Key visualizations of the decision to launch the Space Shuttle Challenger on 27 January 1986. Includes animation of the mechanical failure and data analysis.

1. © Anthony Cutler Limited 2002-2013 public 1.0
The decision to launch Space Shuttle
Challenger – 27 January 1986
Unanticipated knowledge
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2. © Anthony Cutler Limited 2002-2013 public 1.0 2
On 27 January 1986, NASA engineers held a conference to decide
whether the next day’s launch should proceed
The joints, where the stages of the Solid Fuel Rocket Booster (SFRB)
were mated, featured two quarter inch (5mm) rubber o-rings – around
14 feet (3m) in diameter.
When the fuel was ignited, stress was developed in the structure
tending to make the joint “rotate”. The joint-sealing putty was often
dislodged during take off, allowing fuel as far as the first O-ring. Two
O-rings were provided as there were doubts about joint integrity and
some redundancy was thought prudent.
During this brief interval of ignition (fractions of a second), it was
important that the rubber in the O-rings maintained the seal. There
were concerns that at low temperatures, the rubber hardened making
its response slower and failing to seal for a critical few milliseconds.
Space Shuttle Challenger

3. © Anthony Cutler Limited 2002-2013 public 1.0 3
Engineers observed “blow-by” where burning fuel had clearly
escaped the primary O-ring on a number of recovered units.
“Blow-by” of fuel past the primary O-ring had been observed on 7 of
the 24 space-shuttle flights.
Doubts had arisen about the ability of rubber O-rings to seal in rocket
fuel at low temperatures
The forecast temperature for the next day’s launch was 31 F.
For more background see: Vaughan, D (1996) The Challenger
Launch Decision, Chicago University Press
Space Shuttle Challenger

4. © Anthony Cutler Limited 2002-2013 public 1.0 4
pin
Zinc-chromate
putty
1/4” Viton
o-rings
Rocket fuel
Space Shuttle Challenger

5. © Anthony Cutler Limited 2002-2013 public 1.0 5
Rocket fuel
Space Shuttle Challenger
Escaping
rocket fuel

6. © Anthony Cutler Limited 2002-2013 public 1.0 6
O-rings were known to harden at low temperatures and to seal more
slowly
There was a suspicion from data that there were more incidents at
low temperatures
Actual data suggests a temperature effect. When this data was
presented to NASA engineers at the eve-of-launch conference, all the
zeros (incident-free launches) were omitted and only the flights were
there had been an incident featured. NASA engineers were sceptical
of any evidence (signal) that temperature had an effect on risk of
“blow-by”.
Space Shuttle Challenger

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Joint temp (deg F)
numberofincidents
Incidents on "blow-by" on shuttle flights
Data as presented to NASA engineers

8. © Anthony Cutler Limited 2002-2013 public 1.0 8
80706050
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Joint temp (deg F)
numberofincidents
Incidents on "blow-by" on shuttle flights
Full picture of data

9. © Anthony Cutler Limited 2002-2013 public 1.0 9
However, when the data is presented in full with the events where
there were no “blow-by”s, there is a strong feeling that the problem-
free launches only occurred at higher temperatures.
The way the data is presented has a strong effect on its
interpretation.
Space Shuttle Challenger