Space Shuttle Challenger (NASA Orbiter Vehicle Designation: OV-099) was
NASA's second Space Shuttle orbiter to be put into service, Columbia being
the first. Its maiden flight was on April 4, 1983, and it completed nine
missions before breaking apart 73 seconds after the launch of its tenth
mission, STS-51-L on January 28, 1986, resulting in the death of all seven
crew members. The accident led to a two-and-a-half year grounding of the
shuttle fleet, with missions resuming in 1988 with the launch of Space
Shuttle Discovery on STS-26. Challenger itself was replaced by the Space
Shuttle Endeavour, which first launched in 1992.
The Event
The Space Shuttle Challenger disaster occurred on January 28, 1986, when
Space Shuttle Challenger broke apart 73 seconds into its flight, leading
to the deaths of its seven crew members. The spacecraft disintegrated over
the Atlantic Ocean, off the coast of central Florida, United States at
11:39 a.m. EST (16:39 UTC).
Disintegration of the entire vehicle began after an O-ring seal in its
right solid rocket booster (SRB) failed at liftoff. The O-ring failure
caused a breach in the SRB joint it sealed, allowing pressurized hot gas
from within the solid rocket motor to reach the outside and impinge upon
the adjacent SRB attachment hardware and external fuel tank. This led to
the separation of the right-hand SRB's aft attachment and the structural
failure of the external tank. Aerodynamic forces promptly broke up the
orbiter.
The crew compartment and many other vehicle fragments were eventually
recovered from the ocean floor after a lengthy search and recovery
operation. Although the exact timing of the death of the crew is unknown,
several crew members are known to have survived the initial breakup of the
spacecraft. However the shuttle had no escape system and the astronauts
did not survive the impact of the crew compartment with the ocean surface.
The disaster resulted in a 32-month hiatus in the shuttle program and the
formation of the Rogers Commission, a special commission appointed by
United States President Ronald Reagan to investigate the accident. The
Rogers Commission found that NASA's organizational culture and
decision-making processes had been a key contributing factor to the
accident. NASA managers had known that contractor Morton Thiokol's design
of the SRBs contained a potentially catastrophic flaw in the O-rings since
1977, but they failed to address it properly. They also disregarded
warnings from engineers about the dangers of launching on such a cold day
and had failed to adequately report these technical concerns to their
superiors. The Rogers Commission offered NASA nine recommendations that
were to be implemented before shuttle flights resumed.
On January 28, 1986, the Space Shuttle Challenger broke apart 73 seconds
into its flight, leading to the deaths of its seven crew members. The
spacecraft disintegrated over the Atlantic Ocean, off the coast of central
Florida, United States at 11:39 a.m. EST. Disintegration of the entire
vehicle began after an O-ring seal in its right solid rocket booster (SRB)
failed at liftoff. The O-ring failure caused a breach in the SRB joint it
sealed, allowing pressurized hot gas from within the solid rocket motor to
reach the outside and impinge upon the adjacent SRB attachment hardware and
external fuel tank. This led to the separation of the right-hand SRB's aft
attachment and the structural failure of the external tank. Aerodynamic
forces promptly broke up the orbiter. The crew compartment and many other
vehicle fragments were eventually recovered from the ocean floor after a
lengthy search and recovery operation. Although the exact timing of the
death of the crew is unknown, several crew members are known to have
survived the initial breakup of the spacecraft. However the shuttle had no
escape system and the astronauts did not survive the impact of the crew
compartment with the ocean surface. The disaster resulted in a 32-month
hiatus in the shuttle program and the formation of the Rogers Commission, a
special commission appointed by United States President Ronald Reagan to
investigate the accident. The Rogers Commission found that NASA's
organizational culture and decision-making processes had been a key
contributing factor to the accident. NASA managers had known that contractor
Morton Thiokol's design of the SRBs contained a potentially catastrophic
flaw in the O-rings since 1977, but they failed to address it properly. They
also disregarded warnings from engineers about the dangers of launching on
such a cold day and had failed to adequately report these technical concerns
to their superiors. The Rogers Commission offered NASA nine recommendations
that were to be implemented before shuttle flights resumed.
