Case Study of Challenger

Introduction to the Case

On January 28, 1986, seven astronauts were killed when the space shuttle they were
piloting, the Challenger, exploded at just over a minute into the flight. The failure of the
solid rocket booster O-rings to seal properly allowed hot combustion gases to leak from
the side of the booster and burn through the external fuel tank. The failure of the O-ring
was attributed to several factors, including faulty design of the solid rocket boosters,
insufficient low-temperature testing of the O-ring material and of the joints that the O-
ring sealed, and lack of proper communication between different levels of NASA
management.
Organizations/People Involved
Marshall Space Flight Center - in charge of booster rocket development
Larry Mulloy - challenged the engineers' decision not to launch
Morton Thiokol - Contracted by NASA to build the solid rocket booster
Alan McDonald - Director of the Solid Rocket Motors project
Bob Lund - Engineering Vice President
Robert Ebeling - Engineer who worked under McDonald
Roger Boisjoly - Engineer who worked under McDonald
Joe Kilminster - Engineer in a management position
Jerald Mason - Senior executive who encouraged Lund to reassess his decision not to
launch.
Key Dates
1974 - Morton-Thiokol awarded contract to build solid rocket boosters.
1976 - NASA accepts Morton-Thiokol's booster design.
1977 - Morton-Thiokol discovers joint rotation problem.
November 1981 - O-ring erosion discovered after second shuttle flight.
January 24, 1985 - shuttle flight that exhibited the worst O-ring blowby.
July 1985 - Thiokol orders new steel billets for new field joint design.
August 19, 1985 - NASA Level I management briefed on booster problem.
January 27, 1986 - night teleconference to discuss effects of cold temperature on
booster performance.
January 28, 1986 - Challenger explodes 72 seconds after liftoff.
Key Issues
How does the implied social contract of profressionals apply to this case?
What profressional responsibilities were neglected, if any?
Should NASA have done anything differently in their launch decision procedure?
Background
Pressure to launch
NASA managers were anxious to launch the Challenger for several reasons, including
economic considerations, political pressures, and scheduling backlogs. Unforeseen
competition from the European Space Agency put NASA in a position in which it would
have to fly the shuttle dependably on a very ambitious schedule to prove the Space

Challenger study - pg. 1

Transportation System's cost effectiveness and potential for commercialization. This
prompted NASA to schedule a record number of missions in 1986 to make a case for its
budget requests.
The shuttle mission just prior to the Challenger had been delayed a record number of
times due to inclement weather and mechanical factors. NASA wanted to launch
the Challenger without any delays so the launch pad could be refurbished in time for the
next mission, which would be carrying a probe that would examine Halley's Comet. If
launched on time, this probe would have collected data a few days before a similar
Russian probe would be launched.
There was probably also pressure to launch Challenger so that it could be in space
when President Reagan gave his State of the Union address. Reagan's main topic was
to be education, and he was expected to mention the shuttle and the first teacher in
space, Christa McAuliffe.
Solid rocket booster
The shuttle solid rocket boosters (or SRBs), are key elements in the operation of the
shuttle. Without the boosters, the shuttle cannot produce enough thrust to overcome the
earth's gravitational pull and achieve orbit.
An SRB is attached to each side of the external fuel tank. Each booster is 149 feet long
and 12 feet in diameter. Before ignition, each booster weighs 2 million pounds.
Solid rockets, in general, produce much more thrust per pound than their liquid fuel
counterparts. The drawback is that, once the solid rocket fuel has been ignited, it cannot
be turned off or even controlled. So it was extremely important that the shuttle SRBs be
properly designed.
Morton Thiokol was awarded the contract to design and build the SRBs in 1974.
Thiokol's design is a scaled-up version of a Titan missile, which had been used
successfully for years. NASA accepted the design in 1976.
O-rings
Each SRB joint is sealed by two O-rings: the bottom ring known as the primary O-ring,
and the top known as the secondary O-ring. (The Titan booster had only one O-ring.
The second ring was added as a measure of redundancy since the boosters would be
lifting humans into orbit. Except for the increased scale of the rocket's diameter, this
was the only major difference between the shuttle booster and the Titan booster.)
The purpose of the O-rings is to prevent hot combustion gasses from escaping from the
inside of the motor. To provide a barrier between the rubber O-rings and the combustion
gasses, a heat-resistant putty is applied to the inner section of the joint prior to
assembly. The gap between the tang and the clevis determines the amount of
compression on the O-ring. To minimize the gap and increase the squeeze on the O-
ring, shims are inserted between the tang and the outside leg of the clevis.

