Archive for the ‘Estimation’ Category

The Challenger disaster: A tragic lesson in data analysis …

June 6, 2016

Well-intended engineers correctly interpreted the wrong data.

Excerpted from Everydata: The Misinformation Hidden in the Little Data You Consume Every Day


I’m sure all baby-boomers have a vivid recollection, but for younger readers, here’s some background …

“On the morning of 28 January 1986, the Space Shuttle Challenger, mission 51– L, rose into the cold blue sky over the Cape. To exuberant spectators and breathless flight controllers, the launch appeared normal. Within 73 seconds after liftoff, however, the external tank ruptured, its liquid fuel exploded, and Challenger broke apart.”



What happened?

“The specific failure,” noted the Report of the Presidential Commission on the Space Shuttle Challenger Accident, “was the destruction of the seals that are intended to prevent hot gases from leaking.…”

Investigators quickly focused their attention on a key part of the seals— the rubber O-rings that went in between two sections of the solid rocket motor— the “tang” and the “clevis.”

The O-rings on the Challenger needed to be flexible enough to compress and expand, sometimes within milliseconds.

But O-ring resiliency “is directly related to its temperature… a warm O-ring will follow the opening of the tang-to-clevis gap. A cold O-ring may not.”

In fact, investigators found that a compressed O-ring is five times more responsive at 75 degrees Fahrenheit than at 30 degrees Fahrenheit.

The air temperature at launch was 36 degrees Fahrenheit.

The commission’s report found “it is probable” that the O-rings were not compressing and expanding as needed.

The resulting gap allowed the gases to escape, destroying the Challenger.


So why didn’t engineers stop the launch, given the cold temperatures?


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