Comment by jasode | Hacker News Reader

Comment by jasode | Hacker News Reader

Parent Full thread

Boisjoly's rebuttal is that

1) Tufte had temperature datapoints for the previous launches that the Boisjoly's team didn't know[1]. I assume "know" to mean the complete historical data wasn't all consolidated conveniently at his fingertips before the disaster. Presumably, Boisjoly's team could have gotten it if it had occurred to them to gather it. Essentially, Tufte had the benefit of "hindsight" to make his compelling diagram showing cause & effect.

2) GIGO garbage in is garbage out. The Tufte temperature datapoint assumes that the outside ambient temperature is equal to the O-ring temperature[2] so substituting one for the other is wrong. (E.g. It's wrong to put them both on the same X-axis.)

Quotes excerpted from http://www.onlineethics.org/CMS/profpractice/exempindex/RB-i...:

[1]"He thus supposes that they knew the temperatures at launch of all the shuttles and, assuming they acted voluntarily, infers they were incompetent."

[2]", in addition, mixes O-ring temperatures and ambient air temperature as though the two were the same."

I thought the rebuttal was very well written, if a bit dense.

For (1), you're correct that the engineers did not have the historical data. More than that, though, it did occur to them to request the data, but they were stifled by Morton Thiokol Management (and NASA).

To start with, there were a variety of previous problems with the O-rings caused by variables that appear unrelated to temperature. These problems were resolved, but prevented anyone from seeing a pattern. It was only on the basis of the single data point in SRM 15 that Boisjoly requested temperature data in advance of the launch.

Obtaining such data was far from simple, because, as you mention, the temperature of the O-ring isn't the same as the ambient air temperature. Thus, obtaining the data was relatively involved and required knowing many variables: time on the pad, the gradient of ambient temperature, the temperature at which testing was conducted, and so forth. For this reason, the engineers didn't compile the data themselves (unclear what process they'd need to get the data).

The engineers thus requested the data in advance, but had not received it. They had precise data on only two data points (at 53 degrees and 75 degrees), so the rest of the data in the chart was compiled after the fact.

"The data necessary for a calculation of O-ring temperatures was thus not collected all along during the shuttle history. And when Boisjoly asked for that data in September, along with much other data, any one of which might have been the crucial missing piece to explain the anomalous cause, it was not supplied. In fact, the engineers received none of the data they requested."

Reply on news.ycombinator.com