European Ariane 5 Rocket

The purpose of the European Ariane 5 rocket was to deliver satellites into orbit. After over a decade of development and research costing $7 billion, the rocket was ready to be made. The cost to make the actual rocket and satellites was about $500 million. Thirty seven seconds into the first mission, the rocket suddenly curved off to side and exploded. There were no people on board, however this error caused a significant waste of money. Within 2 weeks of the explosion the error was found to be in the software where the horizontal velocity was stored as a 64 bit floating point and was converted to a 16 bit signed integer which was not compatible. This rocket was a huge project and had millions of lines of code which made it all the more important to be correct and test the code. Unfortunately, the coding error was actually from the Ariane 4 rocket software which did not serve any useful purpose on the Ariane 5. The reason the software was not taken off of the Ariane 5 was because it was costly and the designers didn't think it would make a difference. Were the designers wrong to trust the old software or was this just one of those freak accidents that was not really preventable? This was a huge mistake, but this in in hindsight right.

http://www.around.com/ariane.html
http://www.ima.umn.edu/~arnold/disasters/ariane.html
http://royal.pingdom.com/2009/03/19/10-historical-software-bugs-with-extreme-consequences/
http://www.youtube.com/watch?v=bb28dd57H60