Root Cause
The loss of the Space Shuttle Challenger was caused by a failure in the
joint between the two lower segments of the right Solid Rocket Motor. The
specific failure was the destruction of the seals that are intended to
prevent hot gases from leaking through the joint during the propellant burn
of the rocket motor. The decision to launch the Challenger was flawed. Those
who made that decision were unaware of the recent history of problems
concerning the O-rings and the joint and were unaware of the initial written
recommendation of the contractor advising against the launch at temperatures
below 53 degrees Fahrenheit and the continuing opposition of the engineers
at Thiokol after the management reversed its position. They did not have a
clear understanding of Rockwell's concern that it was not safe to launch
because of ice on the pad. If the decision makers had known all of the
facts, it is highly unlikely that they would have decided to launch 51-L on
January 28, 1986.
Time Line
January 28, 1986,11:38:00 a.m. EST. First Shuttle liftoff scheduled from Pad
B. Launch set for 3:43 p.m. EST, Jan. 22, slipped to Jan. 23, then Jan. 24,
due to delays in mission 61-C. Launch reset for Jan. 25 because of bad
weather at transoceanic abort landing (TAL) site in Dakar, Senegal. To
utilize Casablanca (not equipped for night landings) as alternate TAL site,
T-zero moved to morning liftoff time. Launch postponed a day when launch
processing unable to meet new morning liftoff time. Prediction of
unacceptable weather at KSC led to launch rescheduled for 9:37 a.m. EST,
Jan. 27. Launch delayed 24 hours again when ground servicing equipment hatch
closing fixture could not be removed from orbiter hatch. Fixture sawed off
and attaching bolt drilled out before closeout completed. During delay,
cross winds exceeded return-to-launch-site limits at KSC's Shuttle Landing
Facility. Launch Jan. 28 delayed two hours when hardware interface module in
launch processing system, which monitors fire detection system, failed
during liquid hydrogen tanking procedures. Just after liftoff at .678
seconds into the flight, photographic data show a strong puff of gray smoke
was spurting from the vicinity of the aft field joint on the right Solid
Rocket Booster. Computer graphic analysis of film from pad cameras indicated
the initial smoke came from the 270 to 310-degree sector of the
circumference of the aft field joint of the right Solid Rocket Booster. This
area of the solid booster faces the External Tank. The vaporized material
streaming from the joint indicated there was not complete sealing action
within the joint. Eight more distinctive puffs of increasingly blacker smoke
were recorded between .836 and 2.500 seconds. The smoke appeared to puff
upwards from the joint. While each smoke puff was being left behind by the
upward flight of the Shuttle, the next fresh puff could be seen near the
level of the joint. The multiple smoke puffs in this sequence occurred at
about four times per second, approximating the frequency of the structural
load dynamics and resultant joint flexing. As the Shuttle increased its
upward velocity, it flew past the emerging and expanding smoke puffs. The
last smoke was seen above the field joint at 2.733 seconds. The black color
and dense composition of the smoke puffs suggest that the grease, joint
insulation and rubber O-rings in the joint seal were being burned and eroded
by the hot propellant gases. At approximately 37 seconds, Challenger
encountered the first of several high-altitude wind shear conditions, which
lasted until about 64 seconds. The wind shear created forces on the vehicle
with relatively large fluctuations. These were immediately sensed and
countered by the guidance, navigation and control system. The steering
system (thrust vector control) of the Solid Rocket Booster responded to all
commands and wind shear effects. The wind shear caused the steering system
to be more active than on any previous flight. Both the Shuttle main engines
and the solid rockets operated at reduced thrust approaching and passing
through the area of maximum dynamic pressure of 720 pounds per square foot.
