Long before the shuttle Columbia was destroyed on re-entry last month, NASA scientists had considered literally hundreds of problems that might threaten the craft's safety and decided to launch anyway. Columbia had accumulated a thick sheaf of what the rocket business calls safety waivers problems that NASA had noted but decided posed too small a risk to bother with.
"That's a pretty deep stack; it really is," one member of the Columbia Accident Investigation Board told TIME. "A lot of these [waivers] are legitimate every launch is going to have them but others are...