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The Challenger Disaster

A Case-study in Engineering Ethics

• Shuttle Components

– Orbiter

– Liquid Rocket

Booster

– Solid Rocket

Booster

Shuttle Components

Chronology of the Related Events

• 1974

– NASA contracts Morton Thiokol

• 1976

– NASA accepts the design based on the Titan missiles

– The joints are sealed by

• Two synthetic rubber O-rings,

• 177 clevis pins,

• Heat shield putty

The Cause of the Disaster

Early Problems

• 1977

– Tests at Thiokol show O-ring leakage

– Joint is made stronger by changing sizes

• 1981

– Post-launch investigation showed O-ring

erosion due to hot gages.

Early Problems

• January of 1985 launch

– First cold-weather launch

– Post-launch investigation showed joint failure

– Tests showed O-rings inability to fill the gap

due to joint rotation at lower temperatures

Early Problems

• July 1985

– Thiokol redesigns the joints w/o O-rings – The

design was not ready for Challenger launch

Political Climate

• Congress is unhappy with NASA

• Competition with Russians to be the first to

observe Halley’s comet.

• Pressure to launch before President

Reagan’s State of the Union Address

Days before Launch

• First launch attempt postponed

• The next launch date was set and was to be

attended by Vice President Bush.

• The temperature at launch: 29 degrees F.

Days Before Launch

• NASA starts an investigation of the effect

of low temperatures on the O-ring seals

• Organization involved

– NASA

– Marshall Space Flight Center

– Morton Thiokol

Engineering Investigation Before

Launch

• Players at NASA

– Larry Mulloy: SRB Project Manager at Marshall

• Players at Thiokol

– Roger Boisjoly: A SRB engineer

– Arnie Johnson: A SRB engineer

– Joe Kilminster: SRB engineering manager

– Alan McDonald: SRB engineering director

– Bob Lund: Vice president for engineering

– Jerald Mason: General manager

Engineering Investigation Before

Launch

• Boisjoly and Johnson recommend the

launch to be postponed.

• Bob Lund, the VP for engineering agrees

and makes a similar recommendation.

Investigation Before Launch

• Larry Mulloy, the NASA manager of SRB

asks Joe Kilminister, the SRB manager at

Thiokol, for his opinion.

• Kilminister agrees with other Thiokol

engineers and recommends a launch delay.

Investigation Before Launch

• After discussion with Mason

• Lund reverses his decision regarding

launch!

• Thiokol recommend the launch to proceed

The Launch in January 1986

• The overnight temperatures drop to 8 F

• The temperature of SRB at launch is 28 F

• There is an immediate blow-by of hot gas at

launch. The seal fails quickly over an arc of

70 degrees.

The Launch in January 1986

• The by-products of combustion forms a

glassy oxide that reseals the joint.

• The brittle oxide is shattered

• Hot gases quickly burn through the liquid

rocket booster

The Aftermath

• Causes of the accident are attributed to

– Inability of the O-rings to expand and seal at

low temperatures.

– Heat shield putty did not perform at low

temperatures

– Fits and seating of the O-ring was affected by

low temperature.

The Aftermath

• After all the testimonials

– Biosjoly is taken off the project and subtly

harassed by Thiokol management.