERCENT MAXIMUM)
- ULLAGE PRESSURE WAS MAINTAINED WITHIN
LIMITS
- STS 51-L FLIGHT DATA INDICATES NOMINAL
TRAJECTORY PRIOR TO OBSERVED ANOMALY
- NO EXCESSIVE HEATING TO DEGRADE
STRUCTURAL CAPABILITY
- ANALYSIS INDICATES THAT THERMAL PROTECTION
SYSTEM LOSS (TPS) WOULD NOT HAVE RESULTED IN OVERHEATING
FINDING
- IMPROBABLE THAT STRUCTURAL OVERLOAD FROM
FLIGHT LOADS, EXCESSIVE ULLAGE PRESSURE OR EXCESSIVE HEATING
INITIATED THE FAILURE
W-7
[1328] [Ref. 3/21-37 1 of
2] Fault Tree Evaluation.
FAULT TREE EVALUATION
PREMATURE LINEAR SHAPED CHARGE (LSC)
DETONATION
FAILURE MECHANISM
- PREMATURE DETONATION OF LSC INITIATES TANK
FAILURE
ASSESSMENT
- NOT CONSISTENT WITH INITIAL "SMOKE" AT
0.68 SEC. OR OTHER EVENTS FROM FILM AND FLIGHT DATA
- PORTIONS OF L02 AND LH2 TANK LSC WERE
RECOVERED INTACT
FINDING
- PREMATURE DETONATION OF LSC NOT INVOLVED
IN FAILURE
[Ref. 3/21-37 2 of 2]
Fault Tree Evaluation.
FAULT TREE EVALUATION
DAMAGE TO EXTERNAL TANK AT LIFTOFF
FAILURE MECHANISM
- DAMAGE TO TANK CAUSES H2 LEAK
ASSESSMENT
- ICE TEAM SAW NO EVIDENCE OF LEAK AT FINAL
VISIT TO PAD PRIOR TO LAUNCH (T-20 MINUTES)
- POTENTIAL FOR DEBRIS DAMAGE
- NO EVIDENCE OF DEBRIS DAMAGE FROM
FILM
- SPRINGS MISSING FROM HOLDDOWN POST
COVERS
- KSC ANALYSIS INDICATES THAT SPRINGS
COULD NOT BE RELEASED PRIOR TO 0.8 SECOND DUE TO PHYSICAL
CONSTRAINTS
- NOT CONSISTENT WITH 'SMOKE' AT 0.68
SECOND
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