THE DECISION
TO LAUNCH THE
SPACE SHUTTLE
CHALLENGER
Shuttle Challenger in route to the
launch pad
Challenger Launch Decision
“…In contrast [to Dr. John Snow], by
fooling around with displays that
obscured the data, those who decided
to launch the space shuttle got it wrong,
terribly wrong.”
The Crew
What Happened – January 28, 1986?
Space Shuttle
Challenger
was NASA's
second space shuttle orbiter to be put into
service.
Its maiden flight was on April 4, 1983, and it
completed nine missions before breaking
apart after the launch of its tenth mission on
January 28, 1986, resulting in the death of all
seven crew members
A Presidential Commission investigated the
O-rings
failed in
less than 1
second
after
ignition,
but
resealed in
less than 2
seconds
O-Ring Failures at Launch
O-Ring Chronology 1
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.
The two pad 39B cameras that would have recorded
the precise location of the puff were inoperative.
Computer graphic analysis of film from other
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
O-Ring Chronology 2
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. Each smoke puff
was being left behind by the upward flight of the Shuttle. 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.
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
O-Ring Chronology 3
The 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, the flame was
visible without image enhancement. It grew into a continuous, well-defined plume at 59.262 seconds. Also,
telemetry showed a pressure
differential between the chamber
Visual of O-Ring Failures in Flight
The O-rings
failed again
during the
flight. At
58.788
seconds
after
O-Ring Chronology 4
At 64.660 seconds the right Solid Rocket Booster breached the
External Tank indicated by an abrupt change in the shape and color of the plume as it mixed with the leaking hydrogen.
At 72.20 seconds the lower strut linking the Solid Rocket Booster and
the External Tank was severed.
At 73.124 seconds, a 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.
At about the same time, the right Solid Rocket Booster impacted the
inter-tank structure—both structures failed at 73.137 seconds.
Within milliseconds there was massive, almost explosive, burning of
the hydrogen streaming from the failed tank.
At this point in its trajectory, while traveling at a Mach 1.92 at 46,000
24 Hours Before the Flight
Engineers at Thiokol prepared 13 charts to
make the case
NOT
to launch Challenger
Temperatures were in the low 30s
Physics of resiliency - decline exponentially
w/cooling
Unfortunate
ly, it was a
clumsy
O-Ring and Temperature Connection
Thiokol engineers made a temperature connection but
offered a poor presentation of these data because
O-ring damage organized by flight, not temperature Did not look at “undamaged” flights and temperature
NASA Questioned the Recommendation
High level official “Appalled” by no-launch recommendation
Other NASA officials pointed out weaknesses in Thiokol’s
charts
Thiokol managers changed their minds after debate and
skeptical responses from NASA
Thiokol’s Charts
Chart Credibility – No names attached to document
to give it weight or authority
Cause Vs. Effect – Main chart showed damaged
flights, omitted undamaged flights and
temperatures
Ambiguity – Same rocket shown with three
different names
O-Ring Drawing – Good
but no link to temperature
Shows how rotation
of joint degrades Integrity; this is a wind or shear
No Correlation Analyses
Insufficient data
Damage charts left out 22 previous shuttle flights and
their temperature variation and O-ring performance
Missing was 92% of the temperature data for 5 of the
launches with O-ring erosion and 17 launches without
erosion
No Correlation between O-ring distress
and temperature
6 charts contained no data about O-ring temperature,
O-ring blow-by, or O-ring damage
Of 7 remaining charts containing data on launch temps
Presidential Commission
Commission Received
Evidence from Thiokol
Letter codes and
cross-hatching hindered
visual understanding of
damage severity
Data based on
controlled tests from
fixed rockets ignited on
horizontal test stands –
never undergoing
stress of a real flight
No rocket motor in these “controlled” tests sustained
damage. Also, the temperature effect is difficult to visualize
Actual Launch Data
Commission Received
Launch Data
(“Chartjunk”)
Legend shown
previously not attached
here—required
memorization!
Lack of proper order—
showed a time series
and not the temperature
ranking—to show cause
and effect
These 48 little rockets have the data necessary to make a better launch decision. It was
professional misconduct to present the information to the Commission in such a
Tufte Reorders Data by Temperature
On the cover of the Edward Tufte reading is the chart above. The chart shows all shuttle missions, temperatures at launch, and an index of O-ring damages discovered when the solid rocket motors (SRMs) were recovered from the ocean. The nonlinear fitted line is not in the
Richard Feymann (Nobel Prize, 1965)
You do not receive the Nobel Prize in
Physics without being really smart
Clarified link between cold temperature
and loss of resiliency in rubber O-rings
Placed a clamped O-ring into a glass
of ice water
Take clamp out of H
2O, undo the
clamp, the rubber does not spring
back
No resilience at 32 degrees
Feynman: “I believe that has some
significance for our problem”
Additional Factors—Wind Direction
What was also unusual
about this launch was
the direction of the wind
that blew towards the
west-northwest.
As a result, air
descended across the
super-cooled liquid
hydrogen fuel tank
directly into the lower
portion of the right side
solid rocket booster
Ice Team Readings
Ground personnel use infrared cameras to measure
the thickness of the ice on the launch structure
The Ice Team happened to point a camera at the aft
field joint of the right SRB and recorded a
temperature of only 8°F (-13°C), much colder than
the air temperature and far below the design
tolerances of the O-rings
An additional factor that contributed to the tragedy
Additional Factors—Wind Shear
The temporary seal remained intact for nearly one
minute into the flight since the chamber pressure
within the right SRB remained normal.
At 56 seconds after launch, Challenger passed through
the worst wind shear in the history of the shuttle
program, which caused the booster to “flex” and
dislodged the plug that had sealed the damaged
O-rings
This event was marked by a reduction in
Fate of the Crew
The momentum of the crew cabin carried it to an altitude of about 64,000 ft (19,525 m) before it began a free-fall into the ocean.
While it is not known what happened during this period, it is believed that the crew survived the initial breakup of the Challenger since the pressure loads were greater than 4 g's for only a brief period.
However, the cabin did lose electrical power and oxygen as it
separated from the rest of the vehicle. Depressurization during this period would cause unconsciousness due to lack of oxygen.
Even so, the astronauts were equipped with Personal Egress Air Packs (PEAPs) containing an emergency air supply. Of the four PEAPs
recovered, three had been activated and partially used indicating that at least some of the crew survived the initial breakup.
Life or Death Errors
“When we reason about quantitative
evidence, certain methods for displaying
and analyzing data are better than
others. Superior methods are more
likely to produce truthful, credible, and
precise findings. The difference between
an excellent analysis and a faulty one
can sometimes have momentous
consequences.”
