Failure Knowledge Database / 100 Selected Cases

Explosion of the Space Shuttle Challenger[January 28, 1986, USA]by Masayuki Nakao(Tokyo University, Institute of Engineering Innovation)

As people all over the world watched on TV, NASA’s space shuttle Challenger (Fig. 1)
exploded immediately after launch, and took lives of all 7 members of the crew.

Thecauses were loss of elasticity in an o-ring due to low temperature and fuel leak due tofaulty design.

Orbiter

Fuel tankRocket booster

The fuel tank between two rocketboosters is attached to the orbiterFig. 1Overview of the space shuttle [2]１．EventAs people all over the world watched on TV, the space shuttle Challenger of UnitedStates NASA (National Aeronautics and Space Administration) exploded shortly after
the launch, and took lives of all 7 members of the crews.
２．Course
On January 28, 1986, the space shuttle Challenger developed flame on the side of theSolid Rocket Booster shown in Fig. 1 (Photo 1, arrowed) immediately after the launch,and exploded soon after.

1Failure Knowledge Database / 100 Selected Cases

Photo 1. Explosion [2]The above shows pictures of the Orbiter attached facing down.

Here, the black smoke

is spurting from the rocket booster in front due to the gas leak from the arrowed area,
and the picture at the bottom shows white smoke coming out.
３．CauseFeynman, a member of the Presidential Commission headed by William Rogers,
discovered the main cause of the explosion as follows:1) There were two solid Rocket Boosters on this shuttle for shooting the shuttle intoorbit.

Some assembly was necessary for these Solid Rocket Boosters at thelaunch site and O-rings (as shown in Fig. 2) were used in the joint area. (1/4 inch
thickness and 12 feet in diameter).

The ambient temperature at the day of thelaunch was –1 to 2 degree Celsius (36 °F), about 13 to 14 degrees colder than the2Failure Knowledge Database / 100 Selected Cases

next coldest previous launch. Due to the cold weather, the o-rings stiffened andlost elasticity causing seal failure. It is presumed that fuel leaked from the gas
leak inspection hole was ignited by flame from the aft field, and resulting in anexplosion.

Photo 2 shows black smoke puffing due to the gas leak from thebooster before the launch (arrow at right-bottom corner of the photo).

In order toprove this, Feynman did the experiment at a public meeting placing an o-ring in
ice water to prove the loss of elasticity in the o-ring.

Rocket Booster

Joint area
Enlarged
Secondary o-ringPrimary o -ring

putty

Fuel

Insulation (liner)

InsideOutsideExternal wall

Gas leakGreasepin

Inspection HoleFig. 2, Structure of the Joint area of the Rocket Booster [2]3

Failure Knowledge Database / 100 Selected Cases

Photo 2, Black smoke photographed from the launch pad [2]2) The investigation has shown that the o-ring manufacturer and NASA knew theproblem with o-ring elasticity at low temperature, and the launch continued inspite of the manufacturer’s suggestion of canceling the launch.
3) The direct cause of the o-ring seal failure was loss of elasticity due to lowtemperature, but faulty design was also a contributing factor.

When chamberpressure in the rocket booster increased during use, the external walls between
joints expanded, called “joint rotation” phenomenon, because the walls of the joint
area was thicker than the external walls between the joint areas.

In thissituation, (shown in Fig. 3) moment of inertia occurs to break the joint where theo-ring seals.

In addition, there were some distortions from the previous use on

the rocket boosters.

Those distortions were corrected before re-use but there werestill some problems which were not completely corrected and caused gaps in theseal area.

They knew these possibilities, but no effective solutions took place.

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Failure Knowledge Database / 100 Selected Cases

jointmomentExt.
wallChamberpressure

O-ringspin

Cross-section ofRocket Booster

Fig. 3, Joint Rotation [2]4) The analysis showed that in addition to these technical problems, there were otherproblems such as insufficient communication between the management andengineers at the site within NASA.

Another problem was pressure on NASA toignore some technical issues in order to meet the following year’s budget.
４．Immediate Actions
After this accident, the Presidential Committee was formed to investigate the cause of
the accident and former Secretary of State, Rogers, was appointed as the chairman.
Dr. Feynman, who is the author of this report’s references, was also appointed as one of
the commissioners and provided significant contribution to the investigation. In order
to find the cause of the accident and to take necessary measures, the launch of shuttles
were put on hold for two years. This delay had quite an impact on the United States’
Space Plan.
５．Countermeasure:
A. Countermeasures for fuel leaks (Fig. 4)1) J-shape grooved adhesive seals replaced the previous putty seals. Even if thechamber pressure increased after launch, the pressure would go to the J-shapegroove and improves the seal effect.
2)

The seal area had an interference with the o-ring added in order to decrease
gap against joint rotation phenomenon.

3) Heaters were installed to avoid loss of o-ring elasticity
4) Gas leak inspection holes were added to improve the confirmation of o-ring sealfunction.

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Failure Knowledge Database / 100 Selected Cases

Fig. 4, Fuel Leak Prevention after the explosion of Space Shuttle Challenger [5]B. Improvements in management aspects
1) Reconstruct shuttle project management system (Clarification of authorities
and responsibilities)2) Improve risk evaluation and risk analysis in order to secure safe flights
3) Improve communication between on-site engineers and management
4) Understanding and responding to the deterioration level associated with flighthistory.
６．SummaryIn addition to the faulty design allowing gas leak from the joints, the o-ring lost its
elasticity because of the cold temperature. These combined factors caused fuel gas toleak and the rocket booster exploded.

In spite of the designers warning before thelaunch, the management continued the launch as scheduled.
７．Knowledge
1) Cause of a big disaster may be a small problem on a mechanical element, such as
the o-ring.
2) In a large project, an organization may get divided and information may not spreadto the whole organization.

Once an organization is formed, inappropriate decisions

may be made in order to protect the existence of the organization, and often lead to6

Failure Knowledge Database / 100 Selected Casesan accident.
3) Even if there was success in the past, condition and environment variation may
cause an accident (in this case low temperature).
８．BackgroundNASA developed space shuttles as space transportation systems.

Space shuttles

consist of an orbiter, rocket boosters, a fuel tank, and three main engines.
a system to recover the orbiter for reuse was applied.

In addition,

At the time of the development,

the goal was to save money by recycling the orbiter.

This system leads NASA toreduce launching costs by using the same orbiter repeatedly.

The first flight with thissystem was in 1982. Until this Challenger accident, they had completed 9 flights
successfully.

Up to the Colombia 3 disaster in 2003, they had 113 launches, and there

were only two failures, Challenger and Columbia.

In Columbia’s disaster, insulationof the external fuel tank peeled off and hit the wing creating a hole.

If they had reused

the Apollo’s disposed rocket, the crew would have been safe even when the insulation
had fallen off since the crew was at the top part of the ship.
＜References＞
1) What do you care what other people think ?: Further Adventures of a Curious
Character by Richard P. Feynman, and Ralph Leighton (Japanese version,translated by Masako Onuki) Published by Iwanami Shoten in 1988
2) Zoku-Zoku JISSAI NO SEKKEI (Practical Design Vol.3) by Yotaro Hatamura andJissai no Sekkei Society, Published by Nikkan Kogyo shimbun LTD. (1996)
3) NATIONAL SPACE TRANSPORTATION SYSTEM
a. http;//www.fas.org/spp/51L.html
4) The Challenger Accident：
a. http://www.me.utexas.edu/~uer/challenger/summary.html
5) SHIPPAI HYAKUSEN(100 failure cases) by Masayuki Nakao, published by
Morikita Shuppan Co.（2005）

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