Last February 1st, we contemplated, astonished, the images on CNN of the trace of disintegration that the Columbia space shuttle was leaving in Texas’ skies.

The tragic accident that took the lives of 7 people could have its origin in the loosening of a piece of the main propellant tank that collided with the left wing of the shuttle during take off.

Since then much speculation has taken place about the actual causes and it has been said that the diminution of the NASA budget for the shuttle program had reached worrying limits.

On its own side, NASA offers a Flash movie where it explains the advances achieved in the shuttle program. Namely, they offer different types of charts showing, for example, that in the last years:

• The payload capacity has doubled. 
  
  
• The civil service personnel has been reduced by 56%
  
  
• The number of contractors has been lowered by 43%.
  
  
• The probabilities of a failure during launch has been reduced by 80% and those of the whole mission by 75%. 
  
  
• Designed to withstand 100 flights, the one that has more accumulated flights is Discovery, with just 30.

The unfortunate re-entry has been covered graphically, with examples like the newspaper “El Mundo” in Spanish or those of Time Magazine. Some websites like the one of NASA or the CNN offer a wide graphical coverage of the catastrophe.

NASA offers a series of charts where the state of all the relevant sensors of the left wing is indicated, in the different phases of re-entry.

Launch of the Columbia. Moment where the material apparently loosen from the main tank hits the left wing.   Click on the image to enlarge it. Image courtesy of NASA	Diagram of the left wing sensors.  53 seconds before the destruction of Columbia. It shows the sensors that were acting properly and those that apparently were providing extrange readings.  Click on the image to enlarge it.  Image as can be seen at the NASA web page

The investigation begins now. In a few months we’ll know what happened and if, as occurred with the Challenger in 1986, the erroneous interpretation of the data represented in an inefficient way has something to do with the disaster this time or not.

On that occasion the cause of the accident was a rubber ring (O-ring) that sealed the joint between two sections of one of the Challenger’s ancillary rockets (boosters).

The afternoon before the launch, with a temperature forecast between 26 and 29 degrees Fahrenheit, the technicians of Morton Thiokol, manufacturer of the “boosters”, concerned about the behaviour of the joints at low temperatures, advised against the launching. None of the previous launches had occurred at such low temperatures and some flights had problems related with the joints.

The technicians sent a fax of 13 pages to the NASA officers who found the data and tables insufficient to conclude a relation between low temperatures and the O-ring joint . After an intense debate it was decided to go on with the launch, despite the fact that it was the first time that Morton Thiokol advised a no-launch in 12 years.

The posterior investigation showed that the available data about the launch history would have been enough to relate the temperature with risk of failure of the O-rings properly. (See the accompanying charts or those available at the galleríy del of the SCS and the University of Colorado).

Temperature vs number of joints damaged per launch. The launches were no damage was appreciated are lacking in this chart.   Graphical analysis of this and other data were only  performed after the accident. For example similar charts to the one at the right have been performed in several ways after the disaster. Click on the image to enlarge it.   From Volume 1, p.146 of the Report of the Presidential Commission of the Space Shuttle Challenger Accident, 1986, as can be seen in the book Visual Revelations by Howard Wainer

Chart of temperature against damage level.  It takes into account all the launches and the level of damage of the O-ring seals (damage index) according the table in Edward Tufte's book según la tabla presente en el libro Visual Explanations. The chart is made using Excel. The trend line is a cudratic curve. The shaded rectangle covers the temperature range forecasted for that day.  The back extrapolation of the available data makes very uncertain the risk of damage due to the temperature. In any case it can be considerd very high. Click on the image to enlarge it. Image by the author.

Edward Tufte has a complete discussion of this issue in his book “Visual Explanations”. He concludes that the technicians needed a quick and clever analysis of the data on one hand and an efficient way to present it to convince the NASA officers to avoid the launch, on the other. An appropriate representation of the data instead of the study of the individual cases would have been definitive in order to avoid the catastrophe.

The correct visualisation of information usually makes a difference. Sometimes in a tragic way.

In memoriam of the Columbia and Challenger crew.

See also the Report of the Presidential Commission on the Space Shuttle Challenger Accident 

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