Main engines had been throttled up to 104 percent thrust and the Solid
Rocket Boosters were increasing their thrust when the first flickering flame
appeared on the right Solid Rocket Booster in the area of the aft field
joint. This first very small flame was detected on image enhanced film at
58.788 seconds into the flight. It appeared to originate at about 305
degrees around the booster circumference at or near the aft field joint. One
film frame later from the same camera, the flame was visible without image
enhancement. It grew into a continuous, well-defined plume at 59.262
seconds. At about the same time (60 seconds), telemetry showed a pressure
differential between the chamber pressures in the right and left boosters.
The right booster chamber pressure was lower, confirming the growing leak in
the area of the field joint. As the flame plume increased in size, it was
deflected rearward by the aerodynamic slipstream and circumferentially by
the protruding structure of the upper ring attaching the booster to the
External Tank. These deflections directed the flame plume onto the surface
of the External Tank. This sequence of flame spreading is confirmed by
analysis of the recovered wreckage. The growing flame also impinged on the
strut attaching the Solid Rocket Booster to the External Tank. The first
visual indication that swirling flame from the right Solid Rocket Booster
breached the External Tank was at 64.660 seconds when there was an abrupt
change in the shape and color of the plume. This indicated that it was
mixing with leaking hydrogen from the External Tank. Telemetered changes in
the hydrogen tank pressurization confirmed the leak. Within 45 milliseconds
of the breach of the External Tank, a bright sustained glow developed on the
black-tiled underside of the Challenger between it and the External Tank.
Beginning at about 72 seconds, a series of events occurred extremely rapidly
that terminated the flight. Telemetered data indicate a wide variety of
flight system actions that support the visual evidence of the photos as the
Shuttle struggled futilely against the forces that were destroying it. At
about 72.20 seconds the lower strut linking the Solid Rocket Booster and the
External Tank was severed or pulled away from the weakened hydrogen tank
permitting the right Solid Rocket Booster to rotate around the upper
attachment strut. This rotation is indicated by divergent yaw and pitch
rates between the left and right Solid Rocket Boosters. At 73.124 seconds,.
a circumferential white vapor pattern was observed blooming from the side of
the External Tank bottom dome. This was the beginning of the structural
failure of hydrogen tank that culminated in the entire aft dome dropping
away. This released massive amounts of liquid hydrogen from the tank and
created a sudden forward thrust of about 2.8 million pounds, pushing the
hydrogen tank upward into the intertank structure. At about the same time,
the rotating right Solid Rocket Booster impacted the intertank structure and
the lower part of the liquid oxygen tank. These structures failed at 73.137
seconds as evidenced by the white vapors appearing in the intertank region.
Within milliseconds there was massive, almost explosive, burning of the
hydrogen streaming from the failed tank bottom and liquid oxygen breach in
the area of the intertank. At this point in its trajectory, while traveling
at a Mach number of 1.92 at an altitude of 46,000 feet, the Challenger was
totally enveloped in the explosive burn. The Challenger's reaction control
system ruptured and a hypergolic burn of its propellants occurred as it
exited the oxygen-hydrogen flames. The reddish brown colors of the
hypergolic fuel burn are visible on the edge of the main fireball. The
Orbiter, under severe aerodynamic loads, broke into several large sections
which emerged from the fireball. Separate sections that can be identified on
film include the main engine/tail section with the engines still burning,
one wing of the Orbiter, and the forward fuselage trailing a mass of
umbilical lines pulled loose from the payload bay. The Explosion 73 seconds
after liftoff claimed crew and vehicle. Cause of explosion was determined to
be an O-ring failure in right SRB. Cold weather was a contributing factor.
Launch Weight: 268,829 lbs.
Lessons Learned
The Presidential Commission on the Space
Shuttle Challenger Accident made the following recommendations, which were
subsequently implemented by NASA.
