Mission 51-L Launch Decision
On January 28, 1986, the Space Shuttle Challenger was launched for the last time. The decision to launch
the Challenger was not simple. Certainly no one dreamed that the Shuttle would explode less than two
minutes after lift-off. Much has been said and written about the decision to launch. Was the decision to launch
correct? How was the decision made? Could anyone have foreseen the subsequent explosion? Should the
decision-making procedure have been modified? These questions are examined in this case study.
The Space Shuttle:
The Space Shuttle is the most complicated vehicle ever constructed. Its complexity dwarfs any previous project
ever attempted, including the Apollo project. The Apollo project possessed a very specific goal, to send men to
the moon. The Space Shuttle program has a wide variety of goals, some of which conflict. The attempt to
satisfy conflicting goals is one of the chief roots of difficulty with the design of the Space Shuttle. Originally, the
design was to be only a part of NASA’s overall manned space transportation system, but because of politics
and budget cuts, it was transformed from an integral component of a system to the sole component of the
manned space program. The Space Shuttle was the first attempt to produce a truly reusable spacecraft. All
previous spacecraft were designed to fly only a single mission. In the late 1960’s, NASA envisioned a vehicle
which could be used repeatedly, thus reducing both the engineering cost and hardware costs. However,
resulting vehicle was not as envisioned. It had severe design flaws, one of which caused the loss of the
NASA Planning and Politics:
NASA’s post-Apollo plans for the continued manned exploration of space rested on a three legged triad. The
first leg was a reusable space transportation system, the Space Shuttle, which could transport men and cargo
to low earth orbit (LEO) and then land back on Earth to prepare for another mission. The second leg was a
manned orbiting space station which would be resupplied by the Shuttle and would serve as both a transfer
point for activities further from Earth and as a scientific and manufacturing platform. The final leg was the
exploration of Mars, which would start from the Space Station. Unfortunately, the politics and inflation of the
early 70’s forced NASA to retreat from its ambitious program. Both the Space Station and the Journey to Mars
were delayed indefinitely and the United States manned space program was left standing on one leg, the
space shuttle. Even worse, the Shuttle was constantly under attack by a Democratic congress and poorly
defended by a Republican president.
To retain Shuttle funding, NASA was forced to make a series of major concessions. First, facing a highly
constrained budget, NASA sacrificed the research and development necessary to produce a truly reusable
shuttle, and instead accepted a design which was only partially reusable, eliminating one of the features which
made the shuttle attractive in the first place. Solid rocket boosters (SRBs) were used instead of safer liquid
fueled boosters because they required a much smaller research and development effort. Numerous other
design changes were made to reduce the level of research and development required.
Second, to increase its political clout and to guarantee a steady customer base, NASA enlisted the support of
the United States Air Force. The Air Force could provide the considerable political clout of the Defense
Department and had many satellites which required launching. However, Air Force support did not come
without a price. The Shuttle payload bay was required to meet Air Force size and shape requirements which
placed key constraints on the ultimate design. Even more important was the Air Force requirement that the
Shuttle be able to launch from Vandenburg Air Force Base in California. This constraint required a larger cross
range than the Florida site, which in turn decreased the total allowable vehicle weight. The weight reduction
required the elimination of the design’s air breathing engines, resulting in a single-pass unpowered landing.
This greatly limited the safety and landing versatility of the vehicle.
Factors Affecting the Launch Decision
Pressures to Fly:
As the year 1986 began, there was extreme pressure on NASA to “Fly out the Manifest”. From its inception the
Space Shuttle program had been plagued by exaggerated expectations, funding inconsistencies, and political
pressures. The ultimate design was shaped almost as much by politics as physics. President Kennedy’s
declaration that the United States would land a man on the moon before the end of the decade had provided
NASA’s Apollo program with high visibility, a clear direction, and powerful political backing. The space shuttle
program was not as fortunate; it had neither a clear direction nor consistent political backing.
System Status and Competition:
In spite of all its early difficulties, the Shuttle program looked quite good in 1985. A total of 19 flights had been
launched and recovered, and although many had experienced minor problems, all but one of the flights could
rightfully be categorized as successful. However, delays in the program as a whole had lead the Air Force to
request funds to develop an expendable launch vehicle. Worse still, the French launch organization
Arianespace, had developed an independent capability to place satellites into orbit at prices the Shuttle could
not hope to match without greatly increased federal subsidization (which was not likely to occur as Congress
was becoming increasingly dissatisfied with the program). The shuttle was soon going to have to begin
showing that it could pay for itself. There was only one way this could be done–increase the number of flights.
For the shuttle program, 1986 was to be the year of truth. NASA had to prove that it could launch a large
number of flights on time to continue to attract customers and retain Congressional support. Unfortunately,
1986 did not started out well for the shuttle program. Columbia, Flight 61-C, had experienced a record four onpad aborts and had three other schedule slips. Finally, on mission 61-C, Columbia was forced to land at
Edwards Air Force Base rather than at Kennedy Space Center as planned. The delays in Columbia’s launch
and touchdown threatened to upset the launch schedule for the rest of the year.