Challenger study - pg. 2

Launch Delays
The first delay of the Challenger mission was due to a weather front expected to move
into the area, bringing rain and cold temperatures. Usually a mission wasn't postponed
until inclement weather actually entered the area, but the Vice President was expected
to be present for the launch and NASA officials wanted to avoid the necessity of the
Vice President's having to make an unnecessary trip to Florida, so they postponed the
launch early. The Vice President was a key spokesperson for the President on the
space program, and NASA coveted his good will. The weather front stalled, and the
launch window had perfect weather conditions; but the launch had already been
postponed.
The second launch delay was caused by a defective microswitch in the hatch locking
mechanism and by problems in removing the hatch handle. By the time these problems
had been sorted out, winds had become too high. The weather front had started moving
again, and appeared to be bringing record-setting low temperatures to the Florida area.
NASA wanted to check with all of its contractors to determine if there would be any
problems with launching in the cold temperatures. Alan McDonald, director of the Solid
Rocket Motor Project at Morton-Thiokol, was convinced that there were cold-weather
problems with the solid rocket motors and contacted two of the engineers working on
the project, Robert Ebeling and Roger Boisjoly. Thiokol knew there was a problem with
the boosters as early as 1977, and had initiated a redesign effort in 1985. NASA Level I
management had been briefed on the problem on August 19, 1985. Almost half of the
shuttle flights had experienced O-ring erosion in the booster field joints. Ebeling and
Boisjoly had complained to Thiokol that management was not supporting the redesign
task force.
The Night Before the Launch
Temperatures for the next launch date were predicted to be in the low 20°s. This
prompted Alan McDonald to ask his engineers at Thiokol to prepare a presentation on
the effects of cold temperature on booster performance.
A teleconference was held between engineers and management from Kennedy Space
Center, Marshall Space Flight Center in Alabama, and Morton-Thiokol in Utah. Boisjoly
and another engineer, Arnie Thompson, knew this would be another opportunity to
express their concerns about the boosters, but they had only a short time to prepare
their data for the presentation.1
Thiokol's engineers gave an hour-long presentation, presenting a convincing argument
that the cold weather would exaggerate the problems of joint rotation and delayed O-
ring seating. The lowest temperature experienced by the O-rings in any previous
mission was 53°F, on the January 24, 1985 flight. With a predicted ambient temperature
of 26°F at launch, the O-rings were estimated to be at 29°F.
After the technical presentation, Thiokol's Engineering Vice President Bob Lund
presented the conclusions and recommendations. His main conclusion was that 53°F
was the only low-temperature data Thiokol had for the effects of cold on the operational
boosters. The boosters had experienced O-ring erosion at this temperature. Since his
engineers had no low-temperature data below 53°F, they could not prove that it was

Challenger study - pg. 3

unsafe to launch at lower temperatures. He read his recommendations and commented
that the predicted temperatures for the morning's launch was outside the database and
NASA should delay the launch, so the ambient temperature could rise until the O-ring
temperature was at least 53°F. This confused NASA managers because the booster
design specifications called for booster operation as low as 31°F. (It later came out in
the investigation that Thiokol understood that the 31°F limit temperature was for storage
of the booster, and that the launch temperature limit was 40°F. Because of this,
dynamic tests of the boosters had never been performed below 40°F.)
Marshall's Solid Rocket Booster Project Manager, Larry Mulloy, commented that the
data was inconclusive and challenged the engineers' logic. A heated debate went on for
several minutes before Mulloy bypassed Lund and asked Joe Kilminster for his opinion.
Kilminster was in management, although he had an extensive engineering background.
By bypassing the engineers, Mulloy was calling for a middle-management decision, but
Kilminster stood by his engineers. Several other managers at Marshall expressed their
doubts about the recommendations, and finally Kilminster asked for a meeting off of the
net, so Thiokol could review its data. Boisjoly and Thompson tried to convince their
senior managers to stay with their original decision not to launch.
A senior executive at Thiokol, Jerald Mason, commented that a management decision
was required. The managers seemed to believe the O-rings could be eroded up to one-
third of their diameter and still seal properly, regardless of the temperature. The data
presented to them showed no correlation between temperature and the blowby gasses
which eroded the O-rings in previous missions. According to testimony by Kilminster
and Boisjoly, Mason finally turned to Bob Lund and said, "Take off your engineering hat
and put on your management hat."
Joe Kilminster wrote out the new recommendation and went back online with the
teleconference. The new recommendation stated that the cold was still a safety
concern, but their people had found that the original data was indeed inconclusive and
their "engineering assessment" was that launch was recommended, even though the
engineers had no part in writing the new recommendation and refused to sign it.
Alan McDonald, who was present with NASA management in Florida, was surprised to
see the recommendation to launch and appealed to NASA management not to launch.
NASA managers decided to approve the boosters for launch despite the fact that the
predicted launch temperature was outside of their operational specifications.
The Launch
During the night, temperatures dropped to as low as 8°F, much lower than had been
anticipated. To keep the water pipes in the launch platform from freezing, safety
showers and fire hoses had been turned on. Some of this water had accumulated, and
ice had formed all over the platform. There was some concern that the ice would fall off
of the platform during launch and might damage the heat-resistant tiles on the shuttle.
The ice inspection team thought the situation was of great concern, but the launch
director decided to go ahead with the countdown. (Note that safety limitations on low
temperature launching had to be waived and authorized by key personnel several times
during the final countdown. These key personnel were not aware of the teleconference

Challenger study - pg. 4

about the solid rocket boosters that had taken place the night before.)
At launch, the impact of ignition broke loose a shower of ice from the launch platform.
Some of the ice struck the left-hand booster, and some ice was actually sucked into the
booster nozzle itself by an aspiration effect. Although there was no evidence of any ice
damage to the Orbiter itself, NASA analysis of the ice problem was wrong. The booster
ignition transient started six hundredths of a second after the igniter fired. The aft field
joint on the right-hand booster was the coldest spot on the booster: about 28°F. The
booster's segmented steel casing ballooned and the joint rotated, expanding inward as
it had on all other shuttle flights. The primary O-ring was too cold to seal properly, the
cold-stiffened heat resistant putty that protected the rubber O-rings from the fuel
collapsed, and gases at over 5000°F burned past both O-rings across 70 degrees of
arc.
Eight hundredths of a second after ignition, the shuttle lifted off. Engineering cameras
focused on the right-hand booster showed about nine smoke puffs coming from the
booster aft field joint. Before the shuttle cleared the tower, oxides from the burnt
propellant temporarily sealed the field joint before flames could escape.
Fifty-nine seconds into the flight, Challenger experienced the most violent wind shear
ever encountered on a shuttle mission. The glassy oxides that sealed the field joint were
shattered by the stresses of the wind shear, and within seconds flames from the field
joint burned through the external fuel tank. Hundreds of tons of propellant ignited,
tearing apart the shuttle.
One hundred seconds into the flight, the last bit of telemetry data was transmitted from
the Challenger.
Issues for Discussion
1. What could NASA management have done differently?
2. What, if anything, could their subordinates have done differently?
3. What should Roger Boisjoly have done differently (if anything)? In answering this
question, keep in mind that, at his age, the prospect of finding a new job if he was fired
was slim. He also had a family to support.
4. What do you (the students) see as your future engineering professional
responsibilities in
relation to both being loyal to management and protecting the public welfare?
The Challenger disaster presents several issues that are relevant to engineers. These
issues raise many questions that may not have any definite answers, but can serve to
heighten the awareness of engineers when faced with a similar situation.
One of the most important is engineers who are placed in management positions. It is
important that these managers not ignore their own engineering experience, or the
expertise of their subordinate engineers. Often a manager, even if she has engineering
experience, is not as up-to-date on current engineering practices as are the actual
practicing engineers. She should keep this in mind when making any sort of decision
that involves an understanding of technical matters.
Another issue is the fact that managers encouraged launching due to the fact that there

Challenger study - pg. 5

was insufficient low-temperature data. Since there was not enough data available to
make an informed decision, this was not, in their opinion, grounds for stopping a launch.
This was a reversal in the thinking that went on in the early years of the space program,
which discouraged launching until all the facts were known about a particular problem.
This same reasoning can be traced back to an earlier phase in the shuttle program,
when upper-level NASA management was alerted to problems in the booster design,
yet did not halt the program until the problem was solved.
As engineers test designs for ever-increasing speeds, loads, capacities and the like,
they must always be aware of their obligation to society to protect the public welfare.
After all, the public has provided engineers, through the tax base, with the means for
obtaining an education and, through legislation, the means to license and regulate
themselves. In return, engineers have a responsibility to protect the safety and well-
being of the public in all of their professional efforts. This is part of the implicit social
contract all engineers have agreed to when they accepted admission to an engineering
college. The first canon in the ASME Code of Ethics urges engineers to "hold
paramount the safety, health, and welfare of the public in the performance of their
professional duties." Every major engineering code of ethics reminds engineers of the
importance of their responsibility to keep the safety and well being of the public at the
top of their list of priorities. Although company loyalty is important, it must not be
allowed to override the engineer's obligation to the public. Marcia Baron, in an excellent
monograph on loyalty, states: "It is a sad fact about loyalty that it invites...single-
mindedness. Single-minded pursuit of a goal is sometimes delightfully romantic, even a
real inspiration. But it is hardly something to advocate to engineers, whose impact on
the safety of the public is so very significant. Irresponsibility, whether caused by
selfishness or by magnificently unselfish loyalty, can have most unfortunate
consequences."2

Challenger study - pg. 6