Not only did Columbia’s landing at Edwards require it to be ferried back to the Cape, but several key shuttle
parts had to be carried back by T-38 for use on the other vehicles. These parts included a temperature sensor
for the propulsion system, the nose-wheel steering box, an air sensor for the crew cabin, and one of the five
general purpose computers. At the time of the Challenger explosion, NASA supposedly had four complete
shuttles. In reality there were only enough parts for two complete shuttles. Parts were passed around and
reinstalled in the orbiters with the earliest launch dates. Each time a part was removed or inserted, the shuttles
were exposed to a whole host of possible servicing-induced problems.
In addition to problems caused by the flight 61-C of Columbia, the next Columbia flight, 61-E, scheduled for
March also put pressure on NASA to launch the Challenger on schedule. The March flight of Columbia was to
carry the ASTRO spacecraft which had a very tight launch window because NASA wanted it to reach Halley’s
Comet before a Russian probe arrived at the comet. In order to launch Columbia 61-E on time, Challenger had
to carry out its mission and return to Kennedy by January 31.
NASA had much to gain from a successful Flight 51-L. The “Teacher in Space” mission had generated much
more press interest than other recent shuttle flights. Publicity was and continues to be extremely important to
the agency. It is a very important tool which NASA uses to help ensure its funding. The recent success of the
Space Shuttle program had left NASA in a Catch 22 type situation. Successful shuttle flights were no longer
news because they were almost ordinary. However, launch aborts and delayed landings were more news
worthy because they were much less common.
In addition to general publicity gained from flight 51-L, NASA undoubtedly was aware that a successful mission
would play well in the White House. President Reagan shared NASA’s love of publicity and was about to give a
State of the Union speech. The value of an elementary teacher giving a lecture from orbit was obvious and was
lost neither on NASA nor on President Reagan.
Sequence of Events
Monday, January 27:
On Monday NASA had attempted to place Challenger in orbit only to be stymied by a stripped bolt and high
winds. All preliminary procedures had been completed and the crew had just boarded when the first problem
struck. A micro sensor on the hatch indicated that it was not shut securely; it turned out that the hatch was shut
securely and the sensor was malfunctioning, but valuable time was used determining that the sensor was the
After closing the hatch, the external hatch handle could not be removed. The threads on the connecting bolt
were stripped and instead of cleanly disengaging when turned the handle simply spun around. Attempts to use
a portable drill to remove the handle failed. Technicians on the scene asked Mission Control for permission to
saw the bolt off. Fearing some form of structural stress to the hatch, engineers made numerous time
consuming calculations before giving the go-ahead to cut off the bolt. The entire process consumed almost two
hours before the countdown was resumed.
Misfortunes continued. During the attempts to verify the integrity of the hatch and remove the handle, the wind
had been steadily rising. Chief Astronaut John Young flew a series of approaches in the shuttle training aircraft
and confirmed the worst fears of Mission Control. The crosswinds at the Cape were in excess of the level
allowed for the abort contingency. The opportunity had been missed and the flight would have to wait until the
next possible launch window, the following morning. Everyone was quite discouraged especially since
extremely cold weather was forecast for Tuesday which could further postpone the launch.
Tuesday, January 28:
After the canceled launch on Monday morning there was a great deal of concern about the possible effects of
weather. The predicted low for Tuesday morning was 23o F, far below the nominal operating temperature for
many of the Challenger’s subsystems. Undoubtedly, as the sun came up and the launch time approached both
air temperature and vehicle would warm up, but there was still concern. Would the ambient temperature
become high enough to meet launch requirements? NASA’s Launch Commit Criteria stated that no launch
should occur at temperatures below 31o F. There was also concern over any permanent effects on the shuttle
due to the cold overnight temperatures.
All NASA centers and subcontractors involved with the Shuttle were asked to determine the possible effects of
cold weather and present any concerns. In the meantime, Kennedy Space Center went ahead with its freeze
protection plan This included the use of anti-freeze in the huge acoustic damping ponds, and allowing warm
water to bleed through pipes, showers, and hoses to prevent freezing. The weather for Tuesday morning was
to be clear and cold. Because the overnight low was forecast at 23o F, there was doubt that Challenger would
be much above freezing at launch time. The Launch Commit Criteria included very specific temperature limits
for most systems on the shuttle. A special wavier would be required to launch if any of these criteria were not
met. Although these criteria were supposedly legally binding, Marshall Space Flight Center administrator Larry
Mulloy had been routinely writing waivers to cover the problems with the SRBs on the recent shuttle flights.
Engineers at Morton-Thiokol, the SRB manufacturer in Utah, were very concerned about the possible effects of
the cold weather. The problems with the SRBs had been long known to engineers Roger Boisjoly and Allan
McDonald, but both felt that their concerns were being ignored. They felt that the request by NASA to provide
comment on the launch conditions was a golden opportunity to present their concerns. They were sure that
Challenger should not be launched in such conditions as those expected for Tuesday morning. Using weather
data provided by the Air Force, they calculated that at the 9:00 am launch time the temperature of the O-rings
would be only 29o F. Even by 2:00 pm, the O-rings would have warmed only to 38o F.
The design validation tests originally done by Thiokol covered only a very narrow temperature range. The
temperature data base did not include any temperatures below 53o F. The O-rings from Flight 51-C which had
been launched under cold conditions the previous year showed very significant erosion. This was the only data
available on the effects of cold, but all the Thiokol engineers agreed that the cold weather would decrease the
elasticity of the synthetic rubber O-rings, which in turn might cause them to seal slowly and allow hot
combustion gas to surge through the joint